Intra-arterial targeted islet-specific expression of Sirt1 protects β cells from streptozotocin-induced apoptosis in mice

Taurine treatment reverses protein malnutrition-induced endothelial dysfunction of the pancreatic vasculature: The role of hydrogen sulfide

BACKGROUND

Protein malnutrition in childhood predisposes individuals to vascular and pancreatic endocrine dysfunction, thus increasing the risk of diabetes and hypertension. Because taurine may reduce cardiometabolic risk, we hypothesized that taurine treatment has a beneficial effect on the pancreatic vasculature during protein restriction.

METHODS AND RESULTS

Weaned mice were fed a normal or a low-protein diet and were treated with or without taurine for 3 months. The lieno-pancreatic artery (LPA) from low-protein diet-treated mice exhibited impaired endothelium-dependent relaxation to acetylcholine that was associated with decreased endothelium-derived hyperpolarization (EDH), hydrogen sulfide (H₂S) production, and H₂S-synthesizing CBS expression and impaired vasorelaxation to an H₂S-donor, NaHS. These changes were prevented by taurine treatment. We compared the effects of taurine with the effects of the direct vasodilator hydralazine and found that both normalized blood pressure and the endothelial vasodilator function of the LPA in the mice fed a protein-restricted diet. However, only taurine restored the CBS expression in the LPA and insulin secretion in response to high glucose. The LPA supplies the pancreas and shares morphometry with the mesenteric resistance artery (MRA). However, in the MRA, low-protein diet-induced endothelial dysfunction is driven by impaired NOS-derived NO with no changes in H₂S signaling.

CONCLUSIONS

The results suggest that taurine protects against protein malnutrition-induced endothelial dysfunction in the LPA by upregulating the CBS-H₂S pathway. Considering the importance of the pancreatic vasculature for endocrine islet activity, taurine may be a potential therapy for the vascular and metabolic dysfunction associated with malnutrition and comorbidities.

Low dose doxycycline decreases systemic inflammation and improves glycemic control, lipid profiles, and islet morphology and function in db/db mice

The aim of this study was to determine whether low dose doxycycline as an anti-inflammatory agent could improve glucose metabolism in diabetic animals. Therefore, doxycycline was supplemented in drinking water to 6-week-old male db/db mice for 10 weeks. Doxycycline reduced perirenal/epididymal fat, Lee's index, and liver cholesterol. Blood HDL-cholesterol increased, but total cholesterol and aspartate transaminase decreased. Glucose and insulin tolerances were improved, accompanying with reduced fasting blood glucose, insulin, HOMA-IR and advanced glycation end products. Islet number, β-cell percentage and mass increased, while islet size decreased. Consistently, less apoptosis but more β-cell proliferation were found in islets of treated mice. Freshly isolated islets from treated mice showed higher insulin content and enhanced glucose stimulated insulin secretion (GSIS). In addition, purified islets of Balb/c mice showed increased GSIS after cultivation in vitro with doxycycline, but not with chloramphenicol and levofloxacin. Inflammation markers, including lipopolysaccharides (LPS) and C-reactive protein (CRP) in serum as well as CD68-positive cells in treated islets, decreased significantly. Finally, LPS stimulated the production of inflammatory factors but inhibited GSIS of MIN6 cells; however, the effects were completely reversed by doxycycline. The results support further study of possible long-term usage of sub-antimicrobial doxycycline in diabetic patients.

Magnetic resonance imaging of intra-pancreatic ductal nanoparticle delivery to islet cells

BACKGROUND

The absence of reliable drug delivery systems to pancreatic islet cells hampers efficient treatment of type 1 diabetes. Nanoparticle delivery systems equipped with imaging capabilities could enable selective delivery to pancreatic islet cells. Biodistribution of nanoparticles is defined by several factors including the mode of administration, which determines accumulation in various organs.

