RESUMEN
Osteoporotic fractures are a major complication of long-term glucocorticoid therapy. Glucocorticoids transiently increase bone resorption, but they predominantly inhibit bone formation and induce osteocyte apoptosis, leading to bone loss. Current treatments of glucocorticoid-induced osteoporosis aim mainly at reducing bone resorption and are, therefore, inadequate. We previously showed that signaling via the NO/cGMP/protein kinase G pathway plays a key role in skeletal homeostasis. Here, we show that pharmacological PKG activation with the guanylyl cyclase-1 activator cinaciguat or expression of a constitutively active, mutant PKG2R242Q restored proliferation, differentiation, and survival of primary mouse osteoblasts exposed to dexamethasone. Cinaciguat treatment of WT mice or osteoblast-specific expression of PKG2R242Q in transgenic mice prevented dexamethasone-induced loss of cortical bone mass and strength. These effects of cinaciguat and PKG2R242Q expression were due to preserved bone formation parameters and osteocyte survival. The basis for PKG2's effects appeared to be through recovery of Wnt/ß-catenin signaling, which was suppressed by glucocorticoids but critical for proliferation, differentiation, and survival of osteoblast-lineage cells. Cinaciguat reduced dexamethasone activation of osteoclasts, but this did not occur in the PKG2R242Q transgenic mice, suggesting a minor role in osteoprotection. We propose that existing PKG-targeting drugs could represent a novel therapeutic approach to prevent glucocorticoid-induced osteoporosis.
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Proteínas Quinasas Dependientes de GMP Cíclico , Dexametasona , Glucocorticoides , Ratones Transgénicos , Osteoblastos , Osteoporosis , Vía de Señalización Wnt , Animales , Osteoporosis/inducido químicamente , Osteoporosis/metabolismo , Osteoporosis/patología , Ratones , Glucocorticoides/efectos adversos , Osteoblastos/efectos de los fármacos , Osteoblastos/metabolismo , Dexametasona/farmacología , Dexametasona/efectos adversos , Vía de Señalización Wnt/efectos de los fármacos , Proteínas Quinasas Dependientes de GMP Cíclico/metabolismo , Diferenciación Celular/efectos de los fármacos , Osteocitos/metabolismo , Osteocitos/efectos de los fármacos , Osteogénesis/efectos de los fármacos , Modelos Animales de Enfermedad , Femenino , Proliferación Celular/efectos de los fármacos , Densidad Ósea/efectos de los fármacosRESUMEN
Major pathologic changes in the proximal aorta underlie the life-threatening aortic aneurysms and dissections in Marfan Syndrome; current treatments delay aneurysm development without addressing the primary pathology. Because excess oxidative stress and nitric oxide/protein kinase G signaling likely contribute to the aortopathy, we hypothesized that cobinamide, a strong antioxidant that can attenuate nitric oxide signaling, could be uniquely suited to prevent aortic disease. In a well-characterized mouse model of Marfan Syndrome, cobinamide dramatically reduced elastin breaks, prevented excess collagen deposition and smooth muscle cell apoptosis, and blocked DNA, lipid, and protein oxidation and excess nitric oxide/protein kinase G signaling in the ascending aorta. Consistent with preventing pathologic changes, cobinamide diminished aortic root dilation without affecting blood pressure. Cobinamide exhibited excellent safety and pharmacokinetic profiles indicating it could be a practical treatment. We conclude that cobinamide deserves further study as a disease-modifying treatment of Marfan Syndrome.
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Androgen binding to the androgen receptor (AR) in the cytoplasm induces the AR to translocate to the nucleus, where it regulates the expression of target genes. Here, we found that androgens rapidly activated a plasma membrane-associated signaling node that enhanced nuclear AR functions. In murine primary osteoblasts, dihydrotestosterone (DHT) binding to a membrane-associated form of AR stimulated plasma membrane-associated protein kinase G type 2 (PKG2), leading to the activation of multiple kinases, including ERK. Phosphorylation of AR at Ser515 by ERK increased the nuclear accumulation and binding of AR to the promoter of Ctnnb1, which encodes the transcription factor ß-catenin. In male mouse osteoblasts and human prostate cancer cells, DHT induced the expression of Ctnnb1 and CTNN1B, respectively, as well as ß-catenin target genes, stimulating the proliferation, survival, and differentiation of osteoblasts and the proliferation of prostate cancer cells in a PKG2-dependent fashion. Because ß-catenin is a master regulator of skeletal homeostasis, these results explain the reported male-specific osteoporotic phenotype of mice lacking PKG2 in osteoblasts and imply that PKG2-dependent AR signaling is essential for maintaining bone mass in vivo. Our results suggest that widely used pharmacological PKG activators, such as sildenafil, could be beneficial for male and estrogen-deficient female patients with osteoporosis but detrimental in patients with prostate cancer.
