Muscle NAD+ depletion and Serpina3n as molecular determinants of murine cancer cachexia-the effects of blocking myostatin and activins.

OBJECTIVE: Cancer cachexia and muscle loss are associated with increased morbidity and mortality. In preclinical animal models, blocking activin receptor (ACVR) ligands has improved survival and prevented muscle wasting in cancer cachexia without an effect on tumour growth. However, the underlying mechanisms are poorly understood. This study aimed to identify cancer cachexia and soluble ACVR (sACVR) administration-evoked changes in muscle proteome. METHODS: Healthy and C26 tumour-bearing (TB) mice were treated with recombinant sACVR. The sACVR or PBS control were administered either prior to the tumour formation or by continued administration before and after tumour formation. Muscles were analysed by quantitative proteomics with further examination of mitochondria and nicotinamide adenine dinucleotide (NAD+) metabolism. To complement the first prophylactic experiment, sACVR (or PBS) was injected as a treatment after tumour cell inoculation. RESULTS: Muscle proteomics in TB cachectic mice revealed downregulated signatures for mitochondrial oxidative phosphorylation (OXPHOS) and increased acute phase response (APR). These were accompanied by muscle NAD+ deficiency, alterations in NAD+ biosynthesis including downregulation of nicotinamide riboside kinase 2 (Nrk2), and decreased muscle protein synthesis. The disturbances in NAD+ metabolism and protein synthesis were rescued by treatment with sACVR. Across the whole proteome and APR, in particular, Serpina3n represented the most upregulated protein and the strongest predictor of cachexia. However, the increase in Serpina3n expression was associated with increased inflammation rather than decreased muscle mass and/or protein synthesis. CONCLUSIONS: We present evidence implicating disturbed muscle mitochondrial OXPHOS proteome and NAD+ homeostasis in experimental cancer cachexia. Treatment of TB mice with a blocker of activin receptor ligands restores depleted muscle NAD+ and Nrk2, as well as decreased muscle protein synthesis. These results indicate putative new treatment therapies for cachexia and that although acute phase protein Serpina3n may serve as a predictor of cachexia, it more likely reflects a condition of elevated inflammation.

Cardiac function modulates endocardial cell dynamics to shape the cardiac outflow tract.

Physical forces are important participants in the cellular dynamics that shape developing organs. During heart formation, for example, contractility and blood flow generate biomechanical cues that influence patterns of cell behavior. Here, we address the interplay between function and form during the assembly of the cardiac outflow tract (OFT), a crucial connection between the heart and vasculature that develops while circulation is under way. In zebrafish, we find that the OFT expands via accrual of both endocardial and myocardial cells. However, when cardiac function is disrupted, OFT endocardial growth ceases, accompanied by reduced proliferation and reduced addition of cells from adjacent vessels. The flow-responsive TGFß receptor Acvrl1 is required for addition of endocardial cells, but not for their proliferation, indicating distinct modes of function-dependent regulation for each of these essential cell behaviors. Together, our results indicate that cardiac function modulates OFT morphogenesis by triggering endocardial cell accumulation that induces OFT lumen expansion and shapes OFT dimensions. Moreover, these morphogenetic mechanisms provide new perspectives regarding the potential causes of cardiac birth defects.

Perspectives of small molecule inhibitors of activin receptor­like kinase in anti­tumor treatment and stem cell differentiation (Review).

Activin receptor­like kinases (ALKs), members of the type I activin receptor family, belong to the serine/threonine kinase receptors of the transforming growth factor­ß (TGF­ß) superfamily. ALKs mediate the roles of activin/TGF­ß in a wide variety of physiological and pathological processes, ranging from cell differentiation and proliferation to apoptosis. For example, the activities of ALKs are associated with an advanced tumor stage in prostate cancer and the chondrogenic differentiation of mesenchymal stem cells. Therefore, potent and selective small molecule inhibitors of ALKs would not only aid in investigating the function of activin/TGF­ß, but also in developing treatments for these diseases via the disruption of activin/TGF­ß. In recent studies, several ALK inhibitors, including LY­2157299, SB­431542 and A­83­01, have been identified and have been confirmed to affect stem cell differentiation and tumor progression in animal models. This review discusses the therapeutic perspective of small molecule inhibitors of ALKs as drug targets in tumor and stem cells.

Activin Receptor 2 Antagonization Impairs Adipogenic and Enhances Osteogenic Differentiation in Mouse Adipose-Derived Stem Cells and Mouse Bone Marrow-Derived Stem Cells In Vitro and In Vivo.

