Mitochondrial metabolism and diabetes

Exploring the link between estimated glucose disposal rate and Parkinson's disease: cross-sectional and mortality analysis of NHANES 2003-2016

Objectives

To investigate the association between estimated glucose disposal rate (eGDR), a surrogate marker of insulin resistance, and Parkinson's disease (PD) risk, and to examine the relationship between eGDR and all-cause mortality among PD patients.

Methods

Using data from the National Health and Nutrition Examination Survey (NHANES) 2003-2016, we conducted a cross-sectional study of 20,767 participants aged ≥40 years. eGDR was calculated using waist circumference, hypertension status, and HbA1c levels. PD cases were identified through anti-parkinsonian medication use. The association between eGDR and PD was examined using weighted logistic regression models with progressive adjustment for potential confounders. Survival analysis was performed in 255 PD patients to assess the relationship between eGDR and all-cause mortality.

Results

Among participants, 256 had PD (weighted prevalence: 1.23%). Higher eGDR was associated with lower odds of PD in crude analysis (OR: 0.906, 95% CI: 0.856-0.960, P < 0.001). After full adjustment, the highest eGDR tertile showed significantly lower odds of PD compared to the lowest tertile (OR: 0.574, 95% CI: 0.337-0.976, P = 0.040). Restricted cubic spline analysis revealed a significant M-shaped non-linear relationship between eGDR and PD risk (P for non-linearity < 0.001). In survival analysis, higher eGDR was associated with lower mortality risk (adjusted HR: 0.875, 95% CI: 0.775-0.987, P = 0.030), with an inverted U-shaped relationship observed (P for non-linearity = 0.0352).

Conclusion

Higher eGDR levels are associated with lower PD risk and better survival in PD patients, suggesting that insulin sensitivity might play a role in PD pathogenesis and progression. These findings highlight the potential importance of metabolic health in PD.

Forced Degradation Study of an Anti-Diabetic Drug Imeglimin: Impurity Profiling and Structure Elucidation Using LC-Q-ToF-MS/MS and NMR

RATIONALE

The present study aims to establish structures of the degradation products of an anti-diabetic drug, Imeglimin (IMG) approved for the treatment of type 2 diabetes mellitus in the year 2021. Degradation pathways are proposed along with in silico toxicity assessments of the observed degradation products (DPs) of the drug.

METHODS

A reversed-phase high-performance liquid chromatography (RP-HPLC), equipped with a photodiode array detector, was used to separate the observed DPs with a Phenomenex Luna PFP (250 × 4.6 mm, 5 μm) column, using 10 mM ammonium formate (pH 4.5) and methanol as mobile phase. Liquid chromatography quadrupole time of flight mass spectrometry (LC-Q-ToF-MS/MS) and nuclear magnetic resonance (NMR) spectroscopy were employed for structural elucidation. Zeneth and Derek suites were used for in silico assessments.

RESULTS

A total of four degradation products were observed, which were successfully separated on an RP-HPLC. The structural characterization of three of the four DPs was achieved using LC-Q-TOF-MS/MS by employing electro spray ionization as well as atmospheric pressure chemical ionization. Additionally, DP-3 was isolated using a preparative HPLC and was characterized by NMR. Computationally predicted structures were compared with the experimental observations.

CONCLUSION

An HPLC method, capable of separating the Imeglimin and its four DPs, was developed and validated as per the ICH Q2(R1) guideline. Structure elucidation reveals a variety of products with metformin as one of the identified DPs along with a metabolite. The toxicity potential of DPs was assessed through docking studies.

Naringin prevents heart mitochondria dysfunction during diabetic cardiomyopathy in rats

Background and purpose

Cardiac mitochondria dysfunction plays a central pathophysiological role in the abnormal glucose metabolism in the heart during diabetic cardiomyopathy. The present study evaluated the effects of flavonoid glycoside naringin treatment on the interconnection between changes in cardiac mitochondria oxygen consumption, membrane potential and mitochondrial Ca2+ sensitivity during type 1 diabetes.

Experimental approach

Type 1 diabetes was induced by an intraperitoneal injection of streptozotocin (40 mg/kg) in rats and islet morphology, glucose and insulin levels, changes in heart mitochondria respiration, membrane potential, spontaneous and Ca2+ - induced mitochondrial permeability transition (MPT) pore opening were evaluated.

Key results

Diabetes resulted in typical signs of hyperglycaemia, which were accompanied by a rat cardiac mitochondria dysfunction, manifested by decreased V 2 and V 3 rates of oxygen consumption, while the initial membrane potential value remained unchanged. The rates of Ca2+-induced MPT pore opening and Ca2+-induced membrane potential dissipation in isolated mitochondria decreased under type 1 diabetes. The naringin treatment (40 mg/kg of the body weight, 4 weeks) partially recovered impaired cardiac mitochondria respiration, decreased spontaneous and increased Ca2+-induced MPT pore opening, improved pancreatic islets morphology and dystrophic changes, lowered glycated haemoglobin and blood plasma urea, and decreased the oxidative stress level with glucose or insulin concentrations remaining unchanged in diabetic animals.

Conclusions

Naringin administration demonstrated beneficial effects during type 1 diabetes and represents a promising therapeutic (or nutraceutical) approach for diabetes treatment.

Sphingosine-1-Phosphate Signalling Inhibition Suppresses Th1-Like Treg Generation by Reversing Mitochondrial Uncoupling

Inflammatory environments induce the generation of dysfunctional IFNγ+T-bet+FOXP3+ Th1-like Tregs, which show defective function and are found in autoimmune conditions including multiple sclerosis (MS). The pathways that control the generation of Th1-like Tregs are not well understood. Sphingosine-1-phosphate (S1P) signalling molecules are upregulated in Th1-like Tregs, and in vivo S1P inhibition with Fingolimod (FTY720) inhibits the expression of genes responsible for Treg plasticity in MS patients. However, the underlying mechanisms are unknown. Here we show that S1P signalling inhibition by FTY720 inhibits the generation of Th1-like Tregs and rescues their suppressive function. These effects are mediated by a decrease in mTORC1 signalling and reversal of the mitochondrial uncoupling that Tregs undergo during their reprogramming into Th1-like Tregs in vitro. Finally, these results are validated in in vivo-generated Th1-like Tregs, as Tregs from MS patients treated with FTY720 display decreased Th1-like Treg frequency, increased suppressive function and mitochondrial metabolism rebalance. These results highlight the involvement of mitochondrial uncoupling in Treg reprogramming and identify S1P signalling inhibition as a target to suppress the generation of dysfunctional Th1-like Tregs.

Cellular oxygen consumption in patients with diabetic ketoacidosis

BACKGROUND

Diabetic ketoacidosis (DKA) is a potentially life-threatening disorder associated with severe alterations in metabolism and acid-base status. Mitochondrial dysfunction is associated with diabetes and its complications. Thiamine and coenzyme Q10 (CoQ10) are important factors in aerobic metabolism. In this study, we measured cellular oxygen consumption rates (OCRs) and the effects of in vitro administration of thiamine and CoQ10 on OCRs in patients with DKA versus healthy controls.

METHODS

Blood samples were collected from a prospective cohort of patients with DKA and from controls. Cellular OCRs were measured in peripheral blood mononuclear cells (PBMC) without treatment and after treatment with thiamine, CoQ10, or both. The mitochondrial profile was measured using an XFe96 Extracellular Flux Analyzer and XF Cell Mito Stress Test Kit (Seahorse Bioscience). A linear quantile mixed model was used to compare OCRs and estimate treatment effects.

RESULTS

A total of 62 patients with DKA and 48 controls were included in the study. The median basal and maximal OCRs were lower in the DKA group than in the control group (basal: 4.7 [IQR: 3.3, 7.9] vs. 7.9 [5.0, 9.5], p = 0.036; maximal: 16.4 [9.5, 28.1] vs. 31.5 [20.6, 46.0] pmol/min/µg protein, p < 0.001). In DKA samples, basal and maximal OCRs were significantly increased when treated with thiamine, CoQ10, or both. In controls, basal and maximal OCR were significantly increased only with thiamine treatment.

