RF01 | PMON44 Absence of Kisspeptin in KNDy Neurons of Mice Causes Sexually Dimorphic Metabolic Dysfunction on a High-Fat Diet

Kisspeptin neurons in the arcuate nucleus (ARC) of the hypothalamus are considered as the gonadotropin-releasing hormone (GnRH) pulse generator to control the cascade of hormone secretions that constitute the reproductive axis. These neurons typically co-express Neurokinin B and Dynorphin and are thus dubbed KNDy neurons. In addition, KNDy neuron kisspeptin is hypothesized to be a major sensor and regulator of metabolic homeostasis while relaying energy status to the hypothalamic-pituitary-gonad (HPG) axis. However, the direct metabolic impact of KNDy neuron kisspeptin has not been well-characterized. To explore this role, we examined the metabolic profile of our previously established KNDy neuron-specific kisspeptin knock-out mouse model (Pdyn-Cre/Kissfl/fl, or KO). To do so, we performed glucose tolerance tests, EchoMRI body composition analysis, and measured body weight in wild type (WT) control or KO mice fed with either regular chow or a high-fat diet (HFD, 60% kcal fat, Research Diets, New Brunswick, NJ) for 12 weeks post-weaning. At 4 weeks on the HFD, KO females weighed significantly more than HFD WT females, which continued through the remaining 8 weeks. Additionally, we found significantly decreased glucose tolerance and increased fat mass in HFD KO females compared to HFD WT females. However, KO males exhibited no significant differences in body weight, body composition, or glucose tolerance between the genotypes on either diet. This data suggests that KNDy neuron kisspeptin is critical for metabolic homeostasis and preventing metabolic dysfunction when challenged with a high-fat diet. Our findings further suggest a sexual dimorphism whereby KNDy neuron kisspeptin performs this action predominantly in females.

Presentation: Saturday, June 11, 2022 1:18 p.m. - 1:23 p.m., Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.

PMON53 Resistance to weight gain and obesity in mice lacking the IGF-1 receptor in GHRH neurons

IGF-1 signaling plays a pivotal role in regulating GH production through a negative feedback mechanism at the level of the hypothalamus and pituitary. We created a transgenic mouse model with ablation of the IGF-1R in GHRH-neurons (GIGFRKO) that exhibited normal linear growth, however, when fed a normal chow diet, began to have a sustained decrease in weight gain velocity. This was associated with greater energy expenditure and a lower body fat mass, with no change in caloric intake. The aim of the current study was to determine whether this metabolic phenotype would be sustained with a high fat diet challenge. At 4 weeks of age, the mice were placed on a 45% fat diet for 16 weeks. The GIGFRKO mouse model fed a HFD had normal linear growth, but at 10 weeks of age, both male and female mice began to have a sustained decrease in weight gain velocity compared to their age and sex-matched controls. The metabolic assessment demonstrated that the GIGFRKO transgenic mice had higher O2 consumption, lower CO2 production, a reduction in body fat mass, an elevation in energy expenditure, and improved glucose tolerance compared to the control mice on HFD. This was not associated with changes in food intake or activity and was present in males and females. In conclusion, the GIGFRKO transgenic mice are resistant to diet-induced obesity due to the critical role of the GHRH-GH axis in controlling energy expenditure and fat metabolism.

Presentation: Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.

Deficiency of arcuate nucleus kisspeptin results in postpubertal central hypogonadism

