Inhibins are members of the TGFβ superfamily, which regulate many cellular processes including differentiation, proliferation, survival and apoptosis. Although initially described as hormones regulating the hypothalamus-pituitary-gonadal axis, based on their ability to antagonize Activins, our group has recently reported that they play a role in thymocyte differentiation and survival, as well as in thymic stromal cell maturation and nTreg generation. Here, we used Inhibin knock out mice (Inhα-/-) to investigate the role of Inhibins in peripheral dendritic cell maturation and function. We first demonstrated that LPS treated Inhα+/+ bone marrow derived dendritic cells (BMDC) were capable to produce significant levels of Inhibin A. Interestingly, Inhα-/- BMDC showed reduced MHCII and CD86 upregulation and increased PD-L1 expression in response to LPS compared to Inhα+/+, which correlated with reduced ability to induce proliferation of allogeneic T cells. The "semi-mature" phenotype displayed by Inhα-/- mBMDC correlated with increased levels of IL-10 and slightly decreased IL-6 production after LPS stimulation. In addition, Inhα-/- mBMDC showed impaired migration towards CCL19 and CCL21, assessed by in vitro chemotaxis and in vivo competitive homing experiments, despite their normal CCR7 expression. Furthermore, in vivo LPS-induced DC maturation was also diminished in Inhα-/- mice, specially within the LC (CD207+ CD11b+ CD103-) subpopulation. Finally, analysis of delayed type hypersensitivity responses in Inhα-/- mice, showed reduced ear swelling as a result of reduced cellular infiltration in the skin, correlating with impaired homing of CD207+ DCs to the draining lymph nodes. In summary, our data demonstrate for the first time that Inhibins play a key role in peripheral DC maturation and function, regulating the balance between immunity and tolerance.

Inhibin B is a marker of spermatogenesis and Sertoli cell function. The objective of this study was to evaluate the biologic significance of inhibins in subfertile men and the usefulness of inhibin B for the detection of male reproductive dysfunction. Forty-seven subfertile men were evaluated by semen analysis and clinical examination. In addition to semen analysis and hormone determinations, inhibins A and B (Serotec) in all 47 and inhibin A in 25 of these samples using another kit (Biosource) were measured. Higher inhibin B (median, range: 160.3, 81.8-328.5 pg/mL vs. 94.9, 15.6-389.7 pg/mL, P = 0.024) and lower FSH (P = 0.001) were detected in men with sperm concentrations > or =20 million/mL (n = 9), compared to oligozoospermia (sperm concentration <20 million/mL, n = 38). Inhibin B correlated significantly negatively with FSH, LH, and E2, and patient's age and positively with sperm concentration, testicular volume, and TSH. Multiple regression analysis indicated FSH, LH, E2, TSH, and age as the independent variables for inhibin B with a coefficient of determination (R) of 0.53. Simultaneous measurement of both FSH and inhibin B identified more cases with oligozoospermia than either hormone alone. Taking into account the body mass index, the age of the patient, and the indirect mixed antiglobin reaction (MAR) test result in addition to FSH and inhibin B led to the correct semen classification in 45 out of 47 cases. The simultaneous measurement of FSH and inhibin B, taking into account age, body mass index, and the indirect MAR test result appears accurate in identifying subfertility. Inhibin A is detectable in some subfertile men but its significance is not clear.

Inhibins and Activins are members of the TGF-β superfamily that regulate the differentiation of several cell types. These ligands were initially identified as hormones that regulate the hypothalamus-pituitary-gonadal axis; however, increasing evidence has demonstrated that they are key regulators in the immune system. We have previously demonstrated that Inhibins are the main Activin ligands expressed in the murine thymus and that they regulate thymocyte differentiation, promoting the DN3-DN4 transition and the selection of SP thymocytes. As Inhibins are mainly produced by thymic stromal cells, which also express Activin receptors and Smad proteins, we hypothesized that Inhibins might play a role in stromal cell differentiation and function. Here, we demonstrate that, in the absence of Inhibins, thymic conventional dendritic cells display reduced levels of MHC Class II (MHCII) and CD86. In addition, the ratio between cTECs and mTECs was affected, indicating that mTEC differentiation was favoured and cTEC diminished in the absence of Inhibins. These changes appeared to impact thymocyte selection leading to a decreased selection of CD4SP thymocytes and increased generation of natural regulatory T cells. These findings demonstrate that Inhibins tune the T cell selection process by regulating both thymocyte and stromal cell differentiation.