CONCLUSION

Mitochondrial metabolic profiles of patients with DKA demonstrated lower cellular oxygen consumption when compared to healthy controls. Oxygen consumption increased significantly in cells of patients with DKA treated with thiamine or CoQ10. These results suggest that thiamine and CoQ10 could potentially have therapeutic benefits in DKA via their metabolic effects on mitochondrial cellular respiration.

miR-146a-5p mediates inflammation-induced β cell mitochondrial dysfunction and apoptosis

We previously showed that miR-146a-5p is upregulated in pancreatic islets treated with proinflammatory cytokines. Others have reported that miR-146a-5p overexpression is associated with β cell apoptosis and impaired insulin secretion. However, the molecular mechanisms mediating these effects remain elusive. To investigate the role of miR-146a-5p in β cell function, we developed stable MIN6 cell lines to either overexpress or inhibit the expression of miR-146a-5p. Monoclonal cell populations were treated with proinflammatory cytokines (interleukin-1β, interferonγ, and tumor necrosis factor α) to model type 1 diabetes in vitro. We found that overexpression of miR-146a-5p increased cell death under conditions of inflammatory stress and led to mitochondrial membrane depolarization, whereas inhibition of miR-146a-5p reversed these effects. Additionally, inhibition of miR-146a-5p increased insulin secretion, mitochondrial DNA copy number, respiration rate, and ATP production. Further, RNA-seq data showed enrichment of pathways related to insulin secretion, apoptosis, and mitochondrial function when the expression levels of miR-146a-5p were altered. Finally, a temporal increase in miR-146a-5p expression levels and a decrease in mitochondria function markers were observed in islets derived from nonobese diabetic mice. Collectively, these data suggest that miR-146a-5p may promote β cell dysfunction and death during inflammatory stress by suppressing mitochondrial function.

miR-146a-5p mediates inflammation-induced β cell mitochondrial dysfunction and apoptosis

We previously showed that miR-146a-5p is upregulated in pancreatic islets treated with pro-inflammatory cytokines. Others have reported that miR-146a-5p overexpression is associated with β cell apoptosis and impaired insulin secretion. However, the molecular mechanisms mediating these effects remain elusive. To investigate the role of miR-146a-5p in β cell function, we developed stable MIN6 cell lines to either overexpress or inhibit the expression of miR-146a-5p. Monoclonal cell populations were treated with pro-inflammatory cytokines (IL-1β, IFNγ, and TNFα) to model type 1 diabetes (T1D) in vitro. We found that overexpression of miR-146a-5p increased cell death under conditions of inflammatory stress and led to mitochondrial membrane depolarization, whereas inhibition of miR-146a-5p reversed these effects. Additionally, inhibition of miR-146a-5p increased insulin secretion, mitochondrial DNA copy number, respiration rate, and ATP production Further, RNA sequencing data showed enrichment of pathways related to insulin secretion, apoptosis, and mitochondrial function when the expression levels of miR-146a-5p were altered. Finally, a temporal increase in miR-146a-5p expression levels and a decrease in mitochondria function markers was observed in islets derived from NOD mice. Collectively, these data suggest that miR-146a-5p may promote β cell dysfunction and death during inflammatory stress by suppressing mitochondrial function.

Cardiovascular protection of YiyiFuzi powder and the potential mechanisms through modulating mitochondria-endoplasmic reticulum interactions

Cardiovascular diseases (CVD) remain the leading cause of death worldwide and represent a major public health challenge. YiyiFuzi Powder (YYFZ), composed of Coicis semen and Fuzi, is a classical traditional Chinese medicine prescription from the Synopsis of Golden Chamber dating back to the Han Dynasty. Historically, YYFZ has been used to treat various CVD, rooted in Chinese therapeutic principles. Network pharmacology analysis indicated that YYFZ may exhibit direct or indirect effects on mitochondria-endoplasmic reticulum (ER) interactions. This review, focusing on the cardiovascular protective effects of Coicis semen and Fuzi, summarizes the potential mechanisms by which YYFZ acts on mitochondria and the ER. The underlying mechanisms are associated with regulating cardiovascular risk factors (such as blood lipids and glucose), impacting mitochondrial structure and function, modulating ER stress, inhibiting oxidative stress, suppressing inflammatory responses, regulating cellular apoptosis, and maintaining calcium ion balance. The involved pathways include, but were not limited to, upregulating the IGF-1/PI3K/AKT, cAMP/PKA, eNOS/NO/cGMP/SIRT1, SIRT1/PGC-1α, Klotho/SIRT1, OXPHOS/ATP, PPARα/PGC-1α/SIRT3, AMPK/JNK, PTEN/PI3K/AKT, β2-AR/PI3K/AKT, and modified Q cycle signaling pathways. Meanwhile, the MCU, NF-κB, and JAK/STAT signaling pathways were downregulated. The PERK/eIF2α/ATF4/CHOP, PERK/SREBP-1c/FAS, IRE1, PINK1-dependent mitophagy, and AMPK/mTOR signaling pathways were bidirectionally regulated. High-quality experimental studies are needed to further elucidate the underlying mechanisms of YYFZ in CVD treatment.

Mitochondria: A source of potential biomarkers for non-communicable diseases

Mitochondria, as an endosymbiont of eukaryotic cells, controls multiple cellular activities, including respiration, reactive oxygen species production, fatty acid synthesis, and death. Though the majority of functional mitochondrial proteins are translated through a nucleus-controlled process, very few of them (∼10%) are translated within mitochondria through their own machinery. Germline and somatic mutations in mitochondrial and nuclear DNA significantly impact mitochondrial homeostasis and function. Such modifications disturbing mitochondrial biogenesis, metabolism, or mitophagy eventually resulted in cellular pathophysiology. In this chapter, we discussed the impact of mitochondria and its dysfunction on several non-communicable diseases like cancer, diabetes, neurodegenerative, and cardiovascular problems. Mitochondrial dysfunction and its outcome could be screened by currently available omics-based techniques, flow cytometry, and high-resolution imaging. Such characterization could be evaluated as potential biomarkers to assess the disease burden and prognosis.

RNA modifications in physiology and disease: towards clinical applications

The ability of chemical modifications of single nucleotides to alter the electrostatic charge, hydrophobic surface and base pairing of RNA molecules is exploited for the clinical use of stable artificial RNAs such as mRNA vaccines and synthetic small RNA molecules - to increase or decrease the expression of therapeutic proteins. Furthermore, naturally occurring biochemical modifications of nucleotides regulate RNA metabolism and function to modulate crucial cellular processes. Studies showing the mechanisms by which RNA modifications regulate basic cell functions in higher organisms have led to greater understanding of how aberrant RNA modification profiles can cause disease in humans. Together, these basic science discoveries have unravelled the molecular and cellular functions of RNA modifications, have provided new prospects for therapeutic manipulation and have led to a range of innovative clinical approaches.

Mitochondrial Dysfunction and Imeglimin: A New Ray of Hope for the Treatment of Type-2 Diabetes Mellitus

Diabetes is a rapidly growing health challenge and epidemic in many developing countries, including India. India, being the diabetes capital of the world, has the dubious dual distinction of being the leading nations for both undernutrition and overnutrition. Diabetes prevalence has increased in both rural and urban areas, affected the younger population and increased the risk of complications and economic burden. These alarming statistics ring an alarm bell to achieve glycemic targets in the affected population in order to decrease diabetes-related morbidity and mortality. In the recent years, diabetes pathophysiology has been extended from an ominous triad through octet and dirty dozen etc. There is a new scope to target multiple pathways at the molecular level to achieve a better glycemic target and further prevent micro- and macrovascular complications. Mitochondrial dysfunction has a pivotal role in both β-cell failure and insulin resistance. Hence, targeting this molecular pathway may help with both insulin secretion and peripheral tissue sensitization to insulin. Imeglimin is the latest addition to our anti-diabetic armamentarium. As imeglimin targets, this root cause of defective energy metabolism and insulin resistance makes it a new add-on therapy in different diabetic regimes to achieve the proper glycemic targets. Its good tolerability and efficacy profiles in recent studies shows a new ray of hope in the journey to curtail diabetes-related morbidity.

mtDNA Single-Nucleotide Variants Associated with Type 2 Diabetes

Type 2 diabetes (T2D) is a chronic systemic disease with a complex etiology, characterized by insulin resistance and mitochondrial dysfunction in various cell tissues. To explore this relationship, we conducted a secondary analysis of complete mtDNA sequences from 1261 T2D patients and 1105 control individuals. Our findings revealed significant associations between certain single-nucleotide polymorphisms (SNPs) and T2D. Notably, the variants m.1438A>G (rs2001030) (controls: 32 [27.6%], T2D: 84 [72.4%]; OR: 2.46; 95%CI: 1.64-3.78; p < 0.001), m.14766C>T (rs193302980) (controls: 498 [36.9%], T2D: 853 [63.1%]; OR: 2.57, 95%CI: 2.18-3.04, p < 0.001), and m.16519T>C (rs3937033) (controls: 363 [43.4%], T2D: 474 [56.6%]; OR: 1.24, 95%CI: 1.05-1.47, p = 0.012) were significantly associated with the likelihood of developing diabetes. The variant m.16189T>C (rs28693675), which has been previously documented in several studies across diverse populations, showed no association with T2D in our analysis (controls: 148 [13.39] T2D: 171 [13.56%]; OR: 1.03; 95%CI: 0.815-1.31; p = 0.83). These results provide evidence suggesting a link between specific mtDNA polymorphisms and T2D, possibly related to association rules, topological patterns, and three-dimensional conformations associated with regions where changes occur, rather than specific point mutations in the sequence.

Ultrastructural features mirror metabolic derangement in human endothelial cells exposed to high glucose

High glucose-induced endothelial dysfunction is the early event that initiates diabetes-induced vascular disease. Here we employed Cryo Soft X-ray Tomography to obtain three-dimensional maps of high D-glucose-treated endothelial cells and their controls at nanometric spatial resolution. We then correlated ultrastructural differences with metabolic rewiring. While the total mitochondrial mass does not change, high D-glucose promotes mitochondrial fragmentation, as confirmed by the modulation of fission-fusion markers, and dysfunction, as demonstrated by the drop of membrane potential, the decreased oxygen consumption and the increased production of reactive oxygen species. The 3D ultrastructural analysis also indicates the accumulation of lipid droplets in cells cultured in high D-glucose. Indeed, because of the decrease of fatty acid β-oxidation induced by high D-glucose concentration, triglycerides are esterified into fatty acids and then stored into lipid droplets. We propose that the increase of lipid droplets represents an adaptive mechanism to cope with the overload of glucose and associated oxidative stress and metabolic dysregulation.

