In chronic kidney disease altered cardiac metabolism precedes cardiac hypertrophy

Conduit arterial disease in chronic kidney disease (CKD) is an important cause of cardiac complications. Cardiac function in CKD has not been studied in the absence of arterial disease. In an Alport syndrome model bred not to have conduit arterial disease, mice at 225 days of life (dol) had CKD equivalent to humans with CKD stage 4-5. Parathyroid hormone (PTH) and FGF23 levels were one log order elevated, circulating sclerostin was elevated, and renal activin A was strongly induced. Aortic Ca levels were not increased, and vascular smooth muscle cell (VSMC) transdifferentiation was absent. The CKD mice were not hypertensive, and cardiac hypertrophy was absent. Freshly excised cardiac tissue respirometry (Oroboros) showed that ADP-stimulated O2 flux was diminished from 52 to 22 pmol/mg (P = 0.022). RNA-Seq of cardiac tissue from CKD mice revealed significantly decreased levels of cardiac mitochondrial oxidative phosphorylation genes. To examine the effect of activin A signaling, some Alport mice were treated with a monoclonal Ab to activin A or an isotype-matched IgG beginning at 75 days of life until euthanasia. Treatment with the activin A antibody (Ab) did not affect cardiac oxidative phosphorylation. However, the activin A antibody was active in the skeleton, disrupting the effect of CKD to stimulate osteoclast number, eroded surfaces, and the stimulation of osteoclast-driven remodeling. The data reported here show that cardiac mitochondrial respiration is impaired in CKD in the absence of conduit arterial disease. This is the first report of the direct effect of CKD on cardiac respiration.NEW & NOTEWORTHY Heart disease is an important morbidity of chronic kidney disease (CKD). Hypertension, vascular stiffness, and vascular calcification all contribute to cardiac pathophysiology. However, cardiac function in CKD devoid of vascular disease has not been studied. Here, in an animal model of human CKD without conduit arterial disease, we analyze cardiac respiration and discover that CKD directly impairs cardiac mitochondrial function by decreasing oxidative phosphorylation. Protection of cardiac oxidative phosphorylation may be a therapeutic target in CKD.

Roles of Activin A and Gpnmb in Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Metabolic dysfunction-associated steatotic liver disease (MASLD, formerly known as nonalcoholic fatty liver disease [NAFLD]) and metabolic dysfunction-associated steatohepatitis (MASH, formerly known as nonalcoholic steatohepatitis [NASH]) are leading chronic liver diseases, driving cirrhosis, hepatocellular carcinoma, and mortality. MASLD/MASH is associated with increased senescence proteins, including Activin A, and senolytics have been proposed as a therapeutic approach. To test the role of Activin A, we induced hepatic expression of Activin A in a murine MASLD/MASH model. Surprisingly, overexpression of hepatic Activin A dramatically mitigated MASLD, reducing liver steatosis and inflammation as well as systemic fat accumulation, while improving insulin sensitivity. Further studies identified a dramatic decrease in the lipid-associated macrophages marker glycoprotein NMB (Gpnmb) by Activin A, and Gpnmb knockdown in the same model produced similar benefits and transcriptional changes to Activin A expression. These studies reveal a surprising protective role for Activin A in MASLD and the potential for SASP proteins to have context-specific beneficial effects. Moreover, they implicate both Activin A and Gpnmb as potential therapeutic targets for this condition.

ARTICLE HIGHLIGHTS

Potential Roles of Activin in Head and Neck Squamous Cell Carcinoma Progression and Mortality

BACKGROUND/AIM

Activin, a member of the TGF-β super family of cytokines, is involved in head and neck squamous cell carcinoma (HNSCC). This study examined the constituents of the activin axis in order to further elucidate the role of activin A in HNSCC progression.

MATERIALS AND METHODS

Immunohistochemistry (IHC), reverse transcription polymerase chain reaction (RT-PCR), MTT, and matrigel invasion assays, in addition to analysis of the tumor cancer genome atlas (TCGA), were employed.

RESULTS

IHC in HNSCC and oral leukoplakia (OPL) lesions demonstrated increased expression of the inhibin subunit βA (INHBA) (p<0.0001), as well as activin receptor type IB (ACVR1B) (p<0.0032) compared to normal mucosa. TCGA analysis revealed increased INHBA expression was associated with lymph node positive tumors (p=0.024), decreased overall survival (p=0.0167), and decreased promoter methylation (p<0.0001). Concomitant up-regulated expression of gene pathways strongly correlated with INHBA expression demonstrated further deleterious effects on survival (p<0.0148).

CONCLUSION

Activin may be an important component of early carcinogenesis in OPL and HNSCC with unfavorable effects on clinical end-points such as survival.

Activin type I receptor polymorphisms and body composition in older individuals with sarcopenia-Analyses from the LACE randomised controlled trial

BACKGROUND

Ageing is associated with changes in body composition including an overall reduction in muscle mass and a proportionate increase in fat mass. Sarcopenia is characterised by losses in both muscle mass and strength. Body composition and muscle strength are at least in part genetically determined, consequently polymorphisms in pathways important in muscle biology (e.g., the activin/myostatin signalling pathway) are hypothesised to contribute to the development of sarcopenia.

METHODS

We compared regional body composition measured by DXA with genotypes for two polymorphisms (rs10783486, minor allele frequency (MAF) = 0.26 and rs2854464, MAF = 0.26) in the activin 1B receptor (ACVR1B) determined by PCR in a cross-sectional analysis of DNA from 110 older individuals with sarcopenia from the LACE trial.

RESULTS

Neither muscle mass nor strength showed any significant associations with either genotype in this cohort. Initial analysis of rs10783486 showed that males with the AA/AG genotype were taller than GG males (174±7cm vs 170±5cm, p = 0.023) and had higher arm fat mass, (median higher by 15%, p = 0.008), and leg fat mass (median higher by 14%, p = 0.042). After correcting for height, arm fat mass remained significantly higher (median higher by 4% padj = 0.024). No associations (adjusted or unadjusted) were seen in females. Similar analysis of the rs2854464 allele showed a similar pattern with the presence of the minor allele (GG/AG) being associated with greater height (GG/AG = 174±7 cm vs AA = 170 ±5cm, p = 0.017) and greater arm fat mass (median higher by 16%, p = 0.023). Again, the difference in arm fat remained after correction for height. No similar associations were seen in females analysed alone.

CONCLUSION

These data suggest that polymorphic variation in the ACVR1B locus could be associated with body composition in older males. The activin/myostatin pathway might offer a novel potential target to prevent fat accumulation in older individuals.

Activin A/ACVR2A axis inhibits epithelial-to-mesenchymal transition in colon cancer by activating SMAD2

Colorectal cancer is one of the most common malignancies worldwide. Liver metastasis is the major direct cause of colorectal cancer-related deaths. Although radical resection is the most effective treatment for colorectal cancer liver metastasis, several patients are not eligible for surgery. Therefore, there is a need to develop novel treatments based on the understanding of the biological mechanisms underlying liver metastasis in colorectal cancer. This study demonstrated that activin A/ACVR2A inhibits colon cancer cell migration and invasion, as well as suppresses the epithelial-to-mesenchymal transition of mouse colon cancer cells. This finding has been further validated in animal experiments. Mechanistic studies revealed that activin A binds to Smad2 (instead of Smad3) and activates its transcription. Analysis of the paired clinical samples further confirmed that the expression levels of ACVR2A and SMAD2 were the highest in adjacent healthy tissues, followed by primary colon cancer tissues and liver metastasis tissues, suggesting that ACVR2A downregulation may promote colon cancer metastasis. Bioinformatics analysis and clinical studies demonstrated that ACVR2A downregulation was significantly associated with liver metastasis and poor disease-free and progression-free survival of patients with colon cancer. These results suggest that the activin A/ACVR2A axis promotes colon cancer metastasis by selectively activating SMAD2. Thus, targeting ACVR2A is a potential novel therapeutic strategy to prevent colon cancer metastasis.

Characterization of Fibrodysplasia Ossificans Progessiva relevant Acvr1/Acvr2 Activin receptors in medaka (Oryzias latipes)

Activin and Bone Morphogenetic Protein (BMP) signaling plays crucial roles in vertebrate organ formation, including osteo- and angiogenesis, and tissue homeostasis, such as neuronal maintenance. Activin and BMP signaling needs to be precisely controlled by restricted expression of shared receptors, stoichiometric composition of receptor-complexes and presence of regulatory proteins. A R206H mutation in the human (hs) BMP type I receptor hsACVR1, on the other hand, leads to excessive phosphorylation of Sons of mothers against decapentaplegic (SMAD) 1/5/8. This in turn causes increased inflammation and heterotopic ossification in soft tissues of patients suffering from Fibrodysplasia Ossificans Progressiva (FOP). Several animal models have been established to understand the spontaneous and progressive nature of FOP, but often have inherent limitations. The Japanese medaka (Oryzias latipes, ola) has recently emerged as popular model for bone research. To assess whether medaka is suitable as a potential FOP animal model, we determined the expression of Activin receptor type I (ACVR1) orthologs olaAcvr1 and olaAcvr1l with that of Activin type II receptors olaAcvr2ab, olaAcvr2ba and olaAcvr2bb in embryonic and adult medaka tissues by in situ hybridization. Further, we showed that Activin A binding properties are conserved in olaAcvr2, as are the mechanistic features in the GS-Box of both olaAcvr1 and olaAcvr1l. This consequently leads to FOP-typical elevated SMAD signaling when the medaka type I receptors carry the R206H equivalent FOP mutation. Together, this study therefore provides experimental groundwork needed to establish a unique medaka model to investigate mechanisms underlying FOP.

