Evidence suggests that autophagy promotes the development of cellular senescence. Because cellular senescence contributes to renal aging and promotes the progression from AKI to CKD, we investigated the potential effect of tubular autophagy on senescence induction. Compared with kidneys from control mice, kidneys from mice with conditional deletion of autophagy-related 5 (Atg5) for selective ablation of autophagy in proximal tubular S3 segments (Atg5 Dflox/Dflox ) presented with significantly less tubular senescence, reduced interstitial fibrosis, and superior renal function 30 days after ischemia/reperfusion injury. To correlate this long-term outcome with differences in the early injury process, kidneys were analyzed 2 hours and 3 days after reperfusion. Notably, compared with kidneys of control mice, Atg5 Dflox/Dflox kidneys showed more cell death in outer medullary S3 segments at 2 hours but less tubular damage and inflammation at day 3. These data suggest that the lack of autophagy prevents early survival mechanisms in severely damaged tubular cells. However, if such compromised cells persist, then they may lead to maladaptive repair and proinflammatory changes, thereby facilitating the development of a senescent phenotype and CKD.

Renal ischemia-reperfusion (I/R) injury is a major cause of acute kidney injury (AKI). Non-coding RNAs are crucially involved in its pathophysiology. We identified hypoxia-induced long non-coding RNA Malat1 (Metastasis Associated Lung Adenocarcinoma Transcript 1) to be upregulated in renal I/R injury. We here elucidated the functional role of Malat1 in vitro and its potential contribution to kidney injury in vivo. Malat1 was upregulated in kidney biopsies and plasma of patients with AKI, in murine hypoxic kidney tissue as well as in cultured and ex vivo sorted hypoxic endothelial cells and tubular epithelial cells. Malat1 was transcriptionally activated by hypoxia-inducible factor 1-α. In vitro, Malat1 inhibition reduced proliferation and the number of endothelial cells in the S-phase of the cell cycle. In vivo, Malat1 knockout and wildtype mice showed similar degrees of outer medullary tubular epithelial injury, proliferation, capillary rarefaction, inflammation and fibrosis, survival and kidney function. Small-RNA sequencing and whole genome expression analysis revealed only minor changes between ischemic Malat1 knockout and wildtype mice. Contrary to previous studies, which suggested a prominent role of Malat1 in the induction of disease, we did not confirm an in vivo role of Malat1 concerning renal I/R-injury.

Rationale Atherosclerosis is a major cause of death in patients with chronic kidney disease. Chronic inflammation of the arterial wall including invasion, proliferation and differentiation of leukocytes is important in atherosclerotic lesion development. How atherosclerotic inflammation is altered in renal impairment is incompletely understood. Objective This study analyzed leukocytes of the atherosclerotic aorta in mice with impaired and normal renal function and studied a mechanism for the alteration in aortic myeloid leukocytes. Methods and Results Unilateral nephrectomy significantly decreased glomerular filtration rate and increased atherosclerotic lesion size and aortic leukocyte numbers in two murine atherosclerosis models, Apolipoprotein E (Apoe−/−) and LDL receptor (LDLr−/−) deficient mice. The number of aortic myeloid cells increased significantly. They took up less oxidized LDL, while CD11c expression, interaction with T cells and aortic T cell proliferation were significantly enhanced in renal impairment. In human PBMC cultures, chronic kidney disease serum decreased lipid uptake and increased HLAII expression. Supplementation with Interleukin (IL)-17A similarly increased HLAII and CD11c expression and impaired oxLDL uptake. IL-17A expression was increased in atherosclerotic mice with renal impairment. Ablation of IL-17A in LDLr−/− mice by lethal irradiation and reconstitution with Il17a−/− bone marrow abolished the effect of renal impairment on aortic CD11b+ myeloid cell accumulation, CD11c expression and cell proliferation. Atherosclerotic lesion size was decreased to levels observed in normal kidney function. Conclusions Kidney function modifies arterial myeloid cell accumulation and phenotype in atherosclerosis. Our results suggest a central role for IL-17A in aggravation of vascular inflammation and atherosclerosis in renal impairment.

Acute kidney injury is a major clinical problem and advanced age is associated with ineffective renal regeneration and poor functional outcome. Data from kidney injury models suggest that a loss of tubular epithelial proliferation contributes to a decrease in renal repair capacity with aging, but aging can also lead to a higher severity of inflammation and damage which may influence repair. In this study we tested intrinsic age-dependent changes in tubular epithelial proliferation in young and old mice, by injecting low-dose lead acetate as a non-injurious mitogen. In parallel, we explored in vitro techniques of studying cellular senescence in primary tubular epithelial cells (PTEC). Lead acetate induced tubular epithelial proliferation at a significantly higher rate in young as compared to old mice. Old kidneys showed significantly more senescence as demonstrated by increased p16INK4a, senescence associated β-galactosidase, and γH2AX+/Ki-67− cells. This was paralleled in old kidneys by a higher number of Cyclin D1 positive tubular cells. This finding was corroborated by a positive correlation between Cyclin D1 positivity and age in human renal biopsies. When tubular cells were isolated from mouse kidneys they rapidly lost their age-associated differences under culture conditions. However, senescence was readily induced in PTEC by γ-irradiation representing a future model for study of cellular senescence in the renal epithelium. Together, our data indicate that the tubular epithelium of aged kidney has an intrinsically reduced proliferative capacity probably due to a higher load of senescent cells. Moreover, stress induced models of cellular senescence are preferable for study of the renal epithelium in vitro. Finally, the positive correlation of Cyclin D1 with age and cellular senescence in PTEC needs further evaluation as to a functional role of renal epithelial aging.