Increased intracellular calcium is required for spreading of rat islet beta-cells on extracellular matrix

Rat islet beta-cells spread in response to glucose when attached on the matrix produced by a rat bladder carcinoma cell line (804G). Furthermore, in a mixed population of cells, it has been observed previously that spread cells secrete more insulin acutely in response to glucose, compared with cells that remain rounded. These results suggest bi-directional signaling between the islet beta-cell and the extracellular matrix. In the present study, the role of increased intracellular free Ca2+ concentration [Ca2+]i as an intracellular step linking glucose stimulation and beta-cell spreading (inside-out signaling) was investigated. Purified rat beta-cells were attached to this matrix and incubated under various conditions known to affect [Ca2+]i. The effect of glucose on beta-cell spreading was mimicked by 25 mmol/l KCl (which induces calcium influx) and inhibited by diazoxide (which impairs depolarization and calcium entry) and by the L-type Ca2+ channel blocker SR-7037. When a 24-h incubation at 16.7 glucose was followed by 24 h at 2.8 mmol/l, beta-cells that had first spread regained a round phenotype. In the presence of thapsigargin, spreading progressed throughout the experiment, suggesting that capture of calcium by the endoplasmic reticulum is involved in the reversibility of spreading previously induced by glucose. Spreading was still observed in degranulated beta-cells and in botulinum neurotoxin E-expressing beta-cells when exocytosis was prevented. In summary, the results indicate that increased [Ca2+]i is required for the glucose-induced spreading of beta-cells on 804G matrix and that it is not a consequence of exocytotic processes that follow elevation of [Ca2+]i.     

Evaluation of insulin secretion of isolated rat islets cultured in extracellular matrix

Islet isolation involves enzymatic digestion of the interstitial matrix and mechanical disruption of the tissue. It is possible that a fundamental change of islet biology resulting from the loss of critical factors required for islet function or survival will occur. Extracellular matrix (ECM) is one of the most important components of the islet microenvironment. Reconstruction of the cell-matrix relationship seems to be effective for improving the loss of differentiated islet structure and function. The purpose of this study was to characterize and compare the effects of collagen gel mixture or Matrigel on beta-cell function and islet cell survival. After isolation by the collagenase digestion technique, rat islets were divided and cultured with various types of collagen gel mixture. They were assessed for their glucose-stimulated insulin secretion and cell viability. Glucose-induced insulin secretion of islets cultured with collagen type I gel or a mixture of collagen type I and IV was improved after 11 days in culture. In conclusion, a type of gel composed of collagen type I and/or type IV as an islet microenvironment is sufficient to maintain glucose responsiveness and may be useful for islet transplantation.     

5-氟尿嘧啶对胰岛β细胞胰岛素分泌及凋亡的影响

目的 观察5-氟尿嘧啶(5-Fu)对NIT-1细胞株胰岛素分泌、凋亡、超微结构及增殖的影响,探讨其诱发糖尿病的机制.方法 以不同浓度5-Fu处理小鼠胰岛细胞株NIT-1细胞,分别以放射免疫分析法、AnnexinV/PI双染色流式细胞术检测细胞胰岛素释放量及细胞凋亡率的变化;以透射电镜观察细胞超微结构的变化;以噻唑蓝(MTT)比色法检测细胞增殖.结果 在5-Fu(5.0～40.0 mg/L)作用下,NIT-1细胞高浓度葡萄糖刺激下(16.7 mmol/L)的胰岛素释放量明显降低,呈剂量依赖性(P＜0.01).5.0、10.0、20.0和40.0 mg/L浓度的抑制率分别为9.2%、30.4%、50.7%和69.4%.在10.0～40.0mg/L浓度范围内凋亡率明显增高(P＜0.05);透射电镜观察显示,凋亡早期线粒体肿胀、内质网扩张,后期则出现染色体边集等典型的凋亡征象.同时,在5-Fu(5.0～160.0mg/L)作用下,细胞增殖明显降低,其作用呈浓度依赖性(P＜0.01)和时间依赖性(P＜0.05).结论 5-Fu可抑制在高浓度葡萄糖刺激下的胰岛β细胞分泌胰岛素,由此所引起的胰岛素分泌下降可能与诱导细胞凋亡及抑制细胞增殖而导致的β细胞超微结构改变及数量减少有关.     