Rescue of bmp15 deficiency in zebrafish by mutation of inha reveals mechanisms of BMP15 regulation of folliculogenesis

As an oocyte-specific growth factor, bone morphogenetic protein 15 (BMP15) plays a critical role in controlling folliculogenesis. However, the mechanism of BMP15 action remains elusive. Using zebrafish as the model, we created a bmp15 mutant using CRISPR/Cas9 and demonstrated that bmp15 deficiency caused a significant delay in follicle activation and puberty onset followed by a complete arrest of follicle development at previtellogenic (PV) stage without yolk accumulation. The mutant females eventually underwent female-to-male sex reversal to become functional males, which was accompanied by a series of changes in secondary sexual characteristics. Interestingly, the blockade of folliculogenesis and sex reversal in bmp15 mutant could be partially rescued by the loss of inhibin (inha-/-). The follicles of double mutant (bmp15-/-;inha-/-) could progress to mid-vitellogenic (MV) stage with yolk accumulation and the fish maintained their femaleness without sex reversal. Transcriptome analysis revealed up-regulation of pathways related to TGF-β signaling and endocytosis in the double mutant follicles. Interestingly, the expression of inhibin/activin βAa subunit (inhbaa) increased significantly in the double mutant ovary. Further knockout of inhbaa in the triple mutant (bmp15-/-;inha-/-;inhbaa-/-) resulted in the loss of yolk granules again. The serum levels of estradiol (E2) and vitellogenin (Vtg) both decreased significantly in bmp15 single mutant females (bmp15-/-), returned to normal in the double mutant (bmp15-/-;inha-/-), but reduced again significantly in the triple mutant (bmp15-/-;inha-/-;inhbaa-/-). E2 treatment could rescue the arrested follicles in bmp15-/-, and fadrozole (a nonsteroidal aromatase inhibitor) treatment blocked yolk accumulation in bmp15-/-;inha-/- fish. The loss of inhbaa also caused a reduction of Vtg receptor-like molecules (e.g., lrp1ab and lrp2a). In summary, the present study provided comprehensive genetic evidence that Bmp15 acts together with the activin-inhibin system in the follicle to control E2 production from the follicle, Vtg biosynthesis in the liver and its uptake by the developing oocytes.

Functional interaction of Clock genes and bone morphogenetic proteins in the adrenal cortex

The bone morphogenetic protein (BMP) system in the adrenal cortex plays modulatory roles in the control of adrenocortical steroidogenesis. BMP-6 enhances aldosterone production by modulating angiotensin (Ang) II-mitogen-activated protein kinase (MAPK) signaling, whereas activin regulates the adrenocorticotropin (ACTH)-cAMP cascade in adrenocortical cells. A peripheral clock system in the adrenal cortex was discovered and it has been shown to have functional roles in the adjustment of adrenocortical steroidogenesis by interacting with the BMP system. It was found that follistatin, a binding protein of activin, increased Clock mRNA levels, indicating an endogenous function of activin in the regulation of Clock mRNA expression. Elucidation of the interrelationships among the circadian clock system, the BMP system and adrenocortical steroidogenesis regulated by the hypothalamic-pituitary-adrenal (HPA) axis would lead to an understanding of the pathophysiology of adrenal disorders and metabolic disorders and the establishment of better medical treatment from the viewpoint of pharmacokinetics.

Evolving roles of activins and inhibins in ovarian cancer pathophysiology

Activins and inhibins are unique members of the transforming growth factor-β (TGFβ) family of growth factors, with the ability to exert autocrine, endocrine, and paracrine effects in a wide range of complex physiologic and pathologic processes. Although first isolated within the pituitary, emerging evidence suggests broader influence beyond reproductive development and function. Known roles of activin and inhibin in angiogenesis and immunity along with correlations between gene expression and cancer prognosis suggest potential roles in tumorigenesis. Here, we present a review of the current understanding of the biological role of activins and inhibins as it relates to ovarian cancers, summarizing the underlying signaling mechanisms and physiologic influence, followed by detailing their roles in cancer progression, diagnosis, and treatment.

Chlamydia trachomatis infection regulates the expression of tetraspanins, activin-A, and inhibin-A in tubal ectopic pregnancy

Mechanism of Chlamydia trachomatis causing tubal ectopic pregnancy (EP) is not well understood. Tetraspanins (tspans), activin-A, and inhibin-A might play a role in the development of pathological conditions leading to EP. The study aimed to elucidate the expression of tspans, activin-A, and inhibin-A with a role of associated cytokines in C. trachomatis-associated EP and analyze interacting partners of DEGs, with an expression of a few important interacting genes. Fallopian tissue and serum were collected from 100 EP (Group I) and 100 controls (Group II) from SJH, New Delhi, India. Detection of C. trachomatis was done by polymerase chain reaction (PCR) and IgG antibodies were detected by enzyme-linked immunosorbent assay. Expression of tspans, activin-A, inhibin-A, and cytokines was analyzed by real time (RT)-PCR and their interacting genes were assessed by STRING. Expression of few disease-associated interacting genes was studied by RT-PCR. A total of 29% (Group I) were C. trachomatis positive. Tspans and activin-A were significantly upregulated, while inhibin-A was significantly downregulated in Group Ia. ITGA1, TLR-2, ITGB2, and Smad-3 were a few interacting genes. Expression of ITGA1, TLR-2, and Smad-3 was significantly upregulated in C. trachomatis-positive EP. Results suggested dysregulated tspans, activin-A, and inhibin-A might play a role in C. trachomatis-infected tubal EP.

Transcriptional Profiling of TGF-β Superfamily Members in Lumbar DRGs of Rats Following Sciatic Nerve Axotomy and Activin C Inhibits Neuropathic Pain

BACKGROUND

Neuroinflammation and cytokines play critical roles in neuropathic pain and axon degeneration/regeneration. Cytokines of transforming growth factor-β superfamily have implications in pain and injured nerve repair processing. However, the transcriptional profiles of the transforming growth factor-β superfamily members in dorsal root ganglia under neuropathic pain and axon degeneration/regeneration conditions remain elusive.

OBJECTIVE

We aimed to plot the transcriptional profiles of transforming growth factor-β superfamily components in lumbar dorsal root ganglia of sciatic nerve-axotomized rats and to further verify the profiles by testing the analgesic effect of activin C, a representative cytokine, on neuropathic pain.

METHODS

Adult male rats were axotomized in sciatic nerves, and lumbar dorsal root ganglia were isolated for total RNA extraction or section. A custom microarray was developed and employed to plot the gene expression profiles of transforming growth factor-β superfamily components. Realtime RT-PCR was used to confirm changes in the expression of activin/inhibin family genes, and then in situ hybridization was performed to determine the cellular locations of inhibin α, activin βC, BMP-5 and GDF-9 mRNAs. The rat spared nerve injury model was performed, and a pain test was employed to determine the effect of activin C on neuropathic pain.

RESULTS

The expression of transforming growth factor-β superfamily cytokines and their signaling, including some receptors and signaling adaptors, were robustly upregulated. Activin βC subunit mRNAs were expressed in the small-diameter dorsal root ganglion neurons and upregulated after axotomy. Single intrathecal injection of activin C inhibited neuropathic pain in spared nerve injury model.

CONCLUSION

This is the first report to investigate the transcriptional profiles of members of transforming growth factor-β superfamily in axotomized dorsal root ganglia. The distinct cytokine profiles observed here might provide clues toward further study of the role of transforming growth factor-β superfamily in the pathogenesis of neuropathic pain and axon degeneration/regeneration after peripheral nerve injury.