We have previously reported that the absence of inhibins results in impaired dendritic cell (DC) maturation and function, leading to decreased T cell activation and diminished delayed-type hypersensitivity responses. Here, we investigated the role of inhibins in peripheral regulatory T cell (Treg) induction in vitro and in vivo. Inhibin deficient (Inhα-/-) mice showed an increased percentage of peripherally induced Tregs in colonic lamina propria and mesenteric lymph nodes, compared to Inhα+/+ mice, which correlated with increased expression of PD-L1 in CD103+ and CD8α+ DCs. Lipopolysaccharide-stimulated bone marrow-derived and ex vivo spleen- and lymph node-purified CD11c+ Inhα-/- DCs induced higher Tregs in vitro. Moreover, in vivo anti-DEC205-ovalbumin (OVA) DC targeting of mice with adoptively transferred OVA-specific T cells showed enhanced induced peripheral Treg conversion in Inhα-/- mice. These data identify inhibins as key regulators of peripheral T cell tolerance.

Loss-of-function mutations in the X-linked immunoglobulin superfamily, member 1 (IGSF1) gene result in central hypothyroidism, often associated with macroorchidism. Testicular enlargement in these patients might be caused by increases in follicle-stimulating hormone (FSH) levels, as IGSF1 has been proposed to function as an inhibin B receptor or as an inhibitor of activin type I receptor (ALK4) activity in pituitary gonadotrope cells. If true, loss of IGSF1 should lead to reduced inhibin B action or disinhibition of activin signaling, thereby increasing FSH synthesis. Here, we show that FSH levels and sperm counts are normal in male Igsf1 knockout mice, although testis size is mildly increased. Sperm parameters are also normal in men with IGSF1 deficiency, although their FSH levels may trend higher and their testes are enlarged. Inhibin B retains the ability to suppress FSH synthesis in pituitaries of Igsf1-knockout mice and IGSF1 does not interact with ALK4 or alter activin A/ALK4 stimulation of FSHβ (Fshb/FSHB) subunit transcription or expression. In light of these results, it is unlikely that macroorchidism in IGSF1 deficiency derives from alterations in spermatogenesis or inhibin/activin regulation of FSH.

Activin-stimulated FSH synthesis and release by the pituitary gonadotrope is antagonized by gonadally derived inhibins. The two isoforms of inhibin, inhibin A and B, bind to the activin type II receptors, though at a lower affinity than the activins, but do not stimulate intracellular signaling. Theoretically, therefore, inhibins can prevent activin signaling through competitive binding if present at higher concentrations than the activins. In reality, the inhibins have been shown to antagonize activin signaling when the two ligand types are present at equimolar concentrations. These observations led to the hypothesis that inhibin binding proteins or co-receptors exist that either increase the affinity of the inhibins for the activin receptors or propagate inhibin-specific intracellular signals. Two candidate inhibin co-receptors, betaglycan and InhBP/p120, interact with activin receptors and augment inhibin antagonism of activin action. Here, we report the effect of betaglycan and InhBP/p120 on both inhibin A and inhibin B binding to the activin receptors ActRIIA and ActRIIB2. InhBP/p120 did not bind inhibin A or B when expressed alone or in combination with activin receptors, requiring a re-examination of the role of this protein in inhibin biology. Both inhibins bound the activin type II receptor, ActRIIB2. Inhibin B had a higher affinity for this receptor than inhibin A but an approximately 10-fold lower affinity than that of activin A. Inhibin A and B bound betaglycan with high affinity; however, only inhibin A binding to ActRIIB2 was significantly enhanced in the presence of betaglycan. Both inhibin isoforms showed slight but significant binding to ActRIIA, yet this binding was potentiated in the presence of betaglycan. Additionally, the complex formed between the inhibins, ActRIIA, and betaglycan was resistant to disruption by activin A, whereas activin A potently competed for inhibin binding to ActRIIB2 and betaglycan. Collectively, these data show that the inhibin isoforms have different affinities for the activin type II receptors but bind betaglycan with high affinity. A recently developed model of inhibin action proposes that inhibins form a high affinity, activin-resistant ternary complex with activin type II receptors and betaglycan, thereby providing a mechanism for inhibin antagonism of activin signaling. Importantly, the results presented here clearly show that this model does not apply equally to both forms of inhibin nor to the different activin type II receptor isoforms. Thus, it appears that the mechanisms of inhibin action may vary depending on the ligand and receptor types involved.