Effects of high glucose on insulin secretion by isolated rat islets and purified beta-cells and possible role of glycosylation

We investigated the effect of 24 h of exposure to various glucose concentrations on insulin secretion by isolated rat pancreatic islets and purified rat beta-cells. Compared with islets cultured with standard medium (5.5 mM glucose), islets cultured with 16.7 mM glucose showed a higher basal insulin release (means +/- SE, 3.0 +/- 0.5 vs. 0.7 +/- 0.2%, n = 8, P less than .005) and reduced glucose-stimulated insulin secretion (2.4 +/- 0.3 vs. 5.8 +/- 0.4%, n = 8, P less than .005). Similar results were also obtained with purified beta-cells. The effect of high glucose was time dependent (present after 12 h, maximal after 24 h) and reversible: when islets cultured with high glucose were transferred to standard medium, normal responsiveness to glucose was restored within 8 h and normal basal release within 24 h. Mannitol, 3-O-methylglucose, and 2-deoxyglucose were not able to mimic the effects of glucose. Islets or purified beta-cells cultured in the presence of high glucose had a normal response when stimulated with glyburide, dibutyryl cyclic AMP, and isobutylmethylxanthine. Tunicamycin, an inhibitor of N-terminal glycosylation, prevented glucose-induced desensitization when added during 24 h of islet culture with 16.7 mM glucose. Swainsonine, another agent that influences glycosylation, had a similar effect. Our study indicates 1) that 24 h of exposure to high glucose induces a specific and reversible impairment of insulin secretion in response to glucose, 2) that this is a direct effect of glucose on beta-cells, and 3) that islet glucose metabolism and glycosylation processes may play a critical role in determining glucose desensitization.     

细胞外基质对大鼠卵巢颗粒细胞分泌激素和合成蛋白质功能的影响

为了探讨细胞外基质对卵巢颗粒细胞功能的影响。从未成熟ＳＤ大鼠分离出卵巢颗粒细胞，以３×１０５细胞／孔的密度，培养在铺有不同浓度的层粘连蛋白（ＬＮ）或纤粘连蛋白（ＦＮ）的培养板上，观察细胞贴壁情况。４８小时后加入卵泡刺激素和睾酮，再培养４８小时，收集培养液，测定雌二醇和孕酮。另外在双池培养系统中，在铺有和未铺ｍａｔｒｉｇｅｌ的上池中分别加入不同浓度的颗粒细胞，利用３５硫标记蛋氨酸掺入法观察ｍａｔｒｉｇｅｌ对颗粒细胞合成蛋白的影响，并利用免疫印迹法鉴定颗粒细胞膜蛋白中ＬＮ结合蛋白的分子量。结果显示，４μｇＬＮ即可使颗粒细胞在４小时内贴壁及展开，雌二醇和孕酮的产量增加。ＦＮ却无显著影响。从ｍａｔｒｉｇｅｌ双池培养系统中取上池培养液，测定放射活性，铺有ｍａｔｒｉｇｅｌ组显著高于对照组。放射自显影图象显示ｍａｔｒｉｇｅｌ显著刺激颗粒细胞合成功能。免疫印迹结果显示颗粒细胞膜蛋白存在着ＬＮ的多结合位点。本实验证实：ＬＮ对卵巢颗粒细胞的附着、伸展、分泌和合成功能具有促进作用     

