Associations between local acidosis induced by renal LDHA and renal fibrosis and mitochondrial abnormalities in patients with diabetic kidney disease.

During the progression of diabetic kidney disease (DKD), renal lactate metabolism is rewired. The relationship between alterations in renal lactate metabolism and renal fibrosis in patients with diabetes has only been partially established due to a lack of biopsy tissues from patients with DKD and the intricate mechanism of lactate homeostasis. The role of lactate dehydrogenase A (LDHA)-mediated lactate generation in renal fibrosis and dysfunction in human and animal models of DKD was explored in this study. Measures of lactate metabolism (urinary lactate levels and LDHA expression) and measures of DKD progression (estimated glomerular filtration rate and Wilms' tumor-1 expression) were strongly negatively correlated in patients with DKD. Experiments with streptozotocin-induced DKD rat models and the rat renal mesangial cell model confirmed our findings. We found that the pathogenesis of DKD is linked to hypoxia-mediated lactic acidosis, which leads to fibrosis and mitochondrial abnormalities. The pathogenic characteristics of DKD were significantly reduced when aerobic glycolysis or LDHA expression was inhibited. Further studies will aim to investigate whether local acidosis caused by renal LDHA might be exploited as a therapeutic target in patients with DKD.

Vitamin D Rescues Pancreatic ß Cell Dysfunction due to Iron Overload via Elevation of the Vitamin D Receptor and Maintenance of Ca2+ Homeostasis.

SCOPE: Accumulating evidence indicates that micronutrients are related to metabolic diseases. However, comparatively less attention has been devoted to their influence on each other during the development of metabolic diseases. To investigate the underlying mechanisms, the effects of iron and vitamin D on pancreatic ß cell functions are examined. METHODS AND RESULTS: Iron overload is induced in INS-1 rat insulinoma pancreatic ß cells and it is found that iron overload dramatically reduce expression of the vitamin D receptor (VDR). Iron overload-induced ß cell dysfunction is rescued by 1,25-dihydroxyvitamin D3 (1,25(OH)2 D3 ) cotreatment via restoration of VDR level and the consequent maintenance of Ca2+ homeostasis. Iron accumulation is also observed in the islets of 22-month-old C57BL/6 mice fed with a chow diet (1000 IU vitamin D3 per kg). In contrast, islet iron accumulation and hyperinsulinemia are ameliorated in mice fed with a vitamin D3 -supplemented diet (20 000 IU kg-1 ). CONCLUSION: The authors show that functional failure of ß cells due to iron accumulation is rescued by 1,25(OH)2 D3 , and iron overload significantly reduces VDR levels in ß cells. These results suggest that iron and vitamin D inversely influence pancreatic ß cell function.

Down-regulation of the mitochondrial i-AAA protease Yme1L induces muscle atrophy via FoxO3a and myostatin activation.

Muscle atrophy is closely associated with many diseases, including diabetes and cardiac failure. Growing evidence has shown that mitochondrial dysfunction is related to muscle atrophy; however, the underlying mechanisms are still unclear. To elucidate how mitochondrial dysfunction causes muscle atrophy, we used hindlimb-immobilized mice. Mitochondrial function is optimized by balancing mitochondrial dynamics, and we observed that this balance shifted towards mitochondrial fission and that MuRF1 and atrogin-1 expression levels were elevated in these mice. We also found that the expression of yeast mitochondrial escape 1-like ATPase (Yme1L), a mitochondrial AAA protease was significantly reduced both in hindlimb-immobilized mice and carbonyl cyanide m-chlorophenylhydrazone (CCCP)-treated C2C12 myotubes. When Yme1L was depleted in myotubes, the short form of optic atrophy 1 (Opa1) accumulated, leading to mitochondrial fragmentation. Moreover, a loss of Yme1L, but not of LonP1, activated AMPK and FoxO3a and concomitantly increased MuRF1 in C2C12 myotubes. Intriguingly, the expression of myostatin, a myokine responsible for muscle protein degradation, was significantly increased by the transient knock-down of Yme1L. Taken together, our results suggest that a deficiency in Yme1L and the consequential imbalance in mitochondrial dynamics result in the activation of FoxO3a and myostatin, which contribute to the pathological state of muscle atrophy.

Activating transcription factor 3 is a target molecule linking hepatic steatosis to impaired glucose homeostasis.

BACKGROUND & AIMS: Non-alcoholic fatty liver disease (NAFLD) contributes to impaired glucose tolerance, leading to type 2 diabetes (T2D); however, the precise mechanisms and target molecules that are involved remain unclear. Activating transcription factor 3 (ATF3) is associated with ß-cell dysfunction that is induced by severe stress signals in T2D. We aimed to explore the exact functional role of ATF3 as a mechanistic link between hepatic steatosis and T2D development. METHODS: Zucker diabetic fatty (ZDF) rats were utilized for animal experiments. An in vivo-jetPEI siRNA delivery system against ATF3 was used for loss-of-function experiments. We analyzed the baseline cross-sectional data derived from the biopsy-proven NAFLD registry (n=322). Human sera and liver tissues were obtained from 43 patients with biopsy-proven NAFLD and from seven healthy participants. RESULTS: ATF3 was highly expressed in the livers of ZDF rats and in human participants with NAFLD and/or T2D. Insulin resistance and hepatic steatosis were associated with increased ATF3 expression and decreased fatty acid oxidation via mitochondrial dysfunction and were attenuated by in vivo ATF3 silencing. Knockdown of ATF3 also ameliorated glucose intolerance, impaired insulin action, and inflammatory responses in ZDF rats. In patients with NAFLD and/or T2D, a significant positive correlation was observed between hepatic ATF3 expression and surrogate markers of T2D, mitochondrial dysfunction, and macrophage infiltration. CONCLUSIONS: Increased hepatic ATF3 expression is closely associated with hepatic steatosis and incident T2D; therefore, ATF3 may serve as a potential therapeutic target for NAFLD and hepatic steatosis-induced T2D. LAY SUMMARY: Hepatic activating transcription factor 3 (ATF3) may play an important role in oxidative stress-mediated hepatic steatosis and the development of type 2 diabetes (T2D) in a Zucker diabetic fatty (ZDF) rat model and in human patients with non-alcoholic fatty liver disease (NAFLD). Therefore, ATF3 may be a useful biomarker for predicting the progression of NAFLD and the development of T2D. Furthermore, given the significant association between hepatic ATF3 expression and both hepatic steatosis and impaired glucose homeostasis, in vivo ATF3 silencing may be a potential central strategy for preventing and managing NAFLD and T2D.

