378 Leveraging rare genetic syndromes to understand genetic influence on metabolic dysregulation

Objectives/Goals: Bardet-Biedl Syndrome (BBS) is a rare, autosomal recessive syndromic ciliopathy. Obesity in BBS has been attributed to melanocortin 4 receptor (MC4R) pathway in the hypothalamus, which plays a major role in appetite control and energy balance. We aim to understand how BBS proteins play a role in hyperphagia and obesity using zebrafish models. Methods/Study Population: We used a published genetically stable bbs4 mutant zebrafish line to investigate metabolic regulation. Mutants harbor a 5 base pair deletion in bbs4 resulting in loss of gene function. We used behavioral assays to quantify feeding activity, lipid accumulation, and BMI. We monitored expression of appetite regulating and glucose homeostasis genes under fasting and feeding conditions using qRT-PCR in biological triplicate pools of larvae with three technical replicates per experimental condition. Comparative analyses between bbs4 mutants and wildtype (WT) controls were conducted to identify transcriptional and physiological alterations; statistical differences were detected with Dunnett’s multiple comparison test, and p<0.05 was considered significant. Results/Anticipated Results: For the behavioral assays, bbs4 homozygous mutants showed no significant differences compared to WT. Preliminary expression data show a significant decrease in mc4r expression in bbs4 mutants versus WT with concomitant decrease in leptin (lepa/lepb) expression versus WT at hunger initiation. Insulin (insa) showed a 6-fold higher activation and elevated glucagon and gluconeogenesis gene activation for mutants versus WT indicating that bbs4 homozygotes have hyperinsulinism even while fasting. However, in feeding conditions, satiety genes showed no activation in mutants, indicating impaired leptin response. Future studies will elucidate further the interplay between ciliary defects in proximal cellular contexts (i.e., hypothalamus, liver, and pancreas) and whole organism impact of impaired BBS protein. Discussion/Significance of Impact: Our findings indicate that bbs4 mutant zebrafish have preserved ciliary control over appetite and glucose homeostasis, as well as defective leptin-MC4R signaling and fasting-induced hyperinsulinism. Our preclinical model will facilitate the development of treatments for obesity associated with BBS.