Metabolic control of adaptive ß-cell proliferation by the protein deacetylase SIRT2.

Selective and controlled expansion of endogenous ß-cells has been pursued as a potential therapy for diabetes. Ideally, such therapies would preserve feedback control of ß-cell proliferation to avoid excessive ß-cell expansion and an increased risk of hypoglycemia. Here, we identified a regulator of ß-cell proliferation whose inactivation results in controlled ß-cell expansion: the protein deacetylase Sirtuin 2 (SIRT2). Sirt2 deletion in ß-cells of mice increased ß-cell proliferation during hyperglycemia with little effect in homeostatic conditions, indicating preservation of feedback control of ß-cell mass. SIRT2 restrains proliferation of human islet ß-cells cultured in glucose concentrations above the glycemic set point, demonstrating conserved SIRT2 function. Analysis of acetylated proteins in islets treated with a SIRT2 inhibitor revealed that SIRT2 deacetylates enzymes involved in oxidative phosphorylation, dampening the adaptive increase in oxygen consumption during hyperglycemia. At the transcriptomic level, Sirt2 inactivation has context-dependent effects on ß-cells, with Sirt2 controlling how ß-cells interpret hyperglycemia as a stress. Finally, we provide proof-of-principle that systemic administration of a GLP1-coupled Sirt2-targeting antisense oligonucleotide achieves ß-cell selective Sirt2 inactivation and stimulates ß-cell proliferation under hyperglycemic conditions. Overall, these studies identify a therapeutic strategy for increasing ß-cell mass in diabetes without circumventing feedback control of ß-cell proliferation.

Mutations and variants of ONECUT1 in diabetes.

Genes involved in distinct diabetes types suggest shared disease mechanisms. Here we show that One Cut Homeobox 1 (ONECUT1) mutations cause monogenic recessive syndromic diabetes in two unrelated patients, characterized by intrauterine growth retardation, pancreas hypoplasia and gallbladder agenesis/hypoplasia, and early-onset diabetes in heterozygous relatives. Heterozygous carriers of rare coding variants of ONECUT1 define a distinctive subgroup of diabetic patients with early-onset, nonautoimmune diabetes, who respond well to diabetes treatment. In addition, common regulatory ONECUT1 variants are associated with multifactorial type 2 diabetes. Directed differentiation of human pluripotent stem cells revealed that loss of ONECUT1 impairs pancreatic progenitor formation and a subsequent endocrine program. Loss of ONECUT1 altered transcription factor binding and enhancer activity and NKX2.2/NKX6.1 expression in pancreatic progenitor cells. Collectively, we demonstrate that ONECUT1 controls a transcriptional and epigenetic machinery regulating endocrine development, involved in a spectrum of diabetes, encompassing monogenic (recessive and dominant) as well as multifactorial inheritance. Our findings highlight the broad contribution of ONECUT1 in diabetes pathogenesis, marking an important step toward precision diabetes medicine.

Integrated In Vivo Quantitative Proteomics and Nutrient Tracing Reveals Age-Related Metabolic Rewiring of Pancreatic ß Cell Function.

Pancreatic ß cell physiology changes substantially throughout life, yet the mechanisms that drive these changes are poorly understood. Here, we performed comprehensive in vivo quantitative proteomic profiling of pancreatic islets from juvenile and 1-year-old mice. The analysis revealed striking differences in abundance of enzymes controlling glucose metabolism. We show that these changes in protein abundance are associated with higher activities of glucose metabolic enzymes involved in coupling factor generation as well as increased activity of the coupling factor-dependent amplifying pathway of insulin secretion. Nutrient tracing and targeted metabolomics demonstrated accelerated accumulation of glucose-derived metabolites and coupling factors in islets from 1-year-old mice, indicating that age-related changes in glucose metabolism contribute to improved glucose-stimulated insulin secretion with age. Together, our study provides an in-depth characterization of age-related changes in the islet proteome and establishes metabolic rewiring as an important mechanism for age-associated changes in ß cell function.

Selective blockade of the lyso-PS lipase ABHD12 stimulates immune responses in vivo.