Tumors, traumata, burn injuries or surgeries can lead to critical-sized bony defects which need to be reconstructed. Mesenchymal stem cells (MSCs) have the ability to differentiate into multiple cell lineages and thus present a promising alternative for use in tissue engineering and reconstruction. However, there is an ongoing debate whether all MSCs are equivalent in their differentiation and proliferation ability. The goal of this study was to assess osteogenic and adipogenic characteristic changes of adipose-derived stem cells (ASCs) and bone marrow-derived stem cells (BMSCs) upon Myostatin inhibition with Follistatin in vitro and in vivo. We harvested ASCs from mice inguinal fat pads and BMSCs from tibiae of mice. By means of histology, real-time cell analysis, immunohistochemistry, and PCR osteogenic and adipogenic proliferation and differentiation in the presence or absence of Follistatin were analyzed. In vivo, osteogenic capacity was investigated in a tibial defect model of wild-type (WT) mice treated with mASCs and mBMSCs of Myo-/- and WT origin. In vitro, we were able to show that inhibition of Myostatin leads to markedly reduced proliferative capacity in mBMSCs and mASCs in adipogenic differentiation and reduced proliferation in osteogenic differentiation in mASCs, whereas proliferation in mBMSCs in osteogenic differentiation was increased. Adipogenic differentiation was inhibited in mASCs and mBMSCs upon Follistatin treatment, whereas osteogenic differentiation was increased in both cell lineages. In vivo, we could demonstrate increased osteoid formation in WT mice treated with mASCs and mBMSCs of Myo-/- origin and enhanced osteogenic differentiation and proliferation of mASCs of Myo-/- origin. We could demonstrate that the osteogenic potential of mASCs could be raised to a level comparable to mBMSCs upon inhibition of Myostatin. Moreover, Follistatin treatment led to inhibition of adipogenesis in both lineages.

Activin Type II Receptor Blockade for Treatment of Muscle Depletion in Chronic Obstructive Pulmonary Disease. A Randomized Trial.

RATIONALE: Bimagrumab is a fully human monoclonal antibody that blocks the activin type II receptors, preventing the activity of myostatin and other negative skeletal muscle regulators. OBJECTIVES: To assess the effects of bimagrumab on skeletal muscle mass and function in patients with chronic obstructive pulmonary disease (COPD) and reduced skeletal muscle mass. METHODS: Sixty-seven patients with COPD (mean FEV1, 1.05 L [41.6% predicted]; aged 40-80 yr; body mass index < 20 kg/m2 or appendicular skeletal muscle mass index ≤ 7.25 [men] and ≤ 5.67 [women] kg/m2), received two doses of either bimagrumab 30 mg/kg intravenously (n = 33) or placebo (n = 34) (Weeks 0 and 8) over 24 weeks. MEASUREMENTS AND MAIN RESULTS: We assessed changes in thigh muscle volume (cubic centimeters) as the primary endpoint along with 6-minute-walk distance (meters), safety, and tolerability. Fifty-five (82.1%) patients completed the study. Thigh muscle volume increased by Week 4 and remained increased at Week 24 in bimagrumab-treated patients, whereas no changes were observed with placebo (Week 4: +5.9% [SD, 3.4%] vs. 0.0% [3.3%], P < 0.001; Week 8: +7.0% [3.7%] vs. -0.7% [2.8%], P < 0.001; Week 16: +7.8% [5.1%] vs. -0.9% [4.5%], P < 0.001; Week 24: +5.0% [4.9%] vs. -1.3% [4.3%], P < 0.001). Over 24 weeks, 6-minute-walk distance did not increase significantly in either group. Adverse events in the bimagrumab group included muscle-related symptoms, diarrhea, and acne, most of which were mild in severity. CONCLUSIONS: Blocking the action of negative muscle regulators through the activin type II receptors with bimagrumab treatment safely increased skeletal muscle mass but did not improve functional capacity in patients with COPD and low muscle mass. Clinical trial registered with www.clinicaltrials.gov (NCT01669174).

Innate immune system activation in zebrafish and cellular models of Diamond Blackfan Anemia.

