Seipin oligomers can interact directly with AGPAT2 and lipin 1, physically scaffolding critical regulators of adipogenesis

This work was supported by a Merit Scholarship from the Islamic Development Bank (to M.M.U.T.), The Agency for Science, Technology and Research, Singapore (A*STAR) (M.F.M.S), the Medical Research Council (MRC) [NIRG GO800203 and Research Grant MR/L002620/1 (to J.J.R.), Program GrantG09000554 (to S.O.R)], The Wellcome Trust [078986/Z/06/Z (to S.O.R.)], the MRC Centre for Obesity and Related Metabolic Disorders (MRC-CORD) [GO600717] and the NIHR Comprehensive Biomedical Research Centre [CG50826].Peer reviewedPublisher PD

Analysis of naturally occurring mutations in the human lipodystrophy protein seipin reveals multiple potential pathogenic mechanisms

Peer reviewedPublisher PD

Oligomers of the lipodystrophy protein seipin may co-ordinate GPAT3 and AGPAT2 enzymes to facilitate adipocyte differentiation

Abstract: Seipin deficiency causes severe congenital generalized lipodystrophy (CGL) and metabolic disease. However, how seipin regulates adipocyte development and function remains incompletely understood. We previously showed that seipin acts as a scaffold protein for AGPAT2, whose disruption also causes CGL. More recently, seipin has been reported to promote adipogenesis by directly inhibiting GPAT3, leading to the suggestion that GPAT inhibitors could offer novel treatments for CGL. Here we investigated the interactions between seipin, GPAT3 and AGPAT2. We reveal that seipin and GPAT3 associate via direct interaction and that seipin can simultaneously bind GPAT3 and AGPAT2. Inhibiting the expression of seipin, AGPAT2 or GPAT3 led to impaired induction of early markers of adipocyte differentiation in cultured cells. However, consistent with normal adipose mass in GPAT3-null mice, GPAT3 inhibition did not prevent the formation of mature adipocytes. Nonetheless, loss of GPAT3 in seipin-deficient preadipocytes exacerbated the failure of adipogenesis in these cells. Thus, our data indicate that GPAT3 plays a modest positive role in adipogenesis and argue against the potential of GPAT inhibitors to rescue white adipose tissue mass in CGL2. Overall, our study reveals novel mechanistic insights regarding the molecular pathogenesis of severe lipodystrophy caused by mutations in either seipin or AGPAT2

Discovering metabolic disease gene interactions by correlated effects on cellular morphology

Objective: Impaired expansion of peripheral fat contributes to the pathogenesis of insulin resistance and Type 2 Diabetes (T2D). We aimed to identify novel disease-gene interactions for adipogenesis and insulin resistance. Methods: To this end, we mined disease associated loci for T2D, adiposity and insulin resistance for adipose expressed genes and ablated the top 100 in human pre-adipocytes via CRISPR/CAS9. The resulting cellular phenotypes were quantified during adipocyte differentiation with high-content imaging to obtain over 107 morphometric measurements. Morphologic profiles were constructed for each gene from these measurements and clustered by morphologic similarity. Results: Clustering revealed a group of 14 genes characterized by decreased lipid accumulation, and enriched with known lipodystrophy genes. For two lipodystrophy genes, BSCL2 and AGPAT2, sub-clusters with PLIN1 and CEBPA based on morphology were validated by independent experiments as novel protein-protein and gene regulatory interactions. Conclusions: Thus, a morphometric approach in adipocytes can resolve multiple cellular mechanisms for metabolic disease loci; the platform enables mechanistic interrogation of the hundreds of metabolic disease loci whose function still remains unknown