The inhibins are secreted alpha:beta heterodimers of the TGF-beta superfamily that are mainly synthesized in Sertoli cells and granulosa cells, and are critical regulators of testicular and ovarian development and function. Mice homozygous for a targeted deletion of the inhibin alpha subunit gene (Inha(-/-)) develop sex cord-stromal tumors in a gonadotropin-dependent manner. Here, we determine the contribution of LH to gonadal tumorigenesis by generating mice deficient in both inhibins and LH. Inha(-/-)Lhb(-/-) mice have increased survival and delayed tumor progression, and these observations correlate with lower serum FSH and estradiol levels compared to Inha(-/-) controls. Double mutant testicular tumors demonstrate decreased expression of cyclin D2, while double mutant ovarian tumors have elevated expression of p15(INK4b) and trend toward higher levels of p27(Kip1). We conclude that LH is not required for tumor formation in the absence of inhibins but promotes tumor progression, likely through alterations in serum hormone levels and cell cycle regulators.

Inhibins and activins are dimeric ligands belonging to the TGFβ superfamily with emergent roles in cancer. Inhibins contain an α-subunit (INHA) and a β-subunit (either INHBA or INHBB), while activins are mainly homodimers of either βA (INHBA) or βB (INHBB) subunits. Inhibins are biomarkers in a subset of cancers and utilize the coreceptors betaglycan (TGFBR3) and endoglin (ENG) for physiological or pathological outcomes. Given the array of prior reports on inhibin, activin and the coreceptors in cancer, this study aims to provide a comprehensive analysis, assessing their functional prognostic potential in cancer using a bioinformatics approach. We identify cancer cell lines and cancer types most dependent and impacted, which included p53 mutated breast and ovarian cancers and lung adenocarcinomas. Moreover, INHA itself was dependent on TGFBR3 and ENG/CD105 in multiple cancer types. INHA, INHBA, TGFBR3, and ENG also predicted patients' response to anthracycline and taxane therapy in luminal A breast cancers. We also obtained a gene signature model that could accurately classify 96.7% of the cases based on outcomes. Lastly, we cross-compared gene correlations revealing INHA dependency to TGFBR3 or ENG influencing different pathways themselves. These results suggest that inhibins are particularly important in a subset of cancers depending on the coreceptor TGFBR3 and ENG and are of substantial prognostic value, thereby warranting further investigation.

Inhibins are members of the transforming growth factor-β family, composed of a common α-subunit disulfide-linked to 1 of 2 β-subunits (βA in inhibin A or βB in inhibin B). Gonadal-derived inhibin A and B act in an endocrine manner to suppress the synthesis of follicle-stimulating hormone (FSH) by pituitary gonadotrope cells. Roles for inhibins beyond the pituitary, however, have proven difficult to delineate because deletion of the inhibin α-subunit gene (Inha) results in unconstrained expression of activin A and activin B (homodimers of inhibin β-subunits), which contribute to gonadal tumorigenesis and lethal cachectic wasting. Here, we generated mice with a single point mutation (Arg233Ala) in Inha that prevents proteolytic processing and the formation of bioactive inhibin. In vitro, this mutation blocked inhibin maturation and bioactivity, without perturbing activin production. Serum FSH levels were elevated 2- to 3-fold in InhaR233A/R233A mice due to the loss of negative feedback from inhibins, but no pathological increase in circulating activins was observed. While inactivation of inhibin A and B had no discernible effect on male reproduction, female InhaR233A/R233A mice had increased FSH-dependent follicle development and enhanced natural ovulation rates. Nevertheless, inhibin inactivation resulted in significant embryo-fetal resorptions and severe subfertility and was associated with disrupted maternal ovarian function. Intriguingly, heterozygous Inha+/R233A females had significantly enhanced fecundity, relative to wild-type littermates. These studies have revealed novel effects of inhibins in the establishment and maintenance of pregnancy and demonstrated that partial inactivation of inhibin A/B is an attractive approach for enhancing female fertility.

