BAFF neutralization impairs the clearance of dead adipocytes and promotes insulin resistance in obese mice
B cell-activating factor (BAFF) is critical for the survival and maturation of B2 cells. However, excess BAFF breaks the peripheral tolerance of B2-cells leading to the production of autoantibodies that cause autoimmune diseases. During obesity, BAFF is predominantly produced by white adipose tissue (WAT), and IgG autoantibodies against adipocytes are identified in the WAT of obese humans. However, it remains to be determined if the autoantibodies formed during obesity affect WAT remodeling and systemic insulin resistance. Here, we show that IgGs from high-fat diet (HFD)-induced obese mice bind to apoptotic adipocytes and promote their clearance by macrophages. Next, using murine models of obesity in which the gonadal WAT undergoes remodeling, unexpectedly we found that BAFF neutralization increased the number of dead adipocytes and exacerbated WAT inflammation and insulin resistance despite depletion of IgG autoantibodies. RNA sequencing of the stromal vascular fraction from the WAT revealed impaired B cell activation and phagocytosis pathways. In-vitro, the clearance of apoptotic adipocytes by macrophages was attenuated in the presence of IgGs from BAFF-neutralized mice compared to the control mice. Altogether, our study suggests a beneficial role of BAFF and IgG autoantibodies in WAT remodeling in obesity and the regulation of systemic insulin resistance. Overall design: Effect of BAFF neutralization in the stromal vascular fraction of gonadal white adipose tissue of high-fat diet-induced obese male C57BL6J mice undergoing diet intervention: Six-week-old male C57BL/6J mice were placed on a high-fat diet (60% calories from fat) for 12 weeks to induce insulin resistance and two experimental groups were determined based on a glucose tolerance test. Mice were then simultaneously switched from the high-fat diet to a normal chow diet (16% calories from fat) and given an injection of 2 mg/kg of anti-BAFF antibody (Sandy-2, AdipoGen) or an isotype control antibody (IgG1k, BioX Cell) every 2 weeks for a total of 6 weeks. At the end of the experiment, which was week 18, mice were euthanized, one of the gonadal fat pads was isolated, minced, and digested for 1 hour in Hanks Balanced Salt Solution (Gibco) with 2% bovine serum albumin (BSA) and 2 mg/ml of collagenase type I shaking at 37 °C. After digestion, tissue was filtered through a 500 µM nylon mesh strainer and washed with HBSS with 2% BSA. The cells were centrifuged (450xg for 5 min) to allow the stromal vascular cells (SVF) to separate with the adipocytes floating on the top of the buffer. The SVF pellet was collected, and red blood cells were lysed. SVF cells were washed, centrifuged, and resuspended in TRIZOL and sent to SingulOmics (Bronx, New York) for bulk RNA sequencing.