Loss of growth differentiation factor 9 causes an arrest of early folliculogenesis in zebrafish-A novel insight into its action mechanism

Growth differentiation factor 9 (GDF9) was the first oocyte-specific growth factor identified; however, most information about GDF9 functions comes from studies in the mouse model. In this study, we created a mutant for Gdf9 gene (gdf9-/-) in zebrafish using TALEN approach. The loss of Gdf9 caused a complete arrest of follicle development at primary growth (PG) stage. These follicles eventually degenerated, and all mutant females gradually changed to males through sex reversal, which could be prevented by mutation of the male-promoting gene dmrt1. Interestingly, the phenotypes of gdf9-/- could be rescued by simultaneous mutation of inhibin α (inha-/-) but not estradiol treatment, suggesting a potential role for the activin-inhibin system or its signaling pathway in Gdf9 actions. In gdf9-null follicles, the expression of activin βAa (inhbaa), but not βAb (inhbab) and βB (inhbb), decreased dramatically; however, its expression rebounded in the double mutant (gdf9-/-;inha-/-). These results indicate clearly that the activation of PG follicles to enter the secondary growth (SG) requires intrinsic factors from the oocyte, such as Gdf9, which in turn works on the neighboring follicle cells to trigger follicle activation, probably involving activins. In addition, our data also support the view that estrogens are not involved in follicle activation as recently reported.

Pituitary gonadotroph-specific patterns of gene expression and hormone secretion

Pituitary gonadotrophs play a key role in reproductive functions by secreting luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The LH secretory activity of gonadotroph is controlled by hypothalamic gonadotropin-releasing hormone (GnRH) via GnRH receptors and is accompanied by only minor effects on high basal Lhb gene expression. The secretory profiles of GnRH and LH are highly synchronized, with the latter reflecting a depletion of prestored LH in secretory vesicles by regulated exocytosis. In contrast, FSH is predominantly released by constitutive exocytosis, and secretory activity reflects the kinetics of Fshb gene expression controlled by GnRH, activin, and inhibin. Here is a review of recent data to improve the understanding of multiple patterns of gonadotroph gene expression and hormone secretion.

Genetic polymorphisms of muscular fitness in young healthy men

The effects of genetic polymorphisms on muscle structure and function remain elusive. The present study tested for possible associations of 16 polymorphisms (across ten candidate genes) with fittness and skeletal muscle phenotypes in 17- to 37-year-old healthy Caucasian male endurance (n = 86), power/strength (n = 75) and team athletes (n = 60), and non-athletes (n = 218). Skeletal muscle function was measured with eight performance tests covering multiple aspects of muscular fitness. Along with body mass and height, the upper arm and limb girths, and maximal oxygen uptake were measured. Genotyping was conducted on DNA extracted from blood. Of the 16 polymorphisms studied, nine (spanning seven candidate genes and four gene families/signalling pathways) were independently associated with at least one skeletal muscle fitness measure (size or function, or both) measure and explained up to 4.1% of its variation. Five of the studied polymorphisms (activin- and adreno-receptors, as well as myosine light chain kinase 1) in a group of one to three combined with body height, age and/or group explained up to 20.4% of the variation of muscle function. ACVR1B (rs2854464) contributed 2.0–3.6% to explain up to 14.6% of limb proximal girths. The G allele (genotypes AG and GG) of the ACVR1B (rs2854464) polymorphism was significantly overrepresented among team (60.4%) and power (62.0%) athletes compared to controls (52.3%) and endurance athletes (39.2%), and G allele was also most consistently/frequently associated with muscle size and power. Overall, the investigated polymorphisms determined up to 4.1% of the variability of muscular fitness in healthy young humans.

The TGF-β Receptor Gene Saxophone Influences Larval-Pupal-Adult Development in Tribolium castaneum

The transforming growth factor-β (TGF-β) superfamily encodes a large group of proteins, including TGF-β isoforms, bone morphogenetic proteins and activins that act through conserved cell-surface receptors and signaling co-receptors. TGF-β signaling in insects controls physiological events, including growth, development, diapause, caste determination and metamorphosis. In this study, we used the red flour beetle, Tribolium castaneum, as a model species to investigate the role of the type I TGF-β receptor, saxophone (Sax), in mediating development. Developmental and tissue-specific expression profiles indicated Sax is constitutively expressed during development with lower expression in 19- and 20-day (6th instar) larvae. RNAi knockdown of Sax in 19-day larvae prolonged developmental duration from larvae to pupae and significantly decreased pupation and adult eclosion in a dose-dependent manner. At 50 ng dsSax/larva, Sax knockdown led to an 84.4% pupation rate and 46.3% adult emergence rate. At 100 ng and 200 ng dsSax/larva, pupation was down to 75.6% and 50%, respectively, with 0% adult emergence following treatments with both doses. These phenotypes were similar to those following knockdowns of 20-hydroxyecdysone (20E) receptor genes, ecdysone receptor (EcR) or ultraspiracle protein (USP). Expression of 20E biosynthesis genes disembodied and spookier, 20E receptor genes EcR and USP, and 20E downstream genes BrC and E75, were suppressed after the Sax knockdown. Topical application of 20E on larvae treated with dsSax partially rescued the dsSax-driven defects. We can infer that the TGF-β receptor gene Sax influences larval-pupal-adult development via 20E signaling in T. castaneum.

Smad on X is vital for larval-pupal transition in a herbivorous ladybird beetle

Insect development is regulated by a combination of juvenile hormone (JH) and 20-hydroxyecdysone (20E). Production of both JH and 20E is regulated by transforming growth factor-β (TGFβ) signaling. TGFβ can be classified into two branches, the Activin and Bone Morphogenetic Protein (BMP) pathways. In Drosophila melanogaster, BMP signaling is critical for JH synthesis, whereas Activin signal is required to generate the large pulse of 20E necessary for entering metamorphosis. However, to which extent the roles of these signals are conserved remains unknown. Here we studied the role of an Activin component Smad on X (Smox) in post-embryonic development in a defoliating ladybird Henosepilachna vigintioctopunctata. RNA interference (RNAi)-aided knockdown of Hvsmox inhibited larval growth, and impaired larval development. All Hvmyo RNAi larvae arrested at the fourth-instar larval stage. Moreover, knockdown of Hvsmox delayed gut and Malpighian tubules remodeling. Furthermore, the expression of a JH biosynthesis gene (Hvjhamt), a JH receptor gene HvMet and a JH response gene HvKr-h1 was greatly enhanced. Conversely, the expression levels of an ecdysteroidogenesis gene (Hvspo), a 20E receptor gene (HvEcR) and six 20E response genes (HvBrC, HvE74, HvE75, HvE93, HvHR3 and HvHR4) were significantly lowered. Knockdown of HvMet partially restored the negative phenotypes in the Hvsmox RNAi beetles. Our results suggest that Smox exerts regulative roles in JH production, ecdysteroidogenesis and organ remodeling, thus contributing to modulate the larva-pupa-adult transformation in H. vigintioctopunctata.

Human INHBB Gene Variant (c.1079T>C:p.Met360Thr) Alters Testis Germ Cell Content, but Does Not Impact Fertility in Mice

Testicular-derived inhibin B (α/β B dimers) acts in an endocrine manner to suppress pituitary production of follicle-stimulating hormone (FSH), by blocking the actions of activins (β A/B/β A/B dimers). Previously, we identified a homozygous genetic variant (c.1079T>C:p.Met360Thr) arising from uniparental disomy of chromosome 2 in the INHBB gene (β B-subunit of inhibin B and activin B) in a man suffering from infertility (azoospermia). In this study, we aimed to test the causality of the p.Met360Thr variant in INHBB and testis function. Here, we used CRISPR/Cas9 technology to generate InhbbM364T/M364T mice, where mouse INHBB p.Met364 corresponds with human p.Met360. Surprisingly, we found that the testes of male InhbbM364T/M364T mutant mice were significantly larger compared with those of aged-matched wildtype littermates at 12 and 24 weeks of age. This was attributed to a significant increase in Sertoli cell and round spermatid number and, consequently, seminiferous tubule area in InhbbM364T/M364T males compared to wildtype males. Despite this testis phenotype, male InhbbM364T/M364T mutant mice retained normal fertility. Serum hormone analyses, however, indicated that the InhbbM364T variant resulted in reduced circulating levels of activin B but did not affect FSH production. We also examined the effect of this p.Met360Thr and an additional INHBB variant (c.314C>T: p.Thr105Met) found in another infertile man on inhibin B and activin B in vitro biosynthesis. We found that both INHBB variants resulted in a significant disruption to activin B in vitro biosynthesis. Together, this analysis supports that INHBB variants that limit activin B production have consequences for testis composition in males.

