RNAseq in fat pads from Alstrom syndrome 1 (ALMS1) Knockout rats support a role for ALMS1 in leptin release and fat metabolism in adipocytes.

Abstract

Inactivating mutations in the ALMS1 gene in humans cause early onset obesity and metabolic syndrome. Deletion of ALMS1 in rodents induces early onset obesity and insulin resistance on normal chow. The mechanisms by which ALMS1 cause obesity are not clear but likely involve the development of leptin resistance since adult ALMS1 KO rats are hyperphagic and hyperleptinemic. It is not known whether ALMS1 controls leptin release and expression in adipocytes prior to development of obesity. ALMS1 has been associated to ciliary function which may play a role in adipogenesis. We hypothesized that deletion of ALMS1 would alter gene pathways involved in fat metabolism and cilia formation in young ALMS1 KO rats, which should contribute to hyperleptinemia. To study this, we obtained abdominal fat pads from young ALMS1 KO rats shortly after weaning (7 weeks) and prior to changes in body weight. We found that plasma leptin levels were higher in young ALMS1 KO rats (ALMS1: 3530±300 vs. WT: 172±16 pg/ml, p<0.05) despite no differences in body weight or baseline glucose. Leptin release (normalized to fat weight) was 120% higher (wild type: 30±8, ALMS1‐KO: 56± 15 pg/mg tissue/2h) in abdominal fat pads from ALMS1 KO rats. To study the genes involved in higher leptin release we performed RNAseq in freshly isolated abdominal fat pads. 12,860 genes were identified and quantified. In fat pads from ALMS1 KO there were 163 upregulated and 237 significantly downregulated genes. Leptin mRNA was significantly increased (1.68 Log2 fold, p<0.001, n=4) as were several genes involved in lipogenesis (Elovl6, Scd1, Scd2, Mogat2, Acly, Lpl, Dgat2, Fasn). Ingenuity pathway analysis indicated that the top canonical pathways impacted were: oleate biosynthesis, glycolysis I, hepatic fibrosis, and clathrin‐mediated endocytosis signaling. Importantly, at least 10 ciliary genes were significantly decreased (Traf3ip1, Pard6g, Cngb1, Ak7, Ttll1, Mlf1, Ccdc162, Dnah6, Ccdc187, Foxj1) suggesting a role for ALMS1 in ciliary function. To examine this, we immunolabeled cilia in abdominal adipocytes with gamma acetylated tubulin antibodies, and examined sections by confocal microscopy. Short cilia (1–2 μm) were observed in both WT and ALMS1 KO adipocytes. We concluded that ALMS1 is likely involved in leptin release from adipocytes. It is not clear whether increased leptin expression and release is secondary to neuroendocrine alterations or alterations in cilia‐induced signaling. Our data also point to an important role for ALMS1 in regulating adipocyte function and leptin physiology.Support or Funding InformationHenry Ford Hospital Research Fund