Differentially Expressed Genes Regulating Glutathione Metabolism, Protein-Folding, and Unfolded Protein Response in Pancreatic β-Cells in Type 2 Diabetes Mellitus

Impaired redox homeostasis in the endoplasmic reticulum (ER) may contribute to proinsulin misfolding and thus to activate the unfolded protein response (UPR) and apoptotic pathways, culminating in pancreatic β-cell loss and type 2 diabetes (T2D). The present study was designed to identify differentially expressed genes (DEGs) encoding enzymes for glutathione metabolism and their impact on the expression levels of genes regulating protein folding and UPR in β-cells of T2D patients. The GEO transcriptome datasets of β-cells of diabetics and non-diabetics, GSE20966 and GSE81608, were analyzed for 142 genes of interest using limma and GREIN software, respectively. Diabetic β-cells showed dataset-specific patterns of DEGs (FDR ≤ 0.05) implicated in the regulation of glutathione metabolism (ANPEP, PGD, IDH2, and CTH), protein-folding (HSP90AB1, HSP90AA1, HSPA1B, HSPA8, BAG3, NDC1, NUP160, RLN1, and RPS19BP1), and unfolded protein response (CREB3L4, ERP27, and BID). The GCLC gene, encoding the catalytic subunit of glutamate-cysteine ligase, the first rate-limiting enzyme of glutathione biosynthesis, was moderately down-regulated in diabetic β-cells from both datasets (p ≤ 0.05). Regression analysis established that genes involved in the de novo synthesis of glutathione, GCLC, GCLM, and GSS affect the expression levels of genes encoding molecular chaperones and those involved in the UPR pathway. This study showed for the first time that diabetic β-cells exhibit alterations in the expression of genes regulating glutathione metabolism, protein-folding, and UPR and provided evidence for the molecular crosstalk between impaired redox homeostasis and abnormal protein folding, underlying ER stress in type 2 diabetes.

A Receptor Story: Insulin Resistance Pathophysiology and Physiologic Insulin Resensitization's Role as a Treatment Modality

Physiologic insulin secretion consists of an oscillating pattern of secretion followed by distinct trough periods that stimulate ligand and receptor activation. Apart from the large postprandial bolus release of insulin, β cells also secrete small amounts of insulin every 4-8 min independent of a meal. Insulin resistance is associated with a disruption in the normal cyclical pattern of insulin secretion. In the case of type-2 diabetes, β-cell mass is reduced due to apoptosis and β cells secrete insulin asynchronously. When ligand/receptors are constantly exposed to insulin, a negative feedback loop down regulates insulin receptor availability to insulin, creating a relative hyperinsulinemia. The relative excess of insulin leads to insulin resistance (IR) due to decreased receptor availability. Over time, progressive insulin resistance compromises carbohydrate metabolism, and may progress to type-2 diabetes (T2D). In this review, we discuss insulin resistance pathophysiology and the use of dynamic exogenous insulin administration in a manner consistent with more normal insulin secretion periodicity to reverse insulin resistance. Administration of insulin in such a physiologic manner appears to improve insulin sensitivity, lower HgbA1c, and, in some instances, has been associated with the reversal of end-organ damage that leads to complications of diabetes. This review outlines the rationale for how the physiologic secretion of insulin orchestrates glucose metabolism, and how mimicking this secretion profile may serve to improve glycemic control, reduce cellular inflammation, and potentially improve outcomes in patients with diabetes.

Mitochondrial Dysfunction: A Cellular and Molecular Hub in Pathology of Metabolic Diseases and Infection

Mitochondria are semiautonomous doubly membraned intracellular components of cells. The organelle comprises of an external membrane, followed by coiled structures within the membrane called cristae, which are further surrounded by the matrix spaces followed by the space between the external and internal membrane of the organelle. A typical eukaryotic cell contains thousands of mitochondria within it, which make up 25% of the cytoplasm present in the cell. The organelle acts as a common point for the metabolism of glucose, lipids, and glutamine. Mitochondria chiefly regulate oxidative phosphorylation-mediated aerobic respiration and the TCA cycle and generate energy in the form of ATP to fulfil the cellular energy needs. The organelle possesses a unique supercoiled doubly stranded mitochondrial DNA (mtDNA) which encodes several proteins, including rRNA and tRNA crucial for the transport of electrons, oxidative phosphorylation, and initiating genetic repair processors. Defects in the components of mitochondria act as the principal factor for several chronic cellular diseases. The dysfunction of mitochondria can cause a malfunction in the TCA cycle and cause the leakage of the electron respiratory chain, leading to an increase in reactive oxygen species and the signaling of aberrant oncogenic and tumor suppressor proteins, which further alter the pathways involved in metabolism, disrupt redox balance, and induce endurance towards apoptosis and several treatments which play a major role in developing several chronic metabolic conditions. The current review presents the knowledge on the aspects of mitochondrial dysfunction and its role in cancer, diabetes mellitus, infections, and obesity.

Peroxisome proliferator-activated receptor-α (PPARα) regulates wound healing and mitochondrial metabolism in the cornea

Diabetes can result in impaired corneal wound healing. Mitochondrial dysfunction plays an important role in diabetic complications. However, the regulation of mitochondria function in the diabetic cornea and its impacts on wound healing remain elusive. The present study aimed to explore the molecular basis for the disturbed mitochondrial metabolism and subsequent wound healing impairment in the diabetic cornea. Seahorse analysis showed that mitochondrial oxidative phosphorylation is a major source of ATP production in human corneal epithelial cells. Live corneal biopsy punches from type 1 and type 2 diabetic mouse models showed impaired mitochondrial functions, correlating with impaired corneal wound healing, compared to nondiabetic controls. To approach the molecular basis for the impaired mitochondrial function, we found that Peroxisome Proliferator-Activated Receptor-α (PPARα) expression was downregulated in diabetic human corneas. Even without diabetes, global PPARα knockout mice and corneal epithelium-specific PPARα conditional knockout mice showed disturbed mitochondrial function and delayed wound healing in the cornea, similar to that in diabetic corneas. In contrast, fenofibrate, a PPARα agonist, ameliorated mitochondrial dysfunction and enhanced wound healing in the corneas of diabetic mice. Similarly, corneal epithelium-specific PPARα transgenic overexpression improved mitochondrial function and enhanced wound healing in the cornea. Furthermore, PPARα agonist ameliorated the mitochondrial dysfunction in primary human corneal epithelial cells exposed to diabetic stressors, which was impeded by siRNA knockdown of PPARα, suggesting a PPARα-dependent mechanism. These findings suggest that downregulation of PPARα plays an important role in the impaired mitochondrial function in the corneal epithelium and delayed corneal wound healing in diabetes.

Hydrogen sulfide donor AP123 restores endothelial nitric oxide-dependent vascular function in hyperglycemia via a CREB-dependent pathway

Diabetes is associated with severe vascular complications involving the impairment of endothelial nitric oxide synthase (eNOS) as well as cystathionine γ-lyase (CSE) activity. eNOS function is suppressed in hyperglycaemic conditions, resulting in reduced NO bioavailability, which is paralleled by reduced levels of hydrogen sulfide (H₂S). Here we have addressed the molecular basis of the interplay between the eNOS and CSE pathways. We tested the impact of H₂S replacement by using the mitochondrial-targeted H₂S donor AP123 in isolated vessels and cultured endothelial cells in high glucose (HG) environment, at concentrations not causing any vasoactive effect per se. Aorta exposed to HG displayed a marked reduction of acetylcholine (Ach)-induced vasorelaxation that was restored by the addition of AP123 (10 nM). In HG condition, bovine aortic endothelial cells (BAEC) showed reduced NO levels, downregulation of eNOS expression, and suppression of CREB activation (p-CREB). Similar results were obtained by treating BAEC with propargylglycine (PAG), an inhibitor of CSE. AP123 treatment rescued eNOS expression, as well as NO levels, and restored p-CREB expression in both the HG environment and the presence of PAG. This effect was mediated by a PI3K-dependent activity since wortmannin (PI3K inhibitor) blunted the rescuing effects operated by the H₂S donor. Experiments performed in the aorta of CSE^-/- mice confirmed that reduced levels of H₂S not only negatively affect the CREB pathway but also impair Ach-induced vasodilation, significantly ameliorated by AP123. We have demonstrated that the endothelial dysfunction due to HG involves H₂S/PI3K/CREB/eNOS route, thus highlighting a novel aspect of the H₂S/NO interplay in the vasoactive response.

Role of Ceramides and Sphingolipids in Parkinson's Disease

Sphingolipids, including the basic ceramide, are a subset of bioactive lipids that consist of many different species. Sphingolipids are indispensable for proper neuronal function, and an increasing number of studies have emerged on the complexity and importance of these lipids in (almost) all biological processes. These include regulation of mitochondrial function, autophagy, and endosomal trafficking, which are affected in Parkinson's disease (PD). PD is the second most common neurodegenerative disorder and is characterized by the loss of dopaminergic neurons. Currently, PD cannot be cured due to the lack of knowledge of the exact pathogenesis. Nonetheless, important advances have identified molecular changes in mitochondrial function, autophagy, and endosomal function. Furthermore, recent studies have identified ceramide alterations in patients suffering from PD, and in PD models, suggesting a critical interaction between sphingolipids and related cellular processes in PD. For instance, autosomal recessive forms of PD cause mitochondrial dysfunction, including energy production or mitochondrial clearance, that is directly influenced by manipulating sphingolipids. Additionally, endo-lysosomal recycling is affected by genes that cause autosomal dominant forms of the disease, such as VPS35 and SNCA. Furthermore, endo-lysosomal recycling is crucial for transporting sphingolipids to different cellular compartments where they will execute their functions. This review will discuss mitochondrial dysfunction, defects in autophagy, and abnormal endosomal activity in PD and the role sphingolipids play in these vital molecular processes.