Visceral adipose tissue remodeling in pancreatic ductal adenocarcinoma cachexia: the role of activin A signaling

Pancreatic ductal adenocarcinoma (PDAC) patients display distinct phenotypes of cachexia development, with either adipose tissue loss preceding skeletal muscle wasting or loss of only adipose tissue. Activin A levels were measured in serum and analyzed in tumor specimens of both a cohort of Stage IV PDAC patients and the genetically engineered KPC mouse model. Our data revealed that serum activin A levels were significantly elevated in Stage IV PDAC patients in comparison to age-matched non-cancer patients. Little is known about the role of activin A in adipose tissue wasting in the setting of PDAC cancer cachexia. We established a correlation between elevated activin A and remodeling of visceral adipose tissue. Atrophy and fibrosis of visceral adipose tissue was examined in omental adipose tissue of Stage IV PDAC patients and gonadal adipose tissue of an orthotopic mouse model of PDAC. Remarkably, white visceral adipose tissue from both PDAC patients and mice exhibited decreased adipocyte diameter and increased fibrotic deposition. Strikingly, expression of thermogenic marker UCP1 in visceral adipose tissues of PDAC patients and mice remained unchanged. Thus, we propose that activin A signaling could be relevant to the acceleration of visceral adipose tissue wasting in PDAC-associated cachexia.

PGE2 and Thrombin Induce Myofibroblast Transdifferentiation via Activin A and CTGF in Endometrial Stromal Cells

Endometriosis is characterized by inflammation and fibrotic changes. Our previous study using a mouse model showed that proinflammatory factors present in peritoneal hemorrhage exacerbated inflammation in endometriosis-like grafts, at least in part through the activation of prostaglandin (PG) E2 receptor and protease-activated receptor (PAR). In addition, menstruation-related factors, PGE2 and thrombin (P/T), a PAR1 agonist induced epithelial-mesenchymal transition (EMT) of endometrial cells under hypoxia. However, the molecular mechanisms by which P/T induce development of endometriosis have not been fully characterized. To investigate the effects of P/T, RNA extracted from endometrial stromal cells (ESCs) treated with P/T were subjected to RNA sequence analysis, and identified activin A, FOS, and GATA2 as upregulated genes. Activin A increased the expression of connective tissue growth factor (CTGF) and mesenchymal marker genes in ESCs. CTGF induced the expression of fibrosis marker type I collagen, fibronectin, and α-smooth muscle actin (αSMA), indicating fibroblast to myofibroblast transdifferentiation (FMT) of ESCs. In addition, activin A, FOS, GATA2, CTGF, and αSMA were localized in endometriosis lesions. Taken together, our data show that P/T induces changes resembling EMT and FMT in ectopic ESCs derived from retrograde menstruation, and that these are associated with fibrotic changes in the lesions. Pharmacological means that block P/T-induced activin A and CTGF signaling may be strategies to inhibit fibrosis in endometriotic lesions.

circRNA-Mediated Inhibin-Activin Balance Regulation in Ovarian Granulosa Cell Apoptosis and Follicular Atresia

Ovarian granulosa cells (GC) play an essential role in the development and atresia of follicles. Emerging studies suggest that non-coding RNAs are involved in the regulation of GC apoptosis. Here, we aimed to analyze the function of ssc-circINHA-001, coded by the first exon of the inhibin subunit α gene (INHA), in resisting GC apoptosis and follicular atresia by enhancing the expression of the inhibin subunit β A (INHBA) through a cluster of miRNAs. A higher expression of ssc-circINHA-001 in healthy follicles compared to early atretic follicles was detected by qRT-PCR. Its circular structure was confirmed by RNase R treatment and reversed PCR. The function of ssc-circINHA-001 in GC resistance to apoptosis was detected by in vitro transfection of its si-RNA. Furthermore, the dual-luciferase reporter assay suggested that ssc-circINHA-001 adsorbed three miRNAs, termed miR-214-5p, miR-7144-3p, and miR-9830-5p, which share the common target INHBA. A low expression of ssc-circINHA-001 increased the levels of the free miRNAs, inhibited INHBA expression, and thus raised GCs apoptosis through a shift from the secretion of activin to that of inhibin. Our study demonstrated the existence of a circRNA–microRNAs–INHBA regulatory axis in follicular GC apoptosis and provides insight into the relationship between circRNA function and its coding gene in inhibin/activin balance and ovarian physiological functions.

Pathogenic ACVR1R206H activation by Activin A-induced receptor clustering and autophosphorylation

Fibrodysplasia ossificans progressiva (FOP) and diffuse intrinsic pontine glioma (DIPG) are debilitating diseases that share causal mutations in ACVR1, a TGF-β family type I receptor. ACVR1R206H is a frequent mutation in both diseases. Pathogenic signaling via the SMAD1/5 pathway is mediated by Activin A, but how the mutation triggers aberrant signaling is not known. We show that ACVR1 is essential for Activin A-mediated SMAD1/5 phosphorylation and is activated by two distinct mechanisms. Wild-type ACVR1 is activated by the Activin type I receptors, ACVR1B/C. In contrast, ACVR1R206H activation does not require upstream kinases, but is predominantly activated via Activin A-dependent receptor clustering, which induces its auto-activation. We use optogenetics and live-imaging approaches to demonstrate Activin A-induced receptor clustering and show it requires the type II receptors ACVR2A/B. Our data provide molecular mechanistic insight into the pathogenesis of FOP and DIPG by linking the causal activating genetic mutation to disrupted signaling.

Pro-cachectic factors link experimental and human chronic kidney disease to skeletal muscle wasting programs

Skeletal muscle wasting is commonly associated with chronic kidney disease (CKD), resulting in increased morbidity and mortality. However, the link between kidney and muscle function remains poorly understood. Here, we took a complementary interorgan approach to investigate skeletal muscle wasting in CKD. We identified increased production and elevated blood levels of soluble pro-cachectic factors, including activin A, directly linking experimental and human CKD to skeletal muscle wasting programs. Single-cell sequencing data identified the expression of activin A in specific kidney cell populations of fibroblasts and cells of the juxtaglomerular apparatus. We propose that persistent and increased kidney production of pro-cachectic factors, combined with a lack of kidney clearance, facilitates a vicious kidney/muscle signaling cycle, leading to exacerbated blood accumulation and, thereby, skeletal muscle wasting. Systemic pharmacological blockade of activin A using soluble activin receptor type IIB ligand trap as well as muscle-specific adeno-associated virus-mediated downregulation of its receptor ACVR2A/B prevented muscle wasting in different mouse models of experimental CKD, suggesting that activin A is a key factor in CKD-induced cachexia. In summary, we uncovered a crosstalk between kidney and muscle and propose modulation of activin signaling as a potential therapeutic strategy for skeletal muscle wasting in CKD.

CD28 is expressed by macrophages with anti-inflammatory potential and limits their T-cell activating capacity

CD28 expression is generally considered to be T lymphocyte specific. We have previously shown CD28 mRNA expression in M-CSF-dependent anti-inflammatory monocyte-derived macrophages (M-MØ), and now demonstrate that CD28 cell surface expression is higher in M-MØ than in GM-CSF-dependent macrophages, and that macrophage CD28 expression is regulated by MAFB and activin A. In vivo, CD28 was found in tumor-associated macrophages and, to a lower extent, in pro-inflammatory synovial fluid macrophages from rheumatoid arthritis patients. Analysis of mouse macrophages confirmed Cd28 expression in bone-marrow derived M-MØ. Indeed, anti-CD28 antibodies triggered ERK1/2 phosphorylation in mouse M-MØ. At the functional level, Cd28KO M-MØ exhibited a significantly higher capacity to activate the OVA-specific proliferation of OT-II CD4+ T cells than WT M-MØ, as well as enhanced LPS-induced IL-6 production. Besides, the Cd28KO M-MØ transcriptome was significantly different from WT M-MØ regarding the expression IFN response, inflammatory response, and TGF-β signaling related gene sets. Therefore, defective CD28 expression in mouse macrophages associates to changes in gene expression profile, what might contribute to the altered functionality displayed by Cd28KO M-MØ. Thus, CD28 expression appears as a hallmark of anti-inflammatory macrophages and might be a target for immunotherapy.

activin-2 is required for regeneration of polarity on the planarian anterior-posterior axis

Planarians are flatworms and can perform whole-body regeneration. This ability involves a mechanism to distinguish between anterior-facing wounds that require head regeneration and posterior-facing wounds that require tail regeneration. How this head-tail regeneration polarity decision is made is studied to identify principles underlying tissue-identity specification in regeneration. We report that inhibition of activin-2, which encodes an Activin-like signaling ligand, resulted in the regeneration of ectopic posterior-facing heads following amputation. During tissue turnover in uninjured planarians, positional information is constitutively expressed in muscle to maintain proper patterning. Positional information includes Wnts expressed in the posterior and Wnt antagonists expressed in the anterior. Upon amputation, several wound-induced genes promote re-establishment of positional information. The head-versus-tail regeneration decision involves preferential wound induction of the Wnt antagonist notum at anterior-facing over posterior-facing wounds. Asymmetric activation of notum represents the earliest known molecular distinction between head and tail regeneration, yet how it occurs is unknown. activin-2 RNAi animals displayed symmetric wound-induced activation of notum at anterior- and posterior-facing wounds, providing a molecular explanation for their ectopic posterior-head phenotype. activin-2 RNAi animals also displayed anterior-posterior (AP) axis splitting, with two heads appearing in anterior blastemas, and various combinations of heads and tails appearing in posterior blastemas. This was associated with ectopic nucleation of anterior poles, which are head-tip muscle cells that facilitate AP and medial-lateral (ML) pattern at posterior-facing wounds. These findings reveal a role for Activin signaling in determining the outcome of AP-axis-patterning events that are specific to regeneration.

