Inhibin ßE (INHBE) is a possible insulin resistance-associated hepatokine identified by comprehensive gene expression analysis in human liver biopsy samples.

The liver plays a major role in whole-body energy homeostasis by releasing secretory factors, termed hepatokines. To identify novel target genes associated with insulin resistance, we performed a comprehensive analysis of gene expression profiles using a DNA chip method in liver biopsy samples from humans with varying degrees of insulin resistance. Inhibin ßE (INHBE) was identified as a novel putative hepatokine with hepatic gene expression that positively correlated with insulin resistance and body mass index in humans. Quantitative real time-PCR analysis also showed an increase in INHBE gene expression in independent liver samples from insulin-resistant human subjects. Additionally, Inhbe gene expression increased in the livers of db/db mice, a rodent model of type 2 diabetes. To preliminarily screen the role of Inhbe in vivo in whole-body energy metabolic status, hepatic mRNA was knocked down with siRNA for Inhbe (siINHBE) in db/db mice. Treatment with siINHBE suppressed body weight gain during the two-week experimental period, which was attributable to diminished fat rather than lean mass. Additionally, treatment with siINHBE decreased the respiratory quotient and increased plasma total ketone bodies compared with treatment with non-targeting siRNA, both of which suggest enhanced whole-body fat utilization. Our study suggests that INHBE functions as a possible hepatokine to alter the whole-body metabolic status under obese insulin-resistant conditions.

Activin-ßC modulates gonadal, but not adrenal tumorigenesis in the inhibin deficient mice.

Activins and inhibins are involved in the regulation of several biological processes, including reproduction, development and fertility. Deregulation of the inhibin/activin signaling pathway has been implicated in the progression of reproductive and adrenal cancers. Deletion of the inhibin α-subunit results in up-regulation of the circulating levels of activins and this leads to the development of sex-cord stromal tumors followed by a cancer associated-cachexia in mice. When gonadectomy is performed, development of adrenocortical carcinomas is observed. We previously showed that overexpression of activin-ßC modulates the development of sex-cord stromal tumors and reduces cancer-cachexia in the inhibin-deficient mice by antagonizing the activin signaling pathway. The adrenal cortex and gonads share in common a large subset of genes, consistent with their common embryonic lineage. Additionally, it has been shown that adrenocortical carcinomas adopt an altered cellular identity resembling the ovary. Therefore, a study to assess the impact of overexpression of activin-ßC on the onset of adrenocortical carcinoma in gonadectomized inhibin-deficient mice was warranted. Within the current study we evaluated markers of apoptosis, proliferation, tumor burden, survival analysis and serum levels of activin-A in gonadectomized mice versus sham operated controls. Results showed that overexpression of activin-ßC modulated the development of reproductive tumors but had no effect on adrenal tumorigenesis. Our data reinforces the importance of activin-ßC in reproductive biology and suggest that activin-ßC is a tumor modulator with gonadal specificity.

Essential roles of inhibin beta A in mouse epididymal coiling.

Testis-derived testosterone has been recognized as the key factor for morphogenesis of the Wolffian duct, the precursor of several male reproductive tract structures. Evidence supports that testosterone is required for the maintenance of the Wolffian duct via its action on the mesenchyme. However, it remains uncertain how testosterone alone is able to facilitate formation of regionally specific structures such as the epididymis, vas deferens, and seminal vesicle from a straight Wolffian duct. In this study, we identified inhibin beta A (or Inhba) as a regional paracrine factor in mouse mesonephroi that controls coiling of the epithelium in the anterior Wolffian duct, the future epididymis. Inhba was expressed specifically in the mesenchyme of the anterior Wolffian duct at embryonic day 12.5 before the production of androgens. In the absence of Inhba, the epididymis failed to develop the characteristic coiling in the epithelium, which showed a dramatic decrease in proliferation. This loss of epididymal coiling did not result from testosterone deficiency, because testosterone production and parameters for testosterone action such as testis descent and anogenital distance remained normal. We further found that initial Inhba expression did not require testosterone as Inhba was also expressed in the anterior Wolffian duct of female embryos where no testosterone was produced. However, Inhba expression at later stages depended on testosterone. These results demonstrated that Inhba, a mesenchyme-specific gene, acts collectively with testosterone to facilitate epididymal coiling by stimulating epithelial proliferation.

Suppression of activin A in autoimmune lung disease associated with anti-GM-CSF.

Pulmonary alveolar proteinosis (PAP) is an autoimmune disorder characterized by neutralizing autoantibodies to granulocyte-macrophage colony stimulating factor (GM-CSF). Surfactant metabolism is severely dysregulated in PAP, resulting in a foam cell appearance of alveolar macrophages. Microarray analysis of RNA from PAP bronchoalveolar lavage (BAL) cells to explore autoimmune-related genes yielded evidence of a deficiency of activin A, a cytokine implicated in regulation of B-cell proliferation and reduction of foam cell formation. Subsequent studies confirmed a severe deficiency of activin A gene expression and protein secretion in PAP BAL cells and marked reduction of activin A protein in PAP BAL fluids compared to healthy controls. PAP cells, however, like those of healthy controls, were capable of elevated activin A production in response to GM-CSF. Treatment with activin A in vitro suppressed proliferation of PAP peripheral blood B-cells in a receptor-dependent manner and also reduced secretion of anti-GM-CSF autoantibody. These studies are the first to suggest that activin A may play a role in autoimmune disease.

Activins are critical modulators of growth and survival.

Activins betaA and betaB (encoded by Inhba and Inhbb genes, respectively) are related members of the TGF-beta superfamily. Previously, we generated mice with an Inhba knock-in allele (InhbaBK) that directs the expression of activin betaB protein in the spatiotemporal pattern of activin betaA. These mice were small and had shortened life spans, both influenced by the dose of the hypomorphic InhbaBK allele. To understand the mechanism(s) underlying these abnormalities, we now examine growth plates, liver, and kidney and analyze IGF-I, GH, and major urinary proteins. Our studies show that activins modulate the biological effects of IGF-I without substantial effects on GH, and that activin signaling deficiency also has modest effects on hepatic and renal function. To assess the relative influences of activin betaA and activin betaB, we produced mice that express activin betaB from the InhbaBK allele, and not from its endogenous Inhbb locus. InhbaBK/BK, Inhbb-/- mice have failure of eyelid fusion at birth and demonstrate more severe effects on somatic growth and survival than either of the corresponding single homozygous mutants, showing that somatic growth and life span are supported by both activins betaA and betaB, although activin betaA plays a more substantial role.