Increased insulin sensitivity and diminished pancreatic beta-cell function in DNA repair deficient Ercc1d/- mice

Advances in secondary prevention mechanisms of macrovascular complications in type 2 diabetes mellitus patients: a comprehensive review

Type 2 diabetes mellitus (T2DM) poses a significant global health burden. This is particularly due to its macrovascular complications, such as coronary artery disease, peripheral vascular disease, and cerebrovascular disease, which have emerged as leading contributors to morbidity and mortality. This review comprehensively explores the pathophysiological mechanisms underlying these complications, protective strategies, and both existing and emerging secondary preventive measures. Furthermore, we delve into the applications of experimental models and methodologies in foundational research while also highlighting current research limitations and future directions. Specifically, we focus on the literature published post-2020 concerning the secondary prevention of macrovascular complications in patients with T2DM by conducting a targeted review of studies supported by robust evidence to offer a holistic perspective.

Endogenous Glucose Production in Patients With Glycogen Storage Disease Type Ia Estimated by Oral D-[6,6-2H2]-glucose

CONTEXT

Glycogen storage disease type Ia (GSDIa) is an inborn metabolic disorder characterized by impaired endogenous glucose production (EGP). Monitoring of patients with GSDIa is prioritized because of ongoing treatment developments. Stable isotope tracers may enable reliable EGP monitoring.

OBJECTIVE

The aim of this study was to prospectively assess the rate of appearance of endogenous glucose into the bloodstream (Ra) in patients with GSDIa after a single oral D-[6,6-2H2]-glucose dose.

METHODS

Ten adult patients with GSDIa and 10 age-, sex-, and body mass index-matched healthy volunteers (HVs) were enrolled. For each participant, 3 oral glucose tracer tests were performed: (1) preprandial/fasted, (2) postprandial, and (3) randomly fed states. Dried blood spots were collected before D-[6,6-2H2]-glucose administration and 10, 20, 30, 40, 50, 60, 75, 90, and 120 minutes thereafter.

RESULTS

Glucose Ra in fasted HVs was consistent with previously reported data. The time-averaged glucose Ra was significantly higher in (1) preprandial/fasted patients with GSDIa than HV and (2) postprandial HV compared with fasted HV(P < .05). A progressive decrease in glucose Ra was observed in preprandial/fasted patients with GSDIa; the change in glucose Ra time-course was directly correlated with the change in capillary glucose (P < .05).

CONCLUSION

This is the first study to quantify glucose Ra in patients with GSDIa using oral D-[6,6-2H2] glucose. The test can reliably estimate EGP under conditions in which fasting tolerance is unaffected but does not discriminate between relative contributions of EGP (eg, liver, kidney) and exogenous sources (eg, dietary cornstarch). Future application is warranted for longitudinal monitoring after novel genome based treatments in patients with GSDIa in whom nocturnal dietary management can be discontinued.

Failure to repair endogenous DNA damage in β-cells causes adult-onset diabetes in mice

Age is the greatest risk factor for the development of type 2 diabetes mellitus (T2DM). Age-related decline in organ function is attributed to the accumulation of stochastic damage, including damage to the nuclear genome. Islets of T2DM patients display increased levels of DNA damage. However, whether this is a cause or consequence of the disease has not been elucidated. Here, we asked if spontaneous, endogenous DNA damage in β-cells can drive β-cell dysfunction and diabetes, via deletion of Ercc1, a key DNA repair gene, in β-cells. Mice harboring Ercc1-deficient β-cells developed adult-onset diabetes as demonstrated by increased random and fasted blood glucose levels, impaired glucose tolerance, and reduced insulin secretion. The inability to repair endogenous DNA damage led to an increase in oxidative DNA damage and apoptosis in β-cells and a significant loss of β-cell mass. Using electron microscopy, we identified β-cells in clear distress that showed an increased cell size, enlarged nuclear size, reduced number of mature insulin granules, and decreased number of mitochondria. Some β-cells were more affected than others consistent with the stochastic nature of spontaneous DNA damage. Ercc1-deficiency in β-cells also resulted in loss of β-cell function as glucose-stimulated insulin secretion and mitochondrial function were impaired in islets isolated from mice harboring Ercc1-deficient β-cells. These data reveal that unrepaired endogenous DNA damage is sufficient to drive β-cell dysfunction and provide a mechanism by which age increases the risk of T2DM.

