RESUMO
Exercise confers protection against obesity, type 2 diabetes and other cardiometabolic diseases1-5. However, the molecular and cellular mechanisms that mediate the metabolic benefits of physical activity remain unclear6. Here we show that exercise stimulates the production of N-lactoyl-phenylalanine (Lac-Phe), a blood-borne signalling metabolite that suppresses feeding and obesity. The biosynthesis of Lac-Phe from lactate and phenylalanine occurs in CNDP2+ cells, including macrophages, monocytes and other immune and epithelial cells localized to diverse organs. In diet-induced obese mice, pharmacological-mediated increases in Lac-Phe reduces food intake without affecting movement or energy expenditure. Chronic administration of Lac-Phe decreases adiposity and body weight and improves glucose homeostasis. Conversely, genetic ablation of Lac-Phe biosynthesis in mice increases food intake and obesity following exercise training. Last, large activity-inducible increases in circulating Lac-Phe are also observed in humans and racehorses, establishing this metabolite as a molecular effector associated with physical activity across multiple activity modalities and mammalian species. These data define a conserved exercise-inducible metabolite that controls food intake and influences systemic energy balance.
Assuntos
Ingestão de Alimentos , Comportamento Alimentar , Obesidade , Fenilalanina , Condicionamento Físico Animal , Adiposidade/efeitos dos fármacos , Animais , Peso Corporal/efeitos dos fármacos , Diabetes Mellitus Tipo 2 , Modelos Animais de Doenças , Ingestão de Alimentos/fisiologia , Metabolismo Energético , Comportamento Alimentar/fisiologia , Glucose/metabolismo , Ácido Láctico/metabolismo , Camundongos , Obesidade/metabolismo , Obesidade/prevenção & controle , Fenilalanina/administração & dosagem , Fenilalanina/análogos & derivados , Fenilalanina/metabolismo , Fenilalanina/farmacologia , Condicionamento Físico Animal/fisiologiaRESUMO
Ever since Garrod deduced the existence of inborn errors in 1901, a vast array of metabolic diseases has been identified and characterized in molecular terms. In 2018 it is difficult to imagine that there is any uncharted backyard left in the metabolic disease landscape. Nevertheless, it took until 2013 to identify the cause of a relatively frequent inborn error, pseudoxanthoma elasticum (PXE), a disorder resulting in aberrant calcification. The mechanism found was not only biochemically interesting but also points to possible new treatments for PXE, a disease that has remained untreatable. In this review we sketch the tortuous road that led to the biochemical understanding of PXE and to new ideas for treatment. We also discuss some of the controversies still haunting the field.
Assuntos
Erros Inatos do Metabolismo/genética , Pseudoxantoma Elástico/genética , Humanos , Erros Inatos do Metabolismo/metabolismo , Erros Inatos do Metabolismo/terapia , Pseudoxantoma Elástico/metabolismo , Pseudoxantoma Elástico/terapiaRESUMO
Pathologic soft tissue calcification can occur in both genetic and acquired clinical conditions, causing significant morbidity and mortality. Although the pathomechanisms of pathologic calcification are poorly understood, major progress has been made in recent years in defining the underlying genetic defects in Mendelian disorders of ectopic calcification. This review presents an overview of the pathophysiology of five monogenic disorders of pathologic calcification: pseudoxanthoma elasticum, generalized arterial calcification of infancy, arterial calcification due to deficiency of CD73, ankylosis, and progeria. These hereditary disorders, caused by mutations in genes encoding ATP binding cassette subfamily C member 6, ectonucleotide pyrophosphatase/phosphodiesterase 1, CD73, progressive ankylosis protein, and lamin A/C proteins, respectively, are inorganic pyrophosphate (PPi) deficiency syndromes with reduced circulating levels of PPi, the principal physiologic inhibitor of calcium hydroxyapatite deposition in soft connective tissues. In addition to genetic diseases, PPi deficiency has been encountered in acquired clinical conditions accompanied by pathologic calcification. Because specific and effective treatments are lacking for pathologic calcification, the unifying finding of PPi deficiency suggests that PPi-targeted therapies may be beneficial to counteract pathologic soft tissue calcification in both genetic and acquired diseases.