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Andrógenos , Neoplasias de la Próstata , Animales , Humanos , Masculino , Ratones , Andrógenos/farmacología , Andrógenos/metabolismo , beta Catenina/genética , beta Catenina/metabolismo , Línea Celular Tumoral , Membrana Celular/metabolismo , Dihidrotestosterona/farmacología , Dihidrotestosterona/metabolismo , Osteoblastos , Neoplasias de la Próstata/genética , Neoplasias de la Próstata/metabolismo , Receptores Androgénicos/genética , Receptores Androgénicos/metabolismoRESUMEN
CONTEXT: The azide anion (N3-) is highly toxic. It exists most commonly as sodium azide, which is used widely and is readily available, raising the potential for occupational incidents and use as a weapon of mass destruction. Azide-poisoned patients present with vomiting, seizures, hypotension, metabolic acidosis, and coma; death can occur. No specific azide antidote exists, with treatment being solely supportive. Azide inhibits mitochondrial cytochrome c oxidase and is likely oxidized to nitric oxide in vivo. Cytochrome c oxidase inhibition depletes intracellular adenosine triphosphate and increases oxidative stress, while increased nitric oxide causes hypotension and exacerbates oxidative damage. Here, we tested whether the cobalamin (vitamin B12) analog cobinamide, a strong and versatile antioxidant that also neutralizes nitric oxide, can reverse azide toxicity in mammalian cells, Drosophila melanogaster, and mice. RESULTS: We found cobinamide bound azide with a moderate affinity (Ka 2.87 × 105 M-1). Yet, cobinamide improved growth, increased intracellular adenosine triphosphate, and reduced apoptosis and malondialdehyde, a marker of oxidative stress, in azide-exposed cells. Cobinamide rescued Drosophila melanogaster and mice from lethal exposure to azide and was more effective than hydroxocobalamin. Azide likely generated nitric oxide in the mice, as evidenced by increased serum nitrite and nitrate, and reduced blood pressure and peripheral body temperature in the animals; the reduced temperature was likely due to reflex vasoconstriction in response to the hypotension. Cobinamide improved recovery of both blood pressure and body temperature. CONCLUSION: We conclude cobinamide likely acted by neutralizing both oxidative stress and nitric oxide, and that it should be given further consideration as an azide antidote.
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Hipotensión , Vitamina B 12 , Ratones , Animales , Drosophila melanogaster/metabolismo , Azidas/metabolismo , Antídotos/farmacología , Óxido Nítrico , Complejo IV de Transporte de Electrones/metabolismo , Cobamidas , Adenosina Trifosfato , Vitaminas , Mamíferos/metabolismoRESUMEN
Cardiac contraction is modulated by the phosphorylation state of myosin regulatory light chain 2 (MLC-2v). The level of MLC-2v phosphorylation is dependent on the opposing activities of MLC kinases and phosphatases. The predominant MLC phosphatase found in cardiac myocytes contains Myosin Phosphatase Targeting Subunit 2 (MYPT2). Overexpression of MYPT2 in cardiac myocytes results in a decreased level of MLC phosphorylation, reduced left ventricular contraction, and induction of hypertrophy; however, the effect of knocking out MYPT2 on cardiac function is unknown. We obtained heterozygous mice containing a MYPT2 null allele from the Mutant Mouse Resource Center. These mice were produced in a C57BL/6N background which lack MLCK3, the main regulatory light chain kinase in cardiac myocytes. We found that mice null for MYPT2 were viable and had no obvious phenotypic abnormality when compared to WT mice. Additionally, we determined that WT C57BL/6N mice had a low basal level of MLC-2v phosphorylation, which was significantly increased when MYPT2 was absent. At 12-weeks, MYPT2 KO mice had smaller hearts and showed downregulation of genes involved in cardiac remodeling. Using cardiac echo, we found that 24-week-old male MYPT2 KO mice had decreased heart size with increased fractional shortening compared to their MYPT2 WT littermates. Collectively, these studies highlight the important role that MYPT2 plays in cardiac function in vivo and demonstrate that its deletion can partially compensate for the lack of MLCK3.