METHODS

In this study, we tested whether intrapancreatic ductal injection of magnetic nanoparticles would result in efficient cellular uptake by pancreatic islet cells. Dextran-coated iron oxide nanoparticles labeled with the near infrared fluorescent dye Cy5.5 were injected into the intrapancreatic ducts of streptozotocin-induced diabetic and healthy mice. To monitor the distribution of the nanoparticles, we performed in vivo magnetic resonance imaging followed by optical imaging and histology.

RESULTS

Both imaging modalities demonstrated accumulation of the nanoparticles in the pancreas. However, histology revealed a high accumulation of nanoparticles in the insulin-producing cells in the pancreata of diabetic animals. By contrast, in nondiabetic controls, nanoparticles were mainly restricted to nonendocrine tissues.

CONCLUSIONS

Our results demonstrate that pancreatic ductal injection accompanied by image guidance could serve as an alternative pathway for nanoparticle delivery. We expect to utilize this intraductal delivery method for theranostic applications in type 1 diabetes.

Incorporation of VSV-G produces fusogenic plasma membrane vesicles capable of efficient transfer of bioactive macromolecules and mitochondria

The objective of this study was to determine if plasma membrane vesicles (PMVs) could be exploited for efficient transfer of macro-biomolecules and mitochondria. PMVs were derived from mechanical extrusion, and made fusogenic (fPMVs) by incorporating the glycoprotein G of vesicular stomatitis virus (VSV-G). Confocal microscopy examination revealed that cytoplasmic proteins and mitochondria were enclosed in PMVs as evidenced by tracing with cytoplasmically localized and mitochondria-targeted EGFP, respectively. However, no fluorescence signal was detected in PMVs from cells whose nucleus was labeled with an EGFP-tagged histone H2B. Consistently, qRT-PCR measurement showed that mRNA, miRNA and mitochondrial DNA decreased slightly; while nuclear DNA was not measureable. Further, Western blot analysis revealed that cytoplasmic and membrane-bound proteins fell inconspicuously while nuclear proteins were barely detecsle. In addition, fPMVs carrying cytoplamic DsRed proteins transduced about ~40 % of recipient cells. The transfer of protein was further confirmed by using the inducible Cre/loxP system. Mitochondria transfer was found in about 20 % recipient cells after incubation with fPMVs for 5 h. To verify the functionalities of transferred mitochondria, mitochodria-deficient HeLa cells (Rho0) were generated and cultivated with fPMVs. Cell enumeration demonstrated that adding fPMVs into culture media stimulated Rho0 cell growth by 100 % as compared to the control. Lastly, MitoTracker and JC-1 staining showed that transferred mitochondria maintained normal shape and membrane potential in Rho0 cells. This study established a time-saving and efficient approach to delivering proteins and mitochondria by using fPMVs, which would be helpful for finding a cure to mitochondria-associated diseases. Graphical abstract Schematic of the delivery of macro-biomolecules and organelles by fPMVs. VSV-G-expressing cells were extruded through a 3 μm polycarbonate membrane filter to generate fusogenic plasma membrane vesicles (fPMVs), which contain bioactive molecules and organelles but not the nucleus. fPMVs can be endocytosed by target cells, while the cargo is released due to low-pH induced membrane fusion. These nucleus-free fPMVs are efficient at delivery of cytoplasmic proteins and mitochondria, leading to recovery of mitochondrial biogenesis and proliferative ability in mitochondria-deficient cells.

Increased Specific Labeling of INS-1 Pancreatic Beta-Cell by Using RIP-Driven Cre Mutants with Reduced Activity

