The serine/threonine kinase Akt/PKB plays key roles in the regulation of cell growth, survival, and metabolism. It remains unclear, however, whether the functions of individual Akt/PKB isoforms are distinct. To investigate the function of Akt2/PKBβ, mice lacking this isoform were generated. Both male and female Akt2/PKBβ-null mice exhibit mild growth deficiency and an age-dependent loss of adipose tissue or lipoatrophy, with all observed adipose depots dramatically reduced by 22 weeks of age. Akt2/PKBβ-deficient mice are insulin resistant with elevated plasma triglycerides. In addition, Akt2/PKBβ-deficient mice exhibit fed and fasting hyperglycemia, hyperinsulinemia, glucose intolerance, and impaired muscle glucose uptake. In males, insulin resistance progresses to a severe form of diabetes accompanied by pancreatic β cell failure. In contrast, female Akt2/PKBβ-deficient mice remain mildly hyperglycemic and hyperinsulinemic until at least one year of age. Thus, Akt2/PKBβ-deficient mice exhibit growth deficiency similar to that reported previously for mice lacking Akt1/PKBα, indicating that both Akt2/PKBβ and Akt1/PKBα participate in the regulation of growth. The marked hyperglycemia and loss of pancreatic β cells and adipose tissue in Akt2/PKBβ-deficient mice suggest that Akt2/PKBβ plays critical roles in glucose metabolism and the development or maintenance of proper adipose tissue and islet mass for which other Akt/PKB isoforms are unable to fully compensate.This article was published online in advance of the print edition. The date of publication is available from the JCI website, http://www.jci.org.

The islet in non-insulin-dependent diabetes mellitus (NIDDM) is characterized by loss of ,B cells and large local deposits of amyloid derived from the 37-amino acid protein, islet amyloid polypeptide (IAPP Non-insulin-dependent diabetes mellitus (NIDDM) is characterized by (3-cell destruction and islet amyloid derived from islet amyloid polypeptide (IAPP) (1, 2). IAPP is a 37-amino acid protein that possesses amyloidogenic properties in species that spontaneously develop NIDDM (humans, monkeys, cats), but is non-amyloidogenic in mice that do not develop NIDDM (3, 4). Overexpression of human IAPP (h-IAPP), but not rat IAPP, in COS cells resulted in intracellular IAPP amyloidosis that was associated with cell death (5). Thus far, hemizygous transgenic mice for h-IAPP have not been reported to develop islet amyloid or diabetes mellitus spontaneously (6-8). Induction of marked insulin resistance in hemizygous mice transgenic for h-IAPP provokes intra-and extracellular IAPP amyloid formation, which is associated with 13-cell death and hyperglycemia (9).Based on these observations, we hypothesized that sufficiently increased rates of h-IAPP expression and synthesis results in intracellular IAPP amyloidosis and (3-cell death, which results in diabetes mellitus (10). To examine this further, we developed a homozygous line of mice transgenic for h-IAPP, thereby doubling the h-IAPP gene copy number. We report here that these mice spontaneously developed diabetes mellitus due to (3-cell death, which was associated with abnormal intra-and extracellular aggregates of h-IAPP. We conclude that overproduction of IAPP in vulnerable species (humans, monkeys, cats) may cause (3-cell destruction and diabetes mellitus. MATERIALS AND METHODSPreparation of Transgenic Construct. The RIPHAT transgene (2395 bp) is described elsewhere (9). It consists of a PCR-generated cDNA encompassing the h-IAPP coding sequence (270 bp) under the regulation of the rat insulin II promoter/5' untranslated region and followed by intron I (728 bp) from the human albumin gene and the polyadenylylation site/RNA termination region (525 bp) from the human glyceraldehyde-3-phosphate gene (GAPDH). Use of the albumin intron I and GAPDH polyadenylylation site in transgenic constructs has been described (11).Generation of Transgenic Mice. Hemizygotes of the RHF line described in Couce et al. (9) were self-crossed to generate Fl offspring. Transgenic offspring were identified by PCR amplification of RIPHAT from tail DNA. Hemizygotes were distinguished from homozygotes by backcross breeding to nontransgenic FVB/N mice. Homozygotes were defined as those mice that generated more than 20 transgenic and no nontransgenic offspring. Four such homozygotes were used to establish the core RHF breeding colony.Northern Blot Analysis. Total RNA was prepared from whole pancreata of FVB/N, RHF hemizygote, and RHF homozygote males and females. Gels and blots were prepared and hybridized as described (9)

