An analysis of intestinal morphology and incretin-producing cells using tissue optical clearing and 3-D imaging.

Tissue optical clearing permits detailed evaluation of organ three-dimensional (3-D) structure as well as that of individual cells by tissue staining and autofluorescence. In this study, we evaluated intestinal morphology, intestinal epithelial cells (IECs), and enteroendocrine cells, such as incretin-producing cells, in reporter mice by intestinal 3-D imaging. 3-D intestinal imaging of reporter mice using optical tissue clearing enabled us to evaluate both detailed intestinal morphologies and cell numbers, villus length and crypt depth in the same samples. In disease mouse model of lipopolysaccharide (LPS)-injected mice, the results of 3-D imaging using tissue optical clearing in this study was consistent with those of 2-D imaging in previous reports and could added the new data of intestinal morphology. In analysis of incretin-producing cells of reporter mice, we could elucidate the number, the percentage, and the localization of incretin-producing cells in intestine and the difference of those between L cells and K cells. Thus, we established a novel method of intestinal analysis using tissue optical clearing and 3-D imaging. 3-D evaluation of intestine enabled us to clarify not only detailed intestinal morphology but also the precise number and localization of IECs and incretin-producing cells in the same samples.

Single-Cell Transcriptome Analysis Dissects the Replicating Process of Pancreatic Beta Cells in Partial Pancreatectomy Model.

Heterogeneity of gene expression and rarity of replication hamper molecular analysis of ß-cell mass restoration in adult pancreas. Here, we show transcriptional dynamics in ß-cell replication process by single-cell RNA sequencing of murine pancreas with or without partial pancreatectomy. We observed heterogeneity of Ins1-expressing ß-cells and identified the one cluster as replicating ß-cells with high expression of cell proliferation markers Pcna and Mki67. We also recapitulated cell cycle transition accompanied with switching expression of cyclins and E2F transcription factors. Both transient activation of endoplasmic reticulum stress responders like Atf6 and Hspa5 and elevated expression of tumor suppressors like Trp53, Rb1, and Brca1 and DNA damage responders like Atm, Atr, Rad51, Chek1, and Chek2 during the transition to replication associated fine balance of cell cycle progression and protection from DNA damage. Taken together, these results provide a high-resolution map depicting a sophisticated genetic circuit for replication of the ß-cells.

Generation and Characterization of a Novel Mouse Model That Allows Spatiotemporal Quantification of Pancreatic ß-Cell Proliferation.

Pancreatic ß-cell proliferation has been gaining much attention as a therapeutic target for the prevention and treatment of diabetes. In order to evaluate potential ß-cell mitogens, accurate and reliable methods for the detection and quantification of the ß-cell proliferation rate are indispensable. In this study, we developed a novel tool that specifically labels replicating ß-cells as mVenus+ cells by using RIP-Cre; R26Fucci2aR mice expressing the fluorescent ubiquitination-based cell cycle indicator Fucci2a in ß-cells. In response to ß-cell proliferation stimuli, such as insulin receptor antagonist S961 and diet-induced obesity (DIO), the number of 5-ethynyl-2'-deoxyuridine-positive insulin+ cells per insulin+ cells and the number of mVenus+ cells per mCherry+ mVenus- cells + mCherry- mVenus+ cells were similarly increased in these mice. Three-dimensional imaging of optically cleared pancreas tissue from these mice enabled quantification of replicating ß-cells in the islets and morphometric analysis of the islets after known mitogenic interventions such as S961, DIO, pregnancy, and partial pancreatectomy. Thus, this novel mouse line is a powerful tool for spatiotemporal analysis and quantification of ß-cell proliferation in response to mitogenic stimulation.

GPR40 activation initiates store-operated Ca2+ entry and potentiates insulin secretion via the IP3R1/STIM1/Orai1 pathway in pancreatic ß-cells.