Deficiency of ribosomal proteins (RPs) leads to Diamond Blackfan Anemia (DBA) associated with anemia, congenital defects, and cancer. While p53 activation is responsible for many features of DBA, the role of immune system is less defined. The Innate immune system can be activated by endogenous nucleic acids from non-processed pre-rRNAs, DNA damage, and apoptosis that occurs in DBA. Recognition by toll like receptors (TLRs) and Mda5-like sensors induces interferons (IFNs) and inflammation. Dying cells can also activate complement system. Therefore we analyzed the status of these pathways in RP-deficient zebrafish and found upregulation of interferon, inflammatory cytokines and mediators, and complement. We also found upregulation of receptors signaling to IFNs including Mda5, Tlr3, and Tlr9. TGFb family member activin was also upregulated in RP-deficient zebrafish and in RPS19-deficient human cells, which include a lymphoid cell line from a DBA patient, and fetal liver cells and K562 cells transduced with RPS19 shRNA. Treatment of RP-deficient zebrafish with a TLR3 inhibitor decreased IFNs activation, acute phase response, and apoptosis and improved their hematopoiesis and morphology. Inhibitors of complement and activin also had beneficial effects. Our studies suggest that innate immune system contributes to the phenotype of RPS19-deficient zebrafish and human cells.

BMP4 and BMP7 Suppress StAR and Progesterone Production via ALK3 and SMAD1/5/8-SMAD4 in Human Granulosa-Lutein Cells.

Adequate production of progesterone by the corpus luteum is critical to the successful establishment of pregnancy. In animal models, bone morphogenetic protein (BMP) 4 and BMP7 have been shown to suppress either basal or gonadotropin-induced progesterone production, depending on the species examined. However, the effects of BMP4 and BMP7 on progesterone production in human granulosa cells are unknown. In the present study, we used immortalized (SVOG) and primary human granulosa-lutein cells to investigate the effects of BMP4 and BMP7 on steroidogenic acute regulatory protein (StAR) expression and progesterone production and to examine the underlying molecular mechanism. Treatment of primary and immortalized human granulosa cells with recombinant BMP4 or BMP7 decreased StAR expression and progesterone accumulation. In SVOG cells, the suppressive effects of BMP4 and BMP7 on StAR expression were blocked by pretreatment with inhibitors of activin receptor-like kinase (ALK)2/3/6 (dorsomorphin) or ALK2/3 (DMH1) but not ALK4/5/7 (SB-431542). Moreover, small interfering RNA-mediated depletion of ALK3, but not ALK2 or ALK6, reversed the effects of BMP4 and BMP7 on StAR expression. Likewise, BMP4- and BMP7-induced phosphorylation of SMAD 1/5/8 was reversed by treatment with DMH1 or small interfering RNA targeting ALK3. Knockdown of SMAD4, the essential common SMAD for BMP/TGF-ß signaling, abolished the effects of BMP4 and BMP7 on StAR expression. Our results suggest that BMP4 and BMP7 down-regulate StAR and progesterone production via ALK3 and SMAD1/5/8-SMAD4 signaling in human granulosa-lutein cells.

Inhibition of activin A signalling in a mouse model of pre-eclampsia.

INTRODUCTION: Pre-eclampsia remains a major cause of maternal and fetal morbidity and mortality. Despite intensive research over the last 50 years, significant therapeutic advances have yet to be realised. We recently reported on the role of activin A in the pathophysiology of pre-eclampsia, whereby a pre-eclampsia-like disease state was induced in pregnant mice through activin A infusion. Using the same animal model, the effects of inhibiting activin A signalling on this pre-eclampsia-like disease state have now been assessed with low molecular weight compounds structurally related to activin-receptor-like kinase (ALK) inhibitors. METHODS: 23 synthetic compounds were screened for ability to reduce activin A-induced free radical production in HUVECs. Further, following administration of activin A (50 µg) via a subcutaneous mini-osmotic pump from day 10 of pregnancy, the most active inhibitor, MKP-1-140A, (1 mg/kg) was also concomitantly administered via subcutaneous injections. RESULTS: Significant reductions in activin A-induced systolic blood pressure and urine albumin:creatinine ratio were observed with inhibitor-treated animals. However, these findings were accompanied by sustained elevation of liver enzymes and albumin extravasation in the brains of pregnant mice that received MKP-1-140A. Furthermore, inhibition of activin A signalling with MKP-1-140A failed to rescue fetal growth restriction, and treatment with MKP-1-140A alone resulted in craniofacial and karyotypic abnormalities. DISCUSSION: These data indicate that whilst inhibition of activin A signalling by the low molecular weight ALK kinase inhibitor, MKP-1-140A, reduced some of the physiological manifestations of pre-eclampsia, the potential for serious maternal and fetal side effects may preclude it from clinical applications.

