Petrik J, Arany E, McDonald T J, Hill D J
Lawson Research Institute, St. Joseph's Health Center, University of Western Ontario, London, Canada.
Endocrinology. 1998 Jun;139(6):2994-3004. doi: 10.1210/endo.139.6.6042.
Islet cell ontogeny will define adult beta-cell mass and will consist of a balance of islet cell birth and death. We have investigated the ontogeny of factors that may be related to developmental apoptosis in the islets, insulin-like growth factor II (IGF-II) and inducible nitric oxide synthase (iNOS), in pancreata of young Wistar rats. Pancreata were collected from rats of 21 days gestation to 29 days postnatal age. In situ hybridization and immunohistochemistry showed that IGF-II was expressed and present in fetal and neonatal islet cells, but declined rapidly 2 weeks after birth. Little IGF-I was associated with fetal or postnatal islets. Apoptosis in islet cells was visualized by molecular histochemistry for DNA breakage in tissue sections. Apoptosis was low in the fetus, but increased in incidence postnatally so that 13% of islet cells were undergoing apoptosis on postnatal day 14, with the incidence declining thereafter. Immunohistochemistry for iNOS showed that it was expressed within beta-cells and was most abundant 12 days after birth. When islets were isolated from rat pancreata 20-22 days after birth, islet cell viability, DNA synthetic rate, and insulin release were reduced after incubation with interleukin-1beta, tumor necrosis factor, or interferon-gamma. An increased rate of islet cell survival was found after simultaneous incubation with IGF-I or -II. Cytokine-mediated islet cell death involved the induction of apoptosis. Islets isolated from neonatal rats were not killed after exposure to these cytokines at the same concentrations, but cytokine-induced cell death was seen when neonatal islets were incubated with a neutralizing antibody against IGF-II. These experiments show that a peak of islet cell apoptosis that is maximal in the rat pancreas 14 days after birth is temporally associated with a fall in the islet cell expression of IGF-II. IGF-II was shown to function as an islet survival factor in vitro. The induction of islet cell apoptosis in vivo may involve an increased expression of iNOS within beta-cells.
胰岛细胞的个体发生决定了成年期β细胞的数量，它由胰岛细胞的生成与死亡之间的平衡所构成。我们研究了与胰岛发育性凋亡相关的因子——胰岛素样生长因子II（IGF-II）和诱导型一氧化氮合酶（iNOS）在幼年Wistar大鼠胰腺中的个体发生情况。从妊娠21天至出生后29天的大鼠收集胰腺。原位杂交和免疫组化显示，IGF-II在胎儿及新生胰岛细胞中表达并存在，但在出生后2周迅速下降。很少有IGF-I与胎儿或出生后的胰岛相关。通过分子组织化学检测组织切片中的DNA断裂来观察胰岛细胞凋亡。胎儿期凋亡率较低，但出生后发生率增加，以至于出生后第14天有13%的胰岛细胞正在发生凋亡，此后发生率下降。iNOS的免疫组化显示其在β细胞内表达，且在出生后12天最为丰富。当在出生后20 - 22天从大鼠胰腺分离胰岛后，用白细胞介素-1β、肿瘤坏死因子或干扰素-γ孵育后，胰岛细胞活力、DNA合成率及胰岛素释放均降低。同时用IGF-I或 -II孵育后，发现胰岛细胞存活率增加。细胞因子介导的胰岛细胞死亡涉及凋亡的诱导。从新生大鼠分离的胰岛在暴露于相同浓度的这些细胞因子后未被杀死，但当新生胰岛与抗IGF-II的中和抗体一起孵育时，可观察到细胞因子诱导的细胞死亡。这些实验表明，出生后14天大鼠胰腺中胰岛细胞凋亡的峰值在时间上与IGF-II在胰岛细胞中的表达下降相关。IGF-II在体外被证明可作为胰岛存活因子。体内胰岛细胞凋亡的诱导可能涉及β细胞内iNOS表达的增加。