A central problem in animal regeneration is how animals determine what body part to regenerate. Planarians are flatworms that can regenerate any missing body region, and are studied to identify mechanisms underlying regeneration. At transverse amputation planes, a poorly understood mechanism specifies regeneration of either a head or a tail. This head-versus-tail regeneration decision-making process is referred to as regeneration polarity and has been studied for over a century to identify mechanisms that specify what to regenerate. The gene notum, which encodes a Wnt antagonist, is induced within hours after injury preferentially at anterior-facing wounds, where it specifies head regeneration. We report that Activin signaling is required for regeneration polarity, and the underlying asymmetric activation of notum at anterior- over posterior-facing wounds. We propose that Activin signaling is involved in regeneration-specific responses broadly in the animal kingdom.

Involvement of clock gene expression, bone morphogenetic protein and activin in adrenocortical steroidogenesis by human H295R cells

Functional interactions between the levels of clock gene expression and adrenal steroidogenesis were studied in human adrenocortical H295R cells. Fluctuations of Bmal1, Clock, Per2 and Cry1 mRNA levels were found in H295R cells treated with forskolin (FSK) in a serum-free condition. The changes of clock gene expression levels were diverged, with Clock mRNA level being significantly higher than Cry1 and Per2 mRNA levels after 12-h stimulation with FSK. After FSK induction, mRNA levels of StAR and CYP11B2 were highest at 12 hours and CYP17 mRNA level reached a peak at 6 hours, but HSD3B1 mRNA level was transiently decreased at 3 hours. The expression levels of Clock mRNA showed a significant positive correlation with StAR among the interrelationships between mRNA levels of key steroidogenic factors and clock genes. Knockdown of Clock gene by siRNA led to a significant reduction of FSK-induced expression of StAR and CYP17 after 12-h treatment with FSK. BMP-6 and activin, which modulate adrenal steroidogenesis, had inhibitory effects on Clock mRNA expression, whereas treatment with follistatin, a binding protein of activin, increased Clock mRNA levels in the presence of FSK, suggesting an endogenous function of activin in regulation of Clock mRNA expression. Collectively, the results indicated that changes of Clock mRNA expression, being upregulated by FSK and suppressed by BMP-6 and activin, were tightly linked to StAR expression by human adrenocortical cells.

Activin A promotes the development of acquired heterotopic ossification and is an effective target for disease attenuation in mice

Heterotopic ossification (HO) is a common, potentially debilitating pathology that is instigated by inflammation caused by tissue damage or other insults, which is followed by chondrogenesis, osteogenesis, and extraskeletal bone accumulation. Current remedies are not very effective and have side effects, including the risk of triggering additional HO. The TGF-β family member activin A is produced by activated macrophages and other inflammatory cells and stimulates the intracellular effectors SMAD2 and SMAD3 (SMAD2/3). Because HO starts with inflammation and because SMAD2/3 activation is chondrogenic, we tested whether activin A stimulated HO development. Using mouse models of acquired intramuscular and subdermal HO, we found that blockage of endogenous activin A by a systemically administered neutralizing antibody reduced HO development and bone accumulation. Single-cell RNA-seq analysis and developmental trajectories showed that the antibody treatment reduced the recruitment of Sox9+ skeletal progenitors, many of which also expressed the gene encoding activin A (Inhba), to HO sites. Gain-of-function assays showed that activin A enhanced the chondrogenic differentiation of progenitor cells through SMAD2/3 signaling, and inclusion of activin A in HO-inducing implants enhanced HO development in vivo. Together, our data reveal that activin A is a critical upstream signaling stimulator of acquired HO in mice and could represent an effective therapeutic target against forms of this pathology in patients.

Maternal and zygotic activin signaling promotes adequate pattern and differentiation of mesoderm through regulation of pluripotency genes during zebrafish development

To investigate the role of maternal Activin-like factors in the preservation of stemness and mesendoderm induction, their effects were promoted and inhibited using synthetic human Activin A or SB-505124 treatments, respectively, before the maternal to zygotic transition (MZT). To study the role of zygotic Activin-like factors, SB-505124 treatment was also used after the MZT. Promoting the signaling intensity of maternal Activin-like factors led to premature differentiation, loss of stemness, and no mesendoderm malformation, while its alleviation delayed the differentiation and caused various malformations. Inhibition of the zygotic Activin-like factors was associated with suppressing the ndr1, ndr2, oct4 (pou5f3), mycb and notail transcription as well as differentiation retardation at the oblong stage, and a broad spectrum of anomalies in a dose-dependent manner. Together, promoting the signal intensity of maternal Activin-like factors drove development along with mesendodermal differentiation, while suppression of the maternal or zygotic ones maintained the pluripotent state and delayed differentiation.

Human and mouse activin genes: Divergent expression of activin A protein variants and identification of a novel heparan sulfate-binding domain in activin B

Activins are members of the transforming growth factor-β (TGF-β) superfamily of signaling proteins and were originally identified as components of follicular fluid. The proteins are now known to play critical roles in numerous normal and pathological processes and conditions, but less is clear about the relationships between their gene organization and protein variant expression and structure. The four human and mouse activin (Act) genes, termed INHβA, INHβB, INHβC and INHβE, differ in exon numbers. Human INHβA is the most complex with 7 exons and elicits production of three Act A variants (Act A X1, X2 and X3) differing in their pro-region, as we showed previously. Here we further analyzed the mouse INHβA gene and found that its 4 exons encode for a single open reading frame (mouse Act A), corresponding to the shortest human Act A X3 variant. Activins are synthesized and secreted as large complexes made of a long pro-region and a short mature C- terminal ligand and are known to interact with the heparan sulfate (HS) chains of cell surface and matrix proteoglycans. Human Act A X1 and X2 variants do have a HS-binding domain (HBD) with Cardin/Weintraub traits in their pro-region, while the X3 variant does not as shown previously. We found that the mouse Act A lacks a HBD as well. However, we identified a typical HBD in the pro-region of both mouse and human Act B, and synthetic peptides containing that domain interacted with immobilized HS and cell surface with nanomolar affinity. In sum, human and mouse Act A genes elicit expression of different variant sets, while there is concordance in Act B protein expression, reflecting possible evolutionary diversity in function of, and responses to, these signaling proteins in the two species.

Acute heat-treatment disrupts inhibin-related protein production and gene expression in the adult rat testis

Heat reversibly disrupts spermatogenesis, but the effects on Sertoli cell (SC) function and inhibin/activin-related proteins are less well-defined. Adult rat testis weights decreased by 40% within 2 weeks after heat-treatment (43 °C, 15 min), due to loss of pachytene spermatocytes and round spermatids. Coincident effects were reduced SC nuclear volume at one week and >50% reduction in expression of several critical SC genes (Inha, Cld11, Gja1, Tjp1, Cldn3) by 2 weeks. Leydig cell steroidogenic enzymes, Cyp11a1, Hsd3b1, were also reduced. Activin gene expression was unaffected at this time, but expression of the activin-binding protein, follistatin (Fst), increased >2-fold. At 4-8 weeks, coincident with the recovery of spermatocytes and early spermatids, but progressive loss of elongated spermatids, most SC genes had recovered; however, testicular activin A was reduced and activin B increased. At 8 weeks, serum inhibin was decreased and, consequently, serum FSH increased. Crucially, germ cell damage was not associated with a significant inflammatory response. At 14 weeks, most testicular parameters had returned to normal, but testis weights remained slightly reduced. These data indicate that, following acute heat-treatment, expression of several key Sertoli and Leydig cell genes declined in parallel with the initial loss of meiotic germ cells, whereas activins were responsive to the subsequent loss of mature spermatids, leading to an increase in testicular activin B production relative to activin A.