Variants in the Control Region of Mitochondrial Genome Associated with type 2 Diabetes in a Cohort of Mexican Mestizos

BACKGROUND

According to the International Diabetes Federation, Mexico is seventh place in the prevalence of type 2 diabetes (T2D) worldwide. Mitochondrial DNA variant association studies in multifactorial diseases like T2D are scarce in Mexican populations.

AIM OF THE STUDY

The objective of this study was to analyze the association between 18 variants in the mtDNA control region and T2D and related metabolic traits in a Mexican mestizo population from Mexico City.

METHODS

This study included 1001 participants divided into 477 cases with T2D and 524 healthy controls aged between 42 and 62 years and 18 mtDNA variants with frequencies >15%.

RESULTS

Association analyses matched by age and sex showed differences in the distribution between cases and controls for variants m.315_316insC (p = 1.18 × 10^-6), m.489T>C (p = 0.009), m.16362T>C (p = 0.001), and m.16519T>C (p = 0.004). The associations between T2D and variants m.315_316ins (OR = 6.13, CI = 3.42-10.97, p = 1.97 × 10^-6), m.489T>C (OR = 1.45, CI = 1.00-2.11, p = 0.006), m.16362T>C (OR = 2.17, CI = 1.57-3.00, p = 0.001), and m.16519T>C (OR = 1.69, CI = 1.23-2.33, p = 0.006) were significant after performing logistic regression models adjusted for age, sex, and diastolic blood pressure. Metabolic traits in the control group through linear regressions, adjusted for age, sex and BMI, and corrected for multiple comparisons showed nominal association between glucose and variants m.263A>G (p <0.050), m.16183A>C (p <0.010), m.16189T>C (p <0.020), and m.16223C>T (p <0.024); triglycerides, and cholesterol and variant m.309_310insC (p <0.010 and p <0.050 respectively); urea, and creatinine, and variant m.315_316insC (p <0.007, and p <0.004 respectively); diastolic blood pressure and variants m.235A>G (p <0.016), m.263A>G (p <0.013), m.315_316insC (p <0.043), and m.16111C>T (p <0.022).

CONCLUSION

These results demonstrate a strong association between variant m.315_316insC and T2D and a nominal association with T2D traits.

The Effect of Physical Exercise Pretreatment on Spatial Memory and Learning and Function of Mitochondria in the Brain in Type 2 Diabetic Rats

Background

The prevalence of type 2 diabetes mellitus (T2DM) is increasing worldwide, and this issue is one of the major concerns in the pending years. T2DM causes numerous complications, including cognition, learning, and memory impairments. The positive effect of physical exercise as a popular approach has been shown in many chronic diseases. Further, the improvement effects of exercise on cognition and memory impairment have been noticed.

Objectives

This study examines the possible preventative effects of physical exercise on spatial memory attenuation and brain mitochondrial dysfunction caused by T2DM.

Methods

Male Wistar rats received treadmill exercise (30 min per day, five days per week for two or four weeks). Then, T2DM was induced by a high-fat diet and an injection of streptozotocin (30 mg/kg). Spatial learning and memory were assessed by the Morris water maze test. Further, brain mitochondrial function, including reactive oxygen species (ROS) generation, mitochondrial membrane potential (MMP), mitochondrial swelling, outer membrane damage, cytochrome c release, and ADP/ATP ratio, were measured.

Results

Impaired spatial memory in T2DM rats was observed. Furthermore, brain mitochondrial dysfunction was demonstrated proved by increased ROS generation, MMP collapse, mitochondrial swelling, outer membrane damage, cytochrome c release, and ADP/ATP ratio. Conversely, physical exercise, before diabetes onset, significantly ameliorated spatial memory impairment and brain mitochondrial dysfunction.

Conclusions

This study reveals that physical exercise could prevent diabetes-induced spatial memory impairment. Moreover, it could ameliorate brain mitochondrial dysfunction as one of the possible underlying mechanisms of spatial memory impairment in T2DM.

Epigenetic Changes Induced by High Glucose in Human Pancreatic Beta Cells

Epigenetic changes in pancreatic beta cells caused by sustained high blood glucose levels, as seen in prediabetic conditions, may contribute to the etiology of diabetes. To delineate a direct cause and effect relationship between high glucose and epigenetic changes, we cultured human pancreatic beta cells derived from induced pluripotent stem cells and treated them with either high or low glucose, for 14 days. We then used the Arraystar 4x180K HG19 RefSeq Promoter Array to perform whole-genome DNA methylation analysis. A total of 478 gene promoters, out of a total of 23,148 present on the array (2.06%), showed substantial differences in methylation (p < 0.01). Out of these, 285 were hypomethylated, and 193 were hypermethylated in experimental vs. control. Ingenuity Pathway Analysis revealed that the main pathways and networks that were differentially methylated include those involved in many systems, including those related to development, cellular growth, and proliferation. Genes implicated in the etiology of diabetes, including networks involving glucose metabolism, insulin secretion and regulation, and cell cycle regulation, were notably altered. Influence of upstream regulators such as MRTFA, AREG, and NOTCH3 was predicted based on the altered methylation of their downstream targets. The study validated that high glucose levels can directly cause many epigenetic changes in pancreatic beta cells, suggesting that this indeed may be a mechanism involved in the etiology of diabetes.

Mulberry-Derived 1-Deoxynojirimycin Prevents Type 2 Diabetes Mellitus Progression via Modulation of Retinol-Binding Protein 4 and Haptoglobin

Pre-diabetic or early-stage type 2 diabetes patients may develop an adverse diabetic progression, leading to several complications and increasing hospitalization rates. Mulberry leaves, which contain 1-deoxynojirimycin (DNJ), have been used as a complementary medicine for diabetes prevention and treatment. Our recent study demonstrated that mulberry leaf powder with 12 mg of DNJ improves postprandial hyperglycemia, fasting plasma glucose, and glycated hemoglobin. However, the detailed mechanisms are still unknown. This study investigates the effect of long-term (12-week) supplementation of mulberry leaves in obese people with prediabetes and patients with early-stage type 2 diabetes. Participants’ blood was collected before and after supplementation. The protein profile of the plasma was examined by proteomics. In addition, the mitochondrial function was evaluated by energetic and homeostatic markers using immunoelectron microscopy. The proteomics results showed that, from a total of 1291 proteins, 32 proteins were related to diabetes pathogenesis. Retinol-binding protein 4 and haptoglobin protein were downregulated, which are associated with insulin resistance and inflammation, respectively. For mitochondrial function, the haloacid dehalogenase-like hydrolase domain-containing protein 3 (HDHD-3) and dynamin-related protein 1 (Drp-1) displayed a significant increment in the after treatment group. In summary, administration of mulberry leaf powder extract in prediabetes and the early stage of diabetes can alleviate insulin resistance and inflammation and promote mitochondrial function in terms of energy production and fission.

Potential Therapeutic Mechanism of Traditional Chinese Medicine on Diabetes in Rodents: A Review from an NMR-Based Metabolomics Perspective

Traditional Chinese medicine (TCM) has been used to treat diabetes for a long time, but its application has not been widely accepted due to unstandardized product quality and complex pharmacological mechanisms. The modernization of TCM is crucial for its further development, and in recent years the metabolomics technique has largely driven its modernization. This review focuses on the application of NMR-based metabolomics in diabetic therapy using TCM. We identified a series of metabolic pathways that altered significantly after TCM treatment, providing a better understanding of the metabolic mechanisms of TCM for diabetes care.

Mitochondrial Dysfunction in Individuals with Diabetic Kidney Disease: A Systematic Review

Mitochondrial dysfunction is implicated in the pathogenesis of diabetic kidney disease (DKD). Compared to the vast body of evidence from preclinical in vitro and in vivo studies, evidence from human studies is limited. In a comprehensive search of the published literature, findings from studies that reported evidence of mitochondrial dysfunction in individuals with DKD were examined. Three electronic databases (PubMed, Embase, and Scopus) were searched in March 2022. A total of 1339 articles were identified, and 22 articles met the inclusion criteria. Compared to non-diabetic controls (NDC) and/or individuals with diabetes but without kidney disease (DC), individuals with DKD (age ~55 years; diabetes duration ~15 years) had evidence of mitochondrial dysfunction. Individuals with DKD had evidence of disrupted mitochondrial dynamics (11 of 11 articles), uncoupling (2 of 2 articles), oxidative damage (8 of 8 articles), decreased mitochondrial respiratory capacity (1 of 1 article), decreased mtDNA content (5 of 6 articles), and decreased antioxidant capacity (3 of 4 articles) compared to ND and/or DC. Neither diabetes nor glycemic control explained these findings, but rather presence and severity of DKD may better reflect degree of mitochondrial dysfunction in this population. Future clinical studies should include individuals closer to diagnosis of diabetes to ascertain whether mitochondrial dysfunction is implicated in the development of, or is a consequence of, DKD.

