Angiotensin II-Induced Neural Differentiation via Angiotensin II Type 2 (AT2) Receptor-MMS2 Cascade Involving Interaction between AT2Receptor-Interacting Protein and Src Homology 2 Domain-Containing Protein-Tyrosine Phosphatase 1

Angiotensin II (Ang II) type 2 (AT2) receptors are abundantly expressed not only in the fetal brain where they probably contribute to brain development, but also in pathological conditions to protect the brain against stroke; however, the detailed mechanisms are unclear. Here, we demonstrated that AT2 receptor signaling induced neural differentiation via an increase in MMS2, one of the ubiquitin-conjugating enzyme variants. The AT2 receptor, MMS2, Src homology 2 domain-containing protein-tyrosine phosphatase 1 (SHP-1), and newly cloned AT2 receptor-interacting protein (ATIP) were highly expressed in fetal rat neurons and declined after birth. Ang II induced MMS2 expression in a dose-dependent manner, reaching a peak after 4 h of stimulation, and this effect was enhanced with AT1 receptor blocker, valsartan, but inhibited by AT2 receptor blocker PD123319. Moreover, we observed that an AT2 receptor agonist, CGP42112A, alone enhanced MMS2 expression. Neurons treated with small interfering RNA of MMS2 failed to exhibit neurite outgrowth and synapse formation. Moreover, the increase in AT2 receptor-induced MMS2 mRNA expression was enhanced by overexpression of ATIP but inhibited by small interfering RNA of SHP-1 and overexpression of catalytically dominant-negative SHP-1 or a tyrosine phosphatase inhibitor, sodium orthovanadate. After AT2 receptor stimulation, ATIP and SHP-1 were translocated into the nucleus after formation of their complex. Furthermore, increased MMS2 expression mediates the inhibitor of DNA binding 1 proteolysis and promotes DNA repair. These results provide a new insight into the contribution of AT2 receptor stimulation to neural differentiation via transactivation of MMS2 expression involving the association of ATIP and SHP-1.

The calcium-channel blocker, azelnidipine, enhances the inhibitory action of AT1 receptor blockade on ischemic brain damage

OBJECTIVE

The combined effects of a calcium-channel blocker (CCB) with an angiotensin (Ang) II type 1 (AT1) receptor blocker were investigated in focal brain ischemia induced by middle cerebral artery (MCA) occlusion.

METHODS AND RESULTS

In male C57BL/6J mice, permanent occlusion of the MCA-induced focal cerebral ischemia and neurological deficit after 24 h, accompanied by a reduction of cerebral blood flow and an increase in superoxide production in the ischemic area. Administration of azelnidipine, a CCB, at 1.0 mg/kg per day for 10 days significantly suppressed these changes after MCA without affecting systolic blood pressure. Such inhibitory effects of azelnidipine on brain ischemia could be observed in AT1a receptor-deficient mice. In addition, olmesartan, an AT1 receptor blocker, at 3.0 mg/kg per day also diminished the ischemic brain area and neurological score, as well as superoxide production and the reduction of cerebral surface blood flow in C57BL/6 mice. The combination of lower doses of azelnidipine (0.1 mg/kg per day) and olmesartan (0.5 mg/kg per day) significantly attenuated the ischemic brain area, neurological score, superoxide production and the reduction of cerebral surface blood flow after MCA occlusion in C57BL/6 mice, whereas either of these agents alone at these doses did not affect brain ischemia.

CONCLUSION

These results indicate that azelnidipine inhibited ischemic brain damage induced by MCA occlusion, at least in part, through suppression of blood flow change and oxidative stress via a signaling mechanism independent of AT1 receptor stimulation. Moreover, azelnidipine synergistically enhanced the inhibitory action of olmesartan on brain ischemia, suggesting beneficial combined effects of a CCB with an AT1 receptor blocker on ischemic brain damage.

