Prohibitin 1 regulates mtDNA release and downstream inflammatory responses

Exposure of mitochondrial DNA (mtDNA) to the cytosol activates innate immune responses. But the mechanisms by which mtDNA crosses the inner mitochondrial membrane are unknown. Here, we found that the inner mitochondrial membrane protein prohibitin 1 (PHB1) plays a critical role in mtDNA release by regulating permeability across the mitochondrial inner membrane. Loss of PHB1 results in alterations in mitochondrial integrity and function. PHB1‐deficient macrophages, serum from myeloid‐specific PHB1 KO (Phb1MyeKO) mice, and peripheral blood mononuclear cells from neonatal sepsis patients show increased interleukin‐1β (IL‐1β) levels. PHB1 KO mice are also intolerant of lipopolysaccharide shock. Phb1‐depleted macrophages show increased cytoplasmic release of mtDNA and inflammatory responses. This process is suppressed by cyclosporine A and VBIT‐4, which inhibit the mitochondrial permeability transition pore (mPTP) and VDAC oligomerization. Inflammatory stresses downregulate PHB1 expression levels in macrophages. Under normal physiological conditions, the inner mitochondrial membrane proteins, AFG3L2 and SPG7, are tethered to PHB1 to inhibit mPTP opening. Downregulation of PHB1 results in enhanced interaction between AFG3L2 and SPG7, mPTP opening, mtDNA release, and downstream inflammatory responses. Synopsis The inner mitochondrial membrane protein Prohibitin 1 (PHB1) restrains mitochondrial DNA release and inflammation by binding to the mitochondrial membrane proteins AFG3L2 and SPG7. Inflammatory stresses enhance the interaction between AFG3L2 and SPG7, mPTP opening, mtDNA release and downstream inflammatory responses. Inflammatory stresses downregulate PHB1 levels in murine and human macrophages, which promotes inflammatory responses. PHB1 deficiency perturbs mitochondrial homeostasis, including increased mitochondrial permeability transition pore (mPTP) opening and mtDNA release. PHB1 regulates the formation of mPTP by modulating the interaction between the inner mitochondrial membrane proteins SPG7 and AFG3L2. Graphical Abstract Loss of the inner mitochondrial membrane protein PHB1 promotes innate immune responses by altering mitochondrial membrane integrity and mtDNA cytoplasmic release.