ABHD12 metabolizes bioactive lysophospholipids, including lysophosphatidylserine (lyso-PS). Deleterious mutations in human ABHD12 cause the neurological disease PHARC, and ABHD12-/- mice display PHARC-like phenotypes, including hearing loss, along with elevated brain lyso-PS and features of stimulated innate immune cell function. Here, we develop a selective and in vivo-active inhibitor of ABHD12 termed DO264 and show that this compound elevates lyso-PS in mouse brain and primary human macrophages. Unlike ABHD12-/- mice, adult mice treated with DO264 exhibited minimal perturbations in auditory function. On the other hand, both DO264-treated and ABHD12-/- mice displayed heightened immunological responses to lymphocytic choriomeningitis virus (LCMV) clone 13 infection that manifested as severe lung pathology with elevated proinflammatory chemokines. These results reveal similarities and differences in the phenotypic impact of pharmacological versus genetic blockade of ABHD12 and point to a key role for this enzyme in regulating immunostimulatory lipid pathways in vivo.

Advances in ß cell replacement and regeneration strategies for treating diabetes.

In the past decade, new approaches have been explored that are aimed at restoring functional ß cell mass as a treatment strategy for diabetes. The two most intensely pursued strategies are ß cell replacement through conversion of other cell types and ß cell regeneration by enhancement of ß cell replication. The approach closest to clinical implementation is the replacement of ß cells with human pluripotent stem cell-derived (hPSC-derived) cells, which are currently under investigation in a clinical trial to assess their safety in humans. In addition, there has been success in reprogramming developmentally related cell types into ß cells. Reprogramming approaches could find therapeutic applications by inducing ß cell conversion in vivo or by reprogramming cells ex vivo followed by implantation. Finally, recent studies have revealed novel pharmacologic targets for stimulating ß cell replication. Manipulating these targets or the pathways they regulate could be a strategy for promoting the expansion of residual ß cells in diabetic patients. Here, we provide an overview of progress made toward ß cell replacement and regeneration and discuss promises and challenges for clinical implementation of these strategies.

Postnatal ß-cell proliferation and mass expansion is dependent on the transcription factor Nkx6.1.

All forms of diabetes are characterized by a loss of functional ß-cell mass, and strategies for expanding ß-cell mass could have significant therapeutic benefit. We have recently identified the transcription factor Nkx6.1 as an essential maintenance factor of the functional ß-cell state. In addition, Nkx6.1 has been proposed to control ß-cell proliferation, but a role for Nkx6.1 in regulating ß-cell mass has not been demonstrated. Here, we show that Nkx6.1 is required for postnatal ß-cell mass expansion. Genetic inactivation of Nkx6.1 in newly formed ß-cells caused a drastic decrease in early postnatal ß-cell proliferation, leading to reduced ß-cell mass and glucose intolerance. Interestingly, Nkx6.1 was dispensable for prenatal ß-cell proliferation. We found that Nkx6.1 regulates the expression of several ß-cell maturation markers as well as expression of the nutrient sensors Glut2 and Glp1r. Manifestation of the ß-cell mass defect at the transition to postnatal feeding suggests that Nkx6.1 could regulate ß-cell growth by enabling ß-cells to respond to nutrient-dependent proliferation signals, such as glucose and Glp1. Identification of ß-cell-intrinsic regulators that connect nutrient-sensing and proliferation suggests new therapeutic targets for expanding functional ß-cell mass.

Nkx6.1 controls a gene regulatory network required for establishing and maintaining pancreatic Beta cell identity.

All pancreatic endocrine cell types arise from a common endocrine precursor cell population, yet the molecular mechanisms that establish and maintain the unique gene expression programs of each endocrine cell lineage have remained largely elusive. Such knowledge would improve our ability to correctly program or reprogram cells to adopt specific endocrine fates. Here, we show that the transcription factor Nkx6.1 is both necessary and sufficient to specify insulin-producing beta cells. Heritable expression of Nkx6.1 in endocrine precursors of mice is sufficient to respecify non-beta endocrine precursors towards the beta cell lineage, while endocrine precursor- or beta cell-specific inactivation of Nkx6.1 converts beta cells to alternative endocrine lineages. Remaining insulin(+) cells in conditional Nkx6.1 mutants fail to express the beta cell transcription factors Pdx1 and MafA and ectopically express genes found in non-beta endocrine cells. By showing that Nkx6.1 binds to and represses the alpha cell determinant Arx, we identify Arx as a direct target of Nkx6.1. Moreover, we demonstrate that Nkx6.1 and the Arx activator Isl1 regulate Arx transcription antagonistically, thus establishing competition between Isl1 and Nkx6.1 as a critical mechanism for determining alpha versus beta cell identity. Our findings establish Nkx6.1 as a beta cell programming factor and demonstrate that repression of alternative lineage programs is a fundamental principle by which beta cells are specified and maintained. Given the lack of Nkx6.1 expression and aberrant activation of non-beta endocrine hormones in human embryonic stem cell (hESC)-derived insulin(+) cells, our study has significant implications for developing cell replacement therapies.