title: Toll-like Receptor 9 Can be Activated by Endogenous Mitochondrial DNA to Induce Podocyte Apoptosis.
abstract: Toll-like receptor 9 (TLR9) senses bacterial DNA characteristic of unmethylated CpG motifs to induce innate immune response. TLR9 is de novo expressed in podocytes of some patients with glomerular diseases, but its role in podocyte injury remains undetermined. Since TLR9 activates p38 MAPK and NFkB that are known to mediate podocyte apoptosis, we hypothesized that TLR9 induces podocyte apoptosis in glomerular diseases. We treated immortalized podocytes with puromycin aminonucleosides (PAN) and observed podocyte apoptosis, accompanied by TLR9 upregulation. Prevention of TLR9 upregulation by siRNA significantly attenuated NFκB p65 or p38 activity and apoptosis, demonstrating that TLR9 mediates podocyte apoptosis. We next showed that endogenous mitochondrial DNA (mtDNA), whose CpG motifs are also unmethylated, is the ligand for TLR9, because PAN induced mtDNA accumulation in endolysosomes where TLR9 is localized, overexpression of endolysosomal DNase 2 attenuated PAN-induced p38 or p65 activity and podocyte apoptosis, and DNase 2 silencing was sufficient to activate p38 or p65 and induce apoptosis. In PAN-treated rats, TLR9 was upregulated in the podocytes, accompanied by increase of apoptosis markers. Thus, de novo expressed TLR9 may utilize endogenous mtDNA as the ligand to facilitate podocyte apoptosis, a novel mechanism underlying podocyte injury in glomerular diseases.
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Wenduona
authors.initials: W
authors.lastname: Bao
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Xia
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Yaojun
authors.initials: Y
authors.lastname: Liang
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Yuting
authors.initials: Y
authors.lastname: Ye
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Yuqiu
authors.initials: Y
authors.lastname: Lu
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Xu
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Aiping
authors.initials: A
authors.lastname: Duan
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Jing
authors.initials: J
authors.lastname: He
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Zhaohong
authors.initials: Z
authors.lastname: Chen
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Wu
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Xia
authors.initials: X
authors.lastname: Wang
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Chunxia
authors.initials: C
authors.lastname: Zheng
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Zhihong
authors.initials: Z
authors.lastname: Liu
authors.affiliation: National Clinical Research Center of Kidney Diseases, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China.
authors.forename: Shaolin
authors.initials: S
authors.lastname: Shi
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D002461:Cell Line, Transformed; D018899:CpG Islands / Q000276:immunology; D004272:DNA, Mitochondrial / Q000276:immunology*; D005260:Female; D006801:Humans; D007674:Kidney Diseases / Q000276:immunology / Q000473:pathology; D020935:MAP Kinase Signaling System / Q000276:immunology*; D008297:Male; D050199:Podocytes / Q000276:immunology* / Q000473:pathology; D051381:Rats; D051217:Toll-Like Receptor 9 / Q000276:immunology*; D051996:Transcription Factor RelA / Q000276:immunology; D048051:p38 Mitogen-Activated Protein Kinases / Q000276:immunology
chemical_list: D004272:DNA, Mitochondrial; C498143:RELA protein, human; C498145:Rela protein, rat; C495371:TLR9 protein, human; C489640:Tlr9 protein, rat; D051217:Toll-Like Receptor 9; D051996:Transcription Factor RelA; D048051:p38 Mitogen-Activated Protein Kinases