Masaki Imanishi

Smooth muscle cell-specific Hif-1α deficiency suppresses angiotensin II-induced vascular remodelling in mice

AIM Vascular remodelling is mediated by vascular smooth muscle cell (VSMC) proliferation and hypertrophy, both processes of which are linked to medial thickening and fibrosis. Here, we show that hypoxia-inducible factor-1α (Hif-1α) expressed in smooth muscle cells (SMCs) is involved in angiotensin II (Ang II)-induced vascular remodelling in an in vivo model. METHODS AND RESULTS To clarify the role of Hif-1α in vascular remodelling, we created mice lacking the Hif-1α gene in SMCs (SMKO mice). Ang II infusion induced medial thickening and vascular fibrosis, accompanied by Hif-1α up-regulation, in the aortae of control mice, but not in those of SMKO mice. In accordance with those results, our in vitro studies showed that the deletion of SMC-derived Hif-1α suppressed the Ang II-induced hypertrophy of VSMCs, and our in vivo studies showed that the Ang II-induced expression of fibrosis-related genes in aortae was suppressed by SMC-specific Hif-1α deficiency. In addition, the SMC-specific Hif-1α deficiency suppressed Ang II-induced macrophage infiltration and Ang II-induced expression of inflammation-related genes in aortae. The superoxide production observed in the aortae of control mice with Ang II was suppressed in those of SMKO mice with Ang II, and this finding was consistent with the results of little Ang II-induced c-Src phosphorylation in SMKO mouse aortae. Loss- and gain-of-function analysis in in vitro experiments confirmed that VSMC-derived Hif-1α functions as an intrinsic modulator of vascular remodelling-related gene expression. CONCLUSION Our results revealed that SMC-derived Hif-1α is a crucial mediator of Ang II-induced vascular remodelling.

Nitrosonifedipine ameliorates angiotensin II-induced vascular remodeling via antioxidative effects

Nifedipine is unstable under light and decomposes to a stable nitroso analog, nitrosonifedipine (NO-NIF). The ability of NO-NIF to block calcium channels is quite weak compared with that of nifedipine. Recently, we have demonstrated that NO-NIF reacts with unsaturated fatty acid leading to generate NO-NIF radical, which acquires radical scavenging activity. However, the effects of NO-NIF on the pathogenesis related with oxidative stress, such as atherosclerosis and hypertension, are unclear. In this study, we investigated the effects of NO-NIF on angiotensin II (Ang II)-induced vascular remodeling. Ang II-induced thickening and fibrosis of aorta were inhibited by NO-NIF in mice. NO-NIF decreased reactive oxygen species (ROS) in the aorta and urinary 8-hydroxy-20-deoxyguanosine. Ang II-stimulated mRNA expressions of p22phox, CD68, F4/80, monocyte chemoattractant protein-1, and collagen I in the aorta were inhibited by NO-NIF. Moreover, NO-NIF inhibited Ang II-induced cell migration and proliferation of vascular smooth muscle cells (VSMCs). NO-NIF reduced Ang II-induced ROS to the control level detected by dihydroethidium staining and lucigenin chemiluminescence assay in VSMCs. NO-NIF suppressed phosphorylations of Akt and epidermal growth factor receptor induced by Ang II. However, NO-NIF had no effects on intracellular Ca2+ increase and protein kinase C-δ phosphorylation induced by Ang II in VSMCs. The electron paramagnetic resonance spectra indicated the continuous generation of NO-NIF radical of reaction with cultured VSMCs. These findings suggest that NO-NIF improves Ang II-induced vascular remodeling via the attenuation of oxidative stress.

Nitrosonifedipine ameliorates the progression of type 2 diabetic nephropathy by exerting antioxidative effects.