Pancreatic β-cell senescence in diabetes: mechanisms, markers and therapies

Cellular senescence is a response to a wide variety of stressors, including DNA damage, oncogene activation and physiologic aging, and pathologically accelerated senescence contributes to human disease, including diabetes mellitus. Indeed, recent work in this field has demonstrated a role for pancreatic β-cell senescence in the pathogenesis of Type 1 Diabetes, Type 2 Diabetes and monogenic diabetes. Small molecule or genetic targeting of senescent β-cells has shown promise as a novel therapeutic approach for preventing and treating diabetes. Despite these advances, major questions remain around the molecular mechanisms driving senescence in the β-cell, identification of molecular markers that distinguish senescent from non-senescent β-cell subpopulations, and translation of proof-of-concept therapies into novel treatments for diabetes in humans. Here, we summarize the current state of the field of β-cell senescence, highlighting insights from mouse models as well as studies on human islets and β-cells. We identify markers that have been used to detect β-cell senescence to unify future research efforts in this field. We discuss emerging concepts of the natural history of senescence in β-cells, heterogeneity of senescent β-cells subpopulations, role of sex differences in senescent responses, and the consequences of senescence on integrated islet function and microenvironment. As a young and developing field, there remain many open research questions which need to be addressed to move senescence-targeted approaches towards clinical investigation.

Elevated markers of DNA damage and senescence are associated with the progression of albuminuria and restrictive lung disease in patients with type 2 diabetes

BACKGROUND

This study was conducted to investigate the cascade involving DNA damage, senescence, and senescence-associated secretory phenotype (SASP) in experimental diabetes and in a four-year follow-up study in patients with pre-diabetes and type 2 diabetes.

METHODS

Kidney, lung, and liver were studied in 4 months diabetic db/db mice and age-matched controls for the presence of DNA damage and fibrosis. DNA damage (comet-tail-length and ɤH2Ax-positivity in white blood cells), urinary p21-excretion, and plasma IL-6 and TGF-β1 were determined from 115 healthy participants, 34 patients with pre-diabetes and 221 with type 2 diabetes. Urinary albumin-creatinine-ratio, lung function, and transient elastography of the liver were performed in a prospective follow-up study over 4 years.

FINDINGS

db/db mice showed an increased nuclear ɤH2AX signal in all tissues as compared to the background control. Markers for DNA damage, senescence, and SASP were increased in patients with diabetes. The presence of nephropathy, restrictive lung disease (RLD), and increased liver stiffness was in a cross-sectional design associated with increased markers for DNA damage, senescence, and SASP. The progression of nephropathy over 4 years was predicted by increased DNA damage, senescence, and SASP, while the progression of RLD was associated with increased DNA damage and IL-6 only. The progression of liver stiffness was not associated with any of these parameters. HbA1c was not predictive for progression.

INTERPRETATION

In db/db mice, the cascade of DNA damage is associated with diabetes-related complications. In patients with diabetes, the progression of complications in the kidney and lung is predicted by markers reflecting DNA damage, and senescence-triggered organ fibrosis.

FUNDING

This work was supported by the German Research Foundation (DFG) in the CRC 1118 and CRC 1158, by the GRK DIAMICOM, by the German Center for Diabetes Research (DZD e.V.), and by the Ministry of Science, Research and the Arts, Baden-Württemberg (Kompetenznetzwerk Präventivmedizin).

