ИСТИНА

Acute kidney injury (AKI) is a widespread disease that affects about 20% of hospitalized pa-tients and a third of patients in intensive care units. This condition is characterized by high mortality, which reaches 60% in some groups. The vast majority of patients with AKI are elderly people with mean age 64 years. So that the elderly age is of a greater interest for research. In most cases of AKI the main damaging factor is ischemia followed by reperfusion (I/R). One of the approaches to prevent ischemic injury of kidney parenchyma is ischemic preconditioning (IPC). IPC increases tolerance of tissues and organs to prolonged ischemia by preliminarily exposure of organ to one or more episodes of short-term ischemia and reperfusion. The aim of this research was to study the role of protein acetylation and autophagy in mecha-nisms of ischemic tolerance and to study the influence of aging on these processes. There were three objectives; one of them was to compare the effect of IPC on the severity of developing AKI in young, old and OXYS rats. In addition, in renal tissue from these groups of rats we needed to analyze the level of protein acetylation and intensity of autophagy. AKI was performed in male rats by clamping the left renal pedicle by atraumatic clamp for 40 minutes followed by restoration of blood flow. Some rats were additionally subjected to IPC, which consisted of 4 cycles, including 15 seconds of ischemia and 15 seconds of reperfusion, immediately before the clamping renal pedicle for 40 minutes. The severity of I/R was assessed by the serum level of creatinine (SCr) and blood urea nitrogen (BUN) 48 hours after. Some rats were perfused with 4%-buffered formaldehyde solution after 40 minutes of reper-fusion, left kidney was removed and slices of renal tissue were made. Slices of the fixed kidneys were examined by indirect immunofluorescent staining with antibodies against acetylated lysine. Intensity of autophagy was assessed by staining slices of renal cortex with a fluorescent dye LysoTracker Green. All these manipulations were carried out on young (4-6 months), old (20-23 months) rats and strain OXYS with signs of premature aging that were 4-6 months old too. 48 hours after I/R SCr and BUN levels were increased in both young (8 and 6.6 times, respec-tively), old (6 and 5.8 times), and OXYS rats (10 and 12 times), indicating the development of AKI. IPC reduced SCr and BUN concentrations in young rats by 38% and 60%. In old and OXYS rats IPC had no effect on the severity of kidney injury. On fixed slices of renal tissue was examined the level of protein acetylation; the staining mainly affected the nuclei of tubular cells. In young intact animals, a high level of acetylation was only observed in the nuclei of 10% of tubules, the percentage of such tubules increased to 27% after I/R. IPC significantly reduced the level of protein acetylation to 17%. In old intact animals, percent of tubules with high level of acetylation in the nuclei was higher (21%) and it slightly increased after I/R. In contrast to young rats, after IPC the percentage of acetylation-positive tubules was even higher than after I/R (33% greater compared to I/R). In intact OXYS rats, the level of tubules with acetylated nuclei reached 37% and it also increased after IPC (46%). Similar tendency was observed while calculating the percentage of proximal tubules with a high level of protein acetylation in the nuclei. 24 hours after I/R we stained vital kidney slices with fluorescent due LysoTracker Green and studied the amount of lysosomes and autophagolysomes. There was a significant increase in fluorescence intensity of LysoTracker Green after I/R in young rats. This effect was not observed in the group with preliminary IPC. In old and OXYS rats, no increase in fluorescence intensity of LysoTracker Green after I/R or I/R with IPC was detected. Thus, IPC has a protective effect on renal I/R in young rats reducing the severity of AKI, normalizing processes of acetylation and autophagy in the renal tissue. These beneficial effects were ab-sent in old and OXYS rats.