Assuntos
Anquilose , Calcinose , Coristoma , Pseudoxantoma Elástico , Calcificação Vascular , Anquilose/tratamento farmacológico , Calcinose/genética , Calcinose/terapia , Difosfatos/metabolismo , Humanos , Pseudoxantoma Elástico/genética , Pseudoxantoma Elástico/metabolismo , Pseudoxantoma Elástico/terapia , Síndrome , Calcificação Vascular/tratamento farmacológico , Calcificação Vascular/terapiaRESUMO
Inorganic pyrophosphate (PPi) is a crucial extracellular mineralization regulator. Low plasma PPi concentrations underlie the soft tissue calcification present in several rare hereditary mineralization disorders as well as in more common conditions like chronic kidney disease and diabetes. Even though deregulated plasma PPi homeostasis is known to be linked to multiple human diseases, there is currently no reliable assay for its quantification. We here describe a PPi assay that employs the enzyme ATP sulfurylase to convert PPi into ATP. Generated ATP is subsequently quantified by firefly luciferase-based bioluminescence. An internal ATP standard was used to correct for sample-specific interference by matrix compounds on firefly luciferase activity. The assay was validated and shows excellent precision (< 3.5%) and accuracy (93-106%) of PPi spiked into human plasma samples. We found that of several anticoagulants tested only EDTA effectively blocked conversion of ATP into PPi in plasma after blood collection. Moreover, filtration over a 300,000-Da molecular weight cut-off membrane reduced variability of plasma PPi and removed ATP present in a membrane-enclosed compartment, possibly platelets. Applied to plasma samples of wild-type and Abcc6-/- rats, an animal model with established low circulating levels of PPi, the new assay showed lower variability than the assay that was previously in routine use in our laboratory. In conclusion, we here report a new and robust assay to determine PPi concentrations in plasma, which outperforms currently available assays because of its high sensitivity, precision, and accuracy.
Assuntos
Calcinose , Difosfatos , Humanos , Ratos , Animais , Luciferases de Vaga-Lume , Trifosfato de AdenosinaRESUMO
The membrane protein ANKH was known to prevent pathological mineralization of joints and was thought to export pyrophosphate (PPi) from cells. This did not explain, however, the presence of ANKH in tissues, such as brain, blood vessels and muscle. We now report that in cultured cells ANKH exports ATP, rather than PPi, and, unexpectedly, also citrate as a prominent metabolite. The extracellular ATP is rapidly converted into PPi, explaining the role of ANKH in preventing ankylosis. Mice lacking functional Ank (Ankank/ank mice) had plasma citrate concentrations that were 65% lower than those detected in wild type control animals. Consequently, citrate excretion via the urine was substantially reduced in Ankank/ank mice. Citrate was even undetectable in the urine of a human patient lacking functional ANKH. The hydroxyapatite of Ankank/ank mice contained dramatically reduced levels of both, citrate and PPi and displayed diminished strength. Our results show that ANKH is a critical contributor to extracellular citrate and PPi homeostasis and profoundly affects bone matrix composition and, consequently, bone quality.
Assuntos
Osso e Ossos/metabolismo , Calcinose/genética , Ácido Cítrico/metabolismo , Proteínas de Transporte de Fosfato/genética , Trifosfato de Adenosina/metabolismo , Animais , Desenvolvimento Ósseo/genética , Calcinose/metabolismo , Calcinose/patologia , Diferenciação Celular , Células Cultivadas , Difosfatos/metabolismo , Humanos , Fenômenos Mecânicos , Camundongos , Mutação/genética , Proteínas de Transporte de Fosfato/metabolismoRESUMO
ABCC6 promotes ATP efflux from hepatocytes to bloodstream. ATP is metabolized to pyrophosphate, an inhibitor of ectopic calcification. Pathogenic variants of ABCC6 cause pseudoxanthoma elasticum, a highly variable recessive ectopic calcification disorder. Incomplete penetrance may initiate disease heterogeneity, hence symptoms may not, or differently manifest in carriers. Here, we investigated whether incomplete penetrance is a source of heterogeneity in pseudoxanthoma elasticum. By integrating clinical and genetic data of 589 patients, we created the largest European cohort. Based on allele frequency alterations, we identified two incomplete penetrant pathogenic variants, c.2359G>A (p.Val787Ile) and c.1171A>G (p.Arg391Gly), with 6.5% and 2% penetrance, respectively. However, when penetrant, the c.1171A>G (p.Arg391Gly) manifested a clinically unaltered severity. After applying in silico and in vitro characterization, we suggest that incomplete penetrant variants are only deleterious if a yet unknown interacting partner of ABCC6 is mutated simultaneously. The low penetrance of these variants should be contemplated in genetic counseling.
