Metabolomics Identifies a Biomarker Revealing In Vivo Loss of Functional ß-Cell Mass Before Diabetes Onset.

Identification of individuals with decreased functional ß-cell mass is essential for the prevention of diabetes. However, in vivo detection of early asymptomatic ß-cell defect remains unsuccessful. Metabolomics has emerged as a powerful tool in providing readouts of early disease states before clinical manifestation. We aimed at identifying novel plasma biomarkers for loss of functional ß-cell mass in the asymptomatic prediabetes stage. Nontargeted and targeted metabolomics were applied in both lean ß-Phb2-/- (ß-cell-specific prohibitin-2 knockout) mice and obese db/db (leptin receptor mutant) mice, two distinct mouse models requiring neither chemical nor dietary treatments to induce spontaneous decline of functional ß-cell mass promoting progressive diabetes development. Nontargeted metabolomics on ß-Phb2-/- mice identified 48 and 82 significantly affected metabolites in liver and plasma, respectively. Machine learning analysis pointed to deoxyhexose sugars consistently reduced at the asymptomatic prediabetes stage, including in db/db mice, showing strong correlation with the gradual loss of ß-cells. Further targeted metabolomics by gas chromatography-mass spectrometry uncovered the identity of the deoxyhexose, with 1,5-anhydroglucitol displaying the most substantial changes. In conclusion, this study identified 1,5-anhydroglucitol as associated with the loss of functional ß-cell mass and uncovered metabolic similarities between liver and plasma, providing insights into the systemic effects caused by early decline in ß-cells.

Loss of prohibitin induces mitochondrial damages altering ß-cell function and survival and is responsible for gradual diabetes development.

Prohibitins are highly conserved proteins mainly implicated in the maintenance of mitochondrial function and architecture. Their dysfunctions are associated with aging, cancer, obesity, and inflammation. However, their possible role in pancreatic ß-cells remains unknown. The current study documents the expression of prohibitins in human and rodent islets and their key role for ß-cell function and survival. Ablation of Phb2 in mouse ß-cells sequentially resulted in impairment of mitochondrial function and insulin secretion, loss of ß-cells, progressive alteration of glucose homeostasis, and, ultimately, severe diabetes. Remarkably, these events progressed over a 3-week period of time after weaning. Defective insulin supply in ß-Phb2(-/-) mice was contributed by both ß-cell dysfunction and apoptosis, temporarily compensated by increased ß-cell proliferation. At the molecular level, we observed that deletion of Phb2 caused mitochondrial abnormalities, including reduction of mitochondrial DNA copy number and respiratory chain complex IV levels, altered mitochondrial activity, cleavage of L-optic atrophy 1, and mitochondrial fragmentation. Overall, our data demonstrate that Phb2 is essential for metabolic activation of mitochondria and, as a consequence, for function and survival of ß-cells.

Mitochondrial dysfunction in pancreatic ß cells.

In pancreatic ß cells, mitochondria play a central role in coupling glucose metabolism to insulin exocytosis, thereby ensuring strict control of glucose-stimulated insulin secretion. Defects in mitochondrial function impair this metabolic coupling, and ultimately promote apoptosis and ß cell death. Various factors have been identified that may contribute to mitochondrial dysfunction. In this review we address the emerging concept of complex links between these factors. We also discuss the role of the mitochondrial genome and mutations associated with diabetes, the effect of oxidative stress and reactive oxygen species, the sensitivity of mitochondria to lipotoxicity, and the adaptive dynamics of mitochondrial morphology. Better comprehension of the molecular mechanisms contributing to mitochondrial dysfunction will help drive the development of effective therapeutic approaches.