Pregnancy-Specific Mechanisms Regulating Beta-Cell Proliferation and Mass

妊娠期糖尿病（GDM），或妊娠期首次出现的高血糖症，会影响妊娠结局，并对母亲及其后代造成长期健康风险。与所有类型的糖尿病一样，功能性胰腺β细胞的相对不足是导致GDM的基本缺陷。通常，β细胞通过扩大β细胞群来适应妊娠的代谢挑战。这种扩大的质量在产后期间消退。因此，妊娠是一种发生在完全发育的成年人中的独特生理状况，需要β细胞群的快速动态变化。不幸的是，对正常妊娠β细胞适应的机制和GDM的潜在缺陷知之甚少。我们的长期目标是了解妊娠期间调节β细胞增殖和质量的机制，以便利用这些知识在所有类型的糖尿病中进行β细胞的治疗扩展。基于我们建立β细胞中催乳素受体（PRLR）信号传导丢失导致GDM的工作，我们最近鉴定了新的PRLR差异表达基因（PRLR-DEG）和PRLR-DEG表达的关键转录调节因子。这项资助的目的是精确定义PRLR如何在妊娠和产后期间调节β细胞基因表达。我们提出了一个中心假设，即PRLR信号传导协调了妊娠期间β细胞群扩增的预期转录程序和产后消退期间足够β细胞群的存活。我们将通过以下具体目的来验证这一假设：（1）阐明妊娠期间β细胞内PRLR-DEG的转录调控机制。为此，我们将使用ChIP-seq和ATAC-seq来研究PRLR-DEG在妊娠期间或对催乳素刺激的反应中如何在小鼠和人类胰岛中调节。在目的（2）中，我们将使用单细胞RNA测序、谱系追踪和共定位研究来确定妊娠期间PRLR信号依赖性和非依赖性β细胞亚群。对于目的（3），我们将通过妊娠期间增殖的β细胞的脉冲追踪标记和谱系追踪来确定产后早期β细胞质量消退期间β细胞存活的机制，以及检查产后期间PRLR的可诱导损失如何特异性地影响β细胞质量。总之，这些研究的结果将揭示PRLR下游的转录机制，并阐明妊娠期增殖的独特方面（目的1），在怀孕期间在空间和时间上定义β细胞亚群（目的2），并建立PRLR信号传导在产后β细胞调节中的新作用（目的3）。我们的研究意义重大，因为这些发现将阐明妊娠β细胞适应的机制，并扩大我们对PRLR激活如何调节转录的理解。在基础水平上，这些研究将扩大我们对β细胞质量动态变化调节机制的理解，这可能会确定新的策略，以促进β细胞扩增用于治疗目的。

Gestational diabetes (GDM), or hyperglycemia that first manifests during pregnancy, worsens pregnancy outcomes and long-term health risks for both a mother and her offspring. As with all types of diabetes, a relative insufficiency of functional pancreatic β-cells is a fundamental defect contributing to GDM. Normally, β-cells adapt to the metabolic challenges of pregnancy by expanding β-cell mass. This expanded mass regresses in the postpartum period. Thus, pregnancy is a unique physiologic condition that occurs in a fully-developed adult and requires rapid, dynamic changes in β-cell mass. Unfortunately, the mechanisms of normal gestational β-cell adaptation and the defects underlying GDM are poorly understood. Our long-term goal is to understand the mechanisms regulating β-cell proliferation and mass during pregnancy, in order to leverage that knowledge for therapeutic expansion of β-cells in all types of diabetes. Building on our work establishing that loss of prolactin receptor (PRLR) signaling in β-cells results in GDM, we recently identified novel PRLR differentially expressed genes (PRLR-DEGs) and key transcriptional regulators of PRLR-DEG expression. The objective of this grant is to precisely define how PRLR regulates β-cell gene expression during pregnancy and the postpartum period. We propose the central hypothesis that PRLR signaling orchestrates an anticipatory transcriptional program of β-cell mass expansion during gestation and survival of adequate β-cell mass during postpartum regression. We will test this hypothesis with the following Specific Aims: (1) elucidate transcriptional mechanisms regulating PRLR-DEGs within β-cells during pregnancy. To do so, we will use ChIP-seq and ATAC-seq to examine how PRLR-DEGs are regulated in mouse and human islets during pregnancy or in response to prolactin stimulation. In Aim (2) we will define PRLR signaling-dependent and -independent β-cell subpopulations during pregnancy using single-cell RNA sequencing, lineage tracing and colocalization studies. For Aim (3) we will identify mechanisms of β-cell survival during β-cell mass regression in the early postpartum period through pulse-chase labeling and lineage tracing of β-cells that proliferated during pregnancy, as well as examine how inducible loss of PRLR specifically within the postpartum period affects β-cell mass. Together, results from these studies will reveal transcriptional mechanisms downstream of PRLR and illuminate unique aspects of gestational proliferation (Aim 1), define β-cell subpopulations spatially and temporally across pregnancy (Aim 2), and establish a new role for PRLR signaling in regulation of β-cells postpartum (Aim 3). Our research is significant because these findings would clarify mechanisms of gestational β-cell adaptation and expand our understanding of how PRLR activation regulates transcription. At a fundamental level, these studies will expand our understanding of the mechanisms regulating dynamic changes in β-cell mass, which may identify novel strategies to promote β-cell expansion for therapeutic purposes.