Assuntos
Pseudoxantoma Elástico , Humanos , Mutação , Pseudoxantoma Elástico/genética , Pseudoxantoma Elástico/metabolismo , Pseudoxantoma Elástico/patologia , Penetrância , Trifosfato de Adenosina , Proteínas Associadas à Resistência a Múltiplos Medicamentos/genéticaRESUMO
Inactivating mutations in ABCC6 underlie the rare hereditary mineralization disorder pseudoxanthoma elasticum. ABCC6 is an ATP-binding cassette (ABC) integral membrane protein that mediates the release of ATP from hepatocytes into the bloodstream. The released ATP is extracellularly converted into pyrophosphate, a key mineralization inhibitor. Although ABCC6 is firmly linked to cellular ATP release, the molecular details of ABCC6-mediated ATP release remain elusive. Most of the currently available data support the hypothesis that ABCC6 is an ATP-dependent ATP efflux pump, an un-precedented function for an ABC transporter. This hypothesis implies the presence of an ATP-binding site in the substrate-binding cavity of ABCC6. We performed an extensive mutagenesis study using a new homology model based on recently published structures of its close homolog, bovine Abcc1, to characterize the substrate-binding cavity of ABCC6. Leukotriene C4 (LTC4), is a high-affinity substrate of ABCC1. We mutagenized fourteen amino acid residues in the rat ortholog of ABCC6, rAbcc6, that corresponded to the residues in ABCC1 found in the LTC4 binding cavity. Our functional characterization revealed that most of the amino acids in rAbcc6 corresponding to those found in the LTC4 binding pocket in bovine Abcc1 are not critical for ATP efflux. We conclude that the putative ATP binding site in the substrate-binding cavity of ABCC6/rAbcc6 is distinct from the bovine Abcc1 LTC4-binding site.
Assuntos
Sítios de Ligação , Modelos Moleculares , Proteínas Associadas à Resistência a Múltiplos Medicamentos/química , Proteínas Associadas à Resistência a Múltiplos Medicamentos/genética , Mutação , Trifosfato de Adenosina/química , Trifosfato de Adenosina/metabolismo , Sequência de Aminoácidos , Aminoácidos/química , Animais , Ligantes , Conformação Molecular , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Mutagênese , Ligação Proteica , Transporte Proteico , Ratos , Relação Estrutura-Atividade , Especificidade por SubstratoRESUMO
Ectopic mineralization is a global problem and leading cause of morbidity and mortality. The pathomechanisms of ectopic mineralization are poorly understood. Recent studies on heritable ectopic mineralization disorders with defined gene defects have been helpful in elucidation of the mechanisms of ectopic mineralization in general. The prototype of such disorders is pseudoxanthoma elasticum (PXE), a late-onset, slowly progressing disorder with multisystem clinical manifestations. Other conditions include generalized arterial calcification of infancy (GACI), characterized by severe, early-onset mineralization of the cardiovascular system, often with early postnatal demise. In addition, arterial calcification due to CD73 deficiency (ACDC) occurs late in life, mostly affecting arteries in the lower extremities in elderly individuals. These three conditions, PXE, GACI, and ACDC, caused by mutations in ABCC6, ENPP1, and NT5E, respectively, are characterized by reduced levels of inorganic pyrophosphate (PPi) in plasma. Because PPi is a powerful antimineralization factor, it has been postulated that reduced PPi is a major determinant for ectopic mineralization in these conditions. These and related observations on complementary mechanisms of ectopic mineralization have resulted in development of potential treatment modalities for PXE, including administration of bisphosphonates, stable PPi analogs with antimineralization activity. It is conceivable that efficient treatments may soon become available for heritable ectopic mineralization disorders with application to common calcification disorders.