Kisspeptin (encoded by Kiss1), a neuropeptide critically involved in neuroendocrine regulation of reproduction, is primarily synthesized in two hypothalamic nuclei: the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC). AVPV kisspeptin is thought to regulate the estrogen-induced positive feedback control of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH), and the preovulatory LH surge in females. In contrast, ARC kisspeptin neurons, which largely coexpress neurokinin B and dynorphin A (collectively named KNDy neurons), are thought to mediate estrogen-induced negative feedback control of GnRH/LH and be the major regulators of pulsatile GnRH/LH release. However, definitive data to delineate the specific roles of AVPV versus ARC kisspeptin neurons in the control of GnRH/LH release is lacking. Therefore, we generated a novel mouse model targeting deletion of Kiss1 to the ARC nucleus (Pdyn-Cre/Kiss1fl/fl KO) to determine the functional differences between ARC and AVPV kisspeptin neurons on the reproductive axis. The efficacy of the knockout was confirmed at both the mRNA and protein levels. Adult female Pdyn-Cre/Kiss1fl/fl KO mice exhibited persistent diestrus and significantly fewer LH pulses when compared with controls, resulting in arrested folliculogenesis, hypogonadism, and infertility. Pdyn-Cre/Kiss1fl/fl KO males also exhibited disrupted LH pulsatility, hypogonadism, and variable, defective spermatogenesis, and subfertility. The timing of pubertal onset in males and females was equivalent to controls. These findings add to the current body of evidence for the critical role of kisspeptin in ARC KNDy neurons in GnRH/LH pulsatility in both sexes, while directly establishing ARC kisspeptin's role in regulating estrous cyclicity in female mice, and gametogenesis in both sexes, and culminating in disrupted fertility. The Pdyn-Cre/Kiss1fl/fl KO mice present a novel mammalian model of postpubertal central hypogonadism.NEW & NOTEWORTHY We demonstrate through a novel, conditional knockout mouse model of arcuate nucleus (ARC)-specific kisspeptin in the KNDy neuron that ARC kisspeptin is critical for estrous cyclicity in female mice and GnRH/LH pulsatility in both sexes. Our study reveals that ARC kisspeptin is essential for normal gametogenesis, and the loss of ARC kisspeptin results in significant hypogonadism, impacting fertility status. Our findings further confirm that normal puberty occurs despite a loss of ARC kisspeptin.

Mice With Targeted Deletion of ARC Kisspeptin Exhibit Immature Gametogenesis and Impaired Fertility

Hypothalamic kisspeptin is primarily synthesized in two discrete nuclei - the anteroventral periventricular (AVPV) and the arcuate (ARC) nuclei. We have previously developed a selective, conditional ARC kisspeptin knock-out (KO) mouse line, namely the Pdyn-Cre/Kiss^fl/fl KO mice, that exhibited normal puberty onset in both sexes, but impaired estrous cyclicity and LH pulsatility in Pdyn-Cre/Kiss^fl/fl KO females. To examine the end-organ effect of the lack of ARC kisspeptin, we examined gametogenesis, gonad morphology, and fertility. Hematoxylin and eosin (H&E) staining of serial-sectioned whole ovaries demonstrated that Pdyn-Cre/Kiss^fl/fl KO female mice lacked corpora lutea - their ovarian folliculogenesis did not progress beyond antral follicle development, suggesting an ovulatory defect in Pdyn-Cre/Kiss^fl/fl KO females. 75% of the Pdyn-Cre/Kiss^fl/fl KO male mice had testes exhibiting a striking decrease in mature sperm in the seminiferous tubules. The remaining 25% showed evidence of mature sperm. Further evidence of a hypogonadal phenotype of the Pdyn-Cre/Kiss^fl/fl KO mice included the significantly low weight and small size of the ovaries, uteri, and testes when compared to control littermates. In a controlled, continuous mating paradigm with proven WT males, 2-4-month-old Pdyn-Cre/Kiss^fl/fl KO female mice failed to become pregnant or produce any pups, whereas age-matched WT females exhibited normal pregnancies to term. Thus, Pdyn-Cre/Kiss^fl/fl KO females have complete infertility. Ongoing studies of male fertility data suggest that Pdyn-Cre/Kiss^fl/fl KO males are subfertile, in accordance with their variable spermatogenesis phenotype - some KO males sired pups when paired with proven, WT females, whereas other KO males are infertile. Future experiments include assessing the capability of Pdyn-Cre/Kiss^fl/fl KO mice to respond to chronic, exogenous kisspeptin and GnRH administration to rescue abnormal LH pulsatility and estrous cyclicity in females, as well as the impaired fertility in both sexes.

