Taurine ameliorates axonal damage in sciatic nerve of diabetic rats and high glucose exposed DRG neuron by PI3K/Akt/mTOR-dependent pathway.

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes and axonopathy is its main pathological feature. Previous studies suggested an advantage of taurine against diabetes. However, there are few reports which study the effect of taurine against axonopathy. In this study, we confirmed that taurine significantly decreased blood glucose level, mitigated insulin resistance and improved dysfunctional nerve conduction in diabetic rats. Taurine corrected damaged axonal morphology of sciatic nerve in diabetic rats and induced axon outgrowth of Dorsal root ganglion (DRG) neurons exposed to high glucose. Taurine up-regulated phosphorylation levels of PI3K, Akt, and mTOR in sciatic nerve of diabetic rats and DRG neurons exposed to high glucose. However, Akt and mTOR inhibitors (MK-2206 and Rapamycin) blocked the effect of taurine on improving axonal damage. These results indicate that taurine ameliorates axonal damage in sciatic nerve of diabetic rats by activating PI3K/Akt/mTOR signal pathway. Our findings provide taurine as a potential candidate for axonopathy and a new evidence for elucidating protective mechanism of taurine on DPN.

Taurine inhibits neuron apoptosis in hippocampus of diabetic rats and high glucose exposed HT-22 cells via the NGF-Akt/Bad pathway.

Type 2 Diabetes causes learning and memory deficits that might be mediated by hippocampus neuron apoptosis. Studies found that taurine might improve cognitive deficits under diabetic condition because of its ability to prevent hippocampus neuron apoptosis. However, the effect and mechanism is not clear. In this study, we explore the effect and mechanism of taurine on inhibiting hippocampus neuron apoptosis. Sixty male Sprague-Dawley rats were randomly divided into control, T2D, taurine treatment (giving 0.5%, 1%, and 2% taurine in drinking water) groups. Streptozotocin was used to establish the diabetes model. HT-22 cell (hippocampus neurons line) was used for in vitro experiments. Morris Water Maze test was used to check the learning and memory ability, TUNEL assay was used to measure apoptosis and nerve growth factor (NGF); Akt/Bad pathway relevant protein was detected by western blot. Taurine improved learning and memory ability and significantly decreased apoptosis of the hippocampus neurons in T2D rats. Moreover, taurine supplement also inhibited high glucose-induced apoptosis in HT-22 cell in vitro. Mechanistically, taurine increased the expression of NGF, phosphorylation of Trka, Akt, and Bad, as well as reduced cytochrome c release from mitochondria to cytosol. However, beneficial effects of taurine were blocked in the presence of anti-NGF antibody or Akt inhibitor. Taurine could inhibit hippocampus neuron apoptosis via NGF-Akt/Bad pathway. These results provide some clues that taurine might be efficient and feasible candidate for improvement of learning and memory ability in T2D rats.

Taurine protects against myelin damage of sciatic nerve in diabetic peripheral neuropathy rats by controlling apoptosis of schwann cells via NGF/Akt/GSK3ß pathway.

Diabetic peripheral neuropathy is a common complications of Type 2 Diabetes and its main pathological feature is myelin sheath damage of peripheral nerve that was induced by Schwann cells (SCs) apoptosis. Increasing evidence suggested that taurine might play a role in improving DPN because of its ability to prevent SCs apoptosis. In this study, we explore the effect of taurine on preventing SCs apoptosis and its underlying mechanism. Sprague Dawley rats were treated with streptozotocin to establish the diabetes model. Rats were randomly divided into control, diabetes, taurine treatment (as giving 0.5%, 1% and 2% taurine in drinking water) groups. RSC96 cell (a rat SCs line) was used for intervention experiments in vitro. Results showed that taurine significantly corrected morphology of damaged myelin sheath and inhibited SCs apoptosis in sciatic nerve of diabetic rats. Moreover, taurine prevented apoptosis of RSC96 cells exposed to high glucose. Mechanistically, taurine up-regulated NGF expression and phosphorylation levels of Akt and GSK3ß, while, blocking activation of NGF and phosphorylation of Akt and GSK3ß increased apoptosis of high glucose-exposed RSC96 cells with taurine supplement. These results revealed taurine improved the myelin sheath damage of sciatic nerve in diabetic rats by controlling SCs apoptosis via NGF/Akt/GSK3ß signaling pathways, which provides some clues that taurine might be effective and feasible candidate for the treatment of DPN.

Ginsenoside Rb1 mitigates oxidative stress and apoptosis induced by methylglyoxal in SH-SY5Y cells via the PI3K/Akt pathway.

