| Acute kidney injury(AKI)is one of the main kidney diseases which is associated with a high risk of mortality,and has a significant risk of progression to chronic kidney disease and even end-stage renal disease.In recent years,researchers have found that nerves system is involved in the development of renal ischemia reperfusion(IR)injury,and neuro-endocrine modulation has become an important area for the treatment of kidney damage.Studies showed that capsaicin sensitive sensory nerves and their major neuropeptides,calcitonin gene related peptide(CGRP)and substance P(SP),played important roles in myocardial injury and liver injury,but their roles and related mechanisms in AKI have not been fully elucidated.Objective: The role of sensory nerves involved in regulating AKI is controversial.This study was conducted to explore the effect of capsaicin sensitive sensory nerves and their neuropeptides CGRP and SP on AKI induced by IR injury and related mechanisms in rats,and to find a new therapeutic target for improving ischemic renal injury from the neurological level.Methods: 1.Male Sprague-Dawley neonatal rats(within 48 hours)were randomly divided into normal control group and denervation of capsaicin sensitive sensory nerves group(denervation group).The neonatal rats were injected subcutaneously with 50 mg/Kg of capsaicin to establish the model of denervation of capsaicin sensitive sensory nerves.The same volume of vehicle was administrated to the neonatal rats in the normal control group.All animals were reared in an SPF environment and the tail flick test of all the rats was conducted to evaluate the ability to resist noxious stimulation after 12 weeks.2.Rats in the normal control group and denervation group were randomly divided into sham operation group and renal IR group.So there were a total of 4 groups: 1)Sham group,in which the rats were injected the vehicle subcutaneously within 48 h of birth and underwent the sham operation after 12 weeks of growing up;2)IR group,the vehicle was injected and renal IR surgery were carried out in this group;3)Capsaicin group,the rats were injected with capsaicin and suffered sham operation;4)Capsaicin + IR group,the rats were injected with capsaicin and suffered IR insult.The levels of CGRP and SP in spinal cord(T8-T12),dorsal root ganglion(T8-T12)and kidney tissues were measured.3.The renal function,renal pathological morphology,acute kidney injury index NGAL,KIM-1,inflammatory factors TNF-α,IL-6,apoptosis related indicators Bcl-2,BAX,and protein phosphorylation levels in the ERK signaling pathway were measured.Results: 1.The capsaicin treatment extended the tail flick latency to 4.85 s ± 1.02 s compared with 3.08 s ± 0.41 s of the normal control rats.2.The capsaicin treatment reduced the CGRP and SP levels in spinal cord(T8-T12).In dorsal root ganglion,compared with the sham group,the mRNA level of CGRP-a,CGRP-βand SP reduced by 37.97%,38.00% and 74.95% in capsaicin group respectively.Pathological results showed that the number of CGRP and SP positive neurons are also significantly reduced in dorsal root ganglion after capsaicin treatment.In addition,reduction of CGRP and SP in mRNA level was also observed in capsaicin + IR group in the dorsal root ganglion(CGRP-α reduced by 35.87%,CGRP-β reduced by 36.36%,SP reduced by 78.55%),as compared with IR rats.3.The capsaicin treatment markedly decreased CGRP and SP levels in kidney(the protein level of CGRP reduced by 49.27%,the mRNA level of SP reduced by 72.55%),as compared with the sham controls.Meanwhile,marked reduction of CGRP and SP levels was also observed in capsaicin + IR group in the kidney(the protein level of CGRP reduced by 37.98%,the mRNA level of SP reduced by 38.38%),as compared with IR rats.The expression of CGRP and SP significantly increased in kidney after IR injury.4.Compared with IR group,an obvious increase in the serum creatinine(539.15 ±49.93umol/L vs 465.00 ± 39.40umol/L,P<0.0001),and a higher severity for cast formation,tubular dilation and tubular cell necrosis and shedding were observed in the denervated rats of IR-induced AKI.The significant increase of NGAL,KIM-1,TNF-a and IL-6 was also detected in the capsaicin + IR group(NGAL increased by 35.27%;KIM-1 increased by70.32%,TNF-a increased to 1.47 times;IL-6 increased to 2.65 times),as compared with the non-denervated rats of IR injury.The sensory afferent degeneration increased the level of BAX(2.29 ± 0.729 vs 2.03 ± 0.66,P<0.001)and reduced the level of Bcl-2(0.42 ± 0.21 vs1.21 ± 0.32,P<0.0001)in renal IR animals.5.The significant increase of the protein level of P-ERK/ERK was found after degeneration of capsaicin sensitive sensory nerves in spinal cord and kidney,as compared with the sham group(spinal cord: 1.22 ± 0.78 vs 0.54 ± 0.27,kidney: 0.55 ± 0.29 vs 0.27 ± 0.12,P<0.05).Conclusion: We successfully established an animal model of denervation of capsaicin sensitive sensory nerves.The degeneration of capsaicin sensitive sensory nerves aggravated IR-induced AKI in rats,and the activated ERK signaling in spinal cord and kidney after sensory afferent degeneration might be the possible mechanism in the aggravated renal injury. |
PDF Full Text Request