Adipose tissue-specific fibrillin-1 knockdown leads to reduced body weight and causes metabolic dysregulation
Iram Fatima S. Siddiqui1, Muthu L. Muthu1, Ling Li1, Dieter P. Reinhardt1,2
1Faculty of Medicine and Health Sciences and 2Faculty of Dental Medicine and Oral Health Science, 平特五不中, Montreal, Canada
Introduction: Adipose tissue extracellular matrix (ECM) is necessary for structural support and for adipocyte differentiation. Fibrillin-1 is a 350 kDa ECM protein that not only provides a scaffold for elastic
fiber formation but intersects with basement membranes in tissues with low elasticity. It is also present in bones and teeth. Mutations in fibrillin-1 lead to Marfan syndrome and these patients are either lipodystrophic or overweight. Here, we aim to gain insights into the role of fibrillin-1 in fat tissue development and maintenance.
Methods and results: We have developed a novel adipose tissue-specific fibrillin-1 knockout mouse model with fibrillin-1 knockout only in maturing adipocytes (Fbn1-AKO) using Cre-lox recombinase. We used primary mesenchymal stem cells from bone marrow (BM-MSCs) and adipose tissue (ASCs) harvested from wild-type mice to explore the molecular pathway underlying the role of fibrillin-1 in
adipogenesis. Fbn1-AKO mice did not have overt abnormalities at earlier time points however, a reduction of 25% in overall body weight was observed in these mice compared to controls at 30 weeks of age. DEXA analysis showed a significant reduction in fat mass and fat percentage in the Fbn1-AKO mice. These results were supported by a significant downregulation of gene expression levels of
adipogenic markers such as Adiponectin, Cebpa, and Pparg as well as metabolic markers such as Glut4 and Fabp4 in Fbn1-AKO mice. The fat pads harvested from Fbn1-AKO mice showed no difference in the gene expression levels of inflammatory markers such as Mcp1, Tnfa and Il1b. Immunofluorescence staining for CD68 marker shows absence of macrophage for Fbn1-AKO mice. H&E staining revealed that the Fbn1-AKO mice had an increased frequency of small-sized adipocytes (hypotrophy). These mice displayed severe insulin resistance however, the glucose metabolism was not affected. The exogenous addition of a fibrillin-1 sub-fragment containing an integrin-binding RGD motif significantly reduced the level of adipogenesis in both BM-MSCs and ASCs. Contrary, a subfragment with an inactive RGA motif did not affect adipogenesis.
Conclusion: The data highlights the essential role of fibrillin-1 in the maintaining the metabolic homeostasis of maturing adipocytes and integrins seems to relay this fibrillin-1 mediated adipogenesis.