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.

Obesity incidence is increasing worldwide with the urgent need to identify new therapeutics. Sex differences in immune cell activation drive obesity-mediated pathologies where males are more susceptible to obesity co-morbidities and exacerbated inflammation. Here, we demonstrate that the macrophage-secreted protein RELMα critically protects females against high fat diet-induced obesity. Compared to male mice, RELMα levels were elevated in both control and high fat dietfed females and correlated with adipose macrophages and eosinophils. RELMα-deficient females gained more weight and had pro-inflammatory macrophage accumulation and eosinophil loss, while both RELMα treatment and eosinophil transfer rescued this phenotype. Single cell RNAsequencing of the adipose stromal vascular fraction was performed and identified sex and RELMα-dependent changes. Genes involved in oxygen sensing and iron homeostasis, including hemoglobin and lncRNA Gm47283, correlated with increased obesity, while eosinophil chemotaxis and response to amyloid-beta were protective. Monocyte-to-macrophage transition was also dysregulated in RELMα-deficient animals. Collectively, these studies implicate a RELMα-macrophage-eosinophil axis in sex-specific protection against obesity and uncover new therapeutic targets for obesity.

Obesity incidence is increasing worldwide with the urgent need to identify new therapeutics. Sex differences in immune cell activation drive obesity-mediated pathologies where males are more susceptible to obesity comorbidities and exacerbated inflammation. Here, we demonstrate that the macrophage-secreted protein RELMα critically protects females against high-fat diet (HFD)-induced obesity. Compared to male mice, serum RELMα levels were higher in both control and HFD-fed females and correlated with frequency of adipose macrophages and eosinophils. RELMα-deficient females gained more weight and had proinflammatory macrophage accumulation and eosinophil loss in the adipose stromal vascular fraction (SVF), while RELMα treatment or eosinophil transfer rescued this phenotype. Single-cell RNA-sequencing of the adipose SVF was performed and identified sex and RELMα-dependent changes. Genes involved in oxygen sensing and iron homeostasis, including hemoglobin and lncRNA Gm47283/Gm21887, correlated with increased obesity, while eosinophil chemotaxis and response to amyloid-beta were protective. Monocyte-to-macrophage transition was also dysregulated in RELMα-deficient animals. Collectively, these studies implicate a RELMα–macrophage–eosinophil axis in sex-specific protection against obesity and uncover new therapeutic targets for obesity.

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Women carrying a pre-mutation or mutation of the Fragile X mental retardation gene (FMR1) comprise the largest portion of premature ovarian failure (POF) cases due to known genetic factors. FMR1 mutation causes Fragile X syndrome, the most common cause of inherited mental impairment. The mutation inhibits the expression of the fragile X mental retardation protein (FMRP), a ubiquitously expressed mRNA binding protein. The specific molecular mechanism(s) leading to premature ovarian failure in Fragile X carriers are not known. Here, we utilize the complete KO mouse model, to mimic the lack of FMRP in Fragile X mutations and analyze the hypothalamic-pituitary-gonadal axis to uncover causes of POF due to FMR1 mutation. Consistent with mutations in human population, KO females experience early cessation of reproductive function and stop having litters at 150 days of age, compared to controls that stop reproducing at 250 days of age. Since POF can be caused by either insufficient pool of primordial follicles or by increased recruitment in each cycle and early depletion, we analyzed ovaries at 3 weeks of age and determined that the FMR1 KO mice had the same number of primordial follicles when compared to the controls, suggesting that POF is not due to a deficit in primordial follicles. However, at 8 weeks of age, FMR1 KO ovaries had higher number of corpora lutea, and KO females had larger litters, indicating that FMR1 KO mice have more follicles recruited in each estrous cycle. FMR1 KO mice have higher FSH, which corresponds to the high FSH in women. Serum estradiol levels and inhibin b expression levels were unaffected by FMR1 mutation suggesting normally functioning negative feedback signals from the ovaries. Analyses of hypothalamic gene expression demonstrated elevated GnRH mRNA in KO mice. To further investigate alterations is hypothalamic protein levels, western blot analyses determined that FMR1 KO mice have higher levels of NMDAR1 and higher levels of GABAA receptor G2 subunit. Dual label immunofluorescence analyses revealed higher number of NMDAR1 and GABAA receptors specifically in GnRH neurons of FMR1 KO mice when compared to control, suggesting that GnRH neurons themselves are affected by FMR1 mutation. Given that both glutamate and GABA can activate GnRH neurons, alterations in the number of these receptors can potentially cause hyperactivity in the HPG axis at the hypothalamic level leading to elevated FSH and the subsequent POF. In summary, our results reveal a potential mechanism of premature ovarian failure in Fragile X mutation carriers.