Diabetic nephropathy (DN) is the major cause of end-stage renal failure. Oxidative stress is implicated in the pathogenesis of DN. Nitrosonifedipine (NO-NIF) is a weak calcium channel blocker that is converted from nifedipine under light exposure. Recently, we reported that NO-NIF has potential as a novel antioxidant with radical scavenging abilities and has the capacity to treat vascular dysfunction by exerting an endothelial protective effect. In the present study, we extended these findings by evaluating the efficacy of NO-NIF against DN and by clarifying the mechanisms of its antioxidative effect. In a model of type 2 DN (established in KKAy mice), NO-NIF administration reduced albuminuria and proteinuria as well as glomerular expansion without affecting glucose metabolism or systolic blood pressure. NO-NIF also suppressed renal and systemic oxidative stress and decreased the expression of intercellular adhesion molecule (ICAM)-1, a marker of endothelial cell injury, in the glomeruli of the KKAy mice. Similarly, NO-NIF reduced albuminuria, oxidative stress, and ICAM-1 expression in endothelial nitric oxide synthase (eNOS) knockout mice. Moreover, NO-NIF suppressed urinary angiotensinogen (AGT) excretion and intrarenal AGT protein expression in proximal tubular cells in the KKAy mice. On the other hand, hyperglycemia-induced mitochondrial superoxide production was not attenuated by NO-NIF in cultured endothelial cells. These findings suggest that NO-NIF prevents the progression of type 2 DN associated with endothelial dysfunction through selective antioxidative effects.

Hypoxia-Inducible Factor-1α in Smooth Muscle Cells Protects Against Aortic Aneurysms

Objective—The purpose of this study was to determine the role of smooth muscle cell–derived hypoxia-inducible factor-1&agr; (Hif-1&agr;) in the pathogenesis of aortic aneurysms. Approach and Results—Control mice and smooth muscle cell–specific hypoxia-inducible factor-1&agr;–deficient mice were infused with &bgr;-aminopropionitrile for 2 weeks and angiotensin II for 6 weeks to induce aortic aneurysm formation. Mutant mice experienced increased levels of aneurysm formation of the thoracic or abdominal aorta with more severe elastin disruption, compared with control mice. Smooth muscle cell–specific hypoxia-inducible factor-1&agr; deficiency did not affect matrix metalloproteinase-2 activity; however, the activity of lysyl oxidase and the levels of tropoelastin mRNA in the angiotensin II– and &bgr;-aminopropionitrile–treated aortae, associated with elastin fiber formation, were suppressed. Furthermore, we observed reduced volumes of mature cross-linked elastin in the thoracoabdominal aorta after treatment with angiotensin II and &bgr;-aminopropionitrile. Conclusions—Deficiency of smooth muscle cell–derived hypoxia-inducible factor-1&agr; augments aortic aneurysms, accompanied by disruption of elastin fiber formation, but not changes of elastin fiber degradation.

Angiotensin II Receptor Blocker Improves Tumor Necrosis Factor-α-Induced Cytotoxicity via Antioxidative Effect in Human Glomerular Endothelial Cells

Background/Aims: Tumor necrosis factor-α (TNF-α) is known to involve the progression of renal dysfunction through its cytotoxicity and proinflammatory effects such as the induction of intercellular adhesion molecule (ICAM)-1 expression in vascular endothelial cells (ECs). Olmesartan, one of the angiotensin II type 1 receptor blockers (ARBs), has been reported to show protective effects on injured ECs by some causal factors of renal disorder other than angiotensin II. However, the effects of olmesartan on TNF-α-induced glomerular EC damage have not been investigated. In the present study, we investigated the effects of RNH-6270, an active metabolite of olmesartan, on TNF-α-induced human glomerular EC (HGEC) damage to clarify the renoprotective mechanisms of ARBs. Methods: Cultured HGECs were stimulated by TNF-α, and then cell viability and cytotoxicity were measured by MTT assay and lactate dehydrogenase release assay, respectively. TNF-α-induced oxidative stress was estimated by dihydroethidium assay and lucigenin chemiluminescence assay. ICAM-1 expression and the phosphorylations of mitogen-activated protein kinases were measured using Western blotting assay. Results: RNH-6270 suppressed cell death and the increase in ICAM-1 expression induced by TNF-α via the inhibition of reactive oxygen species in HGECs. Conclusion: Our findings suggested that olmesartan might have protective effects against TNF-α-induced glomerular EC dysfunction.