Ectopically expressed Cre recombinase in extrapancreatic tissues in RIP-Cre mice has been well documented. The objective of this study was to find a simple solution that allows for improved beta-cell specific targeting. To this end, the RIP-Cre and reporter CMV-loxP-DsRed-loxP-EGFP expression cassettes were configurated into a one-plasmid and two-plasmid systems, which labeled approximately 80% insulin-positive INS-1 cells after 48 h transfection. However, off-target labeling was robustly found in more than 15% insulin-negative Ad293 cells. When an IRES element was inserted in front of Cre to reduce the translation efficiency, the ratio of recombination between INS-1 and Ad293 cells increased 3-4-fold. Further, a series of Cre mutants were generated by site-directed mutagenesis. When one of the mutants, Cre(H289P) in both configurations, was used in the experiment, the percentage of recombination dropped to background levels in a number of insulin-negative cell lines, but decreased only slightly in INS-1 cells. Consistently, DNA substrate digestion assay showed that the enzymatic activity of Cre(H289P) was reduced by 30-fold as compared to that of wild-type. In this study, we reported the generation of constructs containing RIP and Cre mutants, which enabled enhanced beta-cell specific labeling in vitro. These tools could be invaluable for beta-cell targeting and to the study of islet development.

Gene delivery in tissue engineering and regenerative medicine

As a promising strategy to aid or replace tissue/organ transplantation, gene delivery has been used for regenerative medicine applications to create or restore normal function at the cell and tissue levels. Gene delivery has been successfully performed ex vivo and in vivo in these applications. Excellent proliferation capabilities and differentiation potentials render certain cells as excellent candidates for ex vivo gene delivery for regenerative medicine applications, which is why multipotent and pluripotent cells have been intensely studied in this vein. In this review, gene delivery is discussed in detail, along with its applications to tissue engineering and regenerative medicine. A definition of a stem cell is compared to a definition of a stem property, and both provide the foundation for an in-depth look at gene delivery investigations from a germ lineage angle.

Established and emerging biomarkers for the prediction of type 1 diabetes: a systematic review

Type 1 diabetes (T1D) is an autoimmune disease with a prolonged and variable latent period that culminates in the destruction of pancreatic β-cells and the development of hyperglycemia. There is a need for diagnostic biomarkers to detect more accurately individuals with prediabetes to expedite targeting for prevention and intervention strategies. To assess the current ability to predict the insidious development of T1D, we conducted a comprehensive systematic review for established and prospective predictive markers of T1D using the Medline, OVID, and EMBASE databases. Resulting citations were screened for relevance to subject. Our research generated five major categories of markers that are either currently used or forthcoming: genetic, autoantibody, risk score quantification, cellular immunity, and β-cell function. The current standard used to assess T1D onset or predisposition focuses on autoimmune pathology and disease-associated autoantibodies. Research studies in general go beyond autoantibody screening and assess genetic predisposition, and quantitate risk of developing disease based on additional factors. However, there are few currently used techniques that assess the root of T1D: β-cell destruction. Thus, novel techniques are discussed with the potential to gauge degrees of β-cell stress and failure via protein, RNA, and DNA analyses.

Identification of a SIRT1 mutation in a family with type 1 diabetes

Type 1 diabetes is caused by autoimmune-mediated β cell destruction leading to insulin deficiency. The histone deacetylase SIRT1 plays an essential role in modulating several age-related diseases. Here we describe a family carrying a mutation in the SIRT1 gene, in which all five affected members developed an autoimmune disorder: four developed type 1 diabetes, and one developed ulcerative colitis. Initially, a 26-year-old man was diagnosed with the typical features of type 1 diabetes, including lean body mass, autoantibodies, T cell reactivity to β cell antigens, and a rapid dependence on insulin. Direct and exome sequencing identified the presence of a T-to-C exchange in exon 1 of SIRT1, corresponding to a leucine-to-proline mutation at residue 107. Expression of SIRT1-L107P in insulin-producing cells resulted in overproduction of nitric oxide, cytokines, and chemokines. These observations identify a role for SIRT1 in human autoimmunity and unveil a monogenic form of type 1 diabetes.

The sirtuin family's role in aging and age-associated pathologies

The 7 mammalian sirtuin proteins compose a protective cavalry of enzymes that can be invoked by cells to aid in the defense against a vast array of stressors. The pathologies associated with aging, such as metabolic syndrome, neurodegeneration, and cancer, are either caused by or exacerbated by a lifetime of chronic stress. As such, the activation of sirtuin proteins could provide a therapeutic approach to buffer against chronic stress and ameliorate age-related decline. Here we review experimental evidence both for and against this proposal, as well as the implications that isoform-specific sirtuin activation may have for healthy aging in humans.

