Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Physiology and Pharmacology

Supervisor

Laird, Dale W.

Abstract

Obesity is the unhealthy accumulation of adipose tissue and affects 10% of the global population. A study reported the loss of mouse pannexin 1 (Panx1), a large channel forming protein, increased adipogenesis in murine adipose derived stem cells (ASCs). Our study was designed to determine if human pannexin 1 (PANX1) inhibits adipogenesis in vitro using human ASCs and induced-mesenchymal stem cells (iMSCs) derived from induced pluripotent stem cells (iPSCs). Pharmacological inhibition of PANX1 using carbenoxolone halted adipogenesis in both the ASCs and iMSCs. When PANX1 was inhibited by probenecid, adipogenesis was impeded in iMSCs, but not in ASCs. PANX1-ablated iPSCs were able to differentiate into iMSCs and further differentiate along the adipogenic lineage. Our findings indicate that PANX1 expression is not essential for iPSC differentiation to iMSCs, nor adipogenesis, and the contrasting responses of iMSCs and ASCs to probenecid suggests that mesenchymal stem cells from different origins have distinct characteristics.

Summary for Lay Audience

Approximately 10% of the global population is obese according to the World Health Organization. Obesity is the unhealthy increase of fat tissue, or adipose tissue, and is linked to comorbidities such as cardiovascular disease and type 2 diabetes. Dietary lipids are stored in adipose tissue within cells called adipocytes. During periods of overeating, adipocytes accommodate the additional lipids by increasing in either size or number. Larger adipocyte size leads to mechanical stress and contributes to obesity-related consequences. It has been speculated that by promoting adipocyte production, or adipogenesis, the extra lipids could be distributed among more cells, limiting the need to increase cell size and thus possibly avoiding obesity related disorders.

Adipocytes originate from mesenchymal stem cells (MSCs), a cell type capable of becoming cartilage, bone, or fat cells. MSCs can be collected from various sources, including adipose tissue and induced pluripotent stem cells (iPSCs). During adipogenesis, specific genes are expressed to initiate the MSCs’ transformation into functional adipocytes that can store lipids. The loss of pannexin 1 (Panx1) was reported to increase adipogenesis in mouse adipose derived mesenchymal stem cells (ASCs). Pannexin 1 are channel forming proteins that allow molecules to pass through the cell’s membrane. Although human ASCs express PANX1, it is unclear whether PANX1 influences human adipogenesis.

In our study, human ASCs and iPSC-derived MSCs (iMSCs) were cultured in adipogenic conditions to promote adipogenesis, as indicated by lipid droplet formation. To study PANX1 channel function, cells undergoing adipogenesis were untreated, or treated with either carbenoxolone (CBX) or probenecid (Prob), which are both drugs that block PANX1 channels. CBX inhibited adipogenesis in both the ASCs and iMSCs; however, Prob impeded adipogenesis in only the iMSCs, and not the ASCs. Furthermore, PANX1 was genetically removed from iPSCs, and these cells were able to transition into iMSCs and further undergo adipogenesis in vitro. Overall, we conclude that PANX1 is not required for human adipogenesis in vitro, and the contrasting responses from ASCs and iMSCs to Prob implies that MSCs from different sources have distinct characteristics. These findings suggest that PANX1 may not be an ideal target to regulate human adipogenesis in vitro.

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