Mitophagy-Mediated mtDNA Release Aggravates Stretching-Induced Inflammation and Lung Epithelial Cell Injury via the TLR9/MyD88/NF-κB Pathway

Abstract

Background: In animal models of ventilation-induced lung injury, mitophagy triggers mitochondria damage and the release of mitochondrial (mt) DNA, which activates inflammation. However, the mechanism of this process is unclear. Methods: A model of cyclic stretching (CS)-induced lung epithelial cell injury was established. The genetic intervention of phosphatase and tensin homolog-induced kinase 1 (PINK1) expression via lentivirus transfection was used to identify the relationship between PINK1-mediated mitophagy and mtDNA release in stretchinginduced inflammatory response and injury. Pharmacological inhabitation of Toll-like receptor 9 (TLR9) and myeloid differentiation factor 88 (MyD88) expression was performed via their related inhibitors, while pre-treatment of exogenous mtDNA was used to verify the role of mtDNA in stretching-induced inflammatory response and injury. Results: Using a cell culture model of CS, we found that knocking down PINK1 in lung epithelial cells reduced mitophagy activation and mtDNA release, leading to milder inflammatory response and injury; conversely, up-regulating PINK1 exacerbated stretching-induced inflammation and injury, and similar effects were observed by upregulating TLR9 to induce expression of MyD88 and nuclear factor-κB (NF-κB)/p65. Down-regulating MyD88 protected lung epithelial cells from stretching injury and decreased NF-κB/p65 expression. Conclusion: These findings suggest that PINK1-dependent mitophagy and associated TLR9 activation is indeed a major factor in stretch-induced cell injury via a mechanism

Systemic inflammatory response syndrome is triggered by mitochondrial damage (Review)

“…mtDNA, as a DAMP, is recognized by TLR9 to activate the TLR9/MyD88/NF-κB signaling pathway, exacerbating inflammation and lung injury ( 46 ). Jing et al ( 47 ) studied ventilator-induced lung injury also using a CS cell culture model and suggested that PTEN-induced putative kinase 1 (PINK1)-dependent mitophagy and associated TLR9 activation is a key factor in stretch-induced cell injury. Knockdown of PINK1, which is involved in regulating mitophagy, has also been shown to promote mitochondrial dysfunction, defective mitophagy and more severe lung injury ( 48 ).…”

“…These findings suggested that PINK1-dependent autophagy and TLR9 activation are key factors in stretching-induced cell damage. Release of mtDNA could activate TLR9, which induces the MyD88/NF-κB pathway, leading to lung injury ( 47 ). Inhibiting the release of mtDNA and activation of TLR9 may be a therapeutic approach for preventing lung inflammation and injury.…”

The Trinity of cGAS, TLR9, and ALRs Guardians of the Cellular Galaxy Against Host-Derived Self-DNA

“…Hence, the TLR9 (expressed on mobilized immunogenic DCs)-mediated recognition of self-DNA released from dying AMs plays a crucial role in CBD-induced by soluble or crystalline form. The phosphatase and tensin homolog-induced kinase 1 (PINK-1)-mediated mitophagy induces TLR9 activation in stretch-induced cell injury in response to the mtDNA that further exaggerates the inflammation in patients with mechanical ventilation ( 205 ).…”

Mitochondrial DNA‐Mediated Inflammation in Acute Kidney Injury and Chronic Kidney Disease

“…The interaction between mtDNA and TLR9 has been shown to be involved in the development of a variety of disorders, such as acute myocardial infarction [ 25 ], hepatocellular carcinoma [ 26 , 27 ], nonalcoholic steatohepatitis [ 28 , 29 ], and sterile lung injury [ 30 , 31 ]. Typically, mislocated mtDNA activates TLR9 signaling and downstream myeloid differentiation factor 88 (MyD88), resulting in upregulated expression of nuclear factor- (NF-) κ B and other proinflammatory factors such as tumor necrosis factor- α and interleukin 6, to amplify inflammation and exaggerate cell damage [ 31 ]. Besides, circulating mtDNA was reported to stimulate TLR9 in polymorphonuclear neutrophils, then facilitate p38-MAPK pathway and contribute to neutrophil secretion [ 4 ].…”