The histone deacetylase Sirt6 regulates glucose homeostasis via Hif1alpha.

SIRT6 is a member of a highly conserved family of NAD(+)-dependent deacetylases with various roles in metabolism, stress resistance, and life span. SIRT6-deficient mice develop normally but succumb to a lethal hypoglycemia early in life; however, the mechanism underlying this hypoglycemia remained unclear. Here, we demonstrate that SIRT6 functions as a histone H3K9 deacetylase to control the expression of multiple glycolytic genes. Specifically, SIRT6 appears to function as a corepressor of the transcription factor Hif1alpha, a critical regulator of nutrient stress responses. Consistent with this notion, SIRT6-deficient cells exhibit increased Hif1alpha activity and show increased glucose uptake with upregulation of glycolysis and diminished mitochondrial respiration. Our studies uncover a role for the chromatin factor SIRT6 as a master regulator of glucose homeostasis and may provide the basis for novel therapeutic approaches against metabolic diseases, such as diabetes and obesity.

The activating receptor NKp46 is essential for the development of type 1 diabetes.

The mechanism of action of natural killer (NK) cells in type 1 diabetes is still unknown. Here we show that the activating receptor NKp46 recognizes mouse and human ligands on pancreatic beta cells. NK cells appeared in the pancreas when insulitis progressed to type 1 diabetes, and NKp46 engagement by beta cells led to degranulation of NK cells. NKp46-deficient mice had less development of type 1 diabetes induced by injection of a low dose of streptozotocin. Injection of soluble NKp46 proteins into nonobese diabetic mice during the early phase of insulitis and the prediabetic stage prevented the development of type 1 diabetes. Our findings demonstrate that NKp46 is essential for the development of type 1 diabetes and highlight potential new therapeutic modalities for this disease.

miRNAs control insulin content in pancreatic ß-cells via downregulation of transcriptional repressors.

MicroRNAs (miRNAs) were shown to be important for pancreas development, yet their roles in differentiated ß-cells remain unclear. Here, we show that miRNA inactivation in ß-cells of adult mice results in a striking diabetic phenotype. While islet architecture is intact and differentiation markers are maintained, Dicer1-deficient ß-cells show a dramatic decrease in insulin content and insulin mRNA. As a consequence of the change in insulin content, the animals become diabetic. We provide evidence for involvement of a set of miRNAs in regulating insulin synthesis. The specific knockdown of miR-24, miR-26, miR-182 or miR-148 in cultured ß-cells or in isolated primary islets downregulates insulin promoter activity and insulin mRNA levels. Further, miRNA-dependent regulation of insulin expression is associated with upregulation of transcriptional repressors, including Bhlhe22 and Sox6. Thus, miRNAs in the adult pancreas act in a new network that reinforces insulin expression by reducing the expression of insulin transcriptional repressors.

Recognition and killing of human and murine pancreatic beta cells by the NK receptor NKp46.

Type 1 diabetes is an incurable disease that is currently treated by insulin injections or in rare cases by islet transplantation. We have recently shown that NKp46, a major killer receptor expressed by NK cells, recognizes an unknown ligand expressed by ß cells and that in the absence of NKp46, or when its activity is blocked, diabetes development is inhibited. In this study, we investigate whether NKp46 is involved in the killing of human ß cells that are intended to be used for transplantation, and we also thoroughly characterize the interaction between NKp46 and its human and mouse ß cell ligands. We show that human ß cells express an unknown ligand for NKp46 and are killed in an NKp46-dependent manner. We further demonstrate that the expression of the NKp46 ligand is detected on human ß cells already at the embryonic stage and that it appears on murine ß cells only following birth. Because the NKp46 ligand is detected on healthy ß cells, we wondered why type 1 diabetes does not develop in all individuals and show that NK cells are absent from the vicinity of islets of healthy mice and are detected in situ in proximity with ß cells in NOD mice. We also investigate the molecular mechanisms controlling NKp46 interactions with its ß cell ligand and demonstrate that the recognition is confined to the membrane proximal domain and stalk region of NKp46 and that two glycosylated residues of NKp46, Thr(125) and Asn(216), are critical for this recognition.

Recovery from diabetes in mice by beta cell regeneration.

The mechanisms that regulate pancreatic beta cell mass are poorly understood. While autoimmune and pharmacological destruction of insulin-producing beta cells is often irreversible, adult beta cell mass does fluctuate in response to physiological cues including pregnancy and insulin resistance. This plasticity points to the possibility of harnessing the regenerative capacity of the beta cell to treat diabetes. We developed a transgenic mouse model to study the dynamics of beta cell regeneration from a diabetic state. Following doxycycline administration, transgenic mice expressed diphtheria toxin in beta cells, resulting in apoptosis of 70%-80% of beta cells, destruction of islet architecture, and diabetes. Withdrawal of doxycycline resulted in a spontaneous normalization of blood glucose levels and islet architecture and a significant regeneration of beta cell mass with no apparent toxicity of transient hyperglycemia. Lineage tracing analysis indicated that enhanced proliferation of surviving beta cells played the major role in regeneration. Surprisingly, treatment with Sirolimus and Tacrolimus, immunosuppressants used in the Edmonton protocol for human islet transplantation, inhibited beta cell regeneration and prevented the normalization of glucose homeostasis. These results suggest that regenerative therapy for type 1 diabetes may be achieved if autoimmunity is halted using regeneration-compatible drugs.

