The effect of PACAP38 on MyD88-mediated signal transduction in ischemia-/hypoxia-induced acute kidney injury.
OBJECTIVE
toll-like receptor 4 (TLR4) and its adaptor protein MyD88 play an important role in ischemia/reperfusion (I/R) injury in the kidney, and pituitary adenylate cyclase-activating polypeptide (PACAP) could ameliorate renal I/R injury.


METHODS
primary cultures of proximal tubule epithelial cells (PTEC) were prepared from wild-type and MyD88(-/-) mice, and subjected to hypoxia in vitro. Acute kidney injury (AKI) was induced by I/R in vivo in wild-type mice only.


RESULTS
hypoxia resulted in significant increases in cytokine production and apoptosis/necrosis in wild-type PTEC, but these responses were markedly blunted in MyD88(-/-) PTEC. Treatment with PACAP38 before or after hypoxia further suppressed the hypoxia-induced cytokine responses and apoptosis in both MyD88(+/+) and MyD88(-/-) PTEC cultures. PACAP38 significantly inhibited TLR4/MyD88/TRAF6 as well as TRIF and IRF3 expression in mouse kidney and PTEC, and inhibited the secretion and mRNA expression of cytokines in kidneys from mice after I/R, paralleling the cytokine responses in vitro. Moreover, treatment with PACAP38 protected mice from renal failure, histological damage, neutrophil influx and tubule cell apoptosis after I/R.


CONCLUSIONS
our data reveal that the TLR4-mediated cytokine responses to hypoxia are primarily dependent on MyD88 signaling and highlight the pivotal role of MyD88-dependent mechanisms in the coordination of the innate immune responses to ischemic/hypoxic acute renal tubular injury. The renoprotective effect of PACAP in AKI involves both MyD88-dependent and -independent pathways.
Li
Min
M
Section of Nephrology and Hypertension, Department of Medicine, Tulane University School of Medicine, New Orleans, La., 70112 USA. minlee@tulane.edu
Khan
Altaf-M
AM
Maderdrut
Jerome L
JL
Simon
Eric E
EE
Batuman
Vecihi
V
D058186:Acute Kidney Injury / Q000473:pathology / Q000503:physiopathology*; D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D018932:Chemokine CCL2 / Q000378:metabolism; D054885:Cumulus Cells; D004847:Epithelial Cells / Q000473:pathology; D000860:Hypoxia; D007113:Immunity, Innate; D050838:Interferon Regulatory Factor-3 / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000473:pathology; D051379:Mice; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism / Q000502:physiology*; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide / Q000494:pharmacology* / Q000502:physiology; D015427:Reperfusion Injury / Q000473:pathology / Q000503:physiopathology*; D015398:Signal Transduction / Q000187:drug effects*; D048029:TNF Receptor-Associated Factor 6 / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000378:metabolism / Q000502:physiology*
D033942:Adaptor Proteins, Vesicular Transport; D018932:Chemokine CCL2; D050838:Interferon Regulatory Factor-3; D015850:Interleukin-6; D053594:Myeloid Differentiation Factor 88; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D048029:TNF Receptor-Associated Factor 6; D051197:Toll-Like Receptor 4; C491768:Ccl2 protein, mouse; C494233:Irf3 protein, mouse; C507780:Myd88 protein, mouse; C476286:Ticam1 protein, mouse; C493487:Tlr4 protein, mouse