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Cardiopatías , Quinasa de Cadena Ligera de Miosina , Ratones , Masculino , Animales , Fosfatasa de Miosina de Cadena Ligera/genética , Fosfatasa de Miosina de Cadena Ligera/metabolismo , Quinasa de Cadena Ligera de Miosina/genética , Quinasa de Cadena Ligera de Miosina/metabolismo , Ratones Endogámicos C57BL , Fosfoproteínas Fosfatasas/metabolismo , Miocitos Cardíacos/metabolismo , Fosforilación , Cadenas Ligeras de Miosina/genética , Cadenas Ligeras de Miosina/metabolismoRESUMEN
We previously showed that the NO/cGMP/protein kinase G (PKG) signaling pathway positively regulates osteoblast proliferation, differentiation, and survival in vitro, and that cGMP-elevating agents have bone-anabolic effects in mice. Here, we generated mice with an osteoblast-specific (OB) knockout (KO) of type 2 PKG (gene name Prkg2) using a Col1a1(2.3 kb)-Cre driver. Compared to wild type (WT) littermates, 8-week-old male OB Prkg2-KO mice had fewer osteoblasts, reduced bone formation rates, and lower trabecular and cortical bone volumes. Female OB Prkg2-KO littermates showed no bone abnormalities, despite the same degree of PKG2 deficiency in bone. Expression of osteoblast differentiation- and Wnt/ß-catenin-related genes was lower in primary osteoblasts and bones of male KO but not female KO mice compared to WT littermates. Osteoclast parameters were unaffected in both sexes. Since PKG2 is part of a mechano-sensitive complex in osteoblast membranes, we examined its role during mechanical loading. Cyclical compression of the tibia increased cortical thickness and induced mechanosensitive and Wnt/ß-catenin-related genes to a similar extent in male and female WT mice and female OB Prkg2-KO mice, but loading had a minimal effect in male KO mice. We conclude that PKG2 drives bone acquisition and adaptation to mechanical loading via the Wnt/ß-catenin pathway in male mice. The striking sexual dimorphism of OB Prkg2-KO mice suggests that current U.S. Food and Drug Administration-approved cGMP-elevating agents may represent novel effective treatment options for male osteoporosis. © 2022 American Society for Bone and Mineral Research (ASBMR).
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Huesos , beta Catenina , Femenino , Animales , Ratones , Masculino , beta Catenina/metabolismo , Huesos/metabolismo , Osteoblastos/metabolismo , Osteogénesis , Ratones Noqueados , Vía de Señalización Wnt , Proteínas Quinasas Dependientes de GMP Cíclico/metabolismo , HomeostasisRESUMEN
Increased oxidative stress underlies a variety of diseases, including diabetes. Here, we show that the cobalamin/vitamin B12 analog cobinamide is a strong and multifaceted antioxidant, neutralizing superoxide, hydrogen peroxide, and peroxynitrite, with apparent rate constants of 1.9 × 108, 3.7 × 104, and 6.3 × 106 M-1 s-1, respectively, for cobinamide with the cobalt in the +2 oxidation state. Cobinamide with the cobalt in the +3 oxidation state yielded apparent rate constants of 1.1 × 108 and 8.0 × 102 M-1 s-1 for superoxide and hydrogen peroxide, respectively. In mammalian cells and Drosophila melanogaster, cobinamide outperformed cobalamin and two well-known antioxidants, imisopasem manganese and manganese(III)tetrakis(4-benzoic acid)porphyrin, in reducing oxidative stress as evidenced by: (i) decreased mitochondrial superoxide and return of the mitochondrial membrane potential in rotenone- and antimycin A-exposed H9c2 rat cardiomyocytes; (ii) reduced JNK phosphorylation in hydrogen-peroxide-treated H9c2 cells; (iii) increased growth in paraquat-exposed COS-7 fibroblasts; and (iv) improved survival in paraquat-treated flies. In diabetic mice, cobinamide administered in the animals' drinking water completely prevented an increase in lipid and protein oxidation, DNA damage, and fibrosis in the heart. Cobinamide is a promising new antioxidant that has potential use in diseases with heightened oxidative stress.
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BACKGROUND AND PURPOSE: Heart failure is associated with high morbidity and mortality, and new therapeutic targets are needed. Preclinical data suggest that pharmacological activation of protein kinase G (PKG) can reduce maladaptive ventricular remodelling and cardiac dysfunction in the stressed heart. However, clinical trial results have been mixed and the effects of long-term PKG activation in the heart are unknown. EXPERIMENTAL APPROACH: We characterized the cardiac phenotype of mice carrying a heterozygous knock-in mutation of PKG1 (Prkg1R177Q/+ ), which causes constitutive, cGMP-independent activation of the kinase. We examined isolated cardiac myocytes and intact mice, the latter after stress induced by surgical transaortic constriction or angiotensin II (Ang II) infusion. KEY RESULTS: Cardiac myocytes from Prkg1R177Q/+ mice showed altered phosphorylation of sarcomeric proteins and reduced contractility in response to electrical stimulation, compared to cells from wild type mice. Under basal conditions, young PKG1R177Q/+ mice exhibited no obvious cardiac abnormalities, but aging animals developed mild increases in cardiac fibrosis. In response to angiotensin II infusion or fixed pressure overload induced by transaortic constriction, young PKGR177Q/+ mice exhibited excessive hypertrophic remodelling with increased fibrosis and myocyte apoptosis, leading to increased left ventricular dilation and dysfunction compared to wild type litter mates. CONCLUSION AND IMPLICATIONS: Long-term PKG1 activation in mice may be harmful to the heart, especially in the presence of pressure overload and neurohumoral stress. LINKED ARTICLES: This article is part of a themed issue on cGMP Signalling in Cell Growth and Survival. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.11/issuetoc.