Mutant three-repeat tau expression initiates retinal ganglion cell death through Caspase-2

The microtubule-associated protein tau is implicated in multiple degenerative diseases including retinal diseases such as glaucoma; however, the way tau initiates retinopathy is unclear. Previous retinal assessments in mouse models of tauopathy suggest that mutations in four-repeat (4R) tau are associated with disease-induced retinal dysfunction, while shifting tau isoform ratio to favor three-repeat (3R) tau production enhanced photoreceptor function. To further understand how alterations in tau expression impact the retina, we analyzed the retinas of transgenic mice overexpressing mutant 3R tau (m3R tau-Tg), a model known to exhibit Pick's Disease pathology in the brain. Analysis of retinal cross-sections from young (3 month) and adult (9 month) mice detected asymmetric 3R tau immunoreactivity in m3R tau-Tg retina, concentrated in the retinal ganglion and amacrine cells of the dorsal retinal periphery. Accumulation of hyperphosphorylated tau was detected specifically in the detergent insoluble fraction of the adult m3R tau-Tg retina. RNA-seq analysis highlighted biological pathways associated with tauopathy that were uniquely altered in m3R tau-Tg retina. The upregulation of transcript encoding apoptotic protease caspase-2 coincided with increased immunostaining in predominantly 3R tau positive retinal regions. In adult m3R tau-Tg, the dorsal peripheral retina of the adult m3R tau-Tg exhibited decreased cell density in the ganglion cell layer (GCL) and reduced thickness of the inner plexiform layer (IPL) compared to the ventral peripheral retina. Together, these data indicate that mutant 3R tau may mediate toxicity in retinal ganglion cells (RGC) by promoting caspase-2 expression which results in RGC degeneration. The m3R tau-Tg line has the potential to be used to assess tau-mediated RGC degeneration and test novel therapeutics for degenerative diseases such as glaucoma.

SUN-243 Deletion of KNDy Neuron-Specific KISS1 Disrupts Estrous Cyclicity and LH Pulsatility in Female Mice

Kisspeptin (encoded by Kiss1), a neuropeptide critically involved in neuroendocrine regulation of reproduction, is primarily synthesized in two discrete hypothalamic nuclei: the anteroventral periventricular area (AVPV) and arcuate nucleus (ARC). AVPV Kiss1 is important for the pre-ovulatory luteinizing hormone (LH) surge unique to females as well as estrogen-induced positive feedback control of GnRH and LH. In contrast, ARC Kiss1 neurons, which largely co-express the neuropeptides NKB and dynorphin (collectively known as KNDy neurons), are major regulators of pulsatile release of GnRH and LH, and mediate estrogen-induced negative feedback control of both GnRH and LH. Previous studies have not fully separated the specific roles for Kiss1 in the AVPV versus KNDy-ARC neurons in the downstream control of GnRH and LH release. Therefore, we generated a Pdyn-Cre/Kiss1^fl/fl (KO) mouse model to target Kiss1 in the KNDy neurons to differentiate KNDy neuron-specific function from AVPV Kiss1 function in the maturation and maintenance of the reproductive axis. qRT-PCR data documented a significant reduction of Kiss1 expression in the mediobasal hypothalamus (containing ARC) compared to controls, whereas Kiss1 in the preoptic area (containing AVPV) was similar in both KO and controls. Immunofluorescent IHC confirmed a loss of kisspeptin immunoreactivity in the ARC of KO animals while expression in the AVPV remained intact. Markers of pubertal onset (day of vaginal opening and first estrus in females; day of preputial separation in males) were normal in KO mice, suggesting that AVPV Kiss1 and/or other neural signals may be sufficient for pubertal onset. In addition, body weight throughout pubertal growth was comparable between KO and control animals of both sexes. Interestingly, KO female mice had disrupted estrous cycles presenting with persistent diestrus and a small vaginal opening. In order to test our hypothesis that conditional deletion of Kiss1 in KNDy neurons disrupts or ablates episodic GnRH/LH pulsatile release, we collected serial tail blood samples from mice at diestrus and measured LH. KO female mice exhibited significantly fewer LH pulses in a 3-hour timespan compared to controls, suggesting that KNDy neurons were functionally compromised. These observations indicate the central role of KNDy neurons in the regulation of GnRH/LH pulsatility and estrous cyclicity. The functional effects of disrupted estrous cyclicity and slower LH pulses observed in KO females are currently under study to assess potential abnormalities in ovarian folliculogenesis and fertility. Future experiments will determine whether ARC Kiss1 deletion disrupts the KNDy-driven negative feedback response of LH to gonadectomy, as well as address potential sex differences in ARC Kiss1-mediated negative feedback control of LH release.