Mitochondria-Targeted, Nanoparticle-Based Drug-Delivery Systems: Therapeutics for Mitochondrial Disorders

Apart from ATP generation, mitochondria are involved in a wide range of functions, making them one of the most prominent organelles of the human cell. Mitochondrial dysfunction is involved in the pathophysiology of several diseases, such as cancer, neurodegenerative diseases, cardiovascular diseases, and metabolic disorders. This makes it a target for a variety of therapeutics for the diagnosis and treatment of these diseases. The use of nanoparticles to target mitochondria has significant importance in modern times because they provide promising ways to deliver drug payloads to the mitochondria by overcoming challenges, such as low solubility and poor bioavailability, and also resolve the issues of the poor biodistribution of drugs and pharmacokinetics with increased specificity. This review assesses nanoparticle-based drug-delivery systems, such as liposomes, DQAsome, MITO-Porters, micelles, polymeric and metal nanocarriers, as well as quantum dots, as mitochondria-targeted strategies and discusses them as a treatment for mitochondrial disorders.

Diabetes is an Independent Growth Factor of Ischemic Stroke During Reperfusion Phase Leading to Poor Clinical Outcome

OBJECTIVES

Despite the success of recanalization by bridging therapy, about half of treated stroke patients remain disabled. While numerous reports propose clinical predictors of stroke clinical outcome in this context, we originally aimed to study pre-therapeutic factors influencing infarct growth (IG) and poor clinical outcome in strokes due to large vessel occlusion (LVO) successfully recanalized.

MATERIALS AND METHODS

We enrolled 87 consecutive successfully recanalized patients (mTICI: 2b/2c/3) by mechanical thrombectomy (±rt-PA) after stroke due to middle cerebral artery (M1) occlusion within 6 h according to AHA guidelines. IG was defined by subtracting the initial DWI volume to the final 24 h-TDM volume. Statistical associations between poor clinical outcome (mRS≥2), IG and pertinent clinico-radiological variables, were measured using logistic and linear regression models.

RESULTS

Among 87 enrolled patients (Age(y): 68.4 ± 17.5; NIHSS: 16.0 ± 5.4), 42/87 (48,28%) patients had a mRS ≥ 2 at 3 months. Diabetic history (OR: 3.70 CI95%[1.03;14.29] and initial NIHSS (/1 point: OR: 1.16 CI95%[1.05;1.27]) were independently associated with poor outcome. IG was significantly higher in stroke patients with poor outcome (+7.57 ± 4.52 vs -7.81 ± 1.67; p = 0.0024). Initial volumes were not significantly different (mRS≥2: 16.18 ± 2.67; mRS[0-1]: 14.70 ± 2.30; p = 0.6771). Explanatory variables of IG in linear regression were diabetic history (β: 21.26 CI95%[5.43; 37.09]) and NIHSS (β: 0.83 CI95%[0.02; 1.64]). IG was higher in diabetic stroke patients (23.54 ± 1.43 vs -6.20 ± 9.36; p = 0.0061).

CONCLUSIONS

We conclude that diabetes leads to continued IG after complete recanalization, conditioning clinical outcome in LVO strokes successfully recanalized by bridging therapy. We suggest that poor tissular reperfusion by diabetic microangiopathy could explain this result.

Neurological manifestations in m.3243A>G-related disease triggered by metformin

INTRODUCTION

m.3243A>G-related disease has multi-systemic manifestations including diabetes mellitus. It is uncertain whether metformin would trigger neurological manifestations of this disease. This study aims to review the diagnosis and management of m.3243A>G-related diabetes genetically confirmed by our laboratory and to evaluate the risk of metformin use triggering neurological manifestations.

METHODS

Cases with m.3243A>G detected between 2009 and 2020 were reviewed. Cases with diabetes mellitus were included. Cases with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) before diabetes onset were excluded. Odds ratio was calculated for association between metformin use and newly developed neurological manifestations.

RESULTS

Sixteen patients were identified. Odds ratio for metformin use was 3.50 [0.37-33.0; p = 0.3287]. One illustrative case with clear causal relationship between metformin use and neurological manifestations was described in detail.

CONCLUSION

m.3243A>G-related diabetes mellitus is underdiagnosed. Red flags including positive family history, short stature, low body weight and hearing loss are often overlooked. Early diagnosis allows regular systemic assessment. In the era of precision medicine and novel therapies, it is prudent to avoid metformin as it could trigger neurological manifestations in this condition. Coenzyme Q10, DPP-IV inhibitors, SGLT2 inhibitors and GLP-1 receptor agonists may be considered.

The melatonin MT2 receptor is involved in the anti-apoptotic effects of melatonin in rats with type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a widely prevalent chronic disease and risk factor for several other diseases, such as cardiovascular diseases, neuropathy, nephropathy, and retinopathy. Apoptosis is a homeostatic mechanism to maintain cell numbers at a certain level in tissues. Chronic high blood glucose levels might lead to mitochondrial dysfunction and trigger undesirable apoptosis in T2DM. The pineal hormone melatonin has been shown to regulate apoptosis. The aim of this study was to investigate the impact of the melatonin MT₂ receptor in the role of melatonin to prevent undesirable apotosis in different tissues of diabetic rats. Male Sprague Dawley rats were randomly divided into 4 groups; 1. Control group (only vehicle), 2. Diabetic group (streptozotozin/nicotinamide treated), 3. Diabetic group treated with melatonin (500μg/kg/day), and 4. Diabetic group treated with melatonin (500 μg/kg/day for 6 weeks) and the selective MT₂ receptor antagonist luzindole (0.25 g/kg/day for 6 weeks). Various tissue samples (kidney, liver, adipose tissue, pancreas) were removed after 6 weeks for immunohistochemistry and western blot analysis. Our results demonstrated an increased rate of apoptosis in different tissues of diabetic rats compared to controls with melatonin reducing the apoptotic rate in the tissues of rats with T2DM. Furthermore, the anti-apoptotic effects of melatonin were partly mediated by the melatonin MT₂ receptor.

SENP2 regulates mitochondrial function and insulin secretion in pancreatic β cells

Increasing evidence has shown that small ubiquitin-like modifier (SUMO) modification plays an important role in metabolic regulation. We previously demonstrated that SUMO-specific protease 2 (SENP2) is involved in lipid metabolism in skeletal muscle and adipogenesis. In this study, we investigated the function of SENP2 in pancreatic β cells by generating a β cell-specific knockout (Senp2-βKO) mouse model. Glucose tolerance and insulin secretion were significantly impaired in the Senp2-βKO mice. In addition, glucose-stimulated insulin secretion (GSIS) was decreased in the islets of the Senp2-βKO mice without a significant change in insulin synthesis. Furthermore, islets of the Senp2-βKO mice exhibited enlarged mitochondria and lower oxygen consumption rates, accompanied by lower levels of S616 phosphorylated DRP1 (an active form of DRP1), a mitochondrial fission protein. Using a cell culture system of NIT-1, an islet β cell line, we found that increased SUMO2/3 conjugation to DRP1 due to SENP2 deficiency suppresses the phosphorylation of DRP1, which possibly induces mitochondrial dysfunction. In addition, SENP2 overexpression restored GSIS impairment induced by DRP1 knockdown and increased DRP1 phosphorylation. Furthermore, palmitate treatment decreased phosphorylated DRP1 and GSIS in β cells, which was rescued by SENP2 overexpression. These results suggest that SENP2 regulates mitochondrial function and insulin secretion at least in part by modulating the phosphorylation of DRP1 in pancreatic β cells.

Time-restricted feeding during the inactive phase abolishes the daily rhythm in mitochondrial respiration in rat skeletal muscle

Shift-workers show an increased incidence of type 2 diabetes mellitus (T2DM). A possible mechanism is the disruption of the circadian timing of glucose homeostasis. Skeletal muscle mitochondrial function is modulated by the molecular clock. We used time-restricted feeding (TRF) during the inactive phase to investigate how mistimed feeding affects muscle mitochondrial metabolism. Rats on an ad libitum (AL) diet were compared to those that could eat only during the light (inactive) or dark (active) phase. Mitochondrial respiration, metabolic gene expressions, and metabolite concentrations were determined in the soleus muscle. Rats on AL feeding or dark-fed TRF showed a clear daily rhythm in muscle mitochondrial respiration. This rhythm in mitochondrial oxidative phosphorylation capacity was abolished in light-fed TRF animals and overall 24h respiration was lower. The expression of several genes involved in mitochondrial biogenesis and the fission/fusion machinery was altered in light-fed animals. Metabolomics analysis indicated that light-fed animals had lost rhythmic levels of α-ketoglutarate and citric acid. Contrastingly, lipidomics showed that light-fed animals abundantly gained rhythmicity in levels of triglycerides. Furthermore, while the RER shifted entirely with the food intake in the light-fed animals, many measured metabolic parameters (e.g., activity and mitochondrial respiration) did not strictly align with the shifted timing of food intake, resulting in a mismatch between expected metabolic supply/demand (as dictated by the circadian timing system and light/dark-cycle) and the actual metabolic supply/demand (as dictated by the timing of food intake). These data suggest that shift-work impairs mitochondrial metabolism and causes metabolic inflexibility, which can predispose to T2DM.