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Angiotensina II , Cardiomiopatías , Angiotensina II/metabolismo , Angiotensina II/farmacología , Animales , Proteína Quinasa Dependiente de GMP Cíclico Tipo I/genética , Proteína Quinasa Dependiente de GMP Cíclico Tipo I/metabolismo , Proteínas Quinasas Dependientes de GMP Cíclico/metabolismo , Proteínas Quinasas Dependientes de GMP Cíclico/farmacología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Miocitos Cardíacos , Remodelación VentricularRESUMEN
Cisplatin is a mainstay of cancer chemotherapy. It forms DNA adducts, thereby activating poly(ADP-ribose) polymerases (PARPs) to initiate DNA repair. The PARP substrate NAD+ is synthesized from 5-phosphoribose-1-pyrophosphate (PRPP), and we found that treating cells for 6 h with cisplatin reduced intracellular PRPP availability. The decrease in PRPP was likely from (1) increased PRPP consumption, because cisplatin increased protein PARylation and PARP1 shRNA knock-down returned PRPP towards normal, and (2) decreased intracellular phosphate, which down-regulated PRPP synthetase activity. Depriving cells of a single essential amino acid decreased PRPP synthetase activity with a half-life of ~ 8 h, and combining cisplatin and amino acid deprivation synergistically reduced intracellular PRPP. PRPP is a rate-limiting substrate for purine nucleotide synthesis, and cisplatin inhibited de novo purine synthesis and DNA synthesis, with amino acid deprivation augmenting cisplatin's effects. Amino acid deprivation enhanced cisplatin's cytotoxicity, increasing cellular apoptosis and DNA strand breaks in vitro, and intermittent deprivation of lysine combined with a sub-therapeutic dose of cisplatin inhibited growth of ectopic hepatomas in mice. Augmentation of cisplatin's biochemical and cytotoxic effects by amino acid deprivation suggest that intermittent deprivation of an essential amino acid could allow dose reduction of cisplatin; this could reduce the drug's side effects, and allow its use in cisplatin-resistant tumors.
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Aminoácidos/deficiencia , Apoptosis , Carcinoma Hepatocelular/patología , Cisplatino/farmacología , Neoplasias Hepáticas/patología , Fosforribosil Pirofosfato/metabolismo , Animales , Antineoplásicos/farmacología , Carcinoma Hepatocelular/tratamiento farmacológico , Carcinoma Hepatocelular/metabolismo , Proliferación Celular , Humanos , Neoplasias Hepáticas/tratamiento farmacológico , Neoplasias Hepáticas/metabolismo , Masculino , Ratones , Ratones Desnudos , Células Tumorales Cultivadas , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
Bone fractures are a major cause of morbidity and mortality, particularly in patients with diabetes, who have a high incidence of fractures and exhibit poor fracture healing. Coordinated expression of osteoblast-derived vascular endothelial growth factor (VEGF) and bone morphogenic proteins (BMPs) is essential for fracture repair. The NO/cGMP/protein kinase G (PKG) signaling pathway mediates osteoblast responses to estrogens and mechanical stimulation, but the pathway's role in bone regeneration is unknown. Here, we used a mouse cortical-defect model to simulate bone fractures and studied osteoblast-specific PKG1-knockout and diabetic mice. The knockout mice had normal bone microarchitecture but after injury exhibited poor bone regeneration, with decreased osteoblasts, collagen deposition, and microvessels in the bone defect area. Primary osteoblasts and tibiae from the knockout mice expressed low amounts of Vegfa and Bmp2/4 mRNAs, and PKG1 was required for cGMP-stimulated expression of these genes. Diabetic mice also demonstrated low Vegfa and Bmp2/4 expression in bone and impaired bone regeneration after injury; notably, the cGMP-elevating agent cinaciguat restored Vegfa and BMP2/4 expression and full bone healing. We conclude that PKG1 is a key orchestrator of VEGF and BMP signaling during bone regeneration and propose pharmacological PKG activation as a novel therapeutic approach to enhance fracture healing.