Assuntos
5'-Nucleotidase/deficiência , Difosfonatos/uso terapêutico , Pseudoxantoma Elástico , Calcificação Vascular , Difosfatos/sangue , Proteínas Ligadas por GPI/deficiência , Humanos , Proteínas Associadas à Resistência a Múltiplos Medicamentos/genética , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Diester Fosfórico Hidrolases/genética , Diester Fosfórico Hidrolases/metabolismo , Pseudoxantoma Elástico/sangue , Pseudoxantoma Elástico/tratamento farmacológico , Pseudoxantoma Elástico/genética , Pseudoxantoma Elástico/patologia , Pirofosfatases/genética , Pirofosfatases/metabolismo , Calcificação Vascular/sangue , Calcificação Vascular/tratamento farmacológico , Calcificação Vascular/genética , Calcificação Vascular/patologiaRESUMO
Soft tissue calcification occurs in several common acquired pathologies, such as diabetes and hypercholesterolemia, or can result from genetic disorders. ABCC6, a transmembrane transporter primarily expressed in liver and kidneys, initiates a molecular pathway inhibiting ectopic calcification. ABCC6 facilitates the cellular efflux of ATP, which is rapidly converted into pyrophosphate (PPi), a major calcification inhibitor. Heritable mutations in ABCC6 underlie the incurable calcification disorder pseudoxanthoma elasticum and some cases of generalized arterial calcification of infancy. Herein, we determined that the administration of PPi and the bisphosphonate etidronate to Abcc6-/- mice fully inhibited the acute dystrophic cardiac calcification phenotype, whereas alendronate had no significant effect. We also found that daily injection of PPi to Abcc6-/- mice over several months prevented the development of pseudoxanthoma elasticum-like spontaneous calcification, but failed to reverse already established lesions. Furthermore, we found that the expression of low amounts of the human ABCC6 in liver of transgenic Abcc6-/- mice, resulting in only a 27% increase in plasma PPi levels, led to a major reduction in acute and chronic calcification phenotypes. This proof-of-concept study shows that the development of both acute and chronic calcification associated with ABCC6 deficiency can be prevented by compensating PPi deficits, even partially. Our work indicates that PPi substitution represents a promising strategy to treat ABCC6-dependent calcification disorders.
Assuntos
Transportadores de Cassetes de Ligação de ATP/fisiologia , Calcinose/prevenção & controle , Difosfatos/uso terapêutico , Pseudoxantoma Elástico/prevenção & controle , Transportadores de Cassetes de Ligação de ATP/deficiência , Transportadores de Cassetes de Ligação de ATP/genética , Doença Aguda , Animais , Calcinose/metabolismo , Calcinose/patologia , Doença Crônica , Difosfatos/administração & dosagem , Difosfatos/metabolismo , Modelos Animais de Doenças , Relação Dose-Resposta a Droga , Avaliação Pré-Clínica de Medicamentos/métodos , Ácido Etidrônico/uso terapêutico , Feminino , Fígado/metabolismo , Masculino , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteínas Associadas à Resistência a Múltiplos Medicamentos/genética , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Fenótipo , Pseudoxantoma Elástico/metabolismo , Pseudoxantoma Elástico/patologia , TransgenesRESUMO
Despite technological advances in metabolomics, large parts of the human metabolome are still unexplored. In an untargeted metabolomics screen aiming to identify substrates of the orphan transporter ATP-binding cassette subfamily C member 5 (ABCC5), we identified a class of mammalian metabolites, N-lactoyl-amino acids. Using parallel protein fractionation in conjunction with shotgun proteomics on fractions containing N-lactoyl-Phe-forming activity, we unexpectedly found that a protease, cytosolic nonspecific dipeptidase 2 (CNDP2), catalyzes their formation. N-lactoyl-amino acids are ubiquitous pseudodipeptides of lactic acid and amino acids that are rapidly formed by reverse proteolysis, a process previously considered to be negligible in vivo. The plasma levels of these metabolites strongly correlate with plasma levels of lactate and amino acid, as shown by increased levels after physical exercise and in patients with phenylketonuria who suffer from elevated Phe levels. Our approach to identify unknown metabolites and their biosynthesis has general applicability in the further exploration of the human metabolome.
