Background & Aims Proprotein convertase 1/3 (PC1/3) deficiency, an autosomal-recessive disorder caused by rare mutations in the proprotein convertase subtilisin/kexin type 1 (PCSK1) gene, has been associated with obesity, severe malabsorptive diarrhea, and certain endocrine abnormalities. Common variants in PCSK1 also have been associated with obesity in heterozygotes in several population-based studies. PC1/3 is an endoprotease that processes many prohormones expressed in endocrine and neuronal cells. We investigated clinical and molecular features of PC1/3 deficiency. Methods We studied the clinical features of 13 children with PC1/3 deficiency and performed sequence analysis of PCSK1. We measured enzymatic activity of recombinant PC1/3 proteins. Results We identified a pattern of endocrinopathies that develop in an age-dependent manner. Eight of the mutations had severe biochemical consequences in vitro. Neonates had severe malabsorptive diarrhea and failure to thrive, required prolonged parenteral nutrition support, and had high mortality. Additional endocrine abnormalities developed as the disease progressed, including diabetes insipidus, growth hormone deficiency, primary hypogonadism, adrenal insufficiency, and hypothyroidism. We identified growth hormone deficiency, central diabetes insipidus, and male hypogonadism as new features of PCSK1 insufficiency. Interestingly, despite early growth abnormalities, moderate obesity, associated with severe polyphagia, generally appears. Conclusions In a study of 13 children with PC1/3 deficiency caused by disruption of PCSK1, failure of enteroendocrine cells to produce functional hormones resulted in generalized malabsorption. These findings indicate that PC1/3 is involved in the processing of one or more enteric hormones that are required for nutrient absorption.

Estrogen receptor α (ERα) action plays an important role in pancreatic β-cell function and survival; thus, it is considered a potential therapeutic target for the treatment of type 2 diabetes in women. However, the mechanisms underlying the protective effects of ERα remain unclear. Because ERα regulates mitochondrial metabolism in other cell types, we hypothesized that ERα may act to preserve insulin secretion and promote β-cell survival by regulating mitochondrial-endoplasmic reticulum (EndoRetic) function. We tested this hypothesis using pancreatic islet-specific ERα knockout (PERαKO) mice and Min6 β-cells in culture with Esr1 knockdown (KD). We found that Esr1-KD promoted reactive oxygen species production that associated with reduced fission/fusion dynamics and impaired mitophagy. Electron microscopy showed mitochondrial enlargement and a pro-fusion phenotype. Mitochondrial cristae and endoplasmic reticulum were dilated in Esr1-KD compared with ERα replete Min6 β-cells. Increased expression of Oma1 and Chop was paralleled by increased oxygen consumption and apoptosis susceptibility in ERα-KD cells. In contrast, ERα overexpression and ligand activation reduced both Chop and Oma1 expression, likely by ERα binding to consensus estrogen-response element sites in the Oma1 and Chop promoters. Together, our findings suggest that ERα promotes β-cell survival and insulin secretion through maintenance of mitochondrial fission/fusion-mitophagy dynamics and EndoRetic function, in part by Oma1 and Chop repression.

Diabetes results from an inadequate mass of functional β-cells. Such inadequacy could result from loss of β-cells due to an immune assault or the inability to compensate for insulin resistance. Thus, mechanisms that regulate the number of β-cells will be key to understanding both the pathogenesis of diabetes and for developing therapies. In this study, we show that cell cycle regulator p27 plays a crucial role in establishing the number of β-cells formed before birth. We show that p27 accumulates in terminally differentiated β-cells during embryogenesis. Disabling p27 allows newly differentiated β-cells that are normally quiescent during embryogenesis to reenter the cell cycle and proliferate. As a consequence, excess β-cells are generated in the p27−/− mice, doubling their β-cell mass at birth. The early postnatal expansion of β-cell mass was unaffected in p27−/− mice, indicating that the main function of p27 is to maintain the quiescent state of newly differentiated β-cells generated during embryogenesis. The expanded β-cell mass was accompanied by increased insulin secretion; however, the p27−/− mice were glucose intolerant, as these mice were insulin insensitive. To assess the role of p27 to affect regeneration of β-cells in models of diabetes, p27−/− mice were injected with streptozotocin (STZ). In contrast to control mice that displayed elevated blood glucose levels, p27−/− mice showed decreased susceptibility to develop STZ-induced diabetes. Furthermore, β-cells retained the ability to reenter the cell cycle at a far greater frequency in p27−/− mice after developing STZ-induced diabetes compared with wild-type littermates. These data indicate that p27 is a key regulator in establishing β-cell mass and an important target for facilitating β-cell regeneration in therapies for diabetes.

Diabetes results from an inadequate mass of functional β cells, due to either β cell loss caused by immune assault or the lack of compensation to overcome insulin resistance. Elucidating the mechanisms that regulate β cell mass has important ramifications for fostering β cell regeneration and the treatment of diabetes. We report here that Skp2, a substrate recognition component of Skp1–Cul1–F-box (SCF) ubiquitin ligase, played an essential and specific role in regulating the cellular abundance of p27 and was a critical determinant of β cell proliferation. In Skp2^–/– mice, accumulation of p27 resulted in enlarged polyploid β cells as a result of endoreduplication replacing proliferation. Despite β cell hypertrophy, Skp2^–/– mice exhibited diminished β cell mass, hypoinsulinemia, and glucose intolerance. Increased insulin resistance resulting from diet-induced obesity caused Skp2^–/– mice to become overtly diabetic, because β cell growth in the absence of cell division was insufficient to compensate for increased metabolic demand. These results indicate that the Skp2-mediated degradation pathway regulating the cellular degradation of p27 is essential for establishing β cell mass and to respond to increased metabolic demand associated with insulin resistance.