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Regeneración Ósea , Proteínas Quinasas Dependientes de GMP Cíclico/fisiología , Diabetes Mellitus Experimental , Curación de Fractura , Osteoblastos , Animales , Proteína Morfogenética Ósea 2/metabolismo , Proteína Morfogenética Ósea 4/metabolismo , Proteína Quinasa Dependiente de GMP Cíclico Tipo I , Diabetes Mellitus Experimental/complicaciones , Diabetes Mellitus Experimental/metabolismo , Fracturas Óseas , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Osteoblastos/metabolismo , Osteoblastos/patología , Factor A de Crecimiento Endotelial Vascular/metabolismoRESUMEN
People heterozygous for an activating mutation in protein kinase G1 (PRKG1, p.Arg177Gln) develop thoracic aortic aneurysms and dissections (TAAD) as young adults. Here we report that mice heterozygous for the mutation have a three-fold increase in basal protein kinase G (PKG) activity, and develop age-dependent aortic dilation. Prkg1R177Q/+ aortas show increased smooth muscle cell apoptosis, elastin fiber breaks, and oxidative stress compared to aortas from wild type littermates. Transverse aortic constriction (TAC)-to increase wall stress in the ascending aorta-induces severe aortic pathology and mortality from aortic rupture in young mutant mice. The free radical-neutralizing vitamin B12-analog cobinamide completely prevents age-related aortic wall degeneration, and the unrelated anti-oxidant N-acetylcysteine ameliorates TAC-induced pathology. Thus, increased basal PKG activity induces oxidative stress in the aorta, raising concern about the widespread clinical use of PKG-activating drugs. Cobinamide could be a treatment for aortic aneurysms where oxidative stress contributes to the disease, including Marfan syndrome.
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Aneurisma de la Aorta Torácica/prevención & control , Disección Aórtica/prevención & control , Cobamidas/administración & dosificación , Proteína Quinasa Dependiente de GMP Cíclico Tipo I/genética , Depuradores de Radicales Libres/administración & dosificación , Acetilcisteína/administración & dosificación , Disección Aórtica/genética , Disección Aórtica/patología , Animales , Aorta Torácica/diagnóstico por imagen , Aorta Torácica/efectos de los fármacos , Aorta Torácica/patología , Aneurisma de la Aorta Torácica/genética , Aneurisma de la Aorta Torácica/patología , Proteína Quinasa Dependiente de GMP Cíclico Tipo I/metabolismo , Modelos Animales de Enfermedad , Ecocardiografía , Femenino , Mutación con Ganancia de Función , Técnicas de Sustitución del Gen , Células HEK293 , Humanos , Masculino , Síndrome de Marfan/complicaciones , Síndrome de Marfan/genética , Ratones , Ratones Transgénicos , Miocitos del Músculo Liso , Estrés Oxidativo/efectos de los fármacos , Estrés Oxidativo/genética , Cultivo Primario de CélulasRESUMEN
NO/cGMP signaling is important for bone remodeling in response to mechanical and hormonal stimuli, but the downstream mediator(s) regulating skeletal homeostasis are incompletely defined. We generated transgenic mice expressing a partly-activated, mutant cGMP-dependent protein kinase type 2 (PKG2R242Q) under control of the osteoblast-specific Col1a1 promoter to characterize the role of PKG2 in post-natal bone formation. Primary osteoblasts from these mice showed a two- to three-fold increase in basal and total PKG2 activity; they proliferated faster and were resistant to apoptosis compared to cells from WT mice. Male Col1a1-Prkg2R242Q transgenic mice had increased osteoblast numbers, bone formation rates and Wnt/ß-catenin-related gene expression in bone and a higher trabecular bone mass compared to their WT littermates. Streptozotocin-induced type 1 diabetes suppressed bone formation and caused rapid bone loss in WT mice, but male transgenic mice were protected from these effects. Surprisingly, we found no significant difference in bone micro-architecture or Wnt/ß-catenin-related gene expression between female WT and transgenic mice; female mice of both genotypes showed higher systemic and osteoblastic NO/cGMP generation compared to their male counterparts, and a higher level of endogenous PKG2 activity may be responsible for masking effects of the PKG2R242Q transgene in females. Our data support sexual dimorphism in Wnt/ß-catenin signaling and PKG2 regulation of this crucial pathway in bone homeostasis. This work establishes PKG2 as a key regulator of osteoblast proliferation and post-natal bone formation.
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Enfermedades Óseas Metabólicas/genética , Huesos/patología , Proteína Quinasa Dependiente de GMP Cíclico Tipo II/fisiología , Osteogénesis/genética , Animales , Densidad Ósea/genética , Enfermedades Óseas Metabólicas/metabolismo , Huesos/metabolismo , Diferenciación Celular/genética , Proliferación Celular/genética , Células Cultivadas , Proteína Quinasa Dependiente de GMP Cíclico Tipo II/genética , Complicaciones de la Diabetes/genética , Complicaciones de la Diabetes/metabolismo , Complicaciones de la Diabetes/patología , Diabetes Mellitus Experimental/complicaciones , Diabetes Mellitus Experimental/genética , Diabetes Mellitus Experimental/metabolismo , Diabetes Mellitus Experimental/patología , Femenino , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Tamaño de los Órganos/genética , Osteoblastos/metabolismo , Osteoblastos/fisiologíaRESUMEN
Nitric oxide plays a central role in the regulation of skeletal homeostasis. In cells of the osteoblastic lineage, NO is generated in response to mechanical stimulation and estrogen exposure. Via activation of soluble guanylyl cyclase (sGC) and cGMP-dependent protein kinases (PKGs), NO enhances proliferation, differentiation, and survival of bone-forming cells in the osteoblastic lineage. NO also regulates the differentiation and activity of bone-resorbing osteoclasts; here the effects are largely inhibitory and partly cGMP-independent. We review the skeletal phenotypes of mice deficient in NO synthases and PKGs, and the effects of NO and cGMP on bone formation and resorption. We examine the roles of NO and cGMP in bone adaptation to mechanical stimulation. Finally, we discuss preclinical and clinical data showing that NO donors and NO-independent sGC activators may protect against estrogen deficiency-induced bone loss. sGC represents an attractive target for the treatment of osteoporosis.