Urinary Activin A is a novel biomarker reflecting renal inflammation and tubular damage in ANCA-associated vasculitis

Activin A, a member of the transforming growth factor-beta superfamily, is a critical modulator of inflammation and plays a key role in controlling the cytokine cascade that drives the inflammatory response. However, the role of activin A in inflammatory kidney diseases remains unknown. To address this issue, we examined here whether activin A can be detected in the kidney and/or urine from patients with antineutrophil cytoplasmic antibody (ANCA) -associated vasculitis (AAV). Fifty-one patients who had been diagnosed with AAV and were treated in our department between November 2011 to March 2018 were included in this study. Forty-one patients had renal complications (renal AAV). Serum and urinary activin A levels were measured by enzyme-linked immunosorbent assay. Correlation of urinary activin A concentration with clinical parameters was analyzed. Urinary activin A was undetectable in healthy volunteers. In contrast, urinary activin A concentration was significantly increased in patients with renal AAV but not in those with non-renal AAV. Urinary activin A concentration decreased rapidly after immunosuppressive treatment. There was a significant correlation of urinary activin A level with urinary protein, L-FABP, and NAG. Histologic evaluation revealed that urinary activin A levels were significantly higher in patients with cellular crescentic glomeruli than in those lacking this damage. In situ hybridization demonstrated that the mRNA encoding the activin A βA subunit was undetectable in normal kidneys but accumulated in the proximal tubules and crescentic glomeruli of the kidneys of patients with renal AAV. Immunostaining showed that activin A protein also was present in the proximal tubules, crescentic glomeruli, and macrophages infiltrating into the interstitium in the kidneys of patients with renal AAV. These data suggested that urinary activin A concentration reflects renal inflammation and tubular damage in AAV and may be a useful biomarker for monitoring renal AAV.

Identification and characterization of a novel heparan sulfate-binding domain in Activin A longest variants and implications for function

Activins regulate numerous processes including inflammation and are synthesized as precursors consisting of a long N-terminal pro-region and a mature protein. Genomic human databases currently list three activin A (Act A) variants termed X1, X2 and X3. The X3 variant is the shortest, lacks N-terminal segments present in X1 and X2, and has been the focus of most past literature. Here, we asked whether these variants are expressed by human cells and tissues and what structural features are contained within their pro-regions. Human monocytic-like cells THP1 and U937 expressed X1 and X2 variants after exposure to phorbol ester or granulocyte-macrophage colony-stimulating factor, while X2 transcripts were present in placenta. Expression vectors encoding full length X2 or X3 variants resulted in production and secretion of biologically active Act A from cultured cells. Previous studies reported a putative HS-binding domain (HBD) in the X3 pro-region. Here, we identified a novel HBD with consensus HS-binding motifs near the N-terminal end of X1 and X2 pro-regions. Peptides encompassing this new domain interacted with substrate-bound HS with nanomolar affinity, while peptides from putative X3 HBD did not. In good agreement, full length X2 pro-region interacted with heparin-agarose, while the X3 pro-region did not. In sum, our study reveals that Act A variants are expressed by inflammatory cells and placenta and yield biological activity. The high affinity HBD in X1 and X2 pro-region and its absence in X3 could greatly influence overall Act A distribution, availability and activity in physiological and pathological circumstances.

Crosstalk between Activin A and Shh signaling contributes to the proliferation and differentiation of antler chondrocytes

Chondrocyte proliferation and differentiation are crucial for endochondral ossification and strictly regulated by numerous signaling molecules and transcription factors, but the hierarchical regulatory network remains to be deciphered. The present study emphasized the interplay of Activin A, Foxa, Notch and Shh signaling in the proliferation and differentiation of antler chondrocytes. We found that Activin A promoted chondrocyte proliferation and differentiation, and accelerated the transition of cell cycle from G1 into S phase along with the activation of Notch and Shh signaling whose blockage attenuated above function of Activin A. Inhibition of Notch pathway by DAPT led to a significant reduction in the expression of Shh signaling molecules, whereas addition of exogenous rShh rescued the delayed onset of chondrocyte proliferation and differentiation elicited by DAPT, indicating that Notch pathway is upstream of Shh signaling. Further analysis evidenced that DAPT attenuated the activation of Activin A on Shh signaling. Simultaneously, Foxa transcription factors were downstream targets of Shh signaling in chondrocyte differentiation. Moreover, Shh pathway played an important role in the crosstalk between Activin A-Notch signaling and Foxa. Collectively, Shh signaling may act downstream of Notch pathway to mediate the effects of Activin A on the proliferation and differentiation of antler chondrocytes through targeting Foxa.

The Activin Social Network: Activin, Inhibin, and Follistatin in Breast Development and Cancer

Activins and inhibins are closely related protein heterodimers with a similar tissue distribution; however, these two complexes have opposing functions in development and disease. Both are secreted cytokine hormones, with activin the primary inducer of downstream signaling cascades and inhibin acting as a rheostat that exquisitely governs activin function. Adding to the complexity of activin signaling, follistatin, a highly glycosylated monomeric protein, binds activin with high affinity and restrains downstream pathway activation but through a mechanism distinct from that of inhibin. These three proteins were first identified as key ovarian hormones in the pituitary-gonadal axis that direct the synthesis and secretion of FSH from the pituitary, hence controlling folliculogenesis. Research during the past 30 years has expanded the roles of these proteins, first by discovering the ubiquitous expression of the trio and then by implicating them in a wide array of biological functions. In concert, these three hormones govern tissue development, homeostasis, and disease in multiple organ systems through diverse autocrine and paracrine mechanisms. In the present study, we have reviewed the actions of activin and its biological inhibitors, inhibin, and follistatin, in mammary gland morphogenesis and cancer.

Impaired Glucocorticoid Suppression of TGFβ Signaling in Human Omental Adipose Tissues Limits Adipogenesis and May Promote Fibrosis

Visceral obesity is associated with insulin resistance and higher risk of type 2 diabetes and metabolic diseases. A limited ability of adipose tissues to remodel through the recruitment and differentiation of adipose stem cells (ASCs) is associated with adipose tissue inflammation and fibrosis and the metabolic syndrome. We show that the lower adipogenesis of omental (Om) compared with abdominal subcutaneous (Abdsc) ASCs was associated with greater secretion of TGFβ ligands that acted in an autocrine/paracrine loop to activate SMAD2 and suppress adipogenesis. Inhibition of TGFβ signaling rescued Om ASC differentiation. In Abdsc ASCs, low concentrations of dexamethasone suppressed TGFβ signaling and enhanced adipogenesis, at least in part by increasing TGFBR3 protein that can sequester TGFβ ligands. Om ASCs were resistant to these dexamethasone effects; recombinant TGFBR3 increased their differentiation. Pericellular fibrosis, a hallmark of dysfunctional adipose tissue, was greater in Om and correlated with higher level of tissue TGFβ signaling activity and lower ASC differentiation. We conclude that glucocorticoids restrain cell-autonomous TGFβ signaling in ASCs to facilitate adipogenesis and healthy remodeling in Abdsc and these processes are impaired in Om. Therapies directed at overcoming glucocorticoid resistance in visceral adipose tissue may improve remodeling and help prevent metabolic complications of visceral obesity.

Activin over-expression in the testis of mice lacking the inhibin α-subunit gene is associated with androgen deficiency and regression of the male reproductive tract

Regionalised interaction of the activins, follistatin and inhibin was investigated in the male reproductive tract of mice lacking the inhibin α-subunit (Inha^-/-). Serum and intratesticular activin B, although not activin A and follistatin, were increased in Inha^-/- mice at 25 days of age, but all three proteins were elevated at 56 days. None of these proteins were altered within the epididymis and vas deferens at either age. At 25 days, histology of the epididymis and vas deferens was similar to wild-type. At 56 days, the testis contained extensive somatic cell tumours, leading to Leydig cell regression and testosterone deficiency. The epididymis and vas deferens showed epithelial regression and increased prominence of the interstitial stroma. Immunoregulatory and fibrotic gene expression in the epididymis and vas deferens were unchanged. Thus, absence of the inhibin α-subunit has marginal effects on activins in the epididymis and vas deferens, and regression of these tissues is associated with androgen deficiency.

Bone Morphogenetic Protein 2 Promotes Human Trophoblast Cell Invasion by Inducing Activin A Production

Bone morphogenetic protein (BMP) 2 and activin A belong to the TGF-β superfamily and are highly expressed in human endometrium and placenta. Studies have demonstrated that activin A and BMP2 play essential roles in the process of early embryo implantation by promoting human trophoblast cell invasion. However, whether activin A production can be regulated by BMP2 in human trophoblast cells remains unknown. The aim of our study was to determine the effects of BMP2 on activin A production and its role in human trophoblast invasion. Primary human extravillous trophoblast (EVT) cells were used as study models. BMP2 treatment significantly increased inhibin βA (INHBA) mRNA levels and activin A production without altering inhibin α and inhibin βB levels. BMP2-induced EVT cell invasion was attenuated by knockdown of INHBA. The increased INHBA transcription and activin A production by BMP2 were blocked by the type I receptor activin receptor (ACVR)-like kinase 2 (ALK2) and activin receptor-like kinase 3 (ALK3) inhibitor dorsomorphin homolog 1 (DMH-1). BMP2-induced INHBA upregulation was also inhibited by knockdown of type I receptor ALK3 or combined knockdown of type II receptors for BMP2 (BMPR2) and ACVR2A. Whereas BMP2 initiated both canonical SMAD1/5/8 and noncanonical SMAD2/3 signaling, only knockdown of SMAD4, but not SMAD2 and SMAD3, abolished the effects of BMP2 on INHBA. Our results show that BMP2 increases human trophoblast invasion by upregulating INHBA and activin A production via ALK3-BMPR2/ACVR2A-SMAD1/5/8-SMAD4 signaling.

