Mitochondrial dysfunction in diabetes and the regulatory roles of antidiabetic agents on the mitochondrial function

The prevalence of type 2 diabetes mellitus (T2DM) is increasing rapidly with its associated morbidity and mortality. Many pathophysiological pathways such as oxidative stress, inflammatory responses, adipokines, obesity-induced insulin resistance, improper insulin signaling, and beta cell apoptosis are associated with the development of T2DM. There is increasing evidence of the role of mitochondrial dysfunction in the onset of T2DM, particularly in relation to the development of diabetic complications. Here, the role of mitochondrial dysfunction in T2DM is reviewed together with its modulation by antidiabetic therapeutic agents, an effect that may be independent of their hypoglycemic effect.     

Alterations in circulating angiogenic and anti‐angiogenic factors in type 2 diabetic patients with neuropathy

Diabetic peripheral neuropathy (DPN) is one of the most common diabetic chronic complications. There is an increased attention directed towards the role of angiogenic factors including vascular endothelial growth factor (VEGF) and anti‐angiogenic factors including soluble endoglin (sEng) as contributors to diabetic microvascular complications including neuropathy. The purposes of this study were to determine the role of these angiogenesis regulators in the prognosis of DPN. The study group included 60 patients with type 2 diabetes mellitus (T2DM) and 20 clinically healthy individuals. The patients were divided into two groups. Group I included 20 T2DM patients without peripheral neuropathy, and Group II consisted of 40 T2DM patients with DPN. In all groups, plasma VEGF, sEng and endothelin‐1 (ET‐1), nitric oxide and ET‐1 mRNA were estimated. Plasma levels of VEGF, sEng, ET‐1 and nitric oxide were significantly elevated in diabetic patients (Groups I and II) compared with healthy control subjects, with a higher increase in their levels in patients with DPN compared with diabetic patients without peripheral neuropathy. Measurement of plasma levels of angiogenesis‐related biomarkers in high‐risk diabetic patients might identify who later develop DPN, thus providing opportunities for early detection and targets for novel treatments. Copyright © 2013 John Wiley & Sons, Ltd.     

DUSP1 recuses diabetic nephropathy via repressing JNK-Mff-mitochondrial fission pathways

Excessive mitochondrial fission has been identified as the pathogenesis of diabetic nephropathy (DN), although the upstream regulatory signal for mitochondrial fission activation in the setting of DN remains unknown. In the current study, we found that dual-specificity protein phosphatase-1 (DUSP1) was actually downregulated by chronic hyperglycemia stimulus. Lower DUSP1 expression was associated with glucose metabolism disorder, renal dysfunction, kidney hypertrophy, renal fibrosis, and glomerular apoptosis. At the molecular level, defective DUSP1 expression activated JNK pathway, and the latter selectively opened mitochondrial fission by modulating mitochondrial fission factor (Mff) phosphorylation. Excessive Mff-related mitochondrial fission evoked mitochondrial oxidative stress, promoted mPTP opening, exacerbated proapoptotic protein leakage into the cytoplasm, and finally initiated mitochondria-dependent cellular apoptosis in the setting of diabetes. However, overexpression of DUSP1 interrupted Mff-related mitochondrial fission, reducing hyperglycemia-mediated mitochondrial damage and thus improving renal function. Overall, we have shown that DUSP1 functions as a novel malefactor in diabetic renal damage that mediates via modifying Mff-related mitochondrial fission. Thus, finding strategies to regulate the balance of the DUSP1-JNK-Mff signaling pathway and mitochondrial homeostasis may be a therapeutic target for treating diabetic nephropathy in clinical practice.     