Toward Respiratory-Gated Retrograde Intrarenal Surgery: A Prospective Controlled Randomized Study.

INTRODUCTION: We set out to investigate whether general anesthesia with low ventilation (LV, respiratory rate ≤8/minute and tidal volume <500 mL) could reduce renal mobility and thereby facilitate improved retrograde intrarenal surgery (RIRS) compared with general anesthesia with standard ventilation (SV). MATERIALS AND METHODS: All 60 consecutive patients who presented for RIRS in our department from September 1, 2017 to December 31, 2017 were prospectively randomized 1:1 into one group that was selected to receive SV and another that received LV. Significant factors influencing the study endpoints considered fragmentation rate (FR), removal rate (RR), processing rate (PR), and operating rate (OR), were statistically analyzed for the whole group as well as for comparison by level of surgeon expertise. RESULTS: Univariate analysis revealed that LV was a significant factor in improving all endpoints. Some endpoints were also affected by the stone's volume, number, and density as well as the surgeon expertise. LV remained the single independent factor for FR, RR, and PR in the multivariate analysis. LV significantly improved all four of the fellows' endpoints (p < 0.05 for each) and positively influenced the expert's RR (p = 0.04), PR (p = 0.02) and OR (p = 0.04). The performance gap between the fellows and the experts narrowed under LV. The end-tidal CO2 was significantly higher in the LV group (50 vs 36 mm Hg; p < 0.0001), however, without any clinical significance. The overall stone-free rate (97%) and complication rate (5%) were not significantly different between the two groups. The patient's anesthesia-related safety was not affected by the mode of ventilation as evidenced by no need to convert from LV to SV during the procedures. CONCLUSIONS: LV during RIRS has a significant positive impact on the overall improvement of surgical performance and effectiveness. It does not negatively affect the patient's anesthesia-related safety and may contribute to considerably improving the performance of in-training endourologists.

How to make pancreatic beta cells--prospects for cell therapy in diabetes.

One promising approach for the cure of diabetes is the replacement of lost insulin-expressing beta cells by cell or regenerative therapy. The recent development of an effective islet transplantation procedure has focused attention on the limiting supply of beta cells. Various sources for new beta cells are therefore being considered, including embryonic stem cells, adult stem cells and transdifferentiation of certain types of differentiated cells, so far with limited success. The major physiological mechanism for adult beta cell formation was recently shown to be beta cell proliferation. This finding underscores the potential use of terminally differentiated beta cells as a starting material for enhancement of beta cell mass.

Dysregulation of Dicer1 in beta cells impairs islet architecture and glucose metabolism.

microRNAs (miRNAs) play important roles in pancreas development and in regulation of insulin expression in the adult. Here we show that loss of miRNAs activity in beta-cells during embryonic development results in lower beta-cell mass and in impaired glucose tolerance. Dicer1-null cells initially constitute a significant portion of the total beta-cell population. However, during postnatal development, Dicer1-null cells are depleted. Furthermore, wild-type beta cells are repopulating the islets in complex compensatory dynamics. Because loss of Dicer1 is also associated with changes in the distribution of membranous E-cadherin, we hypothesized that E-cadherin activity may play a role in beta cell survival or islet architecture. However, genetic loss of E-cadherin function does not impair islet architecture, suggesting that miRNAs likely function through other or redundant effectors in the endocrine pancreas.

Ribosomal protein S6 phosphorylation is a determinant of cell size and glucose homeostasis.

The regulated phosphorylation of ribosomal protein (rp) S6 has attracted much attention since its discovery in 1974, yet its physiological role has remained obscure. To directly address this issue, we have established viable and fertile knock-in mice, whose rpS6 contains alanine substitutions at all five phosphorylatable serine residues (rpS6(P-/-)). Here we show that contrary to the widely accepted model, this mutation does not affect the translational control of TOP mRNAs. rpS6(P-/-) mouse embryo fibroblasts (MEFs) display an increased rate of protein synthesis and accelerated cell division, and they are significantly smaller than rpS6(P+/+) MEFs. This small size reflects a growth defect, rather than a by-product of their faster cell division. Moreover, the size of rpS6(P-/-) MEFs, unlike wild-type MEFs, is not further decreased upon rapamycin treatment, implying that the rpS6 is a critical downstream effector of mTOR in regulation of cell size. The small cell phenotype is not confined to embryonal cells, as it also selectively characterizes pancreatic beta-cells in adult rpS6(P-/-) mice. These mice suffer from diminished levels of pancreatic insulin, hypoinsulinemia, and impaired glucose tolerance.