Defining the role of MafA in islet beta cells

我们对胰岛生理学的许多知识都源于对啮齿动物的研究。然而，我们现在知道，标志着 啮齿动物和人类的胰岛在(例如)结构、激素分泌、 和胰岛细胞转录因子(TF)的表达，显示了假设啮齿动物 模型完全模仿人类的胰岛生理和疾病。这种差异的一个例子是在小岛β 细胞富含MAFA Tf，这是一种对出生后啮齿动物的这些细胞至关重要的蛋白质。因此，MAFA 在人的胰岛β细胞中，直到大约9岁才能检测到蛋白质，而这种转铁蛋白是首次检测到的 然后在啮齿动物的整个生命周期内产生胰岛素+细胞。我们认为人类 至少有两个出生后产生MAFA的年龄相关的β细胞群体能够维持 正常血糖：幼年β细胞(即~9岁)含少量MAFA(即MAFALow)和幼年β细胞(含MAFALow) 稳健的MAFA(MAFAHigh)。事实上，独立的研究已经确定了不同的分子和功能 这些人类细胞群体的特性。在这里，我们将研究MAFA对人β细胞和 假设这种转铁蛋白在调节成人胰岛素分泌方面起重要作用。我们在第一阶段的分析 AIM将使用从人类胚胎干细胞(HESC)产生的β样细胞和诱导的 多能干细胞(IPSC)(统称为人类多能干细胞，或hPSCs)。在这里，我们将 确定MAFA的敲除和过表达如何影响β细胞的成熟和功能，欣赏 它们极大地改善了葡萄糖刺激的胰岛素分泌特性，同时也增强了MAFA的表达 移植到免疫低下的NSG小鼠体内。此外，我们将调查一种致病因子是如何 显著提高蛋白质稳定性的MAFA变体(丝氨酸(S)-GT；苯丙氨酸(F))对人类的影响 β细胞活性。值得注意的是，MAFAS64F使受试者容易患上成人发病的糖尿病或胰岛素瘤病(即 非综合征型产生胰岛素的β细胞肿瘤)，性别歧视。我们生成了一个小鼠模型 在内源性Mafa基因中含有这种突变，我们的结果显示男性和 改善了女性的葡萄糖清除，与人类受试者的研究结果相似。值得注意的是， 雄性小鼠与细胞过早衰老和衰老有关。最近，独立报道称 病理性衰老的β细胞群与1型糖尿病和2型糖尿病的胰岛功能障碍有关。我们的 第二个目标的实验将确定MAFAS64F在人类中的分子和功能后果 β细胞。我们对人类胰岛细胞的总体关注被认为是创新的，以及人类 干细胞来源的β样细胞和人类胰岛，以获得新颖的、与生理相关的机制见解。

Much of our knowledge of islet physiology stems from rodent studies. However, we now know that marked discrepancies exist between rodent and human islets in regard to (for example) architecture, hormone secretion, and islet cell transcription factor (TF) expression, demonstrating potential limitations in assuming that rodent models entirely mimic human islet physiology and disease. An example of such a discrepancy lies in the islet β cell enriched MAFA TF, a fundamentally important protein to these cells in postnatal rodents. Thus, the MAFA protein is barely detectable in human islet β cells until ~9 years of age, whereas this TF is first detected developmentally and then produced throughout the lifespan of rodent insulin+ cells. We propose that humans have at least two postnatal, age-dependent MAFA-producing β cell populations capable of maintaining euglycemia: juvenile β cells (i.e. <~9 years old) with little MAFA (i.e. MAFALow) and post-juvenile β cells with robust MAFA (MAFAHigh). In fact, independent studies have established distinct molecular and functional properties of these human cell populations. Here we will examine the impact of MAFA on human β cells and hypothesize that this TF plays an essential role in regulating insulin secretion in adults. Our analysis in the first aim will be conducted using the β-like cells produced from both human embryonic stem cells (hESC) and induced pluripotent stem cells (iPSC) (collectively termed human pluripotent stem cells, or hPSCs). Here we will determine how knockout and over-expression of MAFA influences β cell maturation and function, appreciating that their greatly improved glucose-stimulated insulin secretion properties parallel enhanced MAFA expression after transplantation into immunocompromised NSG mice. In addition, we will investigate how a pathogenic variant of MAFA (Serine (S) 64 -> Phenylalanine (F)) that prominently increases its protein stability affects human β cell activity. Notably, MAFAS64F predisposes subjects to either adult-onset diabetes or insulinomatosis (i.e. non-syndromic insulin-producing β cell tumors) in a gender-biased manner. We generated a mouse model harboring this mutation in the endogenous MafA gene, and our results show glucose intolerance in males and improved glucose clearance in females, mimicking the findings in human subjects. Significantly, dysfunction in male mice was associated with premature cellular aging and senescence. Recently, independent reports have linked pathologic, senescent β cell populations to type 1 diabetes and type 2 diabetes islet dysfunction. Our experimentation in the second aim will define the molecular and functional consequences of MAFAS64F in human β cells. Our overall focus on human islet cells is viewed as innovative, as well as the combined use of human stem cell derived β-like cells and human islets for obtaining novel, physiologically relevant mechanistic insights.