Comparison of MSC-Neurogenin1 administration modality in MCAO rat model.

Intracerebral (IC) grafting of mesenchymal stem cells (MSCs) is not currently used in humans due to its potential complications. On the other hand, intra-arterial (IA) administration can be facilitated for engrafting of intensifed MSCs in the injured human brain. The study is designed to compare the two methods of MSC administration using IA and IC routes through the parameters of behavior, infarct volume, cell distribution, and MSC identification. An ischemic stroke model was generated in Sprague Dawley male rats. This experiment used MSCs/Ngn1 that express Neurogenin1 (Ngn1) to ensure grafted MSC maintenance. MSCs/Ngn1 or normal saline was administrated via the IC or IA route on day 3. All animals were randomly assigned into four groups (five rats in each group): IC-control, IA-control, IC-MSCs/Ngn1, or IA-MSCs/Ngn1. Motor behaviors, infarct volume, and distribution of superparamagnetic iron oxide (SPIO)-labeled cells on magnetic resonance imaging (MRI) were compared from each group. There were no baseline differencess in motor behaviors or infarct volume between IC-MSCs/Ngn1 and IA-MSCs/Ngn1. Hovever, the IA-MSCs/Ngn1 group showed the greatest recovery on Rotarod testing and adhesive removal tests (p = 0.003 and p = 0.009 vs. IC-MSCs/Ngn1, respectively). The IA-MSCs/Ngn1 group also had more evenly distributed SPIO-labeled cells on MRI. The results suggest that IA administration is likely to be benefcial for humans based on its ability to improve behavioral outcomes and ensure even MSC engrafting.

Immune following suppression mesenchymal stem cell transplantation in the ischemic brain is mediated by TGF-ß.

Transplantation of mesenchymal stem cells (MSCs) has been shown to enhance the recovery of brain functions following ischemic injury. Although immune modulation has been suggested to be one of the mechanisms, the molecular mechanisms underlying improved recovery has not been clearly identified. Here, we report that MSCs secrete transforming growth factor-beta (TGF-ß) to suppress immune propagation in the ischemic rat brain. Ischemic stroke caused global death of resident cells in the infarcted area, elevated the monocyte chemoattractant protein-1 (MCP-1) level, and evoked massive infiltration of circulating CD68+ immune cells through the impaired blood-brain barrier. Transplantation of MSCs at day 3 post-ischemia blocked the subsequent upregulation of MCP-1 in the ischemic area and the infiltration of additional CD68+ immune cells. MSC-conditioned media decreased the migration and MCP-1 production of freshly isolated immune cells in vitro, and this effect was blocked by an inhibitor of TGF-ß signaling or an anti-TGF-ß neutralizing antibody. Finally, transplantation of TGF-ß1-silenced MSCs failed to attenuate the infiltration of CD68+ cells into the ischemic brain, and was associated with only minor improvements in motor function. These results indicate that TGF-ß is key to the ability of MSCs to beneficially attenuate immune reactions in the ischemic brain. Our findings offer insight into the interactions between allogeneic MSCs and the host immune system, reinforcing the prospective clinical value of using MSCs in the treatment of neurological disorders involving inflammation-mediated secondary damage.

Homocysteine enhances MMP-9 production in murine macrophages via ERK and Akt signaling pathways.

Homocysteine (Hcy) at elevated levels is an independent risk factor of cardiovascular diseases, including atherosclerosis. In the present study, we investigated the effect of Hcy on the production of matrix metalloproteinases (MMP) in murine macrophages. Among the MMP known to regulate the activities of collagenase and gelatinase, Hcy exclusively increased the gelatinolytic activity of MMP-9 in J774A.1 cells as well as in mouse peritoneal macrophages. Furthermore, this activity was found to be correlated with Western blot findings in J774A.1 cells, which showed that MMP-9 expression was concentration- and time-dependently increased by Hcy. Inhibition of the ERK and Akt pathways led to a significant decrease in Hcy-induced MMP-9 expression, and combined treatment with inhibitors of the ERK and Akt pathways showed an additive effects. Activity assays for ERK and Akt showed that Hcy increased the phosphorylation of both, but these phosphorylation were not affected by inhibitors of the Akt and ERK pathways. In line with these findings, the molecular inhibition of ERK and Akt using siRNA did not affect the Hcy-induced phosphorylation of Akt and ERK, respectively. Taken together, these findings suggest that Hcy enhances MMP-9 production in murine macrophages by separately activating the ERK and Akt signaling pathways.