Altered GnRH neuron and ovarian innervation characterize reproductive dysfunction linked to the Fragile X messenger ribonucleoprotein (Fmr1) gene mutation

Abstract

IntroductionMutations in the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene cause Fragile X Syndrome, the most common monogenic cause of intellectual disability. Mutations of FMR1 are also associated with reproductive disorders, such as early cessation of reproductive function in females. While progress has been made in understanding the mechanisms of mental impairment, the causes of reproductive disorders are not clear. FMR1-associated reproductive disorders were studied exclusively from the endocrine perspective, while the FMR1 role in neurons that control reproduction was not addressed.ResultsHere, we demonstrate that similar to women with FMR1 mutations, female Fmr1 null mice stop reproducing early. However, young null females display larger litters, more corpora lutea in the ovaries, increased inhibin, progesterone, testosterone, and gonadotropin hormones in the circulation. Ovariectomy reveals both hypothalamic and ovarian contribution to elevated gonadotropins. Altered mRNA and protein levels of several synaptic molecules in the hypothalamus are identified, indicating reasons for hypothalamic dysregulation. Increased vascularization of corpora lutea, higher sympathetic innervation of growing follicles in the ovaries of Fmr1 nulls, and higher numbers of synaptic GABAA receptors in GnRH neurons, which are excitatory for GnRH neurons, contribute to increased FSH and LH, respectively. Unmodified and ovariectomized Fmr1 nulls have increased LH pulse frequency, suggesting that Fmr1 nulls exhibit hyperactive GnRH neurons, regardless of the ovarian feedback.ConclusionThese results reveal Fmr1 function in the regulation of GnRH neuron secretion, and point to the role of GnRH neurons, in addition to the ovarian innervation, in the etiology of Fmr1-mediated reproductive disorders.

Impaired ovarian development in a zebrafishfmr1knockout model

“…In addition, in the brains of sexually mature female KO fish, we detected a reproducible increase in the expression of the neuroendocrine hormones gnrh3, and fsh (Fig 3C). These findings support the idea of altered hypothalamic-pituitary control of reproductive development in the female KO fish, similar to that reported in the female KO mice (Villa et al, 2023).…”

“…These findings support the idea of altered hypothalamic-pituitary control of reproductive development in the female KO fish, similar to that reported in the female KO mice (Villa et al, 2023).…”

“…Also important to note that primary ovarian insufficiency is a well reported Fragile-X associated condition, however it is associated with pre-mutation at the FMRP locus, and likely caused by fmr1 RNA toxicity, and not reported to be caused by a reduction or loss of FMRP (Man et al, 2017) Several animal models have been generated to understand the function of FMRP, including knockouts in the fruitfly, zebrafish, mouse and rat. However, there are only a few studies that focus on its role in oogenesis and early embryonic development: several in Drosophila, which reveal the role of dfmr1 in early oocyte development (Costa et al, 2005;Deshpande et al, 2006;Epstein et al, 2009;Monzo et al, 2010;Yang et al, 2007), and a few in mice that suggest a role in fertility (Mok-Lin et al, 2018;Villa et al, 2023). However, a longitudinal study investigating FMRP function at different stages of ovarian development and possible mechanisms of the observed phenotypes, has not yet been reported in a vertebrate model.…”

Effects of Soy Protein Isolate on Fragile X Phenotypes in Mice

“…These isoflavones can interfere with the normal function of endogenous estrogen. It is interesting that the timing of excess weight gain in response to soy in female mice occurs at P9–P18 in Fmr1 HET and at P6–P18 and P168–P224 in Fmr1 KO , which is prior to puberty onset in C57BL/6J (females P28–P36) [ 98 , 99 , 100 ] and at the cessation of reproductive function in Fmr1 KO females (average age of last litter, FVB strain, P163) [ 101 ]. In WT males, the timing of excess weight gain was P32–P39, which is immediately after puberty onset in C57BL/6J (P25–P31) [ 98 ].…”

“…It remains to be determined how the lack of FMRP affects gonadal hormone levels in Fmr1 KO mice over their lifespan and in response to diet and sex. Others have shown early vaginal opening; early cessation of reproductive function; no difference in body weight at any age; and elevated luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone and progesterone at diestrus in FVB Fmr1 KO females compared to WT controls [ 101 ]. Overall, these data suggest an interaction between reproductive hormones and weight gain in mice, and that the Fmr1 KO mutation, particularly in males, could be more sensitive to the endocrine disrupting effects of soy phytoestrogens.…”