Mitochondrial DNA variant for complex I reveals a role in diabetic cardiac remodeling

Myocardial remodeling and dysfunction are serious complications of type 2 diabetes mellitus (T2DM). Factors controlling their development are not well established. To specifically address the role of the mitochondrial genome, we developed novel conplastic rat strains, i.e. strains with the same nuclear genome but a different mitochondrial genome. The new animals were named T2DN(mtFHH) and T2DN(mtWistar), where the acronym T2DN denotes their common nuclear genome (type 2 diabetic nephropathy (T2DN) rats) and mtFHH or mtWistar the origin of their mitochondria, Fawn Hooded Hypertensive (FHH) or Wistar rats, respectively. The T2DN(mtFHH) and T2DN(mtWistar) showed a similar progression of diabetes as determined by HbA1c, cholesterol, and triglycerides with normal blood pressure, thus enabling investigation of the specific role of the mitochondrial genome in cardiac function without the confounding effects of obesity or hypertension found in other models of diabetes. Echocardiographic analysis of 12-week-old animals showed no abnormalities, but at 12 months of age the T2DN(mtFHH) showed left ventricular remodeling that was verified by histology. Decreased complex I and complex IV but not complex II activity within the electron transport chain was found only in T2DN(mtFHH), which was not explained by differences in protein content. Decreased cardiac ATP levels in T2DN(mtFHH) were in agreement with a lower ATP synthetic capacity by isolated mitochondria. Together, our data provide experimental evidence that mtDNA sequence variations have an additional role in energetic heart deficiency. The mitochondrial DNA background may explain the increased susceptibility of certain T2DM patients to develop myocardial dysfunction.     

Photobiomodulation induces antinociception,recovers structural aspects and regulates mitochondrial homeostasis in peripheral nerve of diabetic mice

Diabetic peripheral neuropathy (DPN) is a nervous disorder caused by diabetes mellitus, affecting about 50% of patients in clinical medicine. Chronic pain is one of the major and most unpleasant symptoms developed by those patients, and conventional available treatments for the neuropathy, including the associated pain, are still unsatisfactory and benefit only a small number of patients. Photobiomodulation (PBM) has been gaining clinical acceptance once it is able to promote early nerve regeneration resulting in significant improvement in peripheral nerves disabilities. In this work, the effects of PBM (660 nm, 30 mW, 1.6 J/cm², 0.28 cm², 15 s in a continuous frequency) on treating DPN‐induced pain and nerve damage were evaluated in an experimental model of diabetic‐neuropathy induced by streptozotocin in mice. PBM‐induced antinociception in neuropathic‐pain mice was dependent on central opioids release. After 21 consecutive applications, PBM increased nerve growth factor levels and induced structural recovery increasing mitochondrial content and regulating Parkin in the sciatic nerve of DPN‐mice. Taking together, these data provide new insights into the mechanisms involved in the effects of PBM‐therapy emphasizing its therapeutic potential in the treatment of DPN.      

Association of the SOD2 Ala(–9)Val and SOD3 Arg213Gly Polymorphisms with Diabetic Polyneuropathy in Diabetes Mellitus Type 1

Single-nucleotide polymorphisms of the genes for mitochondrial (SOD2) and extracellular (SOD3) superoxide dismutases were tested for association with diabetic polyneuropathy (DPN) in diabetes mellitus (DM) type 1. Patients (N = 180) were divided into two groups with nonoverlapping (polar) phenotypes. Group DPN+ included 86 individuals with DPN and DM type 1 record of no more than 5 years. Group DPN– included 94 patients with DM type 1 record of more than 10 years but without clinical signs of DPN. Fisher's exact test revealed significant differences in allele and genotype frequencies for the two groups. Higher frequencies of SOD2 allele Val and genotype Val/Val and of SOD3 allele Arg and genotype Arg/Arg were established for group DPN+. On this evidence, SOD2 and SOD3 were associated with DPN in DM type 1.     

