Background. This study evaluated whether the change in the renin-angiotensin system (RAS) is associated with arterial aging in mice. Methods. Histologic changes and expressions of transforming growth factor-β (TGF-β), collagen IV, fibronectin, angiotensin II (Ang II), angiotensin-converting enzyme (ACE), angiotensin-converting enzyme 2 (ACE2), angiotensin II type 1 receptor (AT1R), angiotensin II type 2 receptor (AT2R), prorenin receptor (PRR), Mas receptor (MasR), endothelial nitric oxide synthase (eNOS), NADPH oxidase 2 and oxidase 4 (Nox2 and Nox4), 8-hydroxy-2′-deoxyguanosine (8-OHdG), 3-nitrotyrosine, and superoxide dismutase 1 and dismutase 2 (SOD1 and SOD2) were measured in the thoracic aortas from 2-month-old, 12-month-old, and 24-month-old C57/BL6 mice. Results. Twenty-four-month-old mice showed significantly increased aortic media thickness and expressions of TGF-β, collagen IV, and fibronectin, compared to 2-month-old and 12-month-old mice. The expressions of PRR, ACE, and Ang II, and AT1R-positive area significantly increased, whereas expressions of ACE2 and MasR and AT2R-positive area decreased with age. The expressions of phosphorylated serine1177-eNOS, SOD1, and SOD2 decreased, and the 8-OHdG-positive area and the 3-nitrotyrosine-positive area increased with age. The expression of Nox2 significantly increased with age, but that of Nox4 did not change. Conclusions. The enhanced PRR-ACE-Ang II-AT1R axis and reduced ACE2-MasR axis were associated with arterial aging in mice.

Adiponectin exerts renoprotective effects against diabetic nephropathy (DN) by activating the AMP-activated protein kinase (AMPK)/peroxisome proliferative-activated receptor- (PPAR) pathway through adiponectin receptors (AdipoRs). AdipoRon is an orally active synthetic adiponectin receptor agonist. We investigated the expression of AdipoRs and the associated intracellular pathways in 27 patients with type 2 diabetes and examined the effects of AdipoRon on DN development in male C57BLKS/J mice, glomerular endothelial cells (GECs), and podocytes. The extent of glomerulosclerosis and tubulointerstitial fibrosis correlated with renal function deterioration in human kidneys. Expression of AdipoR1, AdipoR2, and Ca/calmodulin-dependent protein kinase kinase- (CaMKK) and numbers of phosphorylated liver kinase B1 (LKB1)- and AMPK-positive cells significantly decreased in the glomeruli of early stage human DN. AdipoRon treatment restored diabetes-induced renal alterations in mice. AdipoRon exerted renoprotective effects by directly activating intrarenal AdipoR1 and AdipoR2, which increased CaMKK, phosphorylated SerLKB1, phosphorylated ThrAMPK, and PPAR expression independently of the systemic effects of adiponectin. AdipoRon-induced improvement in diabetes-induced oxidative stress and inhibition of apoptosis in the kidneys ameliorated relevant intracellular pathways associated with lipid accumulation and endothelial dysfunction. In high-glucose-treated human GECs and murine podocytes, AdipoRon increased intracellular Ca levels that activated a CaMKK/phosphorylated SerLKB1/phosphorylated ThrAMPK/PPAR pathway and downstream signaling, thus decreasing high-glucose-induced oxidative stress and apoptosis and improving endothelial dysfunction. AdipoRon further produced cardioprotective effects through the same pathway demonstrated in the kidney. Our results show that AdipoRon ameliorates GEC and podocyte injury by activating the intracellular Ca/LKB1-AMPK/PPAR pathway, suggesting its efficacy for treating type 2 diabetes-associated DN.

Background. Two important issues in the aging kidney are mitochondrial dysfunction and oxidative stress. An Nrf2 activator, resveratrol, is known to have various effects. Resveratrol may prevent inflammation and oxidative stress by activating Nrf2 and SIRT1 signaling. We examined whether resveratrol could potentially ameliorate the cellular condition, such as renal injury due to cellular oxidative stress and mitochondrial dysfunction caused by aging. Methods. Male 18-month-old C57BL/6 mice were used. Resveratrol (40 mg/kg) was administered to aged mice for 6 months. We compared histological changes, oxidative stress, and aging-related protein expression in the kidney between the resveratrol-treated group (RSV) and the control group (cont). We performed experiments using small-interfering RNAs (siRNAs) for Nrf2 and SIRT1 in cultured HK2 cells. Results. Resveratrol improved renal function, proteinuria, histological changes and inflammation in aging mice. Also, expression of Nrf2-HO-1-NOQ-1 signaling and SIRT1-AMPK-PGC-1α signaling was increased in the RSV group. Transfection with Nrf2 and SIRT1 siRNA prevented resveratrol-induced anti-oxidative effect in HK2 cells in media treated with H 2 O 2 . Conclusions. Activation of the Nrf2 and SIRT1 signaling pathways ameliorated oxidative stress and mitochondrial dysfunction. Pharmacological targeting of Nrf2 signaling molecules may reduce the pathologic changes of aging in the kidney.