MF-094, a potent and selective USP30 inhibitor, accelerates diabetic wound healing by inhibiting the NLRP3 inflammasome

Diabetes is a prevalent disease worldwide that can result in several complications, including renal failure, blindness, and amputation. Diabetic foot ulcers, which have the characteristics of chronic wounds, are a devastating component of diabetes progression that can lead to lower extremity amputation. In this study, we set out to investigate the mechanisms involved in wound healing of diabetic foot ulcers. The expression of USP30 in skin tissues of patients with diabetic foot ulcers and HSF2 human skin fibroblasts treated with advanced glycation end (AGE) products was detected by qRT-PCR, and CCK-8, cell scratch and ELISA assay were used to detect cell viability, migration and levels of Col I, Col III, MMP-2, MMP-9, IL-1β and IL-18. The interaction between USP30 and NLRP3 was verified by co-immunoprecipitation and ubiquitination assays. The expression of USP30, NLRP3 and caspase-1 p20 was detected by Western blot. USP30 inhibitor MF-094 was used to treat diabetic rat model established by streptozotocin (STZ). We found that USP30, a deubiquitinase, was upregulated in skin tissues of patients with diabetic foot ulcers compared with normal skin tissues. In vitro, we found that treatment of HSF2 human skin fibroblasts with advanced glycation end (AGE) products, known to contribute to diabetic complications, resulted in suppressed viability and migration of HSF2 cells, as well as increased levels of USP30 mRNA and protein. Functionally, downregulation of USP30 via shRNA-mediated knockdown or treatment with the USP30 inhibitor MF-094, restored viability and migration of AGE-treated HSF2 cells. We identified the NLRP3 inflammasome as a critical target of USP30 in AGE-induced functions. Mechanistically, we demonstrate that USP30 activates the NLRP3 inflammasome by deubiquitinating NLRP3. Finally, we show that inhibition of USP30 via MF-094 treatment facilitated wound healing in diabetic rats and resulted in decreased protein levels of NLRP3 and its downstream target caspase-1 p20, thus establishing the physiological importance of the identified USP30-NLRP3 link. Together, our findings suggest a therapeutic potential for USP30 in diabetic foot ulcers.

Molecular Mechanisms and Regulation of Mammalian Mitophagy

Mitochondria in the cell are the center for energy production, essential biomolecule synthesis, and cell fate determination. Moreover, the mitochondrial functional versatility enables cells to adapt to the changes in cellular environment and various stresses. In the process of discharging its cellular duties, mitochondria face multiple types of challenges, such as oxidative stress, protein-related challenges (import, folding, and degradation) and mitochondrial DNA damage. They mitigate all these challenges with robust quality control mechanisms which include antioxidant defenses, proteostasis systems (chaperones and proteases) and mitochondrial biogenesis. Failure of these quality control mechanisms leaves mitochondria as terminally damaged, which then have to be promptly cleared from the cells before they become a threat to cell survival. Such damaged mitochondria are degraded by a selective form of autophagy called mitophagy. Rigorous research in the field has identified multiple types of mitophagy processes based on targeting signals on damaged or superfluous mitochondria. In this review, we provide an in-depth overview of mammalian mitophagy and its importance in human health and diseases. We also attempted to highlight the future area of investigation in the field of mitophagy.

Stress-responsive rhodamine bioconjugates for membrane-potential-independent mitochondrial live-cell imaging and tracking

The 'powerhouses' of cell, mitochondria have seen an upsurge of interest in investigations pertaining to the imaging and mapping of physiological processes. By utilizing sterol-modified rhodamine, we have performed the live-cell imaging of mitochondria without dependence on a membrane potential. The sterol probes are highly biocompatible, and they can track the mitochondrial live-cell dynamics in a background-free manner with improved brightness and impressive contrast. This is the first attempt to study the stress response using a direct fluorescence readout with bio-conjugates of rhodamine inside mitochondria. The results pave the way for developing different sterol markers for understanding cellular responses and function.

Histone deacetylase inhibition improves metabolism and mitochondrial dynamics: A potential novel therapeutic strategy for sarcopenia coexisting with diabetes mellitus

Sarcopenia, the age-associated-fragility with loss of skeletal muscle mass and function, often coexists with type 2 diabetes (T2D) in older individuals. Derangement of muscle metabolism and mitochondrial dynamics is critical, particularly in high-energy-demand organs in patients with metabolic disorder. However, targeted therapies to halt or reverse the pathological progression of sarcopenia coexisting with T2D are unavailable. Studies have identified the pathological roles of class I histone deacetylases (HDACs) in both T2D and sarcopenia. In addition to their proinflammatory properties, HDACs are known to modify muscle metabolism and mitochondrial dynamics in both the development of sarcopenia and pathogenesis of diabetes. Proper quality control of mitochondrial dynamics through protein degradation and the synthesis of new proteins may improve skeletal muscle function in sarcopenia. Class I HDAC inhibitors improve energy metabolism and modulate autophagy-related genes in skeletal muscle. However, class IIa HDAC4 plays a protective role in preserving skeletal muscle structure following long-term denervation, and selective inhibition of class IIa HDAC activity had no impact on oxidative metabolism of muscle mitochondria. These findings suggest the vital role of class I HDAC modulation in bioenergetics and mitochondria quality control, and may lead to a novel therapeutic strategy targeting sarcopenia that coexists with T2D. HDAC inhibitors have been approved for clinical applications, and interventions targeting on HDACs may be promising for the treatment of sarcopenia.

Analysis of miRNA and mRNA expression in the dysregulation of insulin secretion in MIN6 cells exposed to microcystin-leucine-arginine

Microcystin -leucine-arginine (MC-LR), produced by freshwater cyanobacteria, is a potential pancreatic β-cell toxin. In this study, the function of the mouse pancreatic β-cell line, MIN6, was evaluated after MC-LR exposure, and the underlying molecular mechanisms were explored. Exposure to MC-LR for 24 h was found to inhibit cell viability and impair insulin secretion. Such findings indicate that β-cell function would be impaired following MC-LR treatment. The microarray results revealed altered miRNA and mRNA expression profiles that might be responsible for the abnormal function of MIN6 cells. Further, miRNA-gene network analysis demonstrated that miR-29b-3p, miR-6967-5p, miR-3473, miR-7061-5p, Xkr4, Tmem178b, Scp2, Ypel2, and Kcnj11 are key miRNAs and genes in the MC-LR-induced MIN6-cell toxicity. The altered expression levels of several miRNAs (e.g., miR-320-5p, miR-770-5p, miR-99a-3p, and miR-375-5p) and genes (e.g., Pklr and Gpd2) involved in insulin secretion or the onset of diabetes were also identified in MIN6 cells after treatment with MC-LR. Collectively, these findings provide evidence of the toxic effects of MC-LR on β-cells and the underlying molecular mechanisms of its glycometabolism toxicity. MCs may thus possibly play an important role in the development of diabetes mellitus in humans.

Regulation of Cytochrome c Oxidase by Natural Compounds Resveratrol, (-)-Epicatechin, and Betaine

Numerous naturally occurring molecules have been studied for their beneficial health effects. Many compounds have received considerable attention for their potential medical uses. Among them, several substances have been found to improve mitochondrial function. This review focuses on resveratrol, (–)-epicatechin, and betaine and summarizes the published data pertaining to their effects on cytochrome c oxidase (COX) which is the terminal enzyme of the mitochondrial electron transport chain and is considered to play an important role in the regulation of mitochondrial respiration. In a variety of experimental model systems, these compounds have been shown to improve mitochondrial biogenesis in addition to increased COX amount and/or its enzymatic activity. Given that they are inexpensive, safe in a wide range of concentrations, and effectively improve mitochondrial and COX function, these compounds could be attractive enough for possible therapeutic or health improvement strategies.

Improvement of Platelet Respiration by Cell-Permeable Succinate in Diabetic Patients Treated with Statins

Diabetes mellitus (DM) is the most severe metabolic disease that reached the level of a global pandemic and is associated with high cardiovascular morbidity. Statins are the first-line lipid-lowering therapy in diabetic patients with or without a history of atherosclerotic disease. Although well tolerated, chronic treatment may result in side effects that lead to treatment interruption. Mitochondrial dysfunction has emerged as a central pathomechanism in DM- and statin-induced side effects. Assessment of mitochondrial respiration in peripheral platelets has been increasingly used as a mirror of organ mitochondrial dysfunction. The present study aimed to assess the: (i) changes in mitochondrial respiration elicited by statins in patients with type 2 DM and (ii) the effects of cell-permeable succinate (NV118) on respiratory parameters in platelets harvested from these patients. No significant changes were found in global mitochondrial respiration of intact platelets isolated from diabetic patients treated with either atorvastatin or rosuvastatin. Similarly, no significant changes in mitochondrial respiration of permeabilized platelets were found between diabetic patients treated with atorvastatin and healthy controls. Acute ex vivo administration of NV118 significantly improved respiration in isolated platelets. These results prompt further research on the role of permeable succinate as a therapeutic alternative for improving mitochondrial function in metabolic pathologies and point to the role of peripheral platelets as a potential biomarker of treatment response.