The impact of mitochondrial quality control by Sirtuins on the treatment of type 2 diabetes and diabetic kidney disease

The incidence of type 2 diabetes mellitus (T2DM) and diabetic kidney disease (DKD) has significantly increased worldwide in recent decades, and improved treatments for T2DM and DKD are urgently needed. The pathogenesis of aging-related disorders, such as T2DM and DKD, involves multiple mechanisms, including inflammation, autophagy impairment, and oxidative stress, which are closely associated with mitochondrial dysfunction. Therefore, mitochondrial quality control may be a novel therapeutic target for T2DM and DKD. Previous reports have shown that members of the mammalian Sirtuin family, SIRT 1–7, which are recognized as antiaging molecules, play a crucial role in the regulation of mitochondrial function and quality control through the modulation of oxidative stress, inflammation and autophagy. In this review, we summarized the research published in recent years to highlight the role of Sirtuins in mitochondrial quality control as a therapeutic target for T2DM and DKD.     

Diabetic animal fed with high‐fat diet prevents the protective effect of myocardial ischemic preconditioning effect in isolated rat heart perfusion model

Diabetic heart (diabetes mellitus [DM]) has been shown to attenuate the beneficial effect of ischemic preconditioning (IPC) in rat heart. But the effect of IPC on diabetic rat heart that develops myopathy remains unclear. This study was designed to test the impact of IPC on diabetic cardiomyopathy (DCM) rat heart. Male Wistar rats were grouped as (a) normal, (b) DM (streptozotocin: 65 mg/kg; fed with normal diet), and (c) DCM (streptozotocin: 65 mg/kg; fed with high‐fat diet). Isolated rat hearts from each group were randomly subjected to (a) normal perfusion, (b) ischemia‐reperfusion (I/R), and (c) IPC procedure. At the end of the perfusion experiments, hearts were analyzed for injury, contractile function, mitochondrial activity, and oxidative stress. The results obtained from hemodynamics, cardiac injury markers, and caspase‐3 activity showed that DCM rat displayed prominent I/R‐associated cardiac abnormalities than DM rat heart. But the deteriorated physiological performance and cardiac injury were not recovered in both DM and DCM heart by IPC procedure. Unlike normal rat heart, IPC did not reverse mitochondrial dysfunction (determined by electron transport chain enzymes activity, ATP level, and membrane integrity, expression levels of genes like PGC‐1ɑ, GSK3β, complex I, II, and V) in DCM and DM rat heart. The present study demonstrated that IPC failed to protect I/R‐challenged DCM rat heart, and the underlying pathology was associated with deteriorated mitochondrial function.     

A red orange and lemon by-products extract rich in anthocyanins inhibits the progression of diabetic nephropathy

The major cause of end-stage renal disease is the diabetic nephropathy. Oxidative stress contributes to the development of type II diabetes mellitus (T2DM). In this study we have evaluated the effect of a diet with a new standardized of red orange and lemon extract (RLE) rich in anthocyanins (ANT) in the progression of the kidney disease on Zucker diabetic fatty rats. Oxidative stress and renal function were analyzed. In diabetic rats, the RLE restored the blood glucose levels, body weight, and normalized the reactive oxygen species (ROS) total pathways. The kidney inflammation, in diabetic rats, has not shown significant change, showing that the oxidative stress rather than to inflammatory processes is a triggering factor in the renal complication associated with T2DM. Therefore, the administration of the RLE prevents this complication and this effect could be related to the inhibition of ROS production.     

Proanthocyanidins protect against early diabetic peripheral neuropathy by modulating endoplasmic reticulum stress