转化生长因子β1反义RNA对肾小球系膜细胞基质合成及分泌的影响

目的：观察转化生长因子beta1(TGF-β1）反义RNA对系膜细胞基质合成的影响。方法：构建含TGF－β1反义RNA的重组腺病毒，将重组腺病毒转染系膜细胞，用Northern blot检测转染系膜细胞TGF－β1及ColIV mRNA的含量，用免疫组化半定量分析转染的系膜细胞中TGF－β1，纤连蛋白（FN）及胶原（Col)IV蛋白水平，并与无转染的系膜细胞对照组比较其表达的变化。结果：构建了含TGF－β1反义RNA的重组腺病，重组反义TGF－β1腺病毒转染系膜细胞后，与对照组相比，在第24hTGF-β1及Col IV的mRNA无明显抑制，在48hTGF－β1及Col IV mRNA抑制率分别为22．5％，18．2％，72h TGF-β1及Col IV mRNA抑制率分别为29．5％，27．3％，免疫组织化学半定时结果显示；与对照组相比，在48h始转系膜细胞TGF－β1，FN及ColIV蛋白含量开始下降，48h TGF-β1，FN及Col IV蛋白抑制率分别为16．5％，18．2％及14．6％，72h TGF－β1，FN及ColⅣ蛋白抑制率分别为23．5％，27．3％，26．8％。结论：重组反义TGF－β1可抑制系膜细胞合成细胞外基质，在肾小球肾炎及肾小球硬化的研究及治疗中有潜在的应用价值。     

Effect of the insulin mimetic L-783,281 on intracellular Ca2+ and insulin secretion from pancreatic beta-cells

L-783,281, an antidiabetic fungal metabolite that has previously been shown to activate insulin signaling in CHO cells, was tested for its effect on intracellular Ca(2+) ([Ca(2+)](i)) and insulin secretion in single mouse pancreatic beta-cells. Application of 10 micromol/l L-783,281 for 40 s to isolated beta-cells in the presence of 3 mmol/l glucose increased [Ca(2+)](i) to 178 +/- 10% of basal levels (n = 18) as measured by fluo-4 fluorescence. L-767,827, an inactive structural analog of the insulin mimetic, had no effect on beta-cell [Ca(2+)](i). The L-783,281-evoked [Ca(2+)](i) increase was reduced by 82 +/- 4% (n = 6, P < 0.001) in cells incubated with 1 micromol/l of the SERCA (sarco/endoplasmic reticulum calcium ATPase) pump inhibitor thapsigargin and reduced by 33 +/- 6% (n = 6, P < 0.05) in cells incubated with 20 micromol/l of the L-type Ca(2+)-channel blocker nifedipine. L-783,281-stimulated [Ca(2+)](i) increases were reduced to 31 +/- 3% (n = 9, P < 0.05) and 48 +/- 10% (n = 6, P < 0.05) of control values by the phosphatidylinositol 3-kinase (PI3-K) inhibitors LY294002 (25 micromol/l) and wortmannin (100 nmol/l), respectively. In beta-cells from IRS-1-/- mice, 10 micromol/l L-783,281 had no significant effect on [Ca(2+)](i) (n = 5). L-783,281 also resulted in insulin secretion at single beta-cells. Application of 10 micromol/l L-783,281 for 40 s resulted in 12.2 +/- 2.1 (n = 14) exocytotic events as measured by amperometry, whereas the inactive structural analog had no stimulatory effect on secretion. Virtually no secretion was evoked by L-783,281 in IRS-1-/- beta-cells. LY294002 (25 micromol/l) significantly reduced the effect of the insulin mimetic on beta-cell exocytosis. It is concluded that L-783,281 evokes [Ca(2+)](i) increases and exocytosis in beta-cells via an IRS-1/PI3-K-dependent pathway and that the [Ca(2+)](i) increase involves release of Ca(2+) from intracellular stores.     