Activin receptor antagonists for cancer-related anemia and bone disease.

INTRODUCTION: Antagonists of activin receptor signaling may be beneficial for cancer-related anemia and bone disease caused by malignancies such as multiple myeloma and solid tumors. AREAS COVERED: We review evidence of dysregulated signaling by activin receptor pathways in anemia, myeloma-associated osteolysis, and metastatic bone disease, as well as potential involvement in carcinogenesis. We then review properties of activin receptor antagonists in clinical development. EXPERT OPINION: Sotatercept is a novel receptor fusion protein that functions as a soluble trap to sequester ligands of activin receptor type IIA (ActRIIA). Preclinically, the murine version of sotatercept increased red blood cells (RBC) in a model of chemotherapy-induced anemia, inhibited tumor growth and metastasis, and exerted anabolic effects on bone in diverse models of multiple myeloma. Clinically, sotatercept increases RBC markedly in healthy volunteers and patients with multiple myeloma. With a rapid onset of action differing from erythropoietin, sotatercept is in clinical development as a potential first-in-class therapeutic for cancer-related anemia, including those characterized by ineffective erythropoiesis as in myelodysplastic syndromes. Anabolic bone activity in early clinical studies and potential antitumor effects make sotatercept a promising therapeutic candidate for multiple myeloma and malignant bone diseases. Antitumor activity has been observed preclinically with small-molecule inhibitors of transforming growth factor-ß receptor type I (ALK5) that also antagonize the closely related activin receptors ALK4 and ALK7. LY-2157299, the first such inhibitor to enter clinical studies, has shown an acceptable safety profile so far in patients with advanced cancer. Together, these data identify activin receptor antagonists as attractive therapeutic candidates for multiple diseases.

Activin receptor signaling: a potential therapeutic target for osteoporosis.

Current antiresorptive therapies not only prevent bone loss by decreasing osteoclastic bone resorption but also inhibit bone formation. Dual anabolic antiresorptive agents may be required to cure severe osteoporosis by preventing further bone loss and increasing bone mass to normal levels. Recent studies have demonstrated that activin signaling plays a crucial role in the skeleton. Activins, like other TGF-ß superfamily members, transduce their signals through type I and II receptor serine/threonine kinases. The binding of activins to activin type IIA (ActRIIA) or type IIB (ActRIIB) receptors induces the recruitment and phosphorylation of an activin type I receptor (ALK4 and/or ALK7), which then phosphorylates the Smad2 and Smad3 intracellular signaling proteins. Activin signaling is down-regulated by inhibins, follistatin and other proteins, which antagonize activin signaling by a variety of mechanisms. A soluble chimeric protein composed of the extracellular domain of ActRIIA fused to IgG-Fc binds to circulating ligands such as activin A and prevents signaling through the endogenous receptor. In cynomolgus monkeys, the ActRIIA soluble receptor increases bone volume by decreasing bone resorption and increasing bone formation, leading to enhanced mechanical strength and bone quality. In addition, a single dose of the soluble ActRIIA-Fc fusion protein increased serum BSALP and PINP and decreased serum CTX and TRACP 5b in postmenopausal women. These data provide evidence of a dual anabolic antiresorptive effect of the soluble ActRIIA-Fc fusion protein in the skeleton. Therefore, targeting activin receptor signaling may be useful for therapeutic intervention in osteoporosis.

Inhibin removes the inhibitory effects of activin on steroid enzyme expression and androgen production by normal ovarian thecal cells.

