Mechanisms of PPARγ/p38MAPK signaling pathway in regulating macrophage pyroptosis with Mycobacterium tuberculosis infection

OBJECTIVE To investigate whether the peroxisome proliferator-activated receptor γ (PPARγ)/p38 mitogen-activated protein kinase (p38MAPK) pathway regulates pyroptosis in Mycobacterium tuberculosis (MTB)-infected macrophages and their antibacterial ability.

METHODS Raw264.7 macrophages were cultured and divided into the control group, MTB group, PPARγ-inhibited group and PPARγ-overexpressed group. Immunofluorescence staining was used to detect the protein levels of PPARγ, phosphorylated p38MAPK (p-p38MAPK), GSDME and NOD-like receptor pyrin domain-containing protein 3 (NLRP3) in macrophages. Western blotting (WB) was employed to measure the protein levels of GSDME and NLRP3 in macrophages. Reverse transcription quantitative polymerase chain reaction was used to detect the mRNA levels of PPARγ, p-p38MAPK, GSDME and NLRP3 in macrophages. The bacterial load in macrophages was also assessed.

RESULTS Compared with the control group, the MTB group showed increased protein and mRNA levels of PPARγ (6.67±0.59 vs. 0.99±0.02, 4.98±0.31 vs. 1.00±0.02) and p-p38MAPK (5.61±0.44 vs. 0.99±0.01, 4.82±0.43 vs. 0.98±0.02) (P < 0.05). Additionally, there was an increase in the protein and mRNA levels of pyroptosis-related proteins GSDME (4.38±0.27 vs. 0.98±0.02, 3.59±0.29 vs. 0.99±0.02) and NLRP3 (5.61±0.16 vs. 1.01±0.02, 4.65±0.33 vs. 1.00±0.02) (P < 0.05), as well as an increase in the number of bacterial colonies in macrophages (P < 0.05). Compared with the MTB group, the PPARγ-inhibited group exhibited decreased protein and mRNA levels of PPARγ, p-p38MAPK, GSDME and NLRP3 in macrophages (P < 0.05), along with a reduction in the number of macrophage bacterial colonies (P < 0.05). In contrast, compared with the MTB group, the PPARγ-overexpressed group showed increased protein and mRNA levels of GSDME and NLRP3 in macrophages (P < 0.05), but a decrease in the number of macrophage bacterial colonies (P < 0.05).

CONCLUSION The PPARγ/p38MAPK pathway can activate pyroptosis in MTB-infected macrophages and enhance their antibacterial ability.