A Kir6.2 mutation causing neonatal diabetes impairs electrical activity and insulin secretion from INS-1 beta-cells

ATP-sensitive K(+) channels (K(ATP) channels) couple beta-cell metabolism to electrical activity and thereby play an essential role in the control of insulin secretion. Gain-of-function mutations in Kir6.2 (KCNJ11), the pore-forming subunit of this channel, cause neonatal diabetes. We investigated the effect of the most common neonatal diabetes mutation (R201H) on beta-cell electrical activity and insulin secretion by stable transfection in the INS-1 cell line. Expression was regulated by placing the gene under the control of a tetracycline promoter. Transfection with wild-type Kir6.2 had no effect on the ATP sensitivity of the K(ATP) channel, whole-cell K(ATP) current magnitude, or insulin secretion. However, induction of Kir6.2-R201H expression strongly reduced K(ATP) channel ATP sensitivity (the half-maximal inhibitory concentration increased from approximately 20 mumol/l to approximately 2 mmol/l), and the metabolic substrate methyl succinate failed to close K(ATP) channels or stimulate electrical activity and insulin secretion. Thus, these results directly demonstrate that Kir6.2 mutations prevent electrical activity and insulin release from INS-1 cells by increasing the K(ATP) current and hyperpolarizing the beta-cell membrane. This is consistent with the ability of the R201H mutation to cause neonatal diabetes in patients. The relationship between K(ATP) current and the membrane potential reveals that very small changes in current amplitude are sufficient to prevent hormone secretion.     

Immunohistochemical colocalization of GABA and insulin in beta-cells of rat islet

gamma-Aminobutyric acid (GABA) is found in high concentrations in the pancreatic islet. In addition, enzymes regulating the level of GABA (L-glutamate decarboxylase and GABA-alpha-ketoglutarate transaminase) have been immunohistochemically localized in the medullary cells of the islet. In this study, an immunofluorescence and elution/restaining protocol is used to determine the distribution of GABA and either insulin, glucagon, or somatostatin in a tissue section. GABA was not detected within the islet alpha- or delta-cells but was determined to be localized within the insulin-containing beta-cells.     

Overexpression of alpha1beta1 integrin directly affects rat mesangial cell behavior

BACKGROUND: Glomerular mesangial cell (MC) proliferation, hypertrophy, and abnormal matrix remodeling characterized by increased expression of fibronectin, laminin and collagen type IV, and neoexpression of collagen I and III are the main biological features of progressive glomerulonephritis (GN). Especially, persistent pathological matrix remodeling may lead to glomerular scar formation (glomerular scarring). We reported recently that alpha1beta1 integrin, a major collagen receptor for MCs, may be a potential adhesion molecule for MC-mediated pathological collagen matrix remodeling in GN. METHODS: To address further the direct role of alpha1beta1 integrin in MC behavior, such as cell growth and matrix remodeling, alpha1beta1 integrin was overexpressed in MCs by transfecting an expression vector containing a full-length rat alpha1 integrin cDNA. Flow cytometry and immunoprecipitation analysis were applied for selection of transfectants with a stable expression of the alpha1 integrin subunit. The effect of alpha1beta1 integrin overexpression on MC biology was examined with a 3H-thymidine incorporation assay, flow cytometric analysis of cell size and DNA content, Western blot analysis of a cyclin-dependent-kinase inhibitor, p27Kip1, alpha-smooth muscle actin expression, and a collagen gel contraction assay. RESULTS: The alpha1 transfectants displayed a dramatic inhibition of 3H-thymidine incorporation as compared with the mock transfectants. Increased expression of the alpha1 subunit inversely correlated with cell cycle progression and paralleled the expression of p27Kip1 and alpha-smooth muscle actin, as well as the cell size in MCs. In addition, the alpha1-transfectants were able to enhance collagen matrix reorganization effectively. CONCLUSION: These results indicate that MC-alpha1beta1 integrin expression is a critical determinant of MC phenotypes, including cell growth, cell size, and collagen matrix remodeling ability, and thereby contributes to scar matrix remodeling (sclerosis) in GN.     