Activin and inhibin are important local modulators of theca cell steroidogenesis in the ovary. Using a serum-free primary theca cell culture system, this study investigated the effects of inhibin on theca cell androgen production and expression of steroidogenic enzymes. Androstenedione secretion from theca cells cultured in media containing activin, inhibin and follistatin was assessed by RIA over 144 h. Activin (1-100 ng/ml) suppressed androstenedione production. Inhibin (1-100 ng/ml) blocked the suppressive effects of added activin, but increased androstenedione production when added alone, suggesting it was blocking endogenous activin produced by theca cells. Addition of SB-431542 (activin receptor inhibitor) and follistatin (500 ng/ml) increased androstenedione production, supporting this concept. Infection of theca cells with adenoviruses expressing inhibitory Smad6 or 7 increased androstenedione secretion, confirming that the suppressive effects of activin required activation of the Smad2/3 pathway. Activin decreased the expression levels of steroidogenic acute regulatory protein (STAR), whereas STAR expression was increased by inhibin and SB-431542, alone and in combination. CYP11A was unaffected. The expression of CYP17 encoding 17α-hydroxylase was unaffected by activin but increased by inhibin and SB-431542, and when added in combination the effect was further enhanced. The expression of 3ß-hydroxysteroid dehydrogenase (3ß-HSD) was significantly decreased by activin, while inhibin alone and in combination with SB-431542 both potently increased the expression of 3ß-HSD. In conclusion, activin suppressed theca cell androstenedione production by decreasing the expression of STAR and 3ß-HSD. Inhibin and other blockers of activin action reversed this effect, supporting the concept that endogenous thecal activin modulates androgen production in theca cells.

Graded Nodal/Activin signaling titrates conversion of quantitative phospho-Smad2 levels into qualitative embryonic stem cell fate decisions.

Nodal and Activin are morphogens of the TGFbeta superfamily of signaling molecules that direct differential cell fate decisions in a dose- and distance-dependent manner. During early embryonic development the Nodal/Activin pathway is responsible for the specification of mesoderm, endoderm, node, and mesendoderm. In contradiction to this drive towards cellular differentiation, the pathway also plays important roles in the maintenance of self-renewal and pluripotency in embryonic and epiblast stem cells. The molecular basis behind stem cell interpretation of Nodal/Activin signaling gradients and the undertaking of disparate cell fate decisions remains poorly understood. Here, we show that any perturbation of endogenous signaling levels in mouse embryonic stem cells leads to their exit from self-renewal towards divergent differentiation programs. Increasing Nodal signals above basal levels by direct stimulation with Activin promotes differentiation towards the mesendodermal lineages while repression of signaling with the specific Nodal/Activin receptor inhibitor SB431542 induces trophectodermal differentiation. To address how quantitative Nodal/Activin signals are translated qualitatively into distinct cell fates decisions, we performed chromatin immunoprecipitation of phospho-Smad2, the primary downstream transcriptional factor of the Nodal/Activin pathway, followed by massively parallel sequencing, and show that phospho-Smad2 binds to and regulates distinct subsets of target genes in a dose-dependent manner. Crucially, Nodal/Activin signaling directly controls the Oct4 master regulator of pluripotency by graded phospho-Smad2 binding in the promoter region. Hence stem cells interpret and carry out differential Nodal/Activin signaling instructions via a corresponding gradient of Smad2 phosphorylation that selectively titrates self-renewal against alternative differentiation programs by direct regulation of distinct target gene subsets and Oct4 expression.

Negative regulation of activin signal transduction.

Activin is a member of the transforming growth factor ß (TGFß) superfamily. While it was originally isolated as a gonadal factor to regulate secretion of follicle-stimulating hormone (FSH) from the pituitary, it also has nonreproductive roles in immune responses, metabolism, tumorigenesis, and stem cell differentiation. Activin signaling is initiated by ligand-induced formation of a heteromeric complex of type I and type II transmembrane serine/threonine kinase receptors. The activated activin receptors phosphorylate the receptor-regulated Smads, Smad2 and Smad3, which subsequently form a complex with the common mediator, Smad4, and translocate into the nucleus for the transcriptional regulation of specific target genes in cooperation with DNA-binding cofactors and transcriptional coactivators. Activin signaling is controlled both extracellularly and intracellularly by diverse mechanisms to fine tune its duration and strength. This chapter summarizes current understanding of how activin signaling pathway is negatively regulated inside and outside the cells.

Antagonism of activin by activin chimeras.

Activins are pluripotent hormones/growth factors that belong to the TGF-ß superfamily of growth and differentiation factors (GDFs). They play a role in cell growth, differentiation and apoptosis, endocrine function, metabolism, wound repair, immune responses, homeostasis, mesoderm induction, bone growth, and many other biological processes. Activins and the related bone morphogenic proteins (BMPs) transduce their signal through two classes of single transmembrane receptors. The receptors possess intracellular serine/threonine kinase domains. Signaling occurs when the constitutively active type II kinase domain phosphorylates the type I receptor, which upon activation, phosphorylates intracellular signaling molecules. To generate antagonistic ligands, we generated chimeric molecules that disrupt the receptor interactions and thereby the phosphorylation events. The chimeras were designed based on available structural data to maintain high-affinity binding to type II receptors. The predicted type I receptor interaction region was replaced by residues present in inactive homologs or in related ligands with different type I receptor affinities.