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Huesos/metabolismo , GMP Cíclico/metabolismo , Óxido Nítrico/metabolismo , Animales , HumanosRESUMEN
Bone loss and fractures are underrecognized complications of type 1 diabetes and are primarily due to impaired bone formation by osteoblasts. The mechanisms leading to osteoblast dysfunction in diabetes are incompletely understood, but insulin deficiency, poor glycemic control, and hyperglycemia-induced oxidative stress likely contribute. Here we show that insulin promotes osteoblast proliferation and survival via the nitric oxide (NO)/cyclic guanosine monophosphate (cGMP)/protein kinase G (PKG) signal transduction pathway and that PKG stimulation of Akt provides a positive feedback loop. In osteoblasts exposed to high glucose, NO/cGMP/PKG signaling was reduced due in part to the addition of O-linked N-acetylglucosamine to NO synthase-3, oxidative inhibition of guanylate cyclase activity, and suppression of PKG transcription. Cinaciguat-an NO-independent activator of oxidized guanylate cyclase-increased cGMP synthesis under diabetic conditions and restored proliferation, differentiation, and survival of osteoblasts. Cinaciguat increased trabecular and cortical bone in mice with type 1 diabetes by improving bone formation and osteocyte survival. In bones from diabetic mice and in osteoblasts exposed to high glucose, cinaciguat reduced oxidative stress via PKG-dependent induction of antioxidant genes and downregulation of excess NADPH oxidase-4-dependent H2O2 production. These results suggest that cGMP-elevating agents could be used as an adjunct treatment for diabetes-associated osteoporosis.
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Benzoatos/farmacología , Proteínas Quinasas Dependientes de GMP Cíclico/efectos de los fármacos , Diabetes Mellitus Experimental/metabolismo , Diabetes Mellitus Tipo 1/metabolismo , Glucosa/farmacología , Insulina/farmacología , Osteoblastos/efectos de los fármacos , Osteogénesis/efectos de los fármacos , Estrés Oxidativo/efectos de los fármacos , Acetilglucosamina/metabolismo , Animales , Proliferación Celular , Supervivencia Celular , GMP Cíclico/metabolismo , Proteínas Quinasas Dependientes de GMP Cíclico/metabolismo , Retroalimentación Fisiológica , Guanilato Ciclasa/metabolismo , Peróxido de Hidrógeno/metabolismo , Masculino , Ratones , NADPH Oxidasa 4/efectos de los fármacos , NADPH Oxidasa 4/metabolismo , Óxido Nítrico/metabolismo , Óxido Nítrico Sintasa de Tipo III/efectos de los fármacos , Óxido Nítrico Sintasa de Tipo III/metabolismo , Osteoblastos/metabolismo , Proteínas Proto-Oncogénicas c-akt/metabolismo , Transducción de SeñalRESUMEN
The type I cGMP-dependent protein kinases (PKGs) are key regulators of smooth muscle tone, cardiac hypertrophy, and other physiological processes. The two isoforms PKGIα and PKGIß are thought to have unique functions because of their tissue-specific expression, different cGMP affinities, and isoform-specific protein-protein interactions. Recently, a non-canonical pathway of PKGIα activation has been proposed, in which PKGIα is activated in a cGMP-independent fashion via oxidation of Cys43, resulting in disulfide formation within the PKGIα N-terminal dimerization domain. A "redox-dead" knock-in mouse containing a C43S mutation exhibits phenotypes consistent with decreased PKGIα signaling, but the detailed mechanism of oxidation-induced PKGIα activation is unknown. Therefore, we examined oxidation-induced activation of PKGIα, and in contrast to previous findings, we observed that disulfide formation at Cys43 does not directly activate PKGIα in vitro or in intact cells. In transfected cells, phosphorylation of Ras homolog gene family member A (RhoA) and vasodilator-stimulated phosphoprotein was increased in response to 8-CPT-cGMP treatment, but not when disulfide formation in PKGIα was induced by H2O2 Using purified enzymes, we found that the Cys43 oxidation had no effect on basal kinase activity or Km and Vmax values; however, PKGIα containing the C43S mutation was less responsive to cGMP-induced activation. This reduction in cGMP affinity may in part explain the PKGIα loss-of-function phenotype of the C43S knock-in mouse. In conclusion, disulfide formation at Cys43 does not directly activate PKGIα, and the C43S-mutant PKGIα has a higher Ka for cGMP. Our results highlight that mutant enzymes should be carefully biochemically characterized before making in vivo inferences.
