(DCP072) IDENTIFICATION OF PLAKOGLOBIN AS A NOVEL POSITIVE REGULATOR OF ADIPOGENESIS

Background: 14-3-3ζ overexpression in mice results in exacerbated high-fat diet-induced obesity, but since the 14-3-3ζ interactome is large and diverse, elucidating a precise mechanism of action has remained challenging. The use of mass spectrometry has allowed us to compare 14-3-3ζ-interacting proteins within visceral adipose tissue of lean and obese mice, as a means of uncovering novel regulators of adipogenesis. Plakoglobin, also known as γ-catenin, was found to be enriched, and while extensive studies have been performed on its role in cell-cell adhesion, its role in adipogenesis has yet to be uncovered. Plakoglobin’s homolog, β-catenin, is known to hold anti-adipogenic functions due to its role in the Wnt pathway. As plakoglobin has been shown to inhibit β-catenin’s transcriptional activity in a context-dependent manner, we hypothesize that plakoglobin can promote adipogenesis.

METHODS AND RESULTS: Murine 3T3-L1 pre-adipocytes and human adipose-derived stem cells (hADSC), were used for the in vitro contributions of plakoglobin to adipogenesis. 14-3-3ζ , β-catenin, or plakoglobin were depleted via siRNA prior to differentiation. RT-qPCR, immunoblotting, SuperTOPFlash assays, and Oil-Red-O (ORO) staining were used to assess differences in gene expression, protein abundance, Wnt/β-catenin transcriptional activity, and lipid content, respectively. In vivo experiments were performed on adipocyte-specific plakoglobin knockout mice (Adipo-Cre+;Jupflox/flox) to analyze plakoglobin’s influence on overall weight gain. Intra-peritoneal insulin and glucose tolerance tests were used to assess metabolic changes.

Depletion of plakoglobin in 3T3-L1 pre-adipocytes reduced the abundance of PPARγ2, the master transcriptional regulator of adipogenesis, indicating an impairment of adipogenesis progression. Similarly, plakoglobin-depleted in hADSC also diminished PPARγ2 expression post-differentiation. ORO staining revealed reduced lipid content in plakoglobin-depleted 3T3-L1 and hADSC. Wnt transcriptional activity was enhanced following 14-3-3ζ knockdown, but remained unaffected by plakoglobin depletion. Deletion of plakoglobin in mature adipocytes resulted in greater weight gain in female Adipo-Cre+;Jupflox/flox mice on a chow diet. In contrast, Adipo-Cre+;Jupflox/flox male mice weighed less than their littermate Adipo-Cre-;Jupflox/flox controls. No deleterious effects on metabolism were observed following plakoglobin deletion.

Conclusion: Our study reveals novel and complex roles for plakoglobin in adipogenesis and whole-body metabolism. Given the differences in the roles of plakoglobin in vitro and in vivo with respect to adipogenesis and adiposity, additional in-depth studies are required to fully understand its functions. Lastly, adipocyte-specific deletion of plakoglobin produced sexual dimorphic effects on weight gain on chow diet.