MicroRNAs, Parkinson's Disease, and Diabetes Mellitus

Parkinson’s disease (PD) is a neurodegenerative disorder that affects 1% of the population over the age of 60. Diabetes Mellitus (DM) is a metabolic disorder that affects approximately 25% of adults over the age of 60. Recent studies showed that DM increases the risk of developing PD. The link between DM and PD has been discussed in the literature in relation to different mechanisms including mitochondrial dysfunction, oxidative stress, and protein aggregation. In this paper, we review the common microRNA (miRNA) biomarkers of both diseases. miRNAs play an important role in cell differentiation, development, the regulation of the cell cycle, and apoptosis. They are also involved in the pathology of many diseases. miRNAs can mediate the insulin pathway and glucose absorption. miRNAs can also regulate PD-related genes. Therefore, exploring the common miRNA biomarkers of both PD and DM can shed a light on how these two diseases are correlated, and targeting miRNAs is a potential therapeutic opportunity for both diseases.

Sphingolipids as a Culprit of Mitochondrial Dysfunction in Insulin Resistance and Type 2 Diabetes

Insulin resistance is defined as a complex pathological condition of abnormal cellular and metabolic response to insulin. Obesity and consumption of high-fat diet lead to ectopic accumulation of bioactive lipids in insulin-sensitive tissues. Intracellular lipid accumulation is regarded as one of the major factors in the induction of insulin resistance and type 2 diabetes (T2D). A significant number of studies have described the involvement of ceramides and other sphingolipids in the inhibition of insulin-signaling pathway in both skeletal muscles and the liver. Adverse effects of sphingolipid accumulation have recently been linked to the activation of protein kinase Cζ (PKCζ) and protein phosphatase 2A (PP2A), which, in turn, negatively affect phosphorylation of serine/threonine kinase Akt [also known as protein kinase B (PKB)], leading to decreased glucose uptake in skeletal muscles as well as increased gluconeogenesis and glycogenolysis in the liver. Sphingolipids, in addition to their direct impact on the insulin signaling pathway, may be responsible for other negative aspects of diabetes, namely mitochondrial dysfunction and deficiency. Mitochondrial health, which is characterized by appropriate mitochondrial quantity, oxidative capacity, controlled oxidative stress, undisturbed respiratory chain function, adenosine triphosphate (ATP) production and mitochondrial proliferation through fission and fusion, is impaired in the skeletal muscles and liver of T2D subjects. Recent findings suggest that impaired mitochondrial function may play a key role in the development of insulin resistance. Mitochondria stay in contact with the endoplasmic reticulum (ER), Golgi membranes and mitochondria-associated membranes (MAM) that are the main places of sphingolipid synthesis. Moreover, mitochondria are capable of synthesizing ceramide though ceramide synthase (CerS) activity. Recently, ceramides have been demonstrated to negatively affect mitochondrial respiratory chain function and fission/fusion activity, which is also a hallmark of T2D. Despite a significant correlation between sphingolipids, mitochondrial dysfunction, insulin resistance and T2D, this subject has not received much attention compared to the direct effect of sphingolipids on the insulin signaling pathway. In this review, we focus on the current state of scientific knowledge regarding the involvement of sphingolipids in the induction of insulin resistance by inhibiting mitochondrial function.

MicroRNA, Diabetes Mellitus and Colorectal Cancer

Diabetes mellitus (DM) is an endocrinological disorder that is due to either the pancreas not producing enough insulin, or the body does not respond appropriately to insulin. There are many complications of DM such as retinopathy, nephropathy, and peripheral neuropathy. In addition to these complications, DM was reported to be associated with different cancers. In this review, we discuss the association between DM and colorectal cancer (CRC). CRC is the third most commonly diagnosed cancer worldwide that mostly affects older people, however, its incidence and mortality are rising among young people. We discuss the relationship between DM and CRC based on their common microRNA (miRNA) biomarkers. miRNAs are non-coding RNAs playing important functions in cell differentiation, development, regulation of cell cycle, and apoptosis. miRNAs can inhibit cell proliferation and induce apoptosis in CRC cells. miRNAs also can improve glucose tolerance and insulin sensitivity. Therefore, investigating the common miRNA biomarkers of both DM and CRC can shed a light on how these two diseases are correlated and more understanding of the link between these two diseases can help the prevention of both DM and CRC.

Mitochondrial dysfunction in placental trophoblast cells experiencing gestational diabetes mellitus

KEY POINTS

Mitochondrial dysfunction is known to occur in diabetic phenotypes including type 1 and 2 diabetes mellitus. The incidence of gestational diabetes mellitus (GDM) is increasing and defined as the onset of a diabetic phenotype during pregnancy. The role of placental mitochondria in the aetiology of GDM remains unclear and is an emerging area of research. Differing mitochondrial morphologies within the placenta may influence the pathogenesis of the disorder. This study observed mitochondrial dysfunction in GDM placenta when assessing whole tissue. Upon further investigation into mitochondrial isolates from the cytotrophoblast and syncytiotrophoblast, mitochondrial dysfunction appears exaggerated in syncytiotrophoblast. Assessing mitochondrial populations individually enabled the determination of differences between cell lineages of the placenta and established varying levels of mitochondrial dysfunction in GDM, in some instances establishing significance in pathways previously inconclusive or confounded when assessing whole tissue. This research lays the foundation for future work into mitochondrial dysfunction in the placenta and the role it may play in the aetiology of GDM.

ABSTRACT

Mitochondrial dysfunction has been associated with diabetic phenotypes, yet the involvement of placental mitochondria in gestational diabetes mellitus (GDM) remains inconclusive. This is in part complicated by the different mitochondrial subpopulations present in the two major trophoblast cell lineages of the placenta. To better elucidate the role of mitochondria in this pathology, this study examined key aspects of mitochondrial function in placentas from healthy pregnancies and those complicated by GDM in both whole tissue and isolated mitochondria. Mitochondrial content, citrate synthase activity, reactive oxygen species production and gene expression regulating metabolic, hormonal and antioxidant control was examined in placental tissue, before examining functional differences between mitochondrial isolates from cytotrophoblast (Cyto-Mito) and syncytiotrophoblast (Syncytio-Mito). Our study observed evidence of mitochondrial dysfunction across multiple pathways when assessing whole placental tissue from GDM pregnancies compared with healthy controls. Furthermore, by examining isolated mitochondria from the cytotrophoblast and syncytiotrophoblast cell lineages of the placenta we established that although both mitochondrial populations were dysfunctional, they were differentially impacted. These data highlight the need to consider changes in mitochondrial subpopulations at the feto-maternal interface when studying pregnancy pathologies.

Cardiolipin, Perhydroxyl Radicals, and Lipid Peroxidation in Mitochondrial Dysfunctions and Aging

Mitochondrial dysfunctions caused by oxidative stress are currently regarded as the main cause of aging. Accumulation of mutations and deletions of mtDNA is a hallmark of aging. So far, however, there is no evidence that most studied oxygen radicals are directly responsible for mutations of mtDNA. Oxidative damages to cardiolipin (CL) and phosphatidylethanolamine (PEA) are also hallmarks of oxidative stress, but the mechanisms of their damage remain obscure. CL is the only phospholipid present almost exclusively in the inner mitochondrial membrane (IMM) where it is responsible, together with PEA, for the maintenance of the superstructures of oxidative phosphorylation enzymes. CL has negative charges at the headgroups and due to specific localization at the negative curves of the IMM, it creates areas with the strong negative charge where local pH may be several units lower than in the surrounding bulk phases. At these sites with the higher acidity, the chance of protonation of the superoxide radical (O₂^•), generated by the respiratory chain, is much higher with the formation of the highly reactive hydrophobic perhydroxyl radical (HO₂^•). HO₂^• specifically reacts with the double bonds of polyunsaturated fatty acids (PUFA) initiating the isoprostane pathway of lipid peroxidation. Because HO₂^• is formed close to CL aggregates and PEA, it causes peroxidation of the linoleic acid in CL and also damages PEA. This causes disruption of the structural and functional integrity of the respirosomes and ATP synthase. We provide evidence that in elderly individuals with metabolic syndrome (MetS), fatty acids become the major substrates for production of ATP and this may increase several-fold generation of O₂^• and thus HO₂^•. We conclude that MetS accelerates aging and the mitochondrial dysfunctions are caused by the HO₂^•-induced direct oxidation of CL and the isoprostane pathway of lipid peroxidation (IPLP). The toxic products of IPLP damage not only PEA, but also mtDNA and OXPHOS proteins. This results in gradual disruption of the structural and functional integrity of mitochondria and cells.

Breastfeeding predicts blood mitochondrial DNA content in adolescents

Nutrition during early childhood is linked to metabolic programming. We hypothesized that breastfeeding has long-term consequences on the energy metabolism exemplified by mitochondrial DNA (mtDNA). As part of the third cycle of the Flemish Environment and Health Study (FLEHSIII) cohort, 303 adolescents aged 14–15 years were included. We associated breastfeeding and blood mtDNA content 14–15 years later while adjusting for confounding variables. Compared with non-breastfed adolescents, mtDNA content was 23.1% (95%CI: 4.4–45.2; p = 0.013) higher in breastfed adolescents. Being breastfed for 1–10 weeks, 11–20 weeks, and >20 weeks, was associated with a higher mtDNA content of respectively 16.0% (95%CI: −7.1–44.9; p = 0.191), 23.5% (95%CI: 0.8–51.3; p = 0.042), and 31.5% (95%CI: 4.3–65.7; p = 0.021). Our study showed a positive association between breastfeeding and mtDNA content in adolescents which gradually increased with longer periods of breastfeeding. Higher mtDNA content may be an underlying mechanism of the beneficial effects of breastfeeding on children’s metabolism.