Assuntos
Aminoácidos/metabolismo , Dipeptidases/metabolismo , Lactatos/metabolismo , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Aminoácidos/sangue , Citosol/metabolismo , Exercício Físico/fisiologia , Células HEK293 , Humanos , Lactatos/sangue , Metaboloma , ProteóliseRESUMO
Ectonucleotide pyrophosphatase/phosphodiesterase family member 1 (E-NPP1), encoded by ENPP1, is a plasma membrane protein that generates inorganic pyrophosphate (PPi ), a physiologic inhibitor of hydroxyapatite formation. In humans, variants in ENPP1 are associated with generalized arterial calcification of infancy, an autosomal-recessive condition causing premature onset of arterial calcification and intimal proliferation resulting in stenoses. ENPP1 variants also cause pseudoxanthoma elasticum characterized by ectopic calcification of soft connective tissues. To determine the functional impact of ENPP1 missense variants, we analyzed 13 putative pathogenic variants in vitro regarding their functional properties, that is, activity, localization, and PPi generation. Transfection of eight of the 13 variants led to complete loss of NPP activity, whereas four mutants (c.1412A > G, p.Tyr471Cys; c.1510A > C, p.Ser504Arg; c.1976A > G, p.Tyr659Cys; c.2330A > G, p.His777Arg) showed residual activity compared with wild-type E-NPP1. One putative pathologic variant (c.2462 G > A, p.Arg821His) showed normal activity. The five mutants with normal or residual E-NPP1 enzyme activity were still able to generate PPi and localized in the plasma membrane. In this study, we identified a functional ENPP1 polymorphism, which was expected to be pathogenic till now. Furthermore, we identified four mutants (p.Tyr471Cys, p.Ser504Arg, p.Tyr659Cys, p.His777Arg) with residual E-NPP1 function, which would be potential therapeutical targets for conformational-stabilizing agents.
Assuntos
Mutação de Sentido Incorreto , Diester Fosfórico Hidrolases/genética , Diester Fosfórico Hidrolases/metabolismo , Pirofosfatases/genética , Pirofosfatases/metabolismo , Calcificação Vascular/genética , Animais , Células COS , Membrana Celular/metabolismo , Chlorocebus aethiops , Difosfatos/metabolismo , Regulação para Baixo , Células HEK293 , Humanos , Mutagênese Sítio-DirigidaRESUMO
The ubiquitous efflux transporter ABCC5 (ATP-binding cassette subfamily C member 5) is present at high levels in the blood-brain barrier, neurons, and glia, but its in vivo substrates and function are not known. Using untargeted metabolomic screens, we show that Abcc5(-/-) mice accumulate endogenous glutamate conjugates in several tissues, but brain in particular. The abundant neurotransmitter N-acetylaspartylglutamate was 2.4-fold higher in Abcc5(-/-) brain. The metabolites that accumulated in Abcc5(-/-) tissues were depleted in cultured cells that overexpressed human ABCC5. In a vesicular membrane transport assay, ABCC5 also transported exogenous glutamate analogs, like the classic excitotoxic neurotoxins kainic acid, domoic acid, and NMDA; the therapeutic glutamate analog ZJ43; and, as previously shown, the anti-cancer drug methotrexate. Glutamate conjugates and analogs are of physiological relevance because they can affect the function of glutamate, the principal excitatory neurotransmitter in the brain. After CO2 asphyxiation, several immediate early genes were expressed at lower levels in Abcc5(-/-) brains than in wild type brains, suggesting altered glutamate signaling. Our results show that ABCC5 is a general glutamate conjugate and analog transporter that affects the disposition of endogenous metabolites, toxins, and drugs.
Assuntos
Encéfalo/metabolismo , Dipeptídeos/farmacocinética , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Animais , Dipeptídeos/farmacologia , Humanos , Ácido Caínico/análogos & derivados , Ácido Caínico/farmacocinética , Ácido Caínico/farmacologia , Camundongos , Camundongos Knockout , Proteínas Associadas à Resistência a Múltiplos Medicamentos/genética , Proteínas do Tecido Nervoso/genética , Ureia/análogos & derivados , Ureia/farmacocinética , Ureia/farmacologiaRESUMO
Pseudoxanthoma elasticum (PXE) is an autosomal recessive disease characterized by progressive ectopic mineralization of the skin, eyes, and arteries, for which no effective treatment exists. PXE is caused by inactivating mutations in the gene encoding ATP-binding cassette sub-family C member 6 (ABCC6), an ATP-dependent efflux transporter present mainly in the liver. Abcc6(-/-) mice have been instrumental in demonstrating that PXE is a metabolic disease caused by the absence of an unknown factor in the circulation, the presence of which depends on ABCC6 in the liver. Why absence of this factor results in PXE has remained a mystery. Here we report that medium from HEK293 cells overexpressing either human or rat ABCC6 potently inhibits mineralization in vitro, whereas medium from HEK293 control cells does not. Untargeted metabolomics revealed that cells expressing ABCC6 excrete large amounts of nucleoside triphosphates, even though ABCC6 itself does not transport nucleoside triphosphates. Extracellularly, ectonucleotidases hydrolyze the excreted nucleoside triphosphates to nucleoside monophosphates and inorganic pyrophosphate (PPi), a strong inhibitor of mineralization that plays a pivotal role in several mineralization disorders similar to PXE. The in vivo relevance of our data are demonstrated in Abcc6(-/-) mice, which had plasma PPi levels <40% of those found in WT mice. This study provides insight into how ABCC6 affects PXE. Our data indicate that the factor that normally prevents PXE is PPi, which is provided to the circulation in the form of nucleoside triphosphates via an as-yet unidentified but ABCC6-dependent mechanism.