Hypoxia, a driver of tumor growth and metastasis, regulates angiogenic pathways that are targets for vessel normalization and ovarian cancer management. However, toxicities and resistance to anti-angiogenics can limit their use making identification of new targets vital. Inhibin, a heteromeric TGFβ ligand, is a contextual regulator of tumor progression acting as an early tumor suppressor, yet also an established biomarker for ovarian cancers. Here, we find that hypoxia increases inhibin levels in ovarian cancer cell lines, xenograft tumors, and patients. Inhibin is regulated primarily through HIF-1, shifting the balance under hypoxia from activins to inhibins. Hypoxia regulated inhibin promotes tumor growth, endothelial cell invasion and permeability. Targeting inhibin in vivo through knockdown and anti-inhibin strategies robustly reduces permeability in vivo and alters the balance of pro and anti-angiogenic mechanisms resulting in vascular normalization. Mechanistically, inhibin regulates permeability by increasing VE-cadherin internalization via ACVRL1 and CD105, a receptor complex that we find to be stabilized directly by inhibin. Our findings demonstrate direct roles for inhibins in vascular normalization via TGF-β receptors providing new insights into the therapeutic significance of inhibins as a strategy to normalize the tumor vasculature in ovarian cancer.

Activins and inhibins belong to the TGFβ-superfamily, which controls cell proliferation and differentiation in many organs. Activin A, the dimer of inhibin βA subunit, acts strongly anti-proliferative in hepatocytes. Little is known on the other activin/inhibin subunits in human liver and hepatocellular carcinoma (HCC).

The human INHA gene encodes the inhibin subunit alpha protein, which is common to both inhibin A and B. The functional importance of inhibins in male sex development, sexual function, and reproduction remain largely unknown.

Inhibins are transforming growth factor-β family heterodimers that suppress follicle-stimulating hormone (FSH) secretion by antagonizing activin class ligands. Inhibins share a common β chain with activin ligands. Follistatin is another activin antagonist, known to bind the common β chain of both activins and inhibins. In this study, we characterized the antagonist-antagonist complex of inhibin A and follistatin to determine if their interaction impacted activin A antagonism. We isolated the inhibin A:follistatin 288 complex, showing that it forms in a 1:1 stoichiometric ratio, different from previously reported homodimeric ligand:follistatin complexes, which bind in a 1:2 ratio. Small angle X-ray scattering coupled with modeling provided a low-resolution structure of inhibin A in complex with follistatin 288. Inhibin binds follistatin via the shared activin β chain, leaving the α chain free and flexible. The inhibin A:follistatin 288 complex was also shown to bind heparin with lower affinity than follistatin 288 alone or in complex with activin A. Characterizing the inhibin A:follistatin 288 complex in an activin-responsive luciferase assay and by surface plasmon resonance indicated that the inhibitor complex readily dissociated upon binding type II receptor activin receptor type IIb, allowing both antagonists to inhibit activin signaling. Additionally, injection of the complex in ovariectomized female mice did not alter inhibin A suppression of FSH. Taken together, this study shows that while follistatin binds to inhibin A with a substochiometric ratio relative to the activin homodimer, the complex can dissociate readily, allowing both proteins to effectively antagonize activin signaling.