Diabetic encephalopathy is a severe diabetic complication characterized by cognitive dysfunction and neuropsychiatric disability. Methylglyoxal (MGO), a highly reactive metabolite of hyperglycemia, serves as a major precursor of advanced glycation end products that play key roles in diabetic complications. Ginsenoside Rb1 (abbreviated as Rb1) has received extensive attention due to its potential therapeutic effects on diabetes and neurodegeneration. Therefore, this study aimed to investigate the effects of Rb1 on MGO-induced damage in SH-SY5Y cells and the related mechanism. SH-SY5Y cells were pretreated with Rb1 for 8 h and then exposed to MGO (0.5 mM) for 24 h. Cell survival was assessed by the MTT assay. Cell apoptosis was assessed using Hoechst 33342/propidium iodide (PI) staining and an Annexin-V/PI kit. The activities of oxidative stress markers were examined using commercial kits. Reactive oxygen species (ROS) staining and JC-1 staining were used to evaluate mitochondria injury. In addition, protein levels were measured by Western blot analysis. As a result, Rb1 alleviated the injury induced by MGO by increasing the activities of superoxide dismutase, catalase and total glutathione, decreasing the level of malondialdehyde, and alleviating mitochondrial damage and ROS production. Furthermore, Rb1 could enhance the Bcl-2/Bax ratio, inhibit the expression of cleaved caspase-3 and cleaved caspase-9, and enhance the levels of phosphorylated Akt. Moreover, the protective effects of Rb1 against MGO-induced apoptosis were partly abolished by LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K) phosphorylation. Our results demonstrated that Rb1 ameliorated MGO-induced oxidative stress and apoptosis in SH-SY5Y cells via activating the PI3K/Akt signaling pathway.

Correction to: Taurine Ameliorates High Glucose Induced Apoptosis in HT-22 Cells.

Affiliations of authors Muhammad Shahbaz and Shahid Alam were incorrect in the published book. This has now been corrected as below.

Anti-apoptotic Effect of Taurine on Schwann Cells Exposed to High Glucose In Vitro.

It was reported that apoptosis of Schwann cells could increase in the diabetic rats. The studies showed that taurine inhibited apoptosis in a variety of cells. However, there were few reports on studying the protection of taurine against apoptosis of Schwann cells induced by high glucose (HG) and the underlying mechanism. In our study, the cells were divided into five groups: Control: the normal medium; HG group: 50 mM high glucose; T1: 50 mM high glucose+Taurine (10 mM) group; T2: 50 mM high glucose+Taurine (20 mM) group; T3: 50 mM high glucose+Taurine (40 mM) group. We used MTT and Tunel assays to measure the cell viability and apoptosis, respectively. Then, we also used western blotting to detect the protein levels of apoptosis-related protein. The results demonstrate that taurine promoted cell viability and decreased apoptosis in RSC96 cells exposed to HG. Furthermore, taurine markedly improved imbalance of Bax and Bcl-2, inhibited the translocation of Cytochrome C (Cyt C) from mitochondria to cytosol and reduced caspase-3 activity in HG-induced RSC96 cells. Our results indicate that taurine protect against apoptosis of Schwann cells induced by HG via inhibiting mitochondria-dependent caspase-3 pathway.

Protective Effect of Taurine on Apoptosis of Spinal Cord Cells in Diabetic Neuropathy Rats.

Diabetes mellitus (DM) is a condition characterized by chronic hyperglycemia, which leads to diabetic neuropathy and apoptosis in the spinal cord. Taurine has been found to ameliorate the diabetic neuropathy and control apoptosis in various tissues. However, there are few reports that discuss the direct relationship between spinal cord and anti-apoptotic effect of taurine. In this study, DM was induced in male SD rats with STZ @ 25 mg/Kg of body weight in combination with high fat diet. After 2 weeks, they were divided into four groups as DM: diabetic rats, T1 (0.5%), T2 (1%) and T3 (2%) taurine solution, while control group was non-diabetic rats (no treatment). The results showed that DM increased apoptosis, decreased phosphorylated Akt and Bad. DM decreased expression of Bcl-2 and increased the Bax. Moreover, the release of cytochrome c into cytosol was increased in DM and activation of caspase-3 was also increased. However, taurine reversed all these abnormal changes in a dose dependent manner. Our results suggested the involvement of Akt/Bad signaling pathway and mitochondrial apoptosis pathway in protective effect of taurine against apoptosis in the spinal cord of diabetic rats. Therefore, taurine may be a potential medicine against diabetic neuropathy by controlling apoptosis.

Taurine Ameliorates High Glucose Induced Apoptosis in HT-22 Cells.