Assuntos
Difosfatos/sangue , Doenças Metabólicas/genética , Proteínas Associadas à Resistência a Múltiplos Medicamentos/genética , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Pseudoxantoma Elástico/genética , Animais , Primers do DNA/genética , DNA Complementar/genética , Fosfatos de Dinucleosídeos/metabolismo , Células HEK293 , Humanos , Doenças Metabólicas/metabolismo , Doenças Metabólicas/patologia , Metabolômica , Camundongos , Camundongos Knockout , Mutagênese Sítio-Dirigida , Mutação/genética , Pseudoxantoma Elástico/metabolismo , Pseudoxantoma Elástico/patologia , RatosRESUMO
OBJECTIVE: Mutations in ABCC6 underlie the ectopic mineralization disorder pseudoxanthoma elasticum (PXE) and some forms of generalized arterial calcification of infancy, both of which affect the cardiovascular system. Using cultured cells, we recently showed that ATP-binding cassette subfamily C member 6 (ABCC6) mediates the cellular release of ATP, which is extracellularly rapidly converted into AMP and the mineralization inhibitor inorganic pyrophosphate (PPi). The current study was performed to determine which tissues release ATP in an ABCC6-dependent manner in vivo, where released ATP is converted into AMP and PPi, and whether human PXE ptients have low plasma PPi concentrations. APPROACH AND RESULTS: Using cultured primary hepatocytes and in vivo liver perfusion experiments, we found that ABCC6 mediates the direct, sinusoidal, release of ATP from the liver. Outside hepatocytes, but still within the liver vasculature, released ATP is converted into AMP and PPi. The absence of functional ABCC6 in patients with PXE leads to strongly reduced plasma PPi concentrations. CONCLUSIONS: Hepatic ABCC6-mediated ATP release is the main source of circulating PPi, revealing an unanticipated role of the liver in systemic PPi homeostasis. Patients with PXE have a strongly reduced plasma PPi level, explaining their mineralization disorder. Our results indicate that systemic PPi is relatively stable and that PXE, generalized arterial calcification of infancy, and other ectopic mineralization disorders could be treated with PPi supplementation therapy.
Assuntos
Transportadores de Cassetes de Ligação de ATP/fisiologia , Trifosfato de Adenosina/metabolismo , Difosfatos/sangue , Fígado/metabolismo , Proteínas Associadas à Resistência a Múltiplos Medicamentos/fisiologia , Monofosfato de Adenosina/sangue , Idoso , Animais , Células Cultivadas , Meios de Cultivo Condicionados , Feminino , Células HEK293 , Células HeLa , Hepatócitos/metabolismo , Homeostase , Humanos , Fígado/irrigação sanguínea , Masculino , Camundongos , Pessoa de Meia-Idade , Pseudoxantoma Elástico/genética , Pseudoxantoma Elástico/metabolismo , RatosRESUMO
Disc degeneration primarily contributes to chronic low back and neck pain. Consequently, there is an urgent need to understand the spectrum of disc degeneration phenotypes such as fibrosis, ectopic calcification, herniation, or mixed phenotypes. Amongst these phenotypes, disc calcification is the least studied. Ectopic calcification, by definition, is the pathological mineralization of soft tissues, widely studied in the context of conditions that afflict vasculature, skin, and cartilage. Clinically, disc calcification is associated with poor surgical outcomes and back pain refractory to conservative treatment. It is frequently seen as a consequence of disc aging and progressive degeneration but exhibits unique molecular and morphological characteristics: hypertrophic chondrocyte-like cell differentiation; TNAP, ENPP1, and ANK upregulation; cell death; altered Pi and PPi homeostasis; and local inflammation. Recent studies in mouse models have provided a better understanding of the mechanisms underlying this phenotype. It is essential to recognize that the presentation and nature of mineralization differ between AF, NP, and EP compartments. Moreover, the combination of anatomic location, genetics, and environmental stressors, such as aging or trauma, govern the predisposition to calcification. Lastly, the systemic regulation of calcium and Pi metabolism is less important than the local activity of PPi modulated by the ANK-ENPP1 axis, along with disc cell death and differentiation status. While there is limited understanding of this phenotype, understanding the molecular pathways governing local intervertebral disc calcification may lead to developing disease-modifying drugs and better clinical management of degeneration-related pathologies.
