Type 2 diabetes mellitus induces TNFR1 mediated necroptotic cell death of mice alveolar macrophages infected with Mycobacterium tuberculosis

Abstract

Abstract Previously, we developed a mouse model of type 2 diabetes mellitus (T2DM) using streptozotocin and nicotinamide and found that T2DM mice are susceptible to Mycobacterium tuberculosis (Mtb) infection. We also found that alveolar macrophages from T2DM mice were more permissive to Mtb growth ex vivo compared to non-diabetic controls. In the current study, we determined the defective mechanisms that make T2DM mice alveolar macrophages more susceptible to Mtb infection. Mtb infected alveolar macrophages from T2DM mice produced more TNF-α (973.8 ± 13.3 pg/ml vs. 614.6 ± 27.2 pg/ml, p<0.003) and less apoptotic (4.7 ± 1.8% vs. 28.6 ± 2.3%, p<0.001) compared to Mtb infected non-diabetic control mice. Mtb infected alveolar macrophages from T2DM mice expressed higher levels of TNFR1 (12.8 ± 0.5 vs. 2.09 ± 0.01, p<0.001) and markers of necroptosis RIPK1 (11.5 ± 0.57 vs. 2.94 ± 0.20, p<0.002), RIPK3 (16.1 ± 0.58 vs. 2.89 ± 0.2, p<0.001) and MLKL (9.2 ± 0.56 vs. 1.58 ± 0.72, p<0.02) compared to Mtb infected alveolar macrophages from non-diabetic control mice as determined by real-time PCR. This finding was again proved by Western blot and confocal microscopy. Anti-TNFR1 antibody treatment of alveolar macrophages from T2DM mice before or after Mtb infection reduced RIPK1, RIPK3 and MLKL expression as determined by RT-PCR. Our findings demonstrate that T2DM induces necroptosis of alveolar macrophages upon Mtb infection. Enhanced TNFR1 signaling in T2DM mice alveolar macrophages is responsible for enhanced necroptosis. We are also determining the subpopulations of T2DM mice alveolar macrophages that express higher levels of TNFR1 upon Mtb infection. Studies are underway to determine the in vivo relevance of our current findings to Mtb growth in T2DM mice.