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Proteína Quinasa Dependiente de GMP Cíclico Tipo I/metabolismo , Disulfuros/metabolismo , Multimerización de Proteína/fisiología , Sustitución de Aminoácidos , Animales , Línea Celular , GMP Cíclico/análogos & derivados , GMP Cíclico/farmacología , Proteína Quinasa Dependiente de GMP Cíclico Tipo I/genética , Activación Enzimática/efectos de los fármacos , Activación Enzimática/fisiología , Técnicas de Sustitución del Gen , Humanos , Ratones , Ratones Transgénicos , Mutación Missense , Oxidación-Reducción , Multimerización de Proteína/efectos de los fármacos , Tionucleótidos/farmacologíaRESUMEN
Most US Food and Drug Administration (FDA)-approved treatments for osteoporosis target osteoclastic bone resorption. Only PTH derivatives improve bone formation, but they have drawbacks, and novel bone-anabolic agents are needed. Nitrates, which generate NO, improved BMD in estrogen-deficient rats and may improve bone formation markers and BMD in postmenopausal women. However, nitrates are limited by induction of oxidative stress and development of tolerance, and may increase cardiovascular mortality after long-term use. Here we studied nitrosyl-cobinamide (NO-Cbi), a novel, direct NO-releasing agent, in a mouse model of estrogen deficiency-induced osteoporosis. In murine primary osteoblasts, NO-Cbi increased intracellular cGMP, Wnt/ß-catenin signaling, proliferation, and osteoblastic gene expression, and protected cells from apoptosis. Correspondingly, in intact and ovariectomized (OVX) female C57Bl/6 mice, NO-Cbi increased serum cGMP concentrations, bone formation, and osteoblastic gene expression, and in OVX mice, it prevented osteocyte apoptosis. NO-Cbi reduced osteoclasts in intact mice and prevented the known increase in osteoclasts in OVX mice, partially through a reduction in the RANKL/osteoprotegerin gene expression ratio, which regulates osteoclast differentiation, and partially through direct inhibition of osteoclast differentiation, observed in vitro in the presence of excess RANKL. The positive NO effects in osteoblasts were mediated by cGMP/protein kinase G (PKG), but some of the osteoclast-inhibitory effects appeared to be cGMP-independent. NO-Cbi increased trabecular bone mass in both intact and OVX mice, consistent with its in vitro effects on osteoblasts and osteoclasts. NO-Cbi is a novel direct NO-releasing agent that, in contrast to nitrates, does not generate oxygen radicals, and combines anabolic and antiresorptive effects in bone, making it an excellent candidate for treating osteoporosis. © 2016 American Society for Bone and Mineral Research.
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Hueso Esponjoso/anatomía & histología , Donantes de Óxido Nítrico/farmacología , Osteoblastos/metabolismo , Osteoclastos/metabolismo , Ovariectomía , Animales , Apoptosis/efectos de los fármacos , Hueso Esponjoso/efectos de los fármacos , Diferenciación Celular/efectos de los fármacos , Proliferación Celular/efectos de los fármacos , Supervivencia Celular/efectos de los fármacos , Células Cultivadas , Cobamidas/farmacología , GMP Cíclico/sangre , GMP Cíclico/metabolismo , Proteínas Quinasas Dependientes de GMP Cíclico/metabolismo , Estrógenos/deficiencia , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Femenino , Regulación de la Expresión Génica/efectos de los fármacos , Ratones Endogámicos C57BL , Tamaño de los Órganos/efectos de los fármacos , Osteoblastos/citología , Osteoblastos/efectos de los fármacos , Osteoclastos/citología , Osteoclastos/efectos de los fármacos , Osteocitos/citología , Osteocitos/efectos de los fármacos , Osteocitos/metabolismo , Osteoprotegerina/metabolismo , Proteínas Proto-Oncogénicas c-akt/metabolismo , Ligando RANK/metabolismo , Vía de Señalización Wnt/efectos de los fármacosRESUMEN
Osteoporosis is a major health problem leading to fractures that cause substantial morbidity and mortality. Current osteoporosis therapies have significant drawbacks, creating a need for novel bone-anabolic agents. We previously showed that the nitric oxide/cyclic GMP (cGMP)/protein kinase G pathway mediates some of the anabolic effects of estrogens and mechanical stimulation in osteoblasts and osteocytes, leading us to hypothesize that cGMP-elevating agents may have bone-protective effects. We tested cinaciguat, a prototype of a novel class of soluble guanylate cyclase activators, in a mouse model of estrogen deficiency-induced osteoporosis. Compared with sham-operated mice, ovariectomized mice had lower serum cGMP concentrations, which were largely restored to normal by treatment with cinaciguat or low-dose 17ß-estradiol. Microcomputed tomography of tibiae showed that cinaciguat significantly improved trabecular bone microarchitecture in ovariectomized animals, with effect sizes similar to those obtained with estrogen replacement therapy. Cinaciguat reversed ovariectomy-induced osteocyte apoptosis as efficiently as estradiol and enhanced bone formation parameters in vivo, consistent with in vitro effects on osteoblast proliferation, differentiation, and survival. Compared with 17ß-estradiol, which completely reversed the ovariectomy-induced increase in osteoclast number, cinaciguat had little effect on osteoclasts. Direct guanylate cyclase stimulators have been extremely well tolerated in clinical trials of cardiovascular diseases, and our findings provide proof-of-concept for this new class of drugs as a novel, anabolic treatment strategy for postmenopausal osteoporosis, confirming an important role of nitric oxide/cGMP/protein kinase G signaling in bone.
