Involvement of renal tubular Toll-like receptor 9 in the development of tubulointerstitial injury in systemic lupus.
OBJECTIVE
Toll-like receptor 9 (TLR-9), a receptor for CpG DNA, has been implicated in the activation of immune cells in lupus. We undertook this study to determine whether the expression of TLR-9 in resident renal cells in lupus nephritis is related to the development of tubulointerstitial injury.


METHODS
TLR-9 was analyzed in selectively retrieved renal tissue from (NZB x NZW)F1 mice at different stages of disease by laser capture microdissection combined with real-time quantitative reverse transcriptase-polymerase chain reaction, and in renal biopsy specimens from lupus nephritis patients by immunohistochemistry. We investigated for the molecular component responsible for TLR-9 activation by cultured proximal tubular cells in serum from patients with lupus.


RESULTS
Renal tissue from NZB x NZW mice displayed robust TLR-9 expression localized to proximal tubular cells. TLR-9 levels correlated with proteinuria and tubulointerstitial injury to the extent that a cyclin-dependent kinase inhibitor, while reducing proteinuria and renal structural damage, prevented tubular TLR-9 generation in lupus mice. Consistently, exaggerated TLR-9 staining was found in proximal tubular cells of lupus patients, which correlated with tubulointerstitial damage. DNA-containing immune complexes purified from sera of patients with lupus induced TLR-9 in cultured proximal tubular cells. This was prevented by CCGG-rich short oligonucleotides, specific antagonists of CpG DNA, indicating that the DNA component of immune complexes was required for TLR-9 stimulation.


CONCLUSIONS
These findings suggest that tubular TLR-9 activation has a pathogenetic role in tubulointerstitial inflammation and damage in experimental and human lupus nephritis, and they indicate a novel target for future therapies.
Benigni
Ariela
A
Mario Negri Institute for Pharmacological Research, Bergamo, Italy. abenigni@marionegri.it
Caroli
Cristina
C
Longaretti
Lorena
L
Gagliardini
Elena
E
Zoja
Carla
C
Galbusera
Miriam
M
Moioli
Daniela
D
Romagnani
Paola
P
Tincani
Angela
A
Andreoli
Laura
L
Remuzzi
Giuseppe
G
D000818:Animals; D001706:Biopsy; D002478:Cells, Cultured; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000378:metabolism* / Q000473:pathology; D008180:Lupus Erythematosus, Systemic / Q000150:complications* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008814:Mice, Inbred NZB; D008815:Mice, Inbred Strains; D009395:Nephritis, Interstitial / Q000209:etiology* / Q000235:genetics / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011687:Purines / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D000077546:Roscovitine; D051217:Toll-Like Receptor 9 / Q000235:genetics / Q000378:metabolism*
D047428:Protein Kinase Inhibitors; D011687:Purines; D012333:RNA, Messenger; C495371:TLR9 protein, human; C495370:Tlr9 protein, mouse; D051217:Toll-Like Receptor 9; D000077546:Roscovitine