Aging is associated with progressive functional deterioration and structural changes in the kidney. Changes in the activity or responsiveness of the renin-angiotensin system (RAS) occur with aging. RAS changes predispose the elderly to various fluid and electrolyte imbalances as well as acute kidney injury and chronic kidney disease. Among the multiple pathways involved in renal aging, the RAS plays a central role. This review summarizes the association of the RAS with structural and functional changes in the aging kidney and age-related renal injury, and describes the underlying mechanisms of RAS-related renal aging. An improved understanding of the renal aging process may lead to better individualized care of the elderly and improved renal survival in age-related diseases.
Acute Kidney Injury/etiology/metabolism/physiopathology ; Age Factors ; Aging/genetics/*metabolism ; Animals ; Glucuronidase/genetics/metabolism ; Humans ; Kidney/*metabolism/physiopathology ; Kidney Diseases/*etiology/genetics/metabolism/physiopathology ; Prognosis ; *Renin-Angiotensin System ; Risk Factors

BACKGROUND/AIMS: The potential physiologic roles of Klotho in acute kidney injury (AKI) have recently been demonstrated in animal models. However, to date, there have been no human studies investigating the expression of renal Klotho in AKI. METHODS: We retrospectively collected biopsy specimens and clinical data of AKI patients between January 2001 and December 2012. Klotho expression was determined by immunohistochemical staining, and the clinical-pathological correlation was examined. RESULTS: Among the 34 patients diagnosed with acute tubular necrosis or acute tubulointerstitial nephritis, 21 patients without chronic histological lesions were included. The mean age was 37.3 +/- 18.5 years and the mean peak creatinine level was 8.2 +/- 5.5 mg/dL. In total, 10 patients (47.6%) received temporary renal replacement therapy (RRT); however, 17 patients (81%) showed functional recovery with creatinine levels of < 1.3 mg/dL after 1 month. The intensity of Klotho expression was scored as a percentage of Klotho-positive area. The renal Klotho score showed a significant negative correlation with the initial or peak creatinine level. When the patients were divided into three groups according to the Klotho score (low, middle, high), the low group had a significantly higher peak creatinine level and a more frequent requirement for RRT. However, the Klotho score was not a significant predictor of renal recovery. CONCLUSIONS: The results demonstrated that renal Klotho expression in humans decreased significantly according to the severity of AKI, regardless of the etiology, and that low expression was associated with a poor short-term outcome.
Acute Kidney Injury/diagnosis/etiology/*metabolism/physiopathology/therapy ; Adolescent ; Adult ; Biomarkers/analysis ; Biopsy ; Down-Regulation ; Female ; Glucuronidase/*analysis ; Humans ; Immunohistochemistry ; Kidney/*chemistry/pathology/physiopathology ; Kidney Tubular Necrosis, Acute/diagnosis/etiology/*metabolism/physiopathology/therapy ; Male ; Middle Aged ; Necrosis ; Predictive Value of Tests ; Recovery of Function ; Renal Replacement Therapy ; Retrospective Studies ; Risk Factors ; Severity of Illness Index ; Time Factors ; Treatment Outcome ; Young Adult