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.

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 .

SUMMARY Pancreatic β 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 β cell function.

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