Overexpressed HIF-2α in Endothelial Cells Promotes Vascularization and Improves Random Pattern Skin Flap Survival.

Background: The local skin flap procedure is very useful for reconstruction. However, flap necrosis caused by circulatory failure can occur at its distal portion. Hypoxia-inducible factors (HIFs) in endothelial cells (ECs) help to maintain ECs and promote vascularization, and HIF-2&agr; is abundantly expressed in ECs. However, the mechanisms of action of HIF-2&agr; in ECs are not yet fully understood. The aim of this study was to evaluate the in vivo effects of overexpression of HIF-2&agr; in ECs on skin flap survival. Methods: A random pattern skin flap (1.0 × 3.0 cm) was elevated on the dorsum of transgenic mice (Tg mice) with EC-specific HIF-2&agr; conditional overexpression and wild-type littermate control mice (n = 6). Flap survival was evaluated on postoperative day 7. Tissue samples from the skin flaps were harvested and analyzed using Western blotting, quantitative reverse transcriptase-polymerase chain reaction, and immunohistochemistry. Results: The HIF-2&agr; mRNA and protein levels were significantly increased in the Tg mice when compared with control mice. Tg mice had significantly increased skin flap survival areas (72.0% ± 2.7%) when compared with wild-type mice (45.7% ± 1.1%). Moreover, histological examination revealed an increase in the subcutaneous blood vessel counts in the Tg mice. Conclusions: Specific overexpression of HIF-2&agr; in ECs promoted vascularization and enhanced skin flap survival in vivo in a mouse model.

Dietary iron restriction alleviates renal tubulointerstitial injury induced by protein overload in mice

Increased proteinuria causes tubulointerstitial injury due to inflammation in chronic kidney disease (CKD). Iron restriction exhibits protective effects against renal dysfunction; however, its effects against protein overload-induced tubulointerstitial damage remain unclear. Here, we investigated dietary iron restriction effect on tubulointerstitial damage in mice with protein-overload tubulointerstitial injury. Renal tubulointerstitial injury in animal model was induced by intraperitoneal injection of an overdose of bovine serum albumin (BSA). We divided mice into three groups: normal saline + normal diet (ND), BSA + ND, and BSA + iron-restricted diet (IRD). BSA overload induced renal tubulointerstitial injury in the ND mice, which was ameliorated in the IRD mice. Inflammatory cytokines and extracellular matrix mRNA expression was upregulated in BSA + ND mice kidneys and was inhibited by IRD. BSA-induced increase in renal superoxide production, NADPH oxidase activity, and p22phox expression was diminished in the IRD mice. IRD suppression increased BSA-induced renal macrophage infiltration. Moreover, BSA mice exhibited nucleotide-binding oligomerisation domain-like receptor pyrin domain-containing protein (NLRP) inflammasome activation, which was inhibited by IRD. Ferrous iron increased in kidneys with BSA overload and was inhibited by IRD. Thus, iron restriction inhibited oxidative stress and inflammatory changes, contributing to the protective effect against BSA overload-induced tubulointerstitial injury.

The uremic toxin indoxyl sulfate interferes with iron metabolism by regulating hepcidin in chronic kidney disease

