Endocrine Abstracts

Background: Dysfunctional adipose tissue in obesity is known to contribute to metabolic diseases, including type 2 diabetes mellitus (T2DM). This may be due to increased gut-derived endotoxemia (LPS) reducing brown adipose tissue (BAT) activity and altering mitochondrial function. However, the effect of LPS on BAT activity in 3D culture models has not been studied, despite giving a better representation of in-vivo tissue. Therefore, this study investigated the effects of LPS on 2D and 3D brown adipocyte biology and mitochondrial function.

Methods: Immortalized murine brown adipocyte 2D and 3D (spheroid) cultures were differentiated with/without LPS (100 ng/ml). β3-adrenergic stimulator CL316,243 (CL) (10 μM), was used to induce BAT activity via UCP1. Gene and protein expression were analysed using qRT-PCR and immunohistochemistry.

Results: LPS reduced expression of browning genes in 2D and 3D models: CIDEA (2D: FC=-14.11, P<0.0001; 3D: FC=-26.21, P<0.0001), ELOVL3 (2D: FC=-24.84, P<0.0001; 3D: FC=-59.82, P<0.001), PLIN5 (2D: FC=-24.18, P<0.01; 3D: FC=-20.32, P<0.0001). Moreover, LPS decreased UCP1 gene expression in basal conditions (2D: FC=-56.38, P<0.05; 3D: FC=-25, P<0.05) and following CL treatment (2D: FC=-2.82, P<0.01; 3D: FC= -7.41, P<0.0001). Immunohistochemistry identified reduced UCP1 expression in LPS-differentiated 3D spheroids (P<0.0001). Mitochondrial genes were also reduced with LPS including (a) dynamic genes: DRP1 and MFN2, with a maximum reduction of FC=-3.2 (P<0.001) in 2D and FC=-6.03 (P<0.0001) in 3D models, (b) biogenesis genes: PGC1α and POLG with a maximum reduction of FC=-3.31 (P<0.0001) in 2D and FC=-8.67 (P<0.0001) in 3D model, and other key functional genes CPT1β, CS, COX4I1.

Conclusion: This study identified LPS as an inhibitor of brown adipocytes phenotype and mitochondrial function, with more potency in 3D spheroids. This highlights that gut-derived endotoxemia may contribute to individual brown adipocyte dysfunction and reduced browning capacity of the adipocyte cell population. Therefore, targeting this inflammatory pathway may therefore reduce obesity-associated metabolic dysfunction.