Assuntos
Calcinose , Condrocalcinose , Degeneração do Disco Intervertebral , Disco Intervertebral , Animais , Camundongos , Degeneração do Disco Intervertebral/genética , Calcinose/genética , InflamaçãoRESUMO
Despite the high prevalence of age-dependent intervertebral disc calcification, there is a glaring lack of treatment options for this debilitating pathology. Here, we investigate the efficacy of long-term oral K3Citrate supplementation in ameliorating disc calcification in LG/J mice, a model of spontaneous age-associated disc calcification. K3Citrate successfully reduced the incidence of disc calcification in LG/J mice without deleterious effects on vertebral bone structure, plasma chemistry, and locomotion. Notably, a positive effect on grip strength was evident in treated mice. Spectroscopic investigation of the persisting calcified nodules indicated K3Citrate did not alter the mineral composition and revealed that reactivation of an endochondral differentiation program in endplates may drive LG/J disc calcification. Importantly, K3Citrate reduced calcification incidence without altering the pathological endplate chondrocyte hypertrophy, suggesting mitigation of disc calcification primarily occurred through Ca2+ chelation, a conclusion supported by chondrogenic differentiation and Seahorse metabolic assays. Overall, this study underscores the therapeutic potential of K3Citrate as a systemic intervention strategy for disc calcification.
RESUMO
ABCG2 is an ATP-dependent efflux transporter that limits the systemic exposure of its substrates. The preferred substrates of ABCG2 in vivo are largely unknown. We aimed to identify the compounds transported by ABCG2 under physiological conditions. In vitro, ABCG2 transports several sulfate conjugates at high rates. We therefore used targeted metabolomics, specifically detecting compounds conjugated to sulfate, to search in plasma, urine, and bile samples of wild-type and Abcg2-/- mice for differentially present compounds, which are likely to represent in vivo ABCG2 substrates. Levels of many sulfate conjugates were up to 15-fold higher in plasma and urine of Abcg2-/- than of wild-type mice, with the opposite effect seen in bile. These differentially present compounds were identified as the sulfate conjugates of phytoestrogens, compounds with weak pro- or antiestrogenic properties. We confirmed that these sulfate conjugates were ABCG2 substrates using transportomics, a method that uses vesicular transport assays to screen for substrates of ABC transporters in body fluids. In conclusion, our results show that ABCG2 limits the systemic exposure to many different phytoestrogens, a class of compounds to which mammals are exposed on a daily basis via food of plant origin, by directing their sulfate conjugates for excretion via the feces.
Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Proteínas de Membrana Transportadoras/metabolismo , Fitoestrógenos/metabolismo , Membro 2 da Subfamília G de Transportadores de Cassetes de Ligação de ATP , Transportadores de Cassetes de Ligação de ATP/sangue , Transportadores de Cassetes de Ligação de ATP/genética , Transportadores de Cassetes de Ligação de ATP/urina , Animais , Transporte Biológico/genética , Transporte Biológico/fisiologia , Cromatografia Líquida de Alta Pressão , Feminino , Masculino , Espectrometria de Massas , Proteínas de Membrana Transportadoras/sangue , Proteínas de Membrana Transportadoras/genética , Proteínas de Membrana Transportadoras/urina , Metabolômica , Camundongos , Camundongos KnockoutRESUMO
The ATP-binding cassette (ABC) genes encode the largest family of transmembrane proteins. ABC transporters translocate a wide variety of substrates across membranes, but their physiological function is often incompletely understood. We describe a new method to study the substrate spectrum of ABC transporters: We incubate extracts of mouse urine with membrane vesicles prepared from Spodoptera frugiperda Sf9 insect cells overproducing an ABC transporter and determine the compounds transported into the vesicles by LC/MS-based metabolomics. We illustrate the power of this simple "transportomics" approach using ABCC2, a protein present at sites of uptake and elimination. We identified many new substrates of ABCC2 in urine. These included glucuronides of plant-derived xenobiotics, a class of compounds to which humans are exposed on a daily basis. Moreover, we show that the excretion of these compounds in vivo depends on ABCC2: compared to wild-type mice, the urinary excretion of several glucuronides was increased up to 20-fold in Abcc2(-/-) mice. Transportomics has broad applicability, as it is not restricted to urine and can be applied to other ATP-dependent transport proteins as well.