TGF-β type III receptor (TβRIII) is a coreceptor for TGFβ family members required for high-affinity binding of these ligands to their receptors, potentiating their cellular functions. TGF-β [1]-[3], bone morphogenetic proteins (BMP2/4) and inhibins regulate different checkpoints during T cell differentiation. Although TβRIII is expressed on hematopoietic cells, the role of this receptor in the immune system remains elusive. Here, we provide the first evidence that TβRIII is developmentally expressed during T cell ontogeny, and plays a crucial role in thymocyte differentiation. Blocking of endogenous TβRIII in fetal thymic organ cultures led to a delay in DN-DP transition. In addition, in vitro development of TβRIII(-/-) thymic lobes also showed a significant reduction in absolute thymocyte numbers, which correlated with increased thymocyte apoptosis, resembling the phenotype reported in Inhibin α (-/-) thymic lobes. These data suggest that Inhibins and TβRIII may function as a molecular pair regulating T cell development.

The inhibins are disulphide-linked heterodimeric glycoproteins that belong to the TGFβ superfamily. Inhibins have been well studied in mammals but the information about their structure and function is very limited in lower vertebrates. The aim of the present study was to characterize inhibin-A and to understand its receptor binding interaction, and to evaluate its biological function in Clarias batrachus. Structure prediction of inhibin-A revealed two glycosylation sites on inhibin-α (Asp262 and Asn334). Docking of inhibin-A with its receptor; betaglycan and Act RIIA showed that residues Ser321, Gly324 and Leu325 of inhibin-α are involved in high affinity binding with betaglycan while inhibin-βA bound to Act RIIA by forming hydrogen bonds. The mRNA transcript analysis of various tissues indicated the presence of higher to moderate expression of inhibin-α and inhibin-βA in the gonads and the extra-gonadal tissues. Further, stage specific expression showed decreased levels of inhibin-α in the gonads during the annual reproductive cycles. Inhibin-βA, activin-βB and Act RIIA increased in the brain during spawning while FSHr increased in the gonads during the preparatory phase. Our study provides molecular, structural and functional insights of inhibin-A for the first time in C. batrachus.

Inhibins are gonadal hormones that act on pituitary gonadotrope cells to suppress FSH synthesis and secretion. Inhibin A and B are heterodimers of the inhibin ⍺-subunit disulfide-linked to one of two inhibin β-subunits. Homodimers or heterodimers of the inhibin β-subunits form the activins, which stimulate FSH production. Activins signal through complexes of type I and II receptor serine/threonine kinases to increase transcription of the FSHβ subunit gene. According to in vitro observations, inhibins impair FSH synthesis by competitively binding to activin type II receptors, particularly in the presence of the TGFβ type III receptor (TGFBR3, or betaglycan). The role of TGFBR3 in inhibin action in vivo has not been determined. Here, we ablated Tgfbr3 specifically in murine gonadotropes. Conditional knockout females were supra-fertile, exhibiting enhanced folliculogenesis, numbers of ovulated eggs per cycle, and litter sizes relative to control mice. Despite these phenotypes, FSH levels appeared to be unaltered in knockout mice, and the mechanisms underlying their enhanced fertility remain unexplained. Inhibin B is the predominant form of the hormone in males and in females during most stages of the estrous cycle. Remarkably, inhibin A, but not inhibin B, suppression of FSH synthesis was impaired in cultured pituitaries of knockout mice, which may explain the absence of discernible changes in FSH levels in vivo. Collectively, these data challenge current dogma by demonstrating that TGFBR3 (betaglycan) functions as an inhibin A, but not an inhibin B, coreceptor in gonadotrope cells in vivo. Mechanisms of inhibin B action merit further investigation.

Existing studies have investigated the relationship between the levels of serum inhibin B (INHB), anti-müllerian hormone (AMH) and precocious puberty in girls, but the results are inconsistent.

