Downregulation of β1,4-galactosyltransferase 5 improves insulin resistance by promoting adipocyte commitment and reducing inflammation.

Protein glycosylation is an important post-translational modification. Aberrant glycosylation has been implicated in many diseases because of associated changes in protein distribution and biological function. We showed that the expression of β1, 4-galactosyltransferase 5 (B4GalT5) was positively correlated with diabetes and obesity. In vivo, B4GalT5 knockdown in subcutaneous adipose tissue alleviated insulin resistance and adipose tissue inflammation, and increased adipogenesis in high-fat diet (HFD)-fed mice and ob/ob mice. Downregulation of B4GalT5 in preadipocyte cells induced commitment to the adipocyte lineage in the absence of bone morphogenetic protein (BMP) 2/4 treatment, which is typically essential for adipogenic commitment. RNAi silencing experiments showed B4GalT5 knockdown activated Smad and p38 MPAK signaling pathways through both type 1A and 2 BMP receptors. Remarkably, B4GalT5 knockdown decreased BMPRIA glycosylation but increased BMPRIA stability and cellular location, thus leading to redistribution of BMPRIA and activation of the BMP signaling pathway. Meanwhile, downregulation of B4GalT5 decreased the infiltration of macrophages and the markers of M1 macrophages in subcutaneous adipose tissue of HFD mice and ob/ob mice. In bone marrow-derived macrophages (BMDMs) and RAW264.7cells, B4GalT5 knockdown also repressed the markers of M1 by reducing NFκB and JNK signaling. These results demonstrated B4GalT5 downregulation improved insulin resistance by promoting adipogenic commitment and decreasing M1 macrophage infiltration.