Decreased expression of t-SNARE, syntaxin 1, and SNAP-25 in pancreatic beta-cells is involved in impaired insulin secretion from diabetic GK rat islets: restoration of decreased t-SNARE proteins improves impaired insulin secretion

The physiological role of soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) proteins in insulin exocytosis has been reported in pancreatic beta-cells. To determine whether the beta-cells of GK rats, a nonobese rodent model of type 2 diabetes, exhibit abnormalities in their SNARE proteins, we studied the expression and function of target (t)-SNAREs, syntaxin 1A, and synaptosomal-associated protein of 25 kDa (SNAP-25) in GK rat islets. Although insulin release and insulin content of islets isolated from 12-week-old GK rats were reduced, the proinsulin biosynthetic rate was about twofold higher than that in control rat islets, and no change in the preproinsulin mRNA level was observed. Pulse-chase experiments suggested the increased degradation of insulin in GK rat islets. Immunoblot analysis revealed that protein levels of syntaxin 1A and SNAP-25 in GK rat islets decreased to approximately 60% of the levels in control rat islets. We then examined whether the restoration of the decreased expression of t-SNAREs to the normal level in GK rat islets affected insulin secretion. Restoration was achieved by the overexpression of syntaxin 1A and SNAP-25 via the recombinant adenovirus-mediated gene transduction system, which recovered levels of these proteins to almost control levels. Glucose-stimulated insulin release from AdexlCA syntaxin 1A and Adex1CA SNAP-25-infected GK rat islets increased up to approximately 135 and 200%, respectively, of those from uninfected GK rat islets, although no difference in basal (2.2 mmol/l glucose) insulin release was evident between them. We conclude that decreased expression of t-SNAREs in GK rat islets is in part the defect responsible for impaired insulin secretion.     

Leucine regulation of glucokinase and ATP synthase sensitizes glucose-induced insulin secretion in pancreatic beta-cells

We have recently shown that leucine culture upregulates ATP synthase beta-subunit (ATPSbeta) and increases ATP level, cytosolic Ca(2+), and glucose-induced insulin secretion in rat islets. The aim is to test whether glucokinase expression is also affected in rat islets and its role in glucose sensitization during leucine culture. Leucine culture increased glucose-induced NAD(P)H level at 1 and 2 days but not at 1 week. The half-maximal effective concentration of the glucose response curve for NAD(P)H was left-shifted from 5-7 to 2-3 mmol/l. The effect was dose dependent and rapamycin insensitive. Leucine culture did not affect glyceraldehyde effects on NAD(P)H. Leucine pretreatment for 30 min had no effects on NAD(P)H levels. Leucine culture for 2 days also increased glucose-induced cytosolic Ca(2+) elevation, ATP level, and insulin secretion. Leucine increase of glucokinase mRNA levels occurred as early as day 1 and lasted through 1 week. That of ATPSbeta did not occur until day 2 and lasted through 1 week. Leucine effects on both mRNAs were dose dependent. The upregulation of both genes was confirmed by Western blotting. Leucine culture also increased glucose-induced insulin secretion, ATP level, glucokinase, and ATPSbeta levels of type 2 diabetic human islets. In conclusion, leucine culture upregulates glucokinase, which increases NAD(P)H level, and ATPSbeta, which increases oxidation of NADH and production of ATP. The combined upregulation of both genes increases glucose-induced cytosolic Ca(2+) and insulin secretion.     

Sustained pulsatile insulin secretion from adenomatous human beta-cells. Synchronous cycling of insulin, C-peptide, and proinsulin