Ovarian-derived inhibin A and inhibin B (heterodimers of common α- and differing β-subunits) are secreted throughout the menstrual cycle in a discordant pattern, with smaller follicles producing inhibin B, whereas the dominant follicle and corpus luteum produce inhibin A. The classical function for endocrine inhibins is to block signalling by activins (homodimers of β-subunits) in gonadotrope cells of the anterior pituitary and, thereby, inhibit the synthesis of FSH. Whether inhibin A and inhibin B have additional physiological functions is unknown, primarily because producing sufficient quantities of purified inhibins, in the absence of contaminating activins, for preclinical studies has proven extremely difficult. Here, we describe novel methodology to enhance inhibin A and inhibin B activity and to produce these ligands free of contaminating activins. Using computational modeling and targeted mutagenesis, we identified a point mutation in the activin β A-subunit, A347H, which completely disrupted activin dimerization and activity. Importantly, this β A-subunit mutation had minimal effect on inhibin A bioactivity. Mutation of the corresponding residue in the inhibin β B-subunit, G329E, similarly disrupted activin B synthesis/activity without affecting inhibin B production. Subsequently, we enhanced inhibin A potency by modifying the binding site for its co-receptor, betaglycan. Introducing a point mutation into the α-subunit (S344I) increased inhibin A potency ~12-fold. This study has identified a means to eliminate activin A/B interference during inhibin A/B production, and has facilitated the generation of potent inhibin A and inhibin B agonists for physiological exploration.

Superovulation and embryo transfer techniques are important methods in cattle breeding. Combined with traditional superovulation protocols, immunization against inhibin can further improve follicular development and embryo yield. The aim of this study is to determine the efficacy of immunization against inhibin in improving the fertility of cattle through meta-analysis and to provide better clinical veterinary practice guidance. Three English databases (PubMed, EMBASE, Web of Science) were searched for research articles of immunizations against inhibin influence on cattle fertility. Literature screening, data extraction, and meta-analysis were conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. In addition, the Systematic Review Center for Laboratory animal Experimentation (SYRCLE) risk-of-bias (RoB) tool was used to assess the risk of bias of the included animal studies. Potentially relevant studies (317) were identified, and finally 14 eligible studies (all in English) were included. The results of meta-analysis revealed that immunization against inhibin has significant effects on improving the number of ovulations [mean difference (MD) = 0.44, 95% confidence interval (CI) = (0.31, 0.56)], embryos and unfertilized ova [MD = 4.51, 95% CI = (2.28, 6.74)], follicles of the three size categories, the incidence of multiple ovulations [OR = 22.50, 95% CI = (8.13, 62.27)], and the conception rate [OR = 2.36, 95% CI = (1.26, 4.40)]. Moreover, it improved the production of embryos [grades 1 embryos: MD = 3.84, (3.54, 4.15); grade 2 embryos: MD = -0.73, (-0.89, -0.57); grade 3 embryos: MD = -0.50, (-0.75, -0.25); degenerated embryos: MD = 1.16, (-0.51, 2.82); transferable embryos: MD = 2.67, (2.03, 3.31)] and the number of corpora lutea [MD = 1.25, 95% CI = (0.79, 1.71)]. In the above indicators, the differences between the two groups were statistically significant (all p < 0.0001). Additionally, according to the quality evaluation results, the risk of bias in the included studies is relatively high. The quality evaluation of the results of the included studies showed that the risk of bias mainly concentrated in the selective, performance, detection, and reporting of bias aspects.

Follicle-stimulating hormone (FSH), a key regulator of ovarian function, is often used in infertility treatment. Gonadal inhibins suppress FSH synthesis by pituitary gonadotrope cells. The TGFβ type III receptor, betaglycan, is required for inhibin A suppression of FSH. The inhibin B co-receptor was previously unknown. Here, we report that the gonadotrope-restricted transmembrane protein, TGFBR3L, is the elusive inhibin B co-receptor. TGFBR3L binds inhibin B but not other TGFβ family ligands. TGFBR3L knockdown or overexpression abrogates or confers inhibin B activity in cells. Female Tgfbr3l knockout mice exhibit increased FSH levels, ovarian follicle development, and litter sizes. In contrast, female mice lacking both TGFBR3L and betaglycan are infertile. TGFBR3L’s function and cell-specific expression make it an attractive new target for the regulation of FSH and fertility.