Bridging the Obesity Gap : a Role for Connexin and Pannexin Signalling in Adipogenesis

Abstract

Obesity is currently a worldwide health problem associated with conditions such as type 2 diabetes. It has been reported that connexins may be involved in adipogenesis but the underlying mechanism remains unresolved. Adipose tissue from male Zucker fatty rats (fa/fa), male lean rats (fa-/-) and 3T3-L1 cells were investigated for connexin (Cx) and pannexin expression profiles, Cx localization and function and lipid accumulation during the differentiation programme. Adipose tissue of lean Zucker rats and the 3T3-L1 cell model expressed similar connexins (Cx43, and Cx45) and pannexins (Panxl). Real time PCR analysis determined that Cx43, Cx45 and Panxl mRNA was decreased in adipose tissue from obese compared to lean Zucker rats. In 3T3-L1 cells Cx43 mRNA expression and channel function was upregulated after an initial 24 hours of differentiation followed by reduction at terminal differentiation (day 10) (n=3, P=<0.001). Cx43 localised in gap junction plaques at the plasma membrane of undifferentiated 3T3-L1 cells but was perinuclearly located in differentiated cells. Western blot analysis revealed this was associated with an increase in phospho-specific isoforms, but not serine 368 phospho-Cx43. These cells also exhibited an increase in cytoplasmic cholesterol (Chi), triglyceride (TAG) levels at terminal differentiation. Selection of 3T3-L1 cells to over express Cx43 resulted in a decrease in accumulation of FA (n=3, P=<0.05), TAG (n=3, P=<0.001), Chi (n=3, P=<0.001) and cholesterol esters (Chi E) (n=3 , P=< 0.01). Pharmacological enhancement of Cx43 expression by exposure to AAP10 also delayed lipid accumulation in differentiated cells. By contrast over expression of Panxl had limited effect on TAG (n= 3, P=< 0.01), Chi (n=3, P=<0.05) and Chi E (n=3, P=<0.05). We conclude that signalling facilitated via Cx43 plays a role in adipogenesis.

Date of Award	2014
Original language	English
Awarding Institution	Glasgow Caledonian University
Supervisor	Patricia Martin (Supervisor), Annette Graham (Supervisor) & Sharron Dolan (Supervisor)