Assuntos
Transportadores de Cassetes de Ligação de ATP/metabolismo , Transportadores de Cassetes de Ligação de ATP/genética , Animais , Transporte Biológico Ativo , Líquidos Corporais/metabolismo , Glucuronídeos/metabolismo , Glucuronídeos/urina , Humanos , Cinética , Metaboloma , Camundongos , Camundongos Knockout , Proteína 2 Associada à Farmacorresistência Múltipla , Proteínas Associadas à Resistência a Múltiplos Medicamentos/deficiência , Proteínas Associadas à Resistência a Múltiplos Medicamentos/genética , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Fitoestrógenos/metabolismo , Fitoestrógenos/urina , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Xenobióticos/metabolismo , Xenobióticos/urinaRESUMO
Pathological mineralization of intervertebral disc is debilitating and painful and linked to disc degeneration in a subset of human patients. An adenosine triphosphate efflux transporter, progressive ankylosis (ANK) is a regulator of extracellular inorganic pyrophosphate levels and plays an important role in tissue mineralization. However, the function of ANK in intervertebral disc has not been fully explored. Herein we analyzed the spinal phenotype of Ank mutant mice (ank/ank) with attenuated ANK function. Micro-computed tomography and histological analysis showed that loss of ANK function results in the aberrant annulus fibrosus mineralization and peripheral disc fusions with cranial to caudal progression in the spine. Vertebrae in ank mice exhibit elevated cortical bone mass and increased tissue non-specific alkaline phosphatase-positive endplate chondrocytes with decreased subchondral endplate porosity. The acellular dystrophic mineral inclusions in the annulus fibrosus were localized adjacent to apoptotic cells and cells that acquired osteoblast-like phenotype. Fourier transform infrared spectral imaging showed that the apatite mineral in the outer annulus fibrosus had similar chemical composition to that of vertebral bone. Transcriptomic analysis of annulus fibrosus and nucleus pulposus tissues showed changes in several biological themes with a prominent dysregulation of BMAL1/CLOCK circadian regulation. The present study provides new insights into the role of ANK in the disc tissue compartments and highlights the importance of local inorganic pyrophosphate metabolism in inhibiting the mineralization of this important connective tissue.
Assuntos
Calcinose , Degeneração do Disco Intervertebral , Disco Intervertebral , Animais , Humanos , Camundongos , Calcinose/patologia , Difosfatos/metabolismo , Disco Intervertebral/metabolismo , Degeneração do Disco Intervertebral/patologia , Mutação com Perda de Função , Fenótipo , Microtomografia por Raio-XRESUMO
Opioid-induced hyperalgesia (OIH) is a paradoxical increase in pain perception that may manifest during opioid treatment. For morphine, the metabolite morphine-3-glucuronide (M3G) is commonly believed to underlie this phenomenon. Here, in three separate studies, we empirically assess the role of M3G in morphine-induced hyperalgesia. In the first study, CD-1 mice injected with morphine (15 mg/kg subcutaneously) after pretreatment with the opioid receptor antagonist naltrexone (NTX) (15 mg/kg) showed tail withdrawal latency reductions indicative of hyperalgesia (2.5 ± 0.1 s at t = 30 min, P < 0.001 versus baseline). In these mice, the morphine/M3G concentration ratios versus effect showed a negative correlation (r(p) = -0.65, P < 0.001), indicating that higher morphine relative to M3G concentrations are associated with increased OIH. In the second study, similar hyperalgesic responses were observed in mice lacking the multidrug resistance protein 3 (MRP3) transporter protein (Mrp3(-/-) mice) in the liver and their wild-type controls (FVB mice; latency reductions: 3.1 ± 0.2 s at t = 30 min, P < 0.001 versus within-strain baseline). In the final study, the pharmacokinetics of morphine and M3G were measured in Mrp3(-/-) and FVB mice. Mrp3(-/-) mice displayed a significantly reduced capacity to export M3G into the systemic circulation, with plasma M3G concentrations just 7% of those observed in FVB controls. The data confirm previous literature that morphine causes hyperalgesia in the absence of opioid receptor activation but also indicate that this hyperalgesia may occur without a significant contribution of hepatic M3G. The relevance of these data to humans has yet to be demonstrated.