The endocrine pancreas secretes insulin in a pulsatile fashion. This rhythm is generated at a site within the pancreas, although its precise location has not been determined. With an in vitro system, we tested the possibility that beta-cells might generate spontaneous pulsatile insulin secretion in the absence of any external influence. Human insulinoma tissue from five patients was perifused for 7-10 h with RPMI-1640 medium and constant concentrations of glucose (5.5 mM). Insulin, C-peptide, and proinsulin were measured in the effluent collected at 3.3-min intervals. All three peptides demonstrated pulsatility of secretion in a similar, synchronous fashion that was sustained throughout each study. The Clifton cycle detection program demonstrated cycling in all five tumors, with an average period for all tumors of 28, 29, and 26 min for insulin, C-peptide, and proinsulin, respectively. Spectral analysis confirmed the regularity and consistency of the hormonal secretory patterns. Mean hormone concentrations secreted by different tumors varied, but insulin and C-peptide were secreted in a nearly 1:1 ratio. This study demonstrates 1) that beta-cells are able to generate spontaneous pulsatile insulin secretory activity, which is independent of innervation or the presence of other islet cells, and 2) proinsulin secretion from the beta-cell also has an inherent pulsatility. The synchrony observed in the cycles of proinsulin and its peptide products confirms their common secretory pathway in the beta-cell. We conclude that the beta-cell may be the originator of insulin cycling.     

羧甲基壳聚糖对体外培养大鼠椎间盘髓核细胞增殖、细胞周期及细胞外基质分泌的影响

目的 观察羧甲基壳聚糖(CMCS)对体外培养大鼠椎间盘髓核细胞细胞周期进程、细胞周期蛋白表达及分泌细胞外基质的影响.方法 使用酶消化法提取大鼠椎间盘髓核细胞并进行体外培养,Ⅱ型胶原免疫组织化学鉴定髓核细胞.将髓核细胞分为:对照组、不同浓度CMCS处理组(100、200、500 mg/L),作用24 h后通过碘化丙锭(PI)染色流式细胞技术检测细胞周期进程.通过荧光定量聚合酶链反应(FQ-PCR)及Western blot法检测不同浓度(100、200、500 mg/L) CMCS对髓核细胞内增殖相关蛋白增殖细胞核抗原(PCNA)及细胞周期蛋白(Cyclin)D表达的影响,并通过FQ-PCR法检测不同浓度(100、200、500 mg/L) CMCS对髓核细胞分泌细胞外基质Ⅱ型胶原的影响.结果 培养的细胞经Ⅱ型胶原免疫组织化学染色鉴定显示其表达阳性,表明为髓核细胞;通过FQ-PCR及Western blot检测增殖相关蛋白PCNA可见通过100、200、500 mg/L CMCS作用后髓核细胞表达PCNA与对照组比较分别增加12.3％、18.2％、54.2％与25.1％、52.7％、66.9％ (P ＜0.05);经流式细胞仪检测发现经100、200、500 mg/L CMCS处理的髓核细胞处于S期细胞比例是对照组的1.58、2.34与2.61倍(P＜0.05);Cyclin D表达分别是对照组的1.26、2.15、2.64倍与1.53、1.69、1.83倍(P ＜0.05);FQ-PCR及Western blot检测结果表明100、200、500 mg/L CMCS分别促进髓核细胞分泌Ⅱ型胶原表达是对照组的1.67、2.24、2.79倍与1.48、1.65、1.77倍(P＜0.05).结论 CMCS对体外培养髓核细胞增殖相关蛋白PCNA表达具有促进作用,可促进细胞周期进程及细胞周期蛋白表达,对髓核细胞分泌细胞外基质具有促进作用.     

Cytoplasmic retinoid-binding proteins and retinoid effects on insulin release in RINm5F beta-cells

Vitamin A (retinol) is required for insulin secretion, and retinoic acid substitutes for retinol in this function. To determine if retinol acts at the beta-cell level, we assayed beta-cells of the rat insulinoma (RINm5F) line for cytosolic retinol- and retinoic acid-binding proteins (CRBP and CRABP) by radioimmunoassay (RIA) and [3H]retinol and [3H]retinoic acid binding to cytosol extracts. Furthermore, we tested whether insulin release from cells was affected by addition of retinol or retinoic acid to culture medium. RINm5F cells were grown to near confluence before assay of CRBP and CRABP. Scatchard analysis showed the Kd for retinol to be approximately 6 nM at a level of 4.5 pmol/mg protein or 300,000 sites/cell. Sucrose density-gradient assay showed single discrete peaks migrating at 2S for both retinol and retinoic acid. RIA of whole-cell extracts showed CRBP and CRABP levels of 5.27 +/- 0.41 and 2.95 +/- 0.75 pmol/mg protein, respectively. Retinol (1.75 microM) and retinoic acid (0.175 and 1.75 microM) increased KCl-induced insulin release. Considered together, the presence of CRBP and CRABP in a beta-cell line and the increase in KCl-induced insulin release by retinol and retinoic acid are consistent with the idea that retinol has a functional role in insulin secretion and suggest a potential mechanism of action at the beta-cell level similar to that observed in other retinoid-responsive cells.     

