There are two major angiotensin II receptor isoforms, AT1 and AT2. AT1 mediates the well-known pressor and mitogenic effects of angiotensin II, but the signalling mechanism and physiological role of AT2 has not been established. Its abundant expression in fetal tissues and certain brain nuclei suggest possible roles in growth, development and neuronal functions. Here we report the unexpected finding that the targeted disruption of the mouse AT2 gene resulted in a significant increase in blood pressure and increased sensitivity to the pressor action of angiotensin II. Thus AT2 mediates a depressor effect and antagonizes the AT1-mediated pressor action of angiotensin II. In addition, disruption of the AT2 gene attenuated exploratory behaviour and lowered body temperature. Our results show that angiotensin II activates AT1 and AT2, which have mutually counteracting haemodynamic effects, and that AT2 regulates central nervous system functions, including behaviour.

The rapamycin-insensitive mTOR complex 2 (mTORC2) has been suggested to play an important role in growth factor-dependent signaling. To explore this possibility further in a mammalian model system, we disrupted the expression of rictor, a specific component of mTORC2, in mice by using a multiallelic gene targeting strategy. Embryos that lack rictor develop normally until E9.5, and then exhibit growth arrest and die by E11.5. Although placental defects occur in null embryos, an epiblast-specific knockout of rictor only delayed lethality by a few days, thereby suggesting other important roles for this complex in the embryo proper. Analyses of rictor null embryos and fibroblasts indicate that mTORC2 is a primary kinase for Ser473 of Akt/PKB. Rictor null fibroblasts exhibit low proliferation rates, impaired Akt/PKB activity, and diminished metabolic activity. Taken together, these findings indicate that both rictor and mTORC2 are essential for the development of both embryonic and extraembryonic tissues.

Determination of signaling pathways that regulate beta-cell replication is critical for beta-cell therapy. Here, we show that blocking pancreatic macrophage infiltration after pancreatic duct ligation (PDL) completely inhibits beta-cell proliferation. The TGFβ superfamily signaling inhibitor SMAD7 was significantly up-regulated in beta cells after PDL. Beta cells failed to proliferate in response to PDL in beta-cell-specific SMAD7 mutant mice. Forced expression of SMAD7 in beta cells by itself was sufficient to promote beta-cell proliferation in vivo. M2, rather than M1 macrophages, seem to be the inducers of SMAD7-mediated beta-cell proliferation. M2 macrophages not only release TGFβ1 to directly induce up-regulation of SMAD7 in beta cells but also release EGF to activate EGF receptor signaling that inhibits TGFβ1-activated SMAD2 nuclear translocation, resulting in TGFβ signaling inhibition. SMAD7 promotes beta-cell proliferation by increasing CyclinD1 and CyclinD2, and by inducing nuclear exclusion of p27. Our study thus reveals a molecular pathway to potentially increase beta-cell mass through enhanced SMAD7 activity induced by extracellular stimuli.TGFβ superfamily signaling pathway | epidermal growth factor receptor signaling pathway

The ATP-sensitive potassium channel is a key molecular complex for glucose-stimulated insulin secretion in pancreatic ␤ cells. In humans, mutations in either of the two subunits for this channel, the sulfonylurea type 1 receptor (Sur1) or Kir6.2, cause persistent hyperinsulinemic hypoglycemia of infancy. We have generated and characterized Sur1 null mice. Interestingly, these animals remain euglycemic for a large portion of their life despite constant depolarization of membrane, elevated cytoplasmic free Ca 2؉ concentrations, and intact sensitivity of the exocytotic machinery to Ca 2؉ . A comparison of glucose-and meal-stimulated insulin secretion showed that, although Sur1 null mice do not secrete insulin in response to glucose, they secrete nearly normal amounts of insulin in response to feeding. Because Sur1 null mice lack an insulin secretory response to GLP-1, even though their islets exhibit a normal rise in cAMP by GLP-1, we tested their response to cholinergic stimulation. We found that perfused Sur1 null pancreata secreted insulin in response to the cholinergic agonist carbachol in a glucose-dependent manner. Together, these findings suggest that cholinergic stimulation is one of the mechanisms that compensate for the severely impaired response to glucose and GLP-1 brought on by the absence of Sur1, thereby allowing euglycemia to be maintained.Glucose-stimulated insulin secretion by the pancreatic ␤ cell requires the coupling of changes in glucose metabolism to alterations in membrane potential (1-4). In response to a rise in the intracellular ATP/ADP ratio that occurs with glucose metabolism the closure of ATP-sensitive potassium (K ATP ) 1 channels causes the ␤ cell membrane to depolarize. This, in turn, leads to the opening of voltage-gated L-type Ca 2ϩ channels, a rise in the cytoplasmic free Ca 2ϩ concentration ([Ca 2ϩ ] i ), and the subsequent exocytosis of insulin (5). The ␤ cell K ATP channel is an octameric complex of two proteins: an inward-rectifier K ϩ channel, Kir6.2, and the sulfonylurea receptor type 1 (Sur1), which are present in a 4:4 stoichiometry (6, 7). Kir6.2, which forms the channel pore, possesses intrinsic ATP sensitivity (8, 9), whereas Sur1, a member of a superfamily of ATPbinding cassette transporter proteins, provides sites for interaction with Mg-ADP (10). Sulfonylureas, which are widely used for treatment of patients with type 2 diabetes mellitus, act by binding to K ATP channels and stimulating their closure (10).Mutations in Sur1 are a frequent cause of persistent hyperinsulinemic hypoglycemia of infancy (PHHI), an autosomal recessive disorder characterized by excess and unregulated secretion of insulin. Because initial identification of Sur1 as a candidate gene for PHHI by , more than 50 different mutations in this gene, as well as 2 mutations in Kir6.2, have been identified in PHHI patients (12). Analyses of pancreatic ␤ cells from PHHI patients, as well as functional studies of mutated K ATP channels introduced into cultured cells, suggest that impaired K ATP channel...