Diabetic peripheral neuropathy (DPN) is the most common and troublesome complication of type 2 diabetes mellitus (T2DM). Recent findings reveal an important role of endoplasmic reticulum (ER) stress in the development of DPN and identify a potential new therapeutic target. Schwann cells (SC), the myelinating cells in peripheral nervous system, are highly susceptible to ER homeostasis. Grape seed proanthocyanidins (GSPs) have been reported to improve DPN of type 1 diabetic rats and relieve ER stress in skeletal muscles and pancreas of T2DM. We investigated the potential role of ER stress in SC in regulating DPN of T2DM and assessed whether early intervention of GSPs would prevent DPN by modulating ER stress. The present study was performed in Sprague–Dawley rats made T2DM with low-dose streptozotocin and a high-carbohydrate/high-fat diet and in rat SC cultured in serum from type 2 diabetic rats. Diabetic rats showed a typical characteristic of T2DM and slowing of nerve conduction velocity (NCV) in sciatic/tibial nerves. The lesions of SC, Ca²⁺ overload and ER stress were present in sciatic nerves of diabetic rats, as well as in cell culture models. GSPs administration significantly decreased the low-density lipoprotein level and increased NCV in diabetic rats. GSPs or their metabolites also partially prevented cell injury, Ca²⁺ overload and ER stress in animal and cell culture models. Therefore, ER stress is implicated in peripheral neuropathy in animal and cell culture models of T2DM. Prophylactic GSPs treatment might have auxiliary preventive potential for DPN partially by alleviating ER stress.     

Quantitative proteomic profiling identifies new renal targets of copper(II)‐selective chelation in the reversal of diabetic nephropathy in rats

This study aimed to identify new diabetic nephropathy (DN)‐related proteins and renal targets of the copper(II)‐selective chelator, triethylenetetramine (TETA) in streptozotocin‐diabetic rats. We used the recently developed iTRAQ? technology to compare renal protein profiles among non‐diabetic, diabetic, and TETA‐treated diabetic rats. In diabetic kidneys, tubulointerstitial nephritis antigen (TINag), voltage‐dependent anion‐selective channel (VDAC) 1, and VDAC2 were up‐regulated in parallel with alterations in expression of proteins with functions in oxidative stress and oxidative phosphorylation (OxPhos) pathways. By contrast, mitochondrial HSP 60, Cu/Zn‐superoxide dismutase, glutathione S‐transferase α3 and aquaporin‐1 were down‐regulated in diabetic kidneys. Following TETA treatment, levels of D ‐amino acid oxidase‐1, epoxide hydrolase‐1, aquaporin‐1, and a number of mitochondrial proteins were normalized, with concomitant amelioration of albuminuria. Changes in levels of TINag, collagen VIα1, actinin 4α, apoptosis‐inducing factor 1, cytochrome C, histone H3, VDAC1, and aquaporin‐1 were confirmed by Western blotting or immunohistochemistry. Changes in expression of proteins related to tubulointerstitial function, podocyte structure, and mitochondrial apoptosis are implicated in the mechanism of DN and their reversal by TETA. These findings are consistent with the hypothesis that this new experimental therapy may be useful for treatment of DN.     

Altered chaperone and protein turnover regulators expression in cultured skin fibroblasts from type 1 diabetes mellitus with nephropathy

In type-1 diabetes mellitus (T1DM) with diabetic nephropathy (DN), accumulation of abnormal proteins in the kidney and other tissues may derive from constitutive alterations of intracellular protein recognition, assembly, and turnover. We characterized the proteins involved in these functions in cultured skin fibroblasts from long-term T1DM patients with [DN+] or without [DN-] nephropathy but similar metabolic control, and from matched healthy subjects. 2-D gel electrophoresis and MS-MALDI analysis were employed. The [DN+] T1DM patients, compared with the two other groups, exhibited increased abundance of a high-molecular weight isoform of protein disulphide-isomerase A3 and a decrease of two low-molecular weight isoforms. They also had increased levels of heat shock protein (HSP) 60 kDa isoform #A4, of HSP71 kDa isoform #A30, and of HSP27 kDa isoform #6, whereas the HSP27 kDa isoforms #A90 and #A71 were decreased. Cathepsin beta-2 (#40), the cation-independent mannose 6-phosphate receptor binding protein 1 (CIMPR) (#A27), and annexin 2 (#A9) were also decreased in the [DN+] T1DM patients, whereas the RNA-binding protein regulatory subunity (#38) and the translationally-controlled tumor protein (TCTP) (#A45) were increased. These changes of chaperone-like proteins in fibroblasts may highlight those of the kidney and be patho-physiologically related to the development of nephropathy in T1DM.     