Asunto(s)
Benzoatos/uso terapéutico , Remodelación Ósea/efectos de los fármacos , Activadores de Enzimas/uso terapéutico , Osteoblastos/efectos de los fármacos , Osteoporosis Posmenopáusica/tratamiento farmacológico , Animales , Benzoatos/farmacología , Diferenciación Celular/efectos de los fármacos , Proliferación Celular/efectos de los fármacos , Supervivencia Celular/efectos de los fármacos , Células Cultivadas , GMP Cíclico/sangre , Proteínas Quinasas Dependientes de GMP Cíclico/metabolismo , Modelos Animales de Enfermedad , Evaluación Preclínica de Medicamentos , Activadores de Enzimas/farmacología , Femenino , Guanilato Ciclasa/metabolismo , Humanos , Masculino , Ratones Endogámicos C57BL , Osteoblastos/citología , Osteoporosis Posmenopáusica/enzimología , Ovariectomía , Distribución AleatoriaRESUMEN
Postmenopausal osteoporosis due to estrogen deficiency is a major health problem, and available therapies rely largely on the inhibition of bone resorption, because estrogen replacement is associated with risks. Estrogen promotes bone health in large part by increasing osteocyte survival, but the molecular mechanisms involved are only partly understood. We showed that estradiol stimulates nitric oxide (NO) production in osteocytes, leading to increased cGMP synthesis and activation of cGMP-dependent protein kinases (PKGs). Moreover, we found that 17ß-estradiol protects osteocytes against apoptosis via the NO/cGMP signaling pathway: type II PKG mediates estradiol-induced activation of the prosurvival kinases Erk and Akt, whereas type I PKG contributes to prosurvival signaling by directly phosphorylating and inactivating the cell death protein BAD. Preclinical data support an important role of NO in bone biology, and clinical trials suggest that NO donors may prevent bone loss in postmenopausal women. Our data provide novel insights into estrogen signaling through the NO/cGMP/PKG pathway and a rationale for using NO donors and other cGMP-elevating agents for treating postmenopausal osteoporosis.
Asunto(s)
Desarrollo Óseo/fisiología , Estrógenos/metabolismo , Óxido Nítrico/metabolismo , Osteocitos/metabolismo , Animales , Huesos/citología , Huesos/metabolismoRESUMEN
Thyroid hormone (TH) is essential for vertebrate development and the homeostasis of most adult tissues, including bone. TH stimulates target gene expression through the nuclear thyroid receptors TRα and TRß; however, TH also has rapid, transcription-independent (nongenomic) effects. We found a previously uncharacterized plasma membrane-bound receptor that was necessary and sufficient for nongenomic TH signaling in several cell types. We determined that this receptor is generated by translation initiation from an internal methionine of TRα, which produces a transcriptionally incompetent protein that is palmitoylated and associates with caveolin-containing plasma membrane domains. TH signaling through this receptor stimulated a pro-proliferative and pro-survival program by increasing the intracellular concentrations of calcium, nitric oxide (NO), and cyclic guanosine monophosphate (cGMP), which led to the sequential activation of protein kinase G II (PKGII), the tyrosine kinase Src, and extracellular signal-regulated kinase (ERK) and Akt signaling. Hypothyroid mice exhibited a cGMP-deficient state with impaired bone formation and increased apoptosis of osteocytes, which was rescued by a direct stimulator of guanylate cyclase. Our results link nongenomic TH signaling to a previously uncharacterized membrane-bound receptor, and identify NO synthase, guanylate cyclase, and PKGII as TH effectors that activate kinase cascades to regulate cell survival and proliferation.