The role of glycogen-synthase kinase 3 (GSK3) in insulin-stimulated glucose transport and glycogen synthase activation was investigated in 3T3-L1 adipocytes. GSK3 protein was clearly present in adipocytes and was found to be more abundant than in muscle and liver cell lines. The selective GSK3 inhibitor, LiCl, stimulated glucose transport and glycogen synthase activity (20 and 65%, respectively, of the maximal (1 M) insulin response) and potentiated the responses to a submaximal concentration (1 nM) of insulin. LiCl-and insulin-stimulated glucose transport were abolished by the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor, wortmannin; however, LiCl stimulation of glycogen synthase was not. In contrast to the rapid stimulation of glucose transport by insulin, transport stimulated by LiCl increased gradually over 3-5 h reaching 40% of the maximal insulin-stimulated level. Both LiCl-and insulinstimulated glycogen synthase activity were maximal at 25 min. However, insulin-stimulated glycogen synthase activity returned to basal after 2 h, coincident with reactivation of GSK3. After a 2-h exposure to insulin, glycogen synthase was refractory to restimulation with insulin, indicating selective desensitization of this pathway. However, LiCl could partially stimulate glycogen synthase in desensitized cells. Furthermore, coincubation with LiCl during the 2 h exposure to insulin completely blocked desensitization of glycogen synthase activity. In summary, inhibition of GSK3 by LiCl: 1) stimulated glycogen synthase activity directly and independently of PI3-kinase, 2) stimulated glucose transport at a point upstream of PI3-kinase, 3) stimulated glycogen synthase activity in desensitized cells, and 4) prevented desensitization of glycogen synthase due to chronic insulin treatment. These data are consistent with GSK3 playing a central role in the regulation of glycogen synthase activity and a contributing factor in the regulation of glucose transport in 3T3-L1 adipocytes.Insulin stimulates glucose uptake, metabolism, and storage in liver, muscle, and adipose tissue. The binding of insulin to its receptor activates the intrinsic tyrosine kinase of the receptor leading to stimulation of phosphatidylinositol 3-kinase (PI3-kinase) 1 and other downstream kinases such as protein kinase B (PKB/Akt), p70 S6 kinase, and protein kinase C (1). One target of PKB is the Ser/Thr kinase, glycogen-synthase kinase 3 (GSK3) (2, 3). Two isoforms of GSK3, ␣ and ␤, are broadly expressed and play multiple regulatory roles in development and metabolism (4). GSK3 is constitutively active in cells and is transiently inhibited following insulin treatment (3). Inactivation of GSK3 by insulin requires PI3-kinase and appears to be mediated by PKB phosphorylation of GSK3 on Ser-21 (␣) or Ser-9 (␤) (3). GSK3 plays an important role in the regulation of glycogen synthesis via inhibitory phosphorylation of glycogen synthase. Indeed, overexpression of GSK3␤ leads to inhibition of basal and insulin-stimulated glycogen synthase activity (6, 7). Insulin ...

The serine/threonine kinase Akt/PKB plays key roles in the regulation of cell growth, survival, and metabolism. It remains unclear, however, whether the functions of individual Akt/PKB isoforms are distinct. To investigate the function of Akt2/PKBβ, mice lacking this isoform were generated. Both male and female Akt2/PKBβ-null mice exhibit mild growth deficiency and an age-dependent loss of adipose tissue or lipoatrophy, with all observed adipose depots dramatically reduced by 22 weeks of age. Akt2/PKBβ-deficient mice are insulin resistant with elevated plasma triglycerides. In addition, Akt2/PKBβ-deficient mice exhibit fed and fasting hyperglycemia, hyperinsulinemia, glucose intolerance, and impaired muscle glucose uptake. In males, insulin resistance progresses to a severe form of diabetes accompanied by pancreatic β cell failure. In contrast, female Akt2/PKBβ-deficient mice remain mildly hyperglycemic and hyperinsulinemic until at least one year of age. Thus, Akt2/PKBβ-deficient mice exhibit growth deficiency similar to that reported previously for mice lacking Akt1/PKBα, indicating that both Akt2/PKBβ and Akt1/PKBα participate in the regulation of growth. The marked hyperglycemia and loss of pancreatic β cells and adipose tissue in Akt2/PKBβ-deficient mice suggest that Akt2/PKBβ plays critical roles in glucose metabolism and the development or maintenance of proper adipose tissue and islet mass for which other Akt/PKB isoforms are unable to fully compensate.This article was published online in advance of the print edition. The date of publication is available from the JCI website, http://www.jci.org.

Amylin and calcitonin gene-related peptide (CGRP) inhibited insulin-stimulated 2-deoxyglucose uptake in L6 myocytes and isolated soleus muscle. Both peptides were maximally active at 10 pM in L6 cells and inhibited insulin action by 40-50%. In soleus muscle amylin and CGRP inhibited insulin-stimulated uptake by 65-85%. Amylin competed with 125I-CGRP for binding to L6 cells but with 100-fold lower potency than CGRP. Occupancy of the CGRP receptor in L6 cells is coupled to adenylyl cyclase. Amylin increased the cellular content of adenosine 3',5'-cyclic monophosphate (cAMP), but consistent with binding, amylin was 100-fold less potent than CGRP. In soleus muscle, 100 nM amylin, which maximally inhibited 2-deoxyglucose uptake, had no effect cAMP content, whereas CGRP at the same concentration increased cAMP by 50%. The effect of CGRP on cAMP levels was completely suppressed by the competitive antagonist, CGRP-(8-37). In contrast, the suppression of insulin-stimulated glycogen synthesis or 2-deoxyglucose uptake by amylin was unaffected by 1 microM CGRP-(8-37). Our results demonstrate that the inhibition of insulin-stimulated glucose transport by amylin is independent of cAMP and may be mediated by a unique receptor that is distinct from the adenylyl cyclase-coupled CGRP receptor.