Polydatin impairs mitochondria fitness and ameliorates podocyte injury by suppressing Drp1 expression

Polydatin (PD), a resveratrol glycoside, has been shown to protect renal function in diabetic nephropathy (DN), but the underlying molecular mechanism remains unclear. This study demonstrates that PD stabilize the mitochondrial morphology and attenuate mitochondrial malfunction in both KKAy mice and in hyperglycemia (HG)‐induced MPC5 cells. We use Western blot analysis to demonstrate that PD reversed podocyte apoptosis induced by HG via suppressing dynamin‐related protein 1 (Drp1). This effect may depend on the ability of PD to inhibit the generation of cellular reactive oxygen species (ROS). In conclusion, we demonstrate that PD may be therapeutically useful in DN, and that, podocyte apoptosis induced by HG can be reversed by PD through suppressing Drp1 expression.     

Functional changes in the neural retina occur in the absence of mitochondrial dysfunction in a rodent model of diabetic retinopathy

Diabetic retinopathy is a neurovascular diabetes complication resulting in vision loss. A wealth of literature reports retinal molecular changes indicative of neural deficits, inflammation, and vascular leakage with chronic diabetes, but the mechanistic causes of disease initiation and progression are unknown. Microvascular mitochondrial DNA (mtDNA) damage leading to mitochondrial dysfunction has been proposed to drive vascular dysfunction in retinopathy. However, growing evidence suggests that neural retina dysfunction precedes and may cause vascular damage. Therefore, we tested the hypothesis that neural mtDNA damage and mitochondrial dysfunction are an early initiating factor of neural diabetic retinopathy development in a rat streptozotocin‐induced, Type I diabetes model. Mitochondrial function (oxygen consumption rates) was quantified in retinal synaptic terminals from diabetic and non‐diabetic rats with paired retinal structural and function assessment (optical coherence tomography and electroretinography, respectively). Mitochondrial genome damage was assessed by identifying mutations and deletions across the mtDNA genome by high depth sequencing and absolute mtDNA copy number counting through digital PCR. Mitochondrial protein expression was assessed by targeted mass spectrometry. Retinal functional deficits and neural anatomical changes were present after 3 months of diabetes and prevented/normalized by insulin treatment. No marked dysfunction of mitochondrial activity, maladaptive changes in mitochondrial protein expression, alterations in mtDNA copy number, or increase in mtDNA damage was observed in conjunction with retinal functional and anatomical changes. These results demonstrate that neural retinal dysfunction with diabetes begins prior to mtDNA damage and dysfunction, and therefore retinal neurodegeneration initiation with diabetes occurs through other, non‐mitochondrial DNA damage, mechanisms.

     

Diabetes induced renal complications by leukocyte activation of nuclear factor κ-B and its regulated genes expression

Type 2 diabetes mellitus (T2D) is a metabolic disorder characterized by inappropriate insulin function. Despite wide progress in genome studies, defects in gene expression for diabetes prognosis still incompletely identified. Prolonged hyperglycemia activates NF-κB, which is a main player in vascular dysfunctions of diabetes. Activated NF-κB, triggers expression of various genes that promote inflammation and cell adhesion process. Alteration of pro-inflammatory and profibrotic gene expression contribute to the irreversible functional and structural changes in the kidney resulting in diabetic nephropathy (DN). To identify the effect of some important NF-κB related genes on mediation of DN progression, we divided our candidate genes on the basis of their function exerted in bloodstream into three categories (Proinflammatory; NF-κB, IL-1B, IL-6, TNF-α and VEGF); (Profibrotic; FN, ICAM-1, VCAM-1) and (Proliferative; MAPK-1 and EGF). We analyzed their expression profile in leukocytes of patients and explored their correlation to diabetic kidney injury features. Our data revealed the overexpression of both proinflammatory and profibrotic genes in DN group when compared to T2D group and were associated positively with each other in DN group indicating their possible role in DN progression. In DN patients, increased expression of proinflammatory genes correlated positively with glycemic control and inflammatory markers indicating their role in DN progression. Our data revealed that the persistent activation NF-κB and its related genes observed in hyperglycemia might contribute to DN progression and might be a good diagnostic and therapeutic target for DN progression. Large-scale studies are needed to evaluate the potential of these molecules to serve as disease biomarkers.     