Calcium channel blocker azelnidipine reduces glucose intolerance in diabetic mice via different mechanism than angiotensin receptor blocker olmesartan

The potential combined effect and mechanism of calcium channel blockers (CCB) and angiotensin II type 1 receptor blockers (ARB) to improve insulin resistance were investigated in type 2 diabetic KK-Ay mice, focusing on their antioxidative action. Treatment of KK-Ay mice with a CCB, azelnidipine (3 mg/kg/day), or with an ARB, olmesartan (3 mg/kg/day), for 2 weeks lowered the plasma concentrations of glucose and insulin in the fed state, attenuated the increase in plasma glucose in the oral glucose tolerance test (OGTT), and increased 2-[(3)H]deoxy-d-glucose (2-[(3)H]DG) uptake into skeletal muscle with the increase in translocation of glucose transporter 4 (GLUT4) to the plasma membrane. Both blockers also decreased the in situ superoxide production in skeletal muscle. The decrease in plasma concentrations of glucose and insulin in the fed state and superoxide production in skeletal muscle, as well as GLUT4 translocation to the plasma membrane, after azelnidipine administration was not significantly affected by coadministration of an antioxidant, 2,2,6,6-tetramethyl-1-piperidinyloxy (tempol). However, those changes caused by olmesartan were further improved by tempol. Moreover, olmesartan enhanced the insulin-induced tyrosine phosphorylation of insulin receptor substrate-1 induced in skeletal muscle, whereas azelnidipine did not change it. Coadministration of azelnidipine and olmesartan further decreased the plasma concentrations of glucose and insulin, improved OGTT, and increased 2-[(3)H]DG uptake in skeletal muscle. These results suggest that azelnidipine improved glucose intolerance mainly through inhibition of oxidative stress and enhanced the inhibitory effects of olmesartan on glucose intolerance, as well as the clinical possibility that the combination of CCB and ARB could be more effective than monotherapy in the treatment of insulin resistance.

Comparison of inhibitory action of candesartan and enalapril on brain ischemia through inhibition of oxidative stress

The effects of an angiotensin II type 1 (AT1) receptor blocker (ARB) on ischemic brain damage induced by middle cerebral artery (MCA) occlusion were compared with those of an angiotensin converting enzyme (ACE) inhibitor. Treatment of male C57BL/6J mice with an ARB, candesartan, reduced the brain ischemic area and neurological deficit after MCA occlusion at a non-hypotensive dose. In contrast, an ACE inhibitor, enalapril, did not reduce the brain ischemic area, and neurological deficit even at a hypotensive dose. Candesartan improved the reduction of brain surface blood flow after MCA occlusion, and inhibited the increase in superoxide production both in the cortex and brain arterial wall at non-hypotensive and hypotensive doses. However, enalapril did not affect the changes in blood flow and superoxide production in the brain after MCA occlusion. AT2 receptor expression in the ischemic area was increased at 3 h after MCA occlusion by pretreatment with candesartan, but not that with enalapril. AT1 receptor expression was neither affected by candesartan nor by enalapril. These results suggest that candesartan attenuated ischemic brain damage, at least partly, through inhibition of oxidative stress.

The effect and distribution of a protein-bound polysaccharide preparation, PSK (Krestin), intratumorally injected prior to surgery into gastric cancer patients

In order to improve the postoperative prognosis of gastric cancer patients we have performed preoperative endoscopic intratumoral administration of various biological response modifiers. In the present study we have investigated the kinetics and the immune response augmenting effect of intratumorally injected PSK, a protein-bound polysaccharide preparation, by immunohistochemical methods using anti-PSK antibody and various other antibodies. PSK-containing cells were located in the tumor tissues and follicular marginal zones of regional lymph nodes. Intratumorally administered PSK appeared to be phagocytized by the histiocytes and to cause them to become antigen-presenting cells. These cells may play a major role in augmenting immune responses in gastric cancer patients.