Mechanisms of adipocyte loss in laminopathy-induced lipodystrophy in mice and humans

Abstract Lipodystrophy is a disorder characterized by adipose tissue loss and redistribution, with associated metabolic complications including diabetes. The most common form of monogenic lipodystrophy is familial partial lipodystrophy type 2 (FPLD2), which is caused by a mutation in the LMNA gene, encoding nuclear lamins A and C. The mechanisms for how adipose tissues are lost, after developing normally through adolescence are unknown. To address this shortfall, we selectively deleted Lmna in adipocytes (LmnaADKO) of mice. We observed a striking loss of white adipose tissue in adult LmnaADKO mice, along with increased fat deposition in the liver, elevated blood glucose levels in both fasting and fed states, increased circulating insulin levels compared to the Lmnafl/fl controls. Analyses of young mice revealed development of white adipose tissue in LmnaADKO mice, which is progressively lost coincident with puberty. These phenotypes closely mirror those observed in human patients with FPLD2. To further investigate the function of lamin A/C in adipose tissue and mechanisms by which adipocytes are lost, we have now developed inducible LmnaiADKO mice as well as six knock-in mouse lines, each containing a pathological variant that causes lipodystrophy. We hypothesize that lamin A/C is required to maintain mature adipocyte characteristics, and we will ascertain molecular and cellular mechanisms that underly loss of mature adipocytes in mouse models and human patients. To test our hypotheses, we propose 1) to characterize seven lines of mice that contain lipodystrophic variants across Lmna, and test whether mechanisms of adipocyte loss in these mice reflect those found in inducible LmnaADKO mice, as well as in human patients with FPLD2. 2) to study effects of LMNA variant on adipocyte and nuclear morphology, gene expression, cellular composition of adipose tissue depots, and chromatin architecture longitudinally in young patients who do not have all signs of disease, and in healthy controls and parents with FPLD2.