SUN-161 Puberty Onset Occurs At A Lower Body Weight In Male Mice With Mecp2 Deletion

Abstract Disclosure: M. Muhammed: None. H. Kim: None. R.S. Carroll: None. U.B. Kaiser: None. A. Abreu: None. Background: Central precocious puberty (CPP) is defined by premature development of secondary sexual characteristics due to early reactivation of pulsatile hypothalamic (GnRH) secretion. Studies in humans have identified MECP2 variants in girls with CPP. MECP2 is an X-linked gene, subject to X inactivation. It encodes a nuclear protein that binds preferentially to methylated DNA in promoter regions. Mutations in MECP2 are found in 90% of patients with Rett syndrome, a neurodevelopmental disorder. MECP2 is expressed broadly, and we hypothesized that it acts in the hypothalamus to affect puberty initiation. We used a Mecp2 knockout mouse model to investigate how Mecp2 acts to control the reproductive axis. In addition, we tested the effect of Mecp2 overexpression on genes important for puberty regulation. Methods: We performed in vivo and in vitro studies to investigate the role of Mecp2 in puberty. Mice: Adult heterozygous female mice (Mecp2+/-; Jackson Labs) were bred with wild type (WT) male mice and body weight (BW) and pubertal phenotypes (vaginal opening, first estrus, and preputial separation) were monitored in the offspring. Estrous cyclicity was assessed by daily vaginal smears for 17 days (d). Cell culture: We used an immortalized cell line, KTaR-1, derived from mouse arcuate nucleus. KTaR-1 cells were transfected with MECP2 (pDEST-hMeCP2-GFP) or empty vector (pcDNA3-EGFP). Twenty-four hours later, total RNA was isolated. RT-qPCR was performed for Esr-1, Esr-2, Kiss-1, Mkrn3, pDyn. and Tac2. Results: BW of Mecp2+/- females did not differ from WT littermate controls. In contrast, BW of hemizygous male mice (Mecp2-/y) was significantly lower than WT littermate controls (P < 0.0001). Mecp2+/- and WT females were similar in age at vaginal opening (36.9±1.4 d vs. 35.9±2.0 d; P = 0.7), first estrus (41.5±1.8 d vs. 41.9±1.6 d; P = 0.9), number of cycles/17 d (3.9±0.4 vs. 4.1±0.4; P = 0.6), and BW at time of vaginal opening (14.2±0.4 grams (g) vs. 14.5±0.4 g; P = 0.6). Preputial separation in Mecp2-/y males occurred at a later age than in WT males (39.4±1.7 d vs. 32.8±0.9 d; P = 0.003), but at a lower BW than in WT controls (13.3±0.4 g vs. 15.9±0.3 g; P < 0.001). In vitro studies showed no differences in expression of the candidate target genes in cells overexpressing MECP2 compared to cells transfected with empty vector. Conclusions: Mecp2-/y male mice achieved puberty at a lower BW (albeit at a later age) compared to WT males. The time of puberty was not different between WT and Mecp2+/- females. The lack of effect of Mecp2 deletion in females may be due to preferential X inactivation of the mutated X chromosome. These findings suggest that Mecp2 has a role in puberty, at least in males. While there was no effect of MECP2 overexpression in KTaR-1cells, one cannot completely rule out an action of Mecp2 on these genes in vivo. Additional studies are ongoing to further elucidate how Mecp2 affects pubertal onset. Presentation: Sunday, July 13, 2025