Signaling pathways controlling pluripotency and early cell fate decisions of human induced pluripotent stem cells.

Human pluripotent stem cells from embryonic origins and those generated from reprogrammed somatic cells share many characteristics, including indefinite proliferation and a sustained capacity to differentiate into a wide variety of cell types. However, it remains to be demonstrated whether both cell types rely on similar mechanisms to maintain their pluripotent status and to control their differentiation. Any differences in such mechanisms would suggest that reprogramming of fibroblasts to generate induced pluripotent stem cells (iPSCs) results in novel states of pluripotency. In that event, current methods for expanding and differentiating human embryonic stem cells (ESCs) might not be directly applicable to human iPSCs. However, we show here that human iPSCs rely on activin/nodal signaling to control Nanog expression and thereby maintain pluripotency, thus revealing their mechanistic similarity to human ESCs. We also show that growth factors necessary and sufficient for achieving specification of human ESCs into extraembryonic tissues, neuroectoderm, and mesendoderm also drive differentiation of human iPSCs into the same tissues. Importantly, these experiments were performed in fully chemically defined medium devoid of factors that could obscure analysis of developmental mechanisms or render the resulting tissues incompatible with future clinical applications. Together these data reveal that human iPSCs rely on mechanisms similar to human ESCs to maintain their pluripotency and to control their differentiation, showing that these pluripotent cell types are functionally equivalent.

Inhibition of autoregulated TGFbeta signaling simultaneously enhances proliferation and differentiation of kidney epithelium and promotes repair following renal ischemia.

We studied autocrine transforming growth factor (TGF)beta signaling in kidney epithelium. Cultured proximal tubule cells showed regulated signaling that was high during log-phase growth, low during contact-inhibited differentiation, and rapidly increased during regeneration of wounded epithelium. Autoregulation of signaling correlated with TGFbeta receptor and Smad7 levels, but not with active TGFbeta, which was barely measurable in the growth medium. Confluent differentiated cells with low receptor and high Smad7 levels exhibited blunted responses to saturating concentrations of exogenously provided active TGFbeta, suggesting that TGFbeta signaling homeostasis was achieved by cell density-dependent modulation of signaling intermediates. Antagonism of Alk5 kinase, the TGFbeta type I receptor, dramatically accelerated the induction of differentiation in sparse, proliferating cultures and permitted better retention of differentiated features in regenerating cells of wounded, confluent cultures. Alk5 antagonism accelerated the differentiation of cells in proximal tubule primary cultures while simultaneously increasing their proliferation. Consequently, Alk5-inhibited primary cultures formed confluent, differentiated monolayers faster than untreated cultures. Furthermore, treatment with an Alk5 antagonist promoted kidney repair reflected by increased tubule differentiation and decreased tubulo-interstitial pathology during the recovery phase following ischemic injury in vivo. Our results show that autocrine TGFbeta signaling in proliferating proximal tubule cells exceeds the levels that are necessary for physiological regeneration. To that end, TGFbeta signaling is redundant and maladaptive during tubule repair by epithelial regeneration.

Design of novel quinazoline derivatives and related analogues as potent and selective ALK5 inhibitors.

Starting from quinazoline 3a, we designed potent and selective ALK5 inhibitors over p38MAP kinase from a rational drug design approach based on co-crystal structures in the human ALK5 kinase domain. The quinazoline 3d exhibited also in vivo activity in an acute rat model of DMN-induced liver fibrosis when administered orally at 5mg/kg (bid).

Transforming growth factor-beta1 causes pulmonary microvascular endothelial cell apoptosis via ALK5.

