Role of the Nuclear Envelope in the Mechanoregulation Adipogenesis

Mechanical signals are known regulators of mesenchymal stem cell (MSC) fate, regulating their differentiation into osteoblasts, chondrocytes, and adipocytes. These relevant mechanical signals reach to nucleus through nuclear envelope proteins such as Lamin A/C and the Linker of the Nucleoskeleton and Cytoskeleton (LINC) complexes. Within the context of bone, clinically relevant mutations of Lamin A/C and the LINC complexes have been shown to alter adipogenic and osteogenic MSC differentiation patterns, suggesting that that nucleo-cytoskeletal connectivity provided by nuclear envelope is important in regulating MSC fate. Using MSC adipogenesis as a model of MSC mechanical regulation, the goal of this work is to further our understanding of how Lamin A/C and the LINC complex affect the mechanical regulation of MSC adipogenesis during application of mechanical forces. Investigation into the role of Lamin A/C in mechanoregulation revealed that activation of focal adhesions occurs independently from the loss of Lamin A/C. Additionally, Lamin A/C depletion and application daily mechanically challenge repress MSC adipogenesis independent of each other. Depletion of the LINC complex proteins Sun1/2 also significantly inhibited adipogenesis differentiation in MSCs. Depletion of Sun1/2 also increased heterochromatin maker H3K9me3 global levels, H3K9me3 foci count per nucleus, and increased enrichment in adipogenesis marker gene Adipoq. In contrast, expression of dominant-negative KASH domain, the cytoskeletal connector element of the LINC complex, resulted in accelerated MSC adipogenesis and no increased H3K9me3 foci count or enrichment on Adipoq gene. Further research will utilize the dominant-negative KASH expression to investigate the role of the LINC complex in the mechanical regulation of adipognesis and the spatio-temporal changes of adipogenic gene loci that occurs during adipogenesis and application of mechanical forces. Ultimately these studies will help to shed light into understanding the etiology of musculoskeletal problems in conditions that suffer from nuclear envelope instabilities including, aging, progeria, and microgravity