¹H-NMR-based metabonomic analysis of metabolic profiling in diabetic nephropathy rats induced by streptozotocin

Elucidation of the metabolic profiling in diabetic nephropathy (DN) rats is of great assistance for understanding the pathogenesis of DN. In this study, 1H-nuclear magnetic resonance (NMR)-based metabonomics combined with HPLC measurements was used to quantitatively analyze the metabolic changes in urine and kidney extracts from diabetic 2-wk and 8-wk rats induced by streptozotocin (STZ). Pattern recognition analysis of either urine or kidney extracts indicated that the two diabetic groups were separated obviously from the control group, suggesting that the metabolic profiles of the diabetic groups were markedly different from the control. The diabetic 8-wk rats showed lower levels of creatine, dimethylamine, and higher levels of ascorbate, succinate, lactate, citrate, allantoin, 2-ketoglutarate, and 3-hydrobutyrate (3-HB) in the urine samples. Moreover, the diabetic 8-wk rats displayed lower levels of succinate, creatine, myo-inositol, alanine, lactate, and ATP, and higher levels of 3-HB and glucose in the kidney extracts. The observed metabolic changes imply the enhanced pathways of either lipid or ketone body synthesis and decreased pathways of either tricarboxylic acid cycle or glycolysis in DN rats compared with the control. Our results suggest that the energy metabolic changes are associated with the pathogenic process of DN.     

Involvement of miR‐27a‐3p in diabetic nephropathy via affecting renal fibrosis,mitochondrial dysfunction,and endoplasmic reticulum stress

Diabetic nephropathy (DN) is acknowledged as a serious chronic complication of diabetes mellitus. Nevertheless, its pathogenesis is complicated and unclear. Thus, in this study, the role of miR‐27a‐3p‐prohibitin/TMBIM6 signaling axis in the progression of DN was elucidated. Type 2 diabetic db/db mice and high glucose (HG)‐challenged HK‐2 cells were used as in vivo and in vitro models. Our results showed that miR‐27a‐3p was upregulated and prohibitin or transmembrane BAX inhibitor motif containing 6 (TMBIM6) was downregulated in the kidney tissues of db/db mice and HG‐treated HK‐2 cells. Silencing miR‐27a‐3p enhanced the expression of prohibitin and TMBIM6 in the kidney tissues and HK‐2 cells. Inhibition of miR‐27a‐3p improved functional injury, as evidenced by decreased blood glucose, urinary albumin, serum creatinine, and blood urea nitrogen levels. MiR‐27a‐3p silencing ameliorated renal fibrosis, reflected by reduced profibrogenic genes (e.g., transforming growth factor β1, fibronectin, collagen I and III, and α‐smooth muscle actin). Furthermore, inhibition of miR‐27a‐3p relieved mitochondrial dysfunction in the kidney of db/db mice, including upregulation of mitochondrial membrane potential, complex I and III activities, adenosine triphosphate, and mitochondrial cytochrome C, as well as suppressing reactive oxygen species production. In addition, miR‐27a‐3p silencing attenuated endoplasmic reticulum (ER) stress, reflected by reduced expression of p‐IRE1α, p‐eIF2α, XBP1s, and CHOP. Mechanically, we identified prohibitin and TMBIM6 as direct targets of miR‐27a‐3p. Inhibition of miR‐27a‐3p protected HG‐treated HK‐2 cells from apoptosis, extracellular matrix accumulation, mitochondrial dysfunction, and ER stress by regulating prohibitin or TMBIM6. Taken together, we reveal that miR‐27a‐3p‐prohibitin/TMBIM6 signaling axis regulates the progression of DN, which can be a potential therapeutic target.