The Transcription Factor YY1 Is Essential for Normal DNA Repair and Cell Cycle in Human and Mouse β-Cells

Identifying the mechanisms behind the β-cell adaptation to failure is important to develop strategies to manage type 2 diabetes (T2D). Using db/db mice at early stages of the disease process, we took advantage of unbiased RNA sequencing to identify genes/pathways regulated by insulin resistance in β-cells. We demonstrate herein that islets from 4-week-old nonobese and nondiabetic leptin receptor-deficient db/db mice exhibited downregulation of several genes involved in cell cycle regulation and DNA repair. We identified the transcription factor Yin Yang 1 (YY1) as a common gene between both pathways. The expression of YY1 and its targeted genes was decreased in the db/db islets. We confirmed the reduction in YY1 expression in β-cells from diabetic db/db mice, mice fed a high-fat diet (HFD), and individuals with T2D. Chromatin immunoprecipitation sequencing profiling in EndoC-βH1 cells, a human pancreatic β-cell line, indicated that YY1 binding regions regulate cell cycle control and DNA damage recognition and repair. We then generated mouse models with constitutive and inducible YY1 deficiency in β-cells. YY1-deficient mice developed diabetes early in life due to β-cell loss. β-Cells from these mice exhibited higher DNA damage, cell cycle arrest, and cell death as well as decreased maturation markers. Tamoxifen-induced YY1 deficiency in mature β-cells impaired β-cell function and induced DNA damage. In summary, we identified YY1 as a critical factor for β-cell DNA repair and cell cycle progression.

cGAS-STING mediates cytoplasmic mitochondrial-DNA-induced inflammatory signal transduction during accelerated senescence of pancreatic β-cells induced by metabolic stress

Type 2 diabetes mellitus (T2DM) is an age-related disease characterized by impaired pancreatic β cell function and insulin resistance. Recent studies have shown that the accumulation of senescent β cells under metabolic stress conditions leads to the progression of T2DM, while senolysis can improve the prognosis. However, the specific mechanism of β cell senescence is still unclear. In this study, we found that the increased load of senescence pancreatic β cells in both older mice and obese mice induced by high-fat diet (HFD) (DIO mice) was accompanied by activation of the Cyclic GMP-AMP synthase (cGAS) - stimulator of interferon genes (STING) pathway and using cGAS or STING small interfering RNA or STING inhibitor C176 to downregulate this pathway reduced the senescence-associated secretion profile (SASP) and senescence of Min6 cells treated with palmitic acid or hydrogen peroxide. C176 intervention in DIO mice also significantly reduced the inflammation and senescence of the islets, thereby protecting the function of pancreatic β cell and glucose metabolism. Our study further revealed that mitochondrial DNA (mtDNA) leakage under metabolic stress conditions was critical for the activation of the cGAS-STING pathway, which can be reversed by the mtDNA depleting agent ethidium bromide. Consistently, mtDNA leakage was more severe in older mice and was accelerated by a chronic HFD. In conclusion, we demonstrate that cytoplasmic mtDNA activates the cGAS-STING pathway to mediate SASP during the accelerated senescence of pancreatic β-cells induced by metabolic stress, and this process can be downregulated by the STING inhibitor C176.

R-loops trigger the release of cytoplasmic ssDNAs leading to chronic inflammation upon DNA damage

How DNA damage leads to chronic inflammation and tissue degeneration with aging remains to be fully resolved. Here, we show that DNA damage leads to cellular senescence, fibrosis, loss-of-tissue architecture, and chronic pancreatitis in mice with an inborn defect in the excision repair cross complementation group 1 (Ercc1) gene. We find that DNA damage-driven R-loops causally contribute to the active release and buildup of single-stranded DNAs (ssDNAs) in the cytoplasm of cells triggering a viral-like immune response in progeroid and naturally aged pancreata. To reduce the proinflammatory load, we developed an extracellular vesicle (EV)-based strategy to deliver recombinant S1 or ribonuclease H nucleases in inflamed Ercc1^−/− pancreatic cells. Treatment of Ercc1^−/− animals with the EV-delivered nuclease cargo eliminates DNA damage-induced R-loops and cytoplasmic ssDNAs alleviating chronic inflammation. Thus, DNA damage-driven ssDNAs causally contribute to tissue degeneration, Ercc1^−/− paving the way for novel rationalized intervention strategies against age-related chronic inflammation.