Are sirtuins viable targets for improving healthspan and lifespan?

Although the increased lifespan of our populations illustrates the success of modern medicine, the risk of developing many diseases increases exponentially with old age. Caloric restriction is known to retard ageing and delay functional decline as well as the onset of disease in most organisms. Studies have implicated the sirtuins (SIRT1-SIRT7) as mediators of key effects of caloric restriction during ageing. Two unrelated molecules that have been shown to increase SIRT1 activity in some settings, resveratrol and SRT1720, are excellent protectors against metabolic stress in mammals, making SIRT1 a potentially appealing target for therapeutic interventions. This Review covers the current status and controversies surrounding the potential of sirtuins as novel pharmacological targets, with a focus on SIRT1.

Variants in the SIRT1 gene may affect diabetes risk in interaction with prenatal exposure to famine

OBJECTIVE

To investigate whether SIRT1, a nutrient-sensing histone deacetylase, influences fetal programming during malnutrition.

RESEARCH DESIGN AND METHODS

In 793 individuals of the Dutch Famine Birth Cohort, we analyzed the interaction between three SIRT1 single nucleotide polymorphisms (SNPs) and prenatal exposure to famine on type 2 diabetes risk.

RESULTS

In the total population (exposed and unexposed), SIRT1 variants were not associated with type 2 diabetes. A significant interaction was found between two SIRT1 SNPs and exposure to famine in utero on type 2 diabetes risk (P = 0.03 for rs7895833; P = 0.01 for rs1467568). Minor alleles of these SNPs were associated with a lower prevalence of type 2 diabetes only in individuals who had been exposed to famine prenatally (odds ratio for rs7895833 0.50 [95% CI 0.24-1.03], P = 0.06; for rs1467568 0.48 [0.25-0.91], P = 0.02).

CONCLUSIONS

SIRT1 may be an important genetic factor involved in fetal programming during malnutrition, influencing type 2 diabetes risk later in life.

WldS enhances insulin transcription and secretion via a SIRT1-dependent pathway and improves glucose homeostasis

OBJECTIVE Wld(S) (Wallerian degeneration slow), a fusion protein from a spontaneous mutation containing full-length nicotinamide mononucleotide adenylyltransferase 1, has NAD biosynthesis activity and protects axon from degeneration robustly. NAD biosynthesis is also implicated in insulin secretion in β-cells. The aim of this study was to investigate the effect of Wld(S) on β-cells and glucose homeostasis.

RESEARCH DESIGN AND METHODS

Using the Wld(S) mice, we measured the expression of Wld(S) in pancreas and analyzed the effect of Wld(S) on glucose homeostasis. The direct effect of Wld(S) on insulin transcription and secretion and the related mechanisms was measured in isolated islets or β-cell lines. Silent information regulator 1 (SIRT1), an NAD-dependent protein deacetylase, is involved in insulin secretion. Thus, Wld(S) mice with SIRT1 deficiency were generated to study whether the SIRT1-dependent pathway is involved.

RESULTS

Wld(S) is highly expressed in the pancreas and improves glucose homeostasis. Wld(S) mice are resistant to high-fat diet-induced glucose intolerance and streptozotocin (STZ)-induced hyperglycemia. Wld(S) increases insulin transcription dependent on its NAD biosynthesis activity and enhances insulin secretion. SIRT1 is required for the improved insulin transcription, secretion, and resistance to STZ-induced hyperglycemia caused by Wld(S). Moreover, Wld(S) associates with SIRT1 and increases NAD levels in the pancreas, causing the enhanced SIRT1 activity to downregulate uncoupling protein 2 (UCP2) expression and upregulate ATP levels.

CONCLUSIONS

Our results demonstrate that Wld(S) combines an insulinotropic effect with protection against β-cell failure and suggest that enhancing NAD biosynthesis in β-cells to increase SIRT1 activity could be a potential therapeutic approach for diabetes.