BNIP3 is essential for mitochondrial bioenergetics during adipocyte remodelling in mice

Aims/hypothesis Adipose tissue is a highly versatile system in which mitochondria in adipocytes undergo significant changes during active tissue remodelling. BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3) is a mitochondrial protein and a known mitochondrial quality regulator. In this study, we investigated the role of BNIP3 in adipocytes, specifically under conditions of peroxisome proliferator-activated receptor-gamma (PPAR gamma)-induced adipose tissue remodelling. Methods The expression of BNIP3 was evaluated in 3T3-L1 adipocytes in vitro, C57BL/6 mice fed a high-fat diet and db/db mice in vivo. Mitochondrial bioenergetics was investigated in BNIP3-knockdown adipocytes after rosiglitazone treatment. A putative peroxisome proliferator hormone responsive element (PPRE) was characterised by promoter assay and electrophoretic mobility shift assay (EMSA). Results The protein BNIP3 was more abundant in brown adipose tissue than white adipose tissue. Furthermore, BNIP3 expression was upregulated by 3T3-L1 pre-adipocyte differentiation, starvation and rosiglitazone treatment. Conversely, BNIP3 expression in adipocytes decreased under various conditions associated with insulin resistance. This downregulation of BNIP3 was restored by rosiglitazone treatment. Knockdown of BNIP3 in adipocytes inhibited rosiglitazoneinduced mitochondrial biogenesis and function, partially mediated by the 5' AMP-activated protein kinase (AMPK)-peroxisome proliferator-activated receptor gamma, co-activator 1 alpha (PGC1 alpha) signalling pathway. Rosiglitazone treatment increased the transcription level of Bnip3 in the reporter assay and the presence of the PPRE site in the Bnip3 promoter was demonstrated by EMSA. Conclusions/interpretation The protein BNIP3 contributes to the improvement of mitochondrial bioenergetics that occurs on exposure to rosiglitazone. It may be a novel therapeutic target for restoring mitochondrial dysfunction under insulin-resistant conditions.