The obligatory role of Activin A in the formation of heterotopic bone in Fibrodysplasia Ossificans Progressiva

Fibrodysplasia Ossificans Progressiva (FOP) is a rare genetic disorder that presents at birth with only minor patterning defects, but manifests its debilitating pathology early in life with episodic, yet progressive and cumulative, heterotopic ossification (HO) of ligaments, tendons, and a subset of major skeletal muscles. The resulting HO lesions are endochondral in nature, and appear to be linked to inflammatory stimuli arising in association with known injuries, or from inflammation linked to normal tissue repair. FOP is caused by gain-of-function mutations in ACVR1, which encodes a type I BMP receptor. Initial studies on the pathogenic mechanism of FOP-causing mutations in ACVR1 focused on the enhanced function of this receptor in response to certain BMP ligands, or independently of ligands, but did not directly address the fact that HO in FOP is episodic and inflammation-driven. Recently, we and others demonstrated that Activin A is an obligate factor for the initiation of HO in FOP, signaling aberrantly via mutant ACVR1 to transduce osteogenic signals and trigger heterotopic bone formation (Hatsell et al., 2015; Hino et al., 2015). Subsequently, we identified distinct tissue-resident mesenchymal progenitor cells residing in muscles and tendons that recognize Activin A as a pro-osteogenic signal (solely in the context of FOP-causing mutant ACVR1), and give rise to the cartilaginous anlagen that form heterotopic bone (Dey et al., 2016). During the course of these studies, we also found that the activity of FOP-causing ACVR1 mutations does not by itself explain the triggered or inflammatory nature of HO in FOP, suggesting the importance of other, inflammation-introduced, factors or processes. This review presents a synthesis of these findings with a focus on the role of Activin A and inflammation in HO, and lays out perspectives for future research.

Activin/follistatin system in grass carp pituitary cells: - Regulation by local release of growth hormone and luteinizing hormone and its functional role in growth hormone synthesis and secretion

Gonadotrophin regulation by activin/follistatin system is well-documented, but the corresponding effect on growth hormone (GH) has not been fully characterized and with little information available in lower vertebrates, especially in fish models. In grass carp, local interactions of GH and luteinizing hormone (LH) can induce GH release and gene expression at pituitary level via autocrine/paracrine mechanisms. To shed light on the role of activin/follistatin system in GH regulation by local actions of GH and LH, grass carp activin βA and βB were cloned, shown to be single-copy genes expressed in the pituitary, and confirmed to encode activin proteins capable of transactivating promoter with activin-responsive elements. In grass carp pituitary cells, activin A and B were effective in reducing GH secretion and GH cell content with concurrent drop in GH mRNA level whereas the opposite was true for follistatin, the activin-binding protein known to neutralize the effects of endogenous activin. Treatment with activin A and B not only could suppress basal but also inhibit GH mRNA expression induced by GH and human chorionic gonadotropin (hCG), a functional analogue of LH in fish model. Apparently, down-regulation of GH mRNA by activin was mediated by reducing GH transcript stability with concurrent inhibition on GH promoter activity via the SMAD pathway. In reciprocal experiments, GH treatment was found to up-regulate activin βA, activin βB and follistatin mRNA levels in carp pituitary cells but the opposite was noted by removing endogenous GH with GH antiserum. Interestingly, parallel treatment with hCG could also inhibit basal as well as GH-induced activin βA, activin βB and follistatin gene expression. These results, as a whole, indicate that the pituitary activin/follistatin system can serve as a regulatory target for local interactions of GH and LH and contribute to GH regulation by autocrine/paracrine mechanisms in the carp pituitary.

Activin A and Follistatin in Menstrual Blood: Low Concentrations in Women With Dysfunctional Uterine Bleeding

Activin A and follistatin are growth factors produced by several organs, comprising the endometrium, where they modulate cell and tissue differentiation. In this study, the authors tested whether activin A and follistatin are measurable in menstrual blood and whether their concentrations change in women with dysfunctional uterine bleeding (DUB). The authors evaluated healthy women with regular menstrual cycles (n = 15) and women with DUB (n = 12). Activin A and follistatin were measured in both menstrual and peripheral blood samples using highly sensitive enzyme immunoassays, whereas their respective mRNAs were quantified by real-time polymerase chain reaction in endometrial samples collected during the perimenstrual period. Activin A concentrations were 4-fold higher in menstrual than in peripheral serum of healthy women (mean +/- SE, 4.24 +/- 0.18 vs 1.00 +/- 0.15 ng/mL, P < .001) and were significantly lower in women with DUB compared to healthy subjects (P < .001). Follistatin concentration was 8-fold higher in menstrual than in peripheral serum of healthy women (3.94 +/- 0.49 vs 0.49 +/- 0.04 ng/mL, P < .001) and was significantly lower in the menstrual serum of women with DUB compared to controls (P < .001). There was no correlation between menstrual and peripheral serum concentrations of both proteins. The endometrial expression of activin A and follistatin mRNA was lower in women with DUB compared to controls (P < .05). Both activin A and follistatin are measurable in high concentrations in human menstrual blood and are relatively lower in women with DUB. The quantitative assessment of activin A and follistatin in menstrual serum might be a putative clinical marker of endometrial function.

Overexpression of Leap2 impairs Xenopus embryonic development and modulates FGF and activin signals

Besides its widely described function in the innate immune response, no other clear physiological function has been attributed so far to the Liver-Expressed-Antimicrobial-Peptide 2 (LEAP2). We used the Xenopus embryo model to investigate potentially new functions for this peptide. We identified the amphibian leap2 gene which is highly related to its mammalian orthologues at both structural and sequence levels. The gene is expressed in the embryo mostly in the endoderm-derived tissues. Accordingly it is induced in pluripotent animal cap cells by FGF, activin or a combination of vegT/β-catenin. Modulating leap2 expression level by gain-of-function strategy impaired normal embryonic development. When overexpressed in pluripotent embryonic cells derived from blastula animal cap explant, leap2 stimulated FGF while it reduced the activin response. Finally, we demonstrate that LEAP2 blocks FGF-induced migration of HUman Vascular Endothelial Cells (HUVEC). Altogether these findings suggest a model in which LEAP2 could act at the extracellular level as a modulator of FGF and activin signals, thus opening new avenues to explore it in relation with cellular processes such as cell differentiation and migration.

[The Point Mutation in NOGGIN2 Protein That Enhances Its Ability to Bind Activin]

Earlier we have revealed the ability of Noggin family proteins to bind a member of the TUF-β superfamily, ActivinB, and to repress the Activin-dependent Smad2 signaling cascade. In the present work we have characterized a mutant of the Xenopus laevis Noggin2, bearing the substitution W203R. We have shown that this point mutation enhances the affinity of Noggin2 to ActivinB, while weakens its affinity to BMP. Consistently, we have shown that W203 R mutant inhibits Smad2 signaling cascade more efficiently than the wild-type Noggin2. Interestingly, the mutation of human Noggin in the homologous position is associated with hereditary anomalies. The revealed effects of W203R substitution in Noggin2 demonstrate promising potential of such mutagenesis for generation of Noggin variants with enhanced affinity to different members of the TGF-β superfamily.

[Fibrodysplasia ossificans progressiva and osteoimmunology]

Fibrodysplasia ossificans progressive (FOP) is a genetic disorder characterized by progressive heterotopic ossification (HO) in skeletal muscle, tendons and ligaments. FOP is caused by gain-of-function mutations of ALK2, a receptor of bone morphogenetic proteins. Immune responses have been suggested to be involved in HO in FOP, because muscle trauma induces acute HO in patients with FOP. Recently, Activin A, a non-osteogenic ligand, was identified as a ligand of the mutated ALK2 to induce HO. It was suggested that Activin A is a novel interface between FOP and osteoimmunology.

Activin A and follistatin during the oestrous cycle and early pregnancy in ewes

The activin pathway has been postulated to be involved in regulation of multiple reproductive processes important for survival of the conceptus. These processes include luteinisation of the follicular cells and thus function of the corpus luteum, early embryo development and uterine function including implantation of the conceptus. Therefore, the aim of the current study was to determine whether the concentrations of activin A and follistatin (FST), an activin-binding protein, differed between ewes with a lifetime history of enhanced or reduced embryonic survival (ES). The mRNAs encoding FST and activin A (inhibin beta A subunit; INHBA) were present in the uterus and abundant in the uterine luminal or glandular epithelia by day 18 of gestation. A peak of activin A was observed in the systemic circulation around the time of oestrus, and activin A concentrations were elevated in animals with reduced ES during the oestrous cycle and early gestation. Concentrations of activin A in uterine fluid were approximately twofold greater on day 16 of gestation in ewes with reduced ES compared to those with enhanced ES. No consistent differences in FST were observed between these groups. Treatment of luteinising ovine granulosa cells with activin A in vitro suppressed progesterone secretion providing evidence of a potential pathway whereby increased concentrations of activin A may decrease ES.