Overexpression of PACAP in transgenic mouse pancreatic beta-cells enhances insulin secretion and ameliorates streptozotocin-induced diabetes

Pituitary adenylate cyclase-activating polypeptide (PACAP), a member of the vasoactive intestinal peptide/secretin/glucagon family, stimulates insulin secretion from islets in a glucose-dependent manner at femtomolar concentrations. To assess PACAP's pancreatic function in vivo, we generated transgenic mice overexpressing PACAP in the pancreas under the control of human insulin promoter. Northern blot and immunohistochemical analyses showed that PACAP is overexpressed in pancreatic islets, specifically in transgenic mice. Plasma glucose and glucagon levels during a glucose tolerance test were not different between PACAP transgenic mice and nontransgenic littermates. However, plasma insulin levels in transgenic mice were higher after glucose loading. Also, increases of streptozotocin-induced plasma glucose were attenuated in transgenic compared with nontransgenic mice. Notably, an increase in 5-bromo-2-deoxyuridine-positive beta-cells in the streptozotocin-treated transgenic mice was observed but without differences in the staining patterns by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. Morphometric analysis revealed that total islet mass tends to increase in 12-month-old transgenic mice but showed no difference between 12-week-old transgenic and nontransgenic littermates. This is the first time that PACAP has been observed to play an important role in the proliferation of beta-cells.     

Effect of age and diet on insulin secretion and insulin action in the rat

The effects of aging on various aspects of insulin secretion and action were studied in male Sprague-Dawley rats, maintained from 1 1/2 to 12 mo of age on conventional rat chow, sucrose-rich, or calorie-restricted diets. In chow-fed rats, islet volume increased as the animals grew from 1 1/2 to 12 mo of age, but glucose-stimulated insulin secretion (per volume islet) declined over the same interval. In addition, in vivo insulin-stimulated glucose utilization fell in these rats. However, the plasma insulin response to an oral glucose challenge was sufficient to prevent frank decompensation of glucose tolerance (presumably due to an increase in total pancreatic endocrine cell mass). All these changes, with the exception of the decline in glucose-stimulated insulin secretion per volume islet, were accentuated by feeding sucrose. Thus, 12-mo-old sucrose-fed rats had larger islets and higher plasma insulin levels in response to an oral glucose challenge, and the rats were more insulin-resistant than chow-fed rats. However, glucose-stimulated insulin release per volume islet was similar in 12-mo-old chow-fed and sucrose-fed rats. In contrast, calorie restriction led to an amelioration in all but one of the age-related changes, i.e., islets from calorie-restricted rats were comparable in size to those of 2-mo-old rats, the animals had lower plasma insulin levels in response to an oral glucose load, and they were less insulin resistant than the other two groups of 12-mo-old rats. On the other hand, glucose-stimulated insulin secretion per volume islet was similar to that of the other 12-mo-old rats. These results suggest that aging leads to marked changes in both insulin secretion and insulin action. The decline in glucose-stimulated insulin secretion per unit endocrine pancreas appears to be an inevitable consequence of the aging process. In contrast, the age-related changes in islet size, insulin response to a glucose load, and in vivo insulin-stimulated glucose uptake are extremely responsive to variations in amount and kind of calories. DIABETES 32:175-180, February 1983.