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Background. Aging is a multifactorial process characterized by a progressive decline in physiological function. Decreased kidney function is associated with cardiovascular disease and mortality. Therefore, increasing our insight into kidney aging by understanding the anatomic, physiologic, and pathologic changes of aging in the kidney is important to prevent disastrous outcomes in elderly people. Methods. Male two-, 12-, and 24-month-old C57/BL6 mice were used in this study. We measured histological change, oxidative stress, and aging-related protein expression in the kidneys. Results. Twenty-four-month-old mice displayed increased albuminuria. Creatinine clearance decreased with aging, although this was not statistically significant. There were increases in mesangial volume and tubulointerstitial fibrosis in 24-month-old mice. There were also increases in F4/80 expression and in apoptosis detected by TUNEL assay. Urine isoprostane excretion increased with aging and SOD1 and SOD2 were decreased in 24-month-old mice. Oxidative stress may be mediated by a decrease in Sirt1, PGC-1α, ERR-1α, and PPARα expression. Klotho expression also decreased. Conclusions. Our results demonstrate that Sirt1 was decreased with aging and may relate to changed target molecules including PGC-1α/ERR-1α signaling and PPARα. Klotho can also induce oxidative stress. Pharmacologically targeting these signaling molecules may reduce the pathologic changes of aging in the kidney.

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The renin-angiotensin system (RAS), especially the angiotensin II (Ang II)/angiotensin II type 1 receptor (AT1R) axis, plays an important role in the aging process of the kidney, through increased tissue reactive oxygen species production and progressively increased oxidative stress. In contrast, the angiotensin 1-7 (Ang 1-7)/Mas receptor (MasR) axis, which counteracts the effects of Ang II, is protective for end-organ damage. To evaluate the ability of resveratrol (RSV) to modulate the RAS in aging kidneys, eighteen-month-old male C57BL/6 mice were divided into two groups that received either normal mouse chow or chow containing resveratrol, for six months. Renal expressions of RAS components, as well as pro- and antioxidant enzymes, were measured and mouse kidneys were isolated for histopathology. Resveratrol-treated mice demonstrated better renal function and reduced albuminuria, with improved renal histologic findings. Resveratrol suppressed the Ang II/AT1R axis and enhanced the AT2R/Ang 1-7/MasR axis. Additionally, the expression of nicotinamide adenine dinucleotide phosphate oxidase 4, 8-hydroxy-2′-deoxyguanosine, 3-nitrotyrosine, collagen IV, and fibronectin was decreased, while the expression of endothelial nitric oxide synthase and superoxide dismutase 2 was increased by resveratrol treatment. These findings demonstrate that resveratrol exerts protective effects on aging kidneys by reducing oxidative stress, inflammation, and fibrosis, through Ang II suppression and MasR activation.

Apoptosis and autophagy are harmoniously regulated biological processes for maintaining tissue homeostasis. AMP-activated protein kinase (AMPK) functions as a metabolic sensor to coordinate cellular survival and function in various organs, including the kidney. We investigated the renoprotective effects of cinacalcet in high-glucose treated human glomerular endothelial cells (HGECs), murine podocytes and C57BLKS/J-db/db mice. In cultured HGECs and podocytes, cinacalcet decreased oxidative stress and apoptosis and increased autophagy that were attributed to the increment of intracellular Ca2+ concentration and the phosphorylation of Ca2+/calmodulin-dependent protein kinase kinaseβ (CaMKKβ)-Liver kinase B1 (LKB1)-AMPK and their downstream signals including the phosphorylation of endothelial nitric oxide synthase (eNOS) and increases in superoxide dismutases and B cell leukemia/lymphoma 2/BCL-2-associated X protein expression. Interestingly, intracellular chelator BAPTA-AM reversed cinacalcet-induced CaMKKβ elevation and LKB1 phosphorylation. Cinacalcet reduced albuminuria without influencing either blood glucose or Ca2+ concentration and ameliorated diabetes-induced renal damage, which were related to the increased expression of calcium-sensing receptor and the phosphorylation of CaMKKβ-LKB1. Subsequent activation of AMPK was followed by the activation of peroxisome proliferator-activated receptor γ coactivator-1α and phospho-Ser1177eNOS-nitric oxide, resulting in a decrease in apoptosis and oxidative stress as well as an increase in autophagy.Our results suggest that cinacalcet increases intracellular Ca2+ followed by an activation of CaMKKβ-LKB1-AMPK signaling in GECs and podocytes in the kidney, which provides a novel therapeutic means for type 2 diabetic nephropathy by modulation of apoptosis and autophagy.