Background Hepcidin secreted by hepatocytes is a key regulator of iron metabolism throughout the body. Hepcidin concentrations are increased in chronic kidney disease (CKD), contributing to abnormalities in iron metabolism. Levels of indoxyl sulfate (IS), a uremic toxin, are also elevated in CKD. However, the effect of IS accumulation on iron metabolism remains unclear. Methods We used HepG2 cells to determine the mechanism by which IS regulates hepcidin concentrations. We also used a mouse model of adenine-induced CKD. The CKD mice were divided into two groups: one was treated using AST-120 and the other received no treatment. We examined control mice, CKD mice, CKD mice treated using AST-120 and mice treated with IS via drinking water. Results In the in vitro experiments using HepG2 cells, IS increased hepcidin expression in a dose-dependent manner. Silencing of the aryl hydrocarbon receptor (AhR) inhibited IS-induced hepcidin expression. Furthermore, IS induced oxidative stress and antioxidant drugs diminished IS-induced hepcidin expression. Adenine-induced CKD mice demonstrated an increase in hepcidin concentrations; this increase was reduced by AST-120, an oral adsorbent of the uremic toxin. CKD mice showed renal anemia, decreased plasma iron concentration, increased plasma ferritin and increased iron content in the spleen. Ferroportin was decreased in the duodenum and increased in the spleen. These changes were ameliorated by AST-120 treatment. Mice treated by direct IS administration showed hepatic hepcidin upregulation. Conclusions IS affects iron metabolism in CKD by participating in hepcidin regulation via pathways that depend on AhR and oxidative stress.

HIF-2α/ARNT complex regulates hair development via induction of p21Waf1/Cip1 and p27Kip1

The hypoxia‐inducible factors HIF‐1α or HIF‐2α form heterodimeric complexes with the aryl hydrocarbon receptor nuclear translocator (ARNT). HIF‐1α/ARNT and HIF‐2α/ARNT complexes activate hypoxia‐inducible genes that play critical roles in angiogenesis, anaerobic metabolism, and other processes in response to O2 deprivation. HIF‐2α is known to regulate the function and/or differentiation of stem cells by activating the POU domain transcription factor Oct4; however, the precise underlying mechanism is unknown. This study examined the role of HIF‐2α/ARNT in hair development using conditional‐knockout mice, in which Arnt was specifically deleted in keratinocytes. In wild‐type mice, HIF‐2α and ARNT were highly expressed in the precortex above the hair matrix, an area containing differentiating stem cells. An analysis of hair size and type in these mice showed that loss of ARNT decreased the production of zigzag hairs, corresponding to reduced expression of HIF‐2α and induction of the mammalian cyclin‐dependent kinase inhibitors p21Waf1/Cip1 and p27 Kip1 The results suggest that the HIF‐2α/ARNT complex regulates hair follicle differentiation via induction of p21Waf1/Cip1 and possibly p27Kip1, as p27Kip1 expression was not altered in ARNT knockout mice. The findings provide insight into a possible mechanism underlying hair growth disorders and can be useful for future studies on hair follicle response to insults, such as chemotherapy and ionizing radiation.—Imamura, Y., Tomita, S., Imanishi, M., Kihira, Y., Ikeda, Y., Ishizawa, K., Tsuchiya, K., Tamaki, T. HIF‐2α/ARNT complex regulates hair development via induction of p21Waf1/Cip1 and p27Kip1. FASEB J. 28, 2517–2524 (2014). www.fasebj.org

Pharmacological approach for drug repositioning against cardiorenal diseases

New applications of approved clinically used drugs are being discovered. Drug repositioning is a proposed strategy for developing these drugs as therapeutic agents for different diseases. Currently, approximately 2000 drugs are used in Japan. However, the compound targets and pathways involved in the pharmacological actions of 70-80% of these drugs have not been adequately clarified. Pharmacological examination of approved drugs is an important task in drug repositioning and vital for improving drug development efficiency. This review reports that angiotensin II type 1 receptor blockers show receptor-independent effects against reactive oxygen species generation in renal cells. Additionally, nitrosonifedipine has an antioxidative effect and protects endothelial cells against oxidative stress, and pioglitazone has multiple effects that improve dysfunctions in vascular control regulated by adrenergic and calcitonin gene-related peptide-containing nerves in animal models of diabetes. These data suggest that some approved drugs could be useful for treating cardiorenal diseases. Since cardiorenal diseases are likely to have chronic pathological conditions and require chronic drug administration, highly safe drugs are needed. Compared to newly developed drugs, drug repositioning of approved drugs with safety information is considered a particularly useful technique for searching new treatments for cardiorenal diseases. J. Med. Invest. 64: 197-201, August, 2017.