Bilateral multiple oncocytic cysts of the parotid gland in type 2 diabetes patients

AIMS

The hallmarks of type 2 diabetes (T2D) are hyperglycaemia and insulin resistance. These factors, at the cellular level, are associated with mitochondrial dysfunction and increased glucose uptake. Such events are poorly explored in the context of the salivary glands. In this study, we present a series of eight cases of a distinct salivary gland lesion characterised by multiple oncocytic cysts, and we provide new pathological insights regarding its pathogenesis.

METHODS AND RESULTS

Seven patients (87.5%) had confirmed T2D, and obesity was identified in five (62.5%) patients. Clinically, the patients showed bilateral parotid gland swelling with recurrent episodes of pain and enlargement. Imaging examination revealed multiple cystic lesions in both parotid glands. Microscopically, the parotid glands showed multiple cysts of different sizes, lined by oncocytic epithelial cells. Intraluminally, strongly eosinophilic glass-like crystalloid material was observed. Immunohistochemical studies were performed, and the most notable finding was glucose transporter 1 (GLUT1) overexpression in the oncocytic cysts which is not observed in any other oncocytic lesion of patients without T2D. In addition, high expressions of mitochondrial antigen, fission 1 protein and mitofusin-2 were observed in the oncocytic epithelium of the cysts. Furthermore, most of the oncocytic cysts showed a pattern of cytokeratin expression consistent with striated ducts.

CONCLUSIONS

These results strongly suggest that T2D is associated with alterations in GLUT1 expression in the cells of striated ducts with mitochondrial dysfunction, causing a hyperplastic process characterised by multiple oncocytic cysts. For this lesion, the designation of 'diabetes-associated-bilateral multiple oncocytic cysts of the parotid gland' is proposed.

Mitochondrial DNA copy number associates with insulin sensitivity and aerobic capacity, and differs between sedentary, overweight middle-aged males with and without type 2 diabetes

BACKGROUND/OBJECTIVES

Increased risk of type 2 diabetes mellitus (T2DM) is linked to impaired muscle mitochondrial function and reduced mitochondrial DNA copy number (mtDNA^num). However, studies have failed to control for habitual physical activity levels, which directly influences both mtDNA copy number and insulin sensitivity. We, therefore, examined whether physical conditioning status (maximal oxygen uptake, V̇O_2max) was associated with skeletal muscle mitochondrial volume and mtDNA^num, and was predictive of T2DM in overweight, middle-aged men.

METHODS

Whole-body physiological (ISI-insulin sensitivity index, HOMA-IR, V̇O_2max) and muscle biochemical/molecular (vastus lateralis; mtDNA^num, mitochondrial and glycolytic enzymes activity, lipid content and markers of lipid peroxidation) measurements were performed in three groups of overweight, middle-aged male volunteers (n = 10 per group): sedentary T2DM (ST2DM); sedentary control (SC) and non-sedentary control (NSC), who differed in aerobic capacity (ST2DM < SC < NSC).

RESULTS

mtDNA^num was greater in NSC versus SC and ST2DM (P < 0.001; P < 0.001), and less in ST2DM versus SC (P < 0.01). Across all groups, mtDNA^num positively correlated with ISI (P < 0.001; r = 0.688) and V̇O_2max (normalised to free fat mass; r = 0.684, P < 0.001), and negatively correlated to HOMA-IR (r = -0.544, P < 0.01). The activity of mitochondrial enzymes (GluDH, CS and β-HAD) was greater in NSC than ST2DM (P < 0.01, P < 0.001 and P < 0.05) and SC (P < 0.05, P < 0.01 and P < 0.05), but similar between ST2DM and SC. Intramuscular-free fatty acids, triglycerides and malondialdehyde contents were similar between ST2DM and SC.

CONCLUSIONS

Body composition and indices of muscle mitochondrial volume/function were similar between SC and ST2DM. However, mtDNA^num differed and was positively associated with ISI, HOMA-IR and V̇O_2max across all groups. Collectively, the findings support the contention that habitual physical activity is a key component of T2DM development, possibly by influencing mtDNA^num.

Hyperglycemia-Induced Aberrant Cell Proliferation; A Metabolic Challenge Mediated by Protein O-GlcNAc Modification

Chronic hyperglycemia has been associated with an increased prevalence of pathological conditions including cardiovascular disease, cancer, or various disorders of the immune system. In some cases, these associations may be traced back to a common underlying cause, but more often, hyperglycemia and the disturbance in metabolic balance directly facilitate pathological changes in the regular cellular functions. One such cellular function crucial for every living organism is cell cycle regulation/mitotic activity. Although metabolic challenges have long been recognized to influence cell proliferation, the direct impact of diabetes on cell cycle regulatory elements is a relatively uncharted territory. Among other "nutrient sensing" mechanisms, protein O-linked β-N-acetylglucosamine (O-GlcNAc) modification emerged in recent years as a major contributor to the deleterious effects of hyperglycemia. An increasing amount of evidence suggest that O-GlcNAc may significantly influence the cell cycle and cellular proliferation. In our present review, we summarize the current data available on the direct impact of metabolic changes caused by hyperglycemia in pathological conditions associated with cell cycle disorders. We also review published experimental evidence supporting the hypothesis that O-GlcNAc modification may be one of the missing links between metabolic regulation and cellular proliferation.

Mitochondrial Dysfunction in Adipocytes as a Primary Cause of Adipose Tissue Inflammation

Adipose tissue inflammation is considered a major contributing factor in the development of obesity-associated insulin resistance and cardiovascular diseases. However, the cause of adipose tissue inflammation is presently unclear. The role of mitochondria in white adipocytes has long been neglected because of their low abundance. However, recent evidence suggests that mitochondria are essential for maintaining metabolic homeostasis in white adipocytes. In a series of recent studies, we found that mitochondrial function in white adipocytes is essential to the synthesis of adiponectin, which is the most abundant adipokine synthesized from adipocytes, with many favorable effects on metabolism, including improvement of insulin sensitivity and reduction of atherosclerotic processes and systemic inflammation. From these results, we propose a new hypothesis that mitochondrial dysfunction in adipocytes is a primary cause of adipose tissue inflammation and compared this hypothesis with a prevailing concept that "adipose tissue hypoxia" may underlie adipose tissue dysfunction in obesity. Recent studies have emphasized the role of the mitochondrial quality control mechanism in maintaining mitochondrial function. Future studies are warranted to test whether an inadequate mitochondrial quality control mechanism is responsible for mitochondrial dysfunction in adipocytes and adipose tissue inflammation.

The osteogenic effect of liraglutide involves enhanced mitochondrial biogenesis in osteoblasts

Liraglutide (Lira), a long-acting glucagon-like peptide 1 receptor (GLP1R) agonist reduces glycosylated hemoglobin in type 2 diabetes mellitus patients. Lira is reported to have bone conserving effect in ovariectomized (OVX) rats. Here, we investigated the osteoanabolic effect of Lira and studied the underlying mechanism. In established osteopenic OVX rats, Lira completely restored bone mass and strength comparable to parathyroid hormone (PTH 1-34). Body mass index normalized bone mineral density of Lira was higher than PTH. The serum levels of osteogenic surrogate pro-collagen type 1 N-terminal pro-peptide (P1NP) and surface referent bone formation parameters were comparable between Lira and PTH. GLP1R, adiponectin receptor 1 (AdipoR1) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) levels in bones were downregulated in the OVX group but restored in the Lira group whereas PTH had no effect. In cultured osteoblasts, Lira time-dependently increased GLP1R, AdipoR1 and PGC1α expression. In osteoblasts, Lira rapidly phosphorylated AMP-dependent protein kinase (AMPK), the cellular energy sensor. Exendin 3, a selective GLP1R antagonist and PKA inhibitor H89 blocked Lira-induced increases in osteoblast differentiation, and expression levels of AdipoR1 and PGC1α. Furthermore, H89 inhibited Lira-induced phosphorylation of AMPK and dorsomorphin, an AMPK inhibitor blocked the Lira-induced increases in osteoblast differentiation and AdipoR1 and PGC1α levels. Lira increased mitochondrial number, respiratory proteins and respiration in osteoblasts in vitro and in vivo, and blocking mitochondrial respiration mitigated Lira-induced osteoblast differentiation. Taken together, our data show that Lira has a strong osteoanabolic effect which involves upregulation of mitochondrial function.

Mitochondrial stress triggers a pro-survival response through epigenetic modifications of nuclear DNA

Mitochondrial dysfunction represents an important cellular stressor and when intense and persistent cells must unleash an adaptive response to prevent their extinction. Furthermore, mitochondria can induce nuclear transcriptional changes and DNA methylation can modulate cellular responses to stress. We hypothesized that mitochondrial dysfunction could trigger an epigenetically mediated adaptive response through a distinct DNA methylation patterning. We studied cellular stress responses (i.e., apoptosis and autophagy) in mitochondrial dysfunction models. In addition, we explored nuclear DNA methylation in response to this stressor and its relevance in cell survival. Experiments in cultured human myoblasts revealed that intense mitochondrial dysfunction triggered a methylation-dependent pro-survival response. Assays done on mitochondrial disease patient tissues showed increased autophagy and enhanced DNA methylation of tumor suppressor genes and pathways involved in cell survival regulation. In conclusion, mitochondrial dysfunction leads to a "pro-survival" adaptive state that seems to be triggered by the differential methylation of nuclear genes.