New insights into implication of the SLIT/ROBO pathway in the prehierarchical follicle development of hen ovary

The SLIT/Roundabout (ROBO) pathway is involved in follicle development of mammalian ovary, and 2 secreted hormones activin A and inhibin A have potential roles in modulation of the SLIT/ROBO system, but the related actions remain poorly understood in bird. The aims of the present study were to examine the spatial and temporal expression of the SLIT ligand genes (SLIT1, SLIT2, and SLIT3) and their receptor ROBO1, ROBO2, ROBO3, and ROBO4 genes in various-sized prehierarchical follicles during hen ovary development and the effects of activin A and inhibin A on the expression of these genes in the cultured hen follicles. Our result demonstrated that the transcripts of the 3 SLIT genes were highly expressed in the developing follicles and expression patterns of the SLIT transcripts were different from those of ROBO genes detected by real-time quantitative reverse transcriptase PCR. Both SLIT and ROBO transcripts were predominantly expressed in oocytes and granulosa cells from the prehierarchichal follicles examined by in situ hybridization. The localization for SLIT and ROBO proteins was revealed by immunohistochemistry similar to the spatial distribution of their transcript. In cultured follicles (4 to 8 mm in diameter), the expression levels of SLIT and ROBO members are hormonally regulated by activin A (10 ng/mL) and/or inhibin A (20 ng/mL) after treatment for 24 h. However, the expression of only SLIT2, SLIT3, and ROBO3 mRNA presented a directly opposite response to activin A and inhibin A hormones. These results indicate that SLIT/ROBO pathway is implicated in the prehierarchical follicular development of the hen ovary by an intrafollicular autocrine and/or paracrine action, and is influenced by activin A and inhibin A hormones.

Low miR-143/miR-145 Cluster Levels Induce Activin A Overexpression in Oral Squamous Cell Carcinomas, Which Contributes to Poor Prognosis

Deregulated expression of activin A is reported in several tumors, but its biological functions in oral squamous cell carcinoma (OSCC) are unknown. Here, we investigate whether activin A can play a causal role in OSCCs. Activin A expression was assessed by qPCR and immunohistochemistry in OSCC tissues. Low activin A-expressing cells were treated with recombinant activin A and assessed for apoptosis, proliferation, adhesion, migration, invasion and epithelial-mesenchymal transition (EMT). Those phenotypes were also evaluated in high activin A-expressing cells treated with follistatin (an activin A antagonist) or stably expressing shRNA targeting activin A. Transfections of microRNA mimics were performed to determine whether the overexpression of activin A is regulated by miR-143/miR-145 cluster. Activin A was overexpressed in OSCCs in comparison with normal oral mucosa, and high activin A levels were significantly associated with lymph node metastasis, tumor differentiation and poor survival. High activin A levels promoted multiple properties associated with malignant transformation, including decreased apoptosis and increased proliferation, migration, invasion and EMT. Both miR-143 and miR-145 were markedly downregulated in OSCC cell lines and in clinical specimens, and inversely correlated to activin A levels. Forced expression of miR-143 and miR-145 in OSCC cells significantly decreased the expression of activin A. Overexpression of activin A in OSCCs, which is controlled by downregulation of miR-143/miR-145 cluster, regulates apoptosis, proliferation and invasiveness, and it is clinically correlated with lymph node metastasis and poor survival.

Activin A protects midbrain neurons in the 6-hydroxydopamine mouse model of Parkinson's disease

Parkinson’s disease (PD) is a chronic neurodegenerative disease characterized by a significant loss of dopaminergic neurons within the substantia nigra pars compacta (SNpc) and a subsequent loss of dopamine (DA) within the striatum. Despite advances in the development of pharmacological therapies that are effective at alleviating the symptoms of PD, the search for therapeutic treatments that halt or slow the underlying nigral degeneration remains a particular challenge. Activin A, a member of the transforming growth factor β superfamily, has been shown to play a role in the neuroprotection of midbrain neurons against 6-hydroxydopamine (6-OHDA) in vitro, suggesting that activin A may offer similar neuroprotective effects in in vivo models of PD. Using robust stereological methods, we found that intrastriatal injections of 6-OHDA results in a significant loss of both TH positive and NeuN positive populations in the SNpc at 1, 2, and 3 weeks post-lesioning in drug naïve mice. Exogenous application of activin A for 7 days, beginning the day prior to 6-OHDA administration, resulted in a significant survival of both dopaminergic and total neuron numbers in the SNpc against 6-OHDA-induced toxicity. However, we found no corresponding protection of striatal DA or dopamine transporter (DAT) expression levels in animals receiving activin A compared to vehicle controls. These results provide the first evidence that activin A exerts potent neuroprotection in a mouse model of PD, however this neuroprotection may be localized to the midbrain.

In vivo repopulating activity emerges at the onset of hematopoietic specification during embryonic stem cell differentiation

The generation of in vivo repopulating hematopoietic cells from in vitro differentiating embryonic stem cells has remained a long-standing challenge. To date, hematopoietic engraftment has mostly been achieved through the enforced expression of ectopic transcription factors. Here, we describe serum-free culture conditions that allow the generation of in vivo repopulating hematopoietic cells in the absence of ectopically expressed factors. We show that repopulating activity arises immediately upon the commitment of mesodermal precursors to the blood program, within the first wave of hematopoietic specification. We establish that the formation of these progenitors is extremely transient and exquisitely sensitive to the cytokine milieu. Our findings define the precise differentiating stage at which hematopoietic repopulating activity first appears in vitro, and suggest that during embryonic stem cell differentiation, all hematopoietic programs are unraveled simultaneously from the mesoderm in the absence of cues that restrict the coordinated emergence of each lineage as is normally observed during embryogenesis.

Recombinant BMP4 and BMP7 increase activin A production by up-regulating inhibin βA subunit and furin expression in human granulosa-lutein cells

CONTEXT

Granulosa cell-derived activins play important roles in the regulation of ovarian functions. To date, there is limited information pertaining to the intracellular regulation, assembly, and secretion of endogenous activin A in human granulosa cells.

OBJECTIVE

The aim of this study was to examine the effects of BMP4 and BMP7 on furin expression and activin A production as well as the underlying mechanisms of action in human granulosa cells.

DESIGN

An established immortalized human granulosa cell line (SVOG) and primary granulosa-lutein cells were used as study models. Expression of inhibin subunits and furin as well as activin A accumulation were examined after exposure to recombinant human BMP4 or BMP7. A BMP type I receptor inhibitor (dorsomorphin), a furin inhibitor (Decanoyl-Arg-Val-Lys-Arg-chloromethylketone), and small interfering RNAs targeting SMAD4 and furin were used to verify the specificity of the effects and investigate potential mechanisms.

SETTING

The study was conducted in an academic center.

MAIN OUTCOME MEASURES

Specific mRNA and protein levels were examined using real time qPCR and Western blot. Activin A levels were measured using enzyme immunoassay.

RESULTS

Treatment with bone morphogenetic protein (BMP) 4 and BMP7 significantly increased furin mRNA and protein, inhibin βA mRNA, and activin A accumulation. Pre-treatment with dorsomorphin or SMAD4 knockdown reversed the stimulatory effects of BMP4 and BMP7 on furin and inhibin βA expression. In addition, furin knockdown or pre-treatment with a furin inhibitor attenuated the BMP4- and BMP7-induced accumulation of activin A.

CONCLUSION

Recombinant BMP4 and BMP7 increase the production of bioactive mature activin A by up-regulating both the production and proteolytic processing of inhibin βA subunit in human granulosa cells. The enhancement of inhibin βA subunit processing is attributable to a SMAD-dependent up-regulation of its proprotein convertase, furin. These findings provide a potential mechanism by which theca cells can regulate neighboring granulosa cells in the ovary.

Activin/Nodal signalling in stem cells

Activin/Nodal growth factors control a broad range of biological processes, including early cell fate decisions, organogenesis and adult tissue homeostasis. Here, we provide an overview of the mechanisms by which the Activin/Nodal signalling pathway governs stem cell function in these different stages of development. We describe recent findings that associate Activin/Nodal signalling to pathological conditions, focusing on cancer stem cells in tumorigenesis and its potential as a target for therapies. Moreover, we will discuss future directions and questions that currently remain unanswered on the role of Activin/Nodal signalling in stem cell self-renewal, differentiation and proliferation.