Functional analysis of the human inhibin   subunit variant A257T and its potential role in premature ovarian failure

Abstract

BACKGROUND: A nucleotide substitution in the inhibin a subunit (INHA 769G>A, A257T) has been associated with premature ovarian failure (POF). We hypothesize this mutation causes a reduction in inhibin bioactivity, removing its suppression on the pituitary FSH secretion. The aim of this study is to establish if A257T inhibin has reduced bioactivity. METHODS: Mouse LbT2 pituitary gonadotrope, human granulosa (COV434) and human embryonic kidney (HEK293) cells were co-transfected with an activin-responsive reporter and increasing amounts of wild-type or variant A257T inhibin a subunit, and the degree of inhibin antagonism of activin signalling determined. RESULTS: A 5-fold inhibition was observed with wild-type inhibin a subunit overexpression (P < 0.001) (confirmed in HEK293 cells), while the A257T inhibin showed no inhibitory activity. In human ovarian COV434 transfected cells, while wild-type and A257T inhibin A had similar bioactivities, there was a significant reduction in the bioactivity of A257T inhibin B compared with wild-type inhibin B (P < 0.005). In all the three cell systems, overexpression of wildtype and A257T a subunit resulted in a 2-to 6-fold increase in secretion of dimeric inhibin indicating the reduced inhibin response was not due to a failure of dimerization. CONCLUSIONS: This study supports the hypothesis that the INHA 769G>A variant may increase susceptibility to POF with impaired inhibin B bioactivity and provides insight into the complex aetiology of POF.

Mutational analysis of inhibin alpha gene revealed three novel variations in Indian women with premature ovarian failure

“…The functional significance of this amino acid change has recently been reported (44). The alanine-to-threonine change occurs within the putative receptor-binding region of the mature peptide.…”

“…The alanine-to-threonine change occurs within the putative receptor-binding region of the mature peptide. Therefore, it appears that the change would impair the binding of inhibin to its receptor, resulting in an inability to activate subsequent signal transduction (29,44).…”

TGF-β/TGF-β receptor system and its role in physiological and pathological conditions

“…Most of these mutations involve the propeptide region and lead to a defective production of bioactive protein, providing further support for their implication in the development of POF. Moreover, inhibin-A is one of the most important regulators of the female reproductive cycle [102], and one mutation in the INHA (inhibin α) gene has been identified in patients with POF, resulting in an inactive mutant protein (A257T).…”

Inhibin α-Subunit N Terminus Interacts with Activin Type IB Receptor to Disrupt Activin Signaling

“…POF is typically characterized by hypergonadotropism with circulating levels of follicle-stimulating hormone (FSH) in the postmenopausal range, and in some patients, at levels greater than 30 mIU/ml (29). Functional analysis of the inhibin ␣-subunit A257T variant revealed impaired inhibin B bioactivity and elevated FSH levels (30). Others have reported that the N-terminal fragment of the inhibin ␣-subunit has biological function (31).…”