We have previously shown that transforming growth factor (TGF)-beta1 protected against main pulmonary artery endothelial cell (PAEC) apoptosis induced by serum deprivation and VEGF receptor blockade through a mechanism associated with ALK5-mediated Bcl-2 upregulation. In the current study, we investigated the effect of TGF-beta1 on pulmonary microvascular endothelial cell (PMVEC) apoptosis. We found that, in contrast to the results seen in conduit PAEC, TGF-beta1 caused apoptosis of PMVEC, an effect that was also dependent on ALK5 activity. We noted that non-SMAD signaling pathways did not play a role in TGF-beta1-induced apoptosis. Both SMAD2 and SMAD1/5 were activated upon exposure to TGF-beta1. TGF-beta1-induced activation of SMAD2, but not SMAD1/5, was abolished by ALK5 inhibition, an effect that associated with prevention of TGF-beta1-induced apoptosis. These results suggest that SMAD2 is important in TGF-beta1-induced apoptosis of PMVEC. While caspase-12 activity was not altered, caspase-8 was activated by TGF-beta1, an effect that correlated with a reduction of cFLIP protein levels. Additionally, TGF-beta1 decreased Bcl-2 protein levels and induced cytochrome c cytosolic redistribution. These results suggest that TGF-beta1 caused apoptosis of PMVEC likely through both caspase-8-dependent extrinsic pathway and mitochondria-mediated intrinsic pathway. We noted that inhibition of ALK5 attenuated serum deprivation-induced apoptosis, an effect that correlated with increased expression and activation of CREB and its potential target genes, Bcl-2 and cFLIP. These results suggest that CREB may be important in mediating apoptosis resistance of PMVEC upon ALK5 inhibition perhaps through upregulation of Bcl-2 and cFLIP. Finally, we noted that SMAD1/5 were activated upon ALK5 inhibition in the presence of low levels of TGF-beta1, an effect associated with enhanced endothelial proliferation. We speculate that imbalance of ALK1 and ALK5 may contribute to the development of pulmonary artery hypertension.

p38-Mitogen-activated protein kinase stimulated steroidogenesis in granulosa cell-oocyte cocultures: role of bone morphogenetic proteins 2 and 4.

Roles of the p38-MAPK pathway in steroidogenesis were investigated using coculture of rat granulosa cells with oocytes. Activin and FSH readily phosphorylated p38 in granulosa cells. Activin effect on p38 phosphorylation was abolished by a selective activin receptor-like kinase-4, -5, and -7 inhibitor, SB431542. SB431542 decreased FSH-induced estradiol but had no effect on progesterone production with a marginal cAMP reduction, suggesting that endogenous activin is primarily involved in estradiol synthesis. FSH-induced p38 activation was not affected either by SB431542 or follistatin, suggesting that FSH activates p38 not through the endogenous activin. Bone morphogenetic protein (BMP)-2 and BMP-4 also enhanced FSH-induced p38 phosphorylation, which was augmented by oocyte action. A specific p38 inhibitor, SB203580, decreased FSH-induced estradiol production. However, FSH-induced cAMP accumulation was not changed by SB203580, suggesting that p38 activation is linked to estradiol synthesis independently of cAMP. BMP-2 and BMP-4 inhibited FSH- and forskolin (FSK)-induced progesterone and cAMP synthesis regardless of oocyte action. BMP-2, BMP-4, and activin increased FSH-induced estradiol production, which was enhanced in the presence of oocytes. In contrast to activin that enhanced FSK-induced estradiol, BMP-2 and BMP-4 had no effects on FSK-induced estradiol production, suggesting that BMP-2 and BMP-4 directly activate FSH-receptor signaling. Given that activin increased, but BMP-2 and BMP-4 decreased, FSH-induced cAMP, the effects of BMP-2 and BMP-4 on estradiol enhancement appeared to be diverged from the cAMP-protein kinase A pathway. Thus, BMP-2 and BMP-4 differentially regulate steroidogenesis by stimulating FSH-induced p38 and suppressing cAMP. The former is involved in estradiol production and enhanced by oocyte action, whereas the latter leads to reduction of progesterone synthesis.

Specificity of the inhibitory effects of Dad on TGF-beta family type I receptors, Thickveins, Saxophone, and Baboon in Drosophila.

In mammals, two inhibitory Smads (I-Smads), Smad6 and Smad7, play pivotal roles in negative regulation of TGF-beta family signaling. Smad7 ubiquitously inhibits TGF-beta family signaling, whereas Smad6 inhibits signaling from the ALK-3/6 subfamily in preference to that from the ALK-1/2 and ALK-4/5/7 subfamilies of TGF-beta family type I receptors. In Drosophila, only one I-Smad, Dad, has been identified. Here we examined inhibitory effects of Dad on type I receptors in Drosophila. Dad inhibited Saxophone (ALK-1/2 orthologue) and Thickveins (ALK-3/6 orthologue) but not Baboon (ALK-4/5/7 orthologue). The differential modes of action of I-Smads in mammals and Drosophila are discussed.