The long-chain fatty acid receptor GPR40 plays an important role in potentiation of glucose-induced insulin secretion (GIIS) from pancreatic ß-cells. Previous studies demonstrated that GPR40 activation enhances Ca2+ release from the endoplasmic reticulum (ER) by activating inositol 1,4,5-triphosphate (IP3) receptors. However, it remains unknown how ER Ca2+ release via the IP3 receptor is linked to GIIS potentiation. Recently, stromal interaction molecule (STIM) 1 was identified as a key regulator of store-operated Ca2+ entry (SOCE), but little is known about its contribution in GPR40 signaling. We show that GPR40-mediated potentiation of GIIS is abolished by knockdown of IP3 receptor 1 (IP3R1), STIM1 or Ca2+-channel Orai1 in insulin-secreting MIN6 cells. STIM1 and Orai1 knockdown significantly impaired SOCE and the increase of intracellular Ca2+ by the GPR40 agonist, fasiglifam. Furthermore, ß-cell-specific STIM1 knockout mice showed impaired fasiglifam-mediated GIIS potentiation not only in isolated islets but also in vivo. These results indicate that the IP3R1/STIM1/Orai1 pathway plays an important role in GPR40-mediated SOCE initiation and GIIS potentiation in pancreatic ß-cells.

Sphingosine kinase 1-interacting protein is a dual regulator of insulin and incretin secretion.

Our previous study demonstrated that sphingosine kinase 1-interacting protein (SKIP, or Sphkap) is expressed in pancreatic ß-cells, and depletion of SKIP enhances glucose-stimulated insulin secretion. We find here that SKIP is also expressed in intestinal K- and L-cells and that secretion of gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) as well as insulin are significantly increased, and blood glucose levels are decreased in SKIP-deficient (SKIP-/-) mice compared with those in wild-type mice. Plasma triglyceride (Tg), LDL cholesterol, and mRNA levels of proinflammatory cytokines in adipose tissues, livers, and intestines were found to be significantly decreased in SKIP-/- mice. The phenotypic characteristics of SKIP-/- mice, including adiposity and attenuation of basal inflammation, were abolished by genetic depletion of GIP. The improvement of glucose tolerance and lipid profiles in SKIP-/- mice were cancelled by GLP-1 receptor antagonist exendin-(9-39) treatment. In summary, depletion of SKIP ameliorates glucose tolerance by enhancing secretion of insulin and incretins, improves lipid metabolism, and reduces basal inflammation levels. Thus, inhibition of SKIP action may emerge as a new option for treatment of type 2 diabetes mellitus with metabolic dysfunction.-Liu, Y., Harashima, S., Wang, Y., Suzuki, K., Tokumoto, S., Usui, R., Tatsuoka, H., Tanaka, D., Yabe, D., Harada, N., Hayashi, Y., Inagaki, N. Sphingosine kinase 1-interacting protein is a dual regulator of insulin and incretin secretion.

Basal and Bolus Insulin Dose Changes after Switching Basal Insulin to Insulin Degludec in Patients with Type 1 Diabetes Mellitus: A Pilot Study.

BACKGROUND AND OBJECTIVES: Ultra-long-acting insulin degludec (DEG) has a longer duration of action and less daily variability relative to other basal insulin (BI), and thus may benefit patients with type 1 diabetes mellitus (T1DM). We examined the impact of switching BI to DEG on glycemic control and insulin dose in T1DM. METHODS: T1DM patients (n = 22; six male; mean age: 64.5 ± 12.6 years) receiving basal-bolus insulin therapy were included. Initially, the BI dose was replaced with DEG in a 1:1 ratio; 80-100% of the total dose was replaced with DEG for multiple basal insulin injections. DEG was titrated according to study protocol. Changes in HbA1c, daily insulin dose, glycemic self-monitored blood glucose variations, and hypoglycemia frequency were evaluated for 24 weeks. RESULTS: Once-daily DEG significantly decreased HbA1c levels when switched from once-daily BI (7.9 ± 0.8 vs. 7.5 ± 0.9%, p = 0.020) and maintained HbA1c when switched from twice-daily BI (8.5 ± 1.6 vs. 8.4 ± 1.2%, p = 0.457). The BI dose decreased by -7.8 ± 13.9% (p = 0.017) and -16.6 ± 16.9% (p = 0.050) when switched from once-daily BI and twice-daily BI, respectively. The total bolus insulin dose significantly decreased when switched from once-daily BI (21.7 ± 8.3 to 19.3 ± 8.8 U/day, p = 0.016) especially in the injection before breakfast and evening meal. Body weight and hypoglycemia frequency was not significantly different. CONCLUSION: DEG improved glycemic control when switched from once-daily BI and maintained glycemic control when switched from twice-daily BI without increasing hypoglycemia.