Diabetes causes memory loss. Hippocampus is responsible for memory and increased apoptosis was found in diabetes patients. Taurine improved memory in diabetes condition. However, mechanism is unclear. In current study, hippocampal cell line HT-22 cells were subjected to analysis as five groups i.e. Control, High glucose (HG) at concentration of 150 mM, HG + 10 mM (T1), 20 mM (T2) and 40 mM (T3) taurine solution. TUNEL assay showed that HG increased the number of apoptotic cell significantly while taurine reduced apoptosis. Taurine increased phosphorylation of Akt in HT-22 cell treated with HG, and increased phosphorylation of Bad (p-Bad) was seen suggesting involvement of Akt/Bad signaling pathway. Expression of Bcl-2 was reduced in HG group but taurine improved this. Bax expression showed opposite trend. This indicated that taurine may reduce apoptosis by controlling balance of Bcl-2 and Bax. When the activation of Akt was blocked by using of perifosine, the effect of taurine disappears either partially or altogether. Thus, it was clear that taurine reduces apoptosis via Akt/Bad pathway in HT-22 cells exposed to HG which further improves downstream balance of Bcl-2 and Bax. This mechanism may be involved in apoptosis of hippocampus cells in diabetic condition.

Taurine Promotes Neuritic Growth of Dorsal Root Ganglion Cells Exposed to High Glucose in Vitro.

Diabetic neuropathy (DN) is the most common chronic complication of DM and its major pathological changes show axonal dysfunction, atrophy and loss. However, there are few reports that taurine promotes neurite growth of dorsal root ganglion (DRG) cells. In current study, DRG neurons were exposed to high glucose (HG) with or without taurine. The neurite outgrowth of DRG neurons was observed by fluorescent immunohistochemistry method. Expression of Gap-43, Akt, phosphorylated Akt, mTOR and phosphorylated mTOR was determined by Western blot assay. Our results showed that HG significantly decreased the neurite outgrowth and expression of Gap-43 in DRG neurons. Moreover, phosphorylated levels of Akt and mTOR were downregulated in DRG neurons exposed to HG. On the contrary, taurine supplementation significantly reversed the decreased neurite outgrowth and Gap-43 expression, and the downregulated phosphorylated levels of Akt and mTOR. However, the protective effects of taurine were blocked in the presence of PI3K antagonists LY294002 or Akt antagonists Perifosine. These results indicate that taurine promotes neurite outgrowth of DRG neurons exposed to HG via activating Akt/mTOR signal pathway.

The microRNAs Expression Profile in Sciatic Nerves of Diabetic Neuropathy Rats After Taurine Treatment by Sequencing.

Taurine protect against diabetic neuropathy. However, the protective mechanism of taurine has been poorly understood. It has been demonstrated that microRNAs (miRNAs) are involved in regulating gene expression. Therefore, it is interested in whether taurine affects miRNAs expression profile in peripheral nerve tissue of diabetic neuropathy. In the present study, rats were treated as three group: (1) control (Con) group, (2) diabetic mellitus (DM) group and (3) taurine treatment (Tau) group. Sciatic nerve tissue was harvested and miRNA expression was determined using sequencing. The results showed that 80 miRNAs showed significant difference in DM group compared to Con group, of which 20 miRNAs showed up-regulating, as well as, 60 miRNAs showed down-regulating. On the other hand, 215 differential miRNAs were found between DM and Tau groups. Moreover, the numbers of up-regulated and down-regulated miRNAs were 1 and 214, respectively. Twelve specific miRNAs were screened out and the target genes were obtained by target analysis software. GO and KEGG enrichment analyses showed that these potential target genes for the miRNAs might be involved in axon guidance, generation of neurons, nervous system development and neurogenesis. Our results provided a miRNA profile for further exploring protective mechanisms of taurine against diabetic peripheral neuropathy.

Ameliorative effects of taurine against diabetes: a review.

Diets in rats and humans have shown promising results. Taurine improved glucagon activity, promoted glycemic stability, modified glucose levels, successfully addressed hyperglycemia via advanced glycation end-product control, improved insulin secretion and had a beneficial effect on insulin resistance. Taurine treatment performed well against oxidative stress in brain, increased the secretion of required hormones and protected against neuropathy, retinopathy and nephropathy in diabetes compared with the control. Taurine has been observed to be effective in treatments against diabetic hepatotoxicity, vascular problems and heart injury in diabetes. Taurine was shown to be effective against oxidative stress. The mechanism of action of taurine cannot be explained by one pathway, as it has many effects. Several of the pathways are the advanced glycation end-product pathway, PI3-kinase/AKT pathway and mitochondrial apoptosis pathway. The worldwide threat of diabetes underscores the urgent need for novel therapeutic measures against this disorder. Taurine (2-aminoethane sulfonic acid) is a natural compound that has been studied in diabetes and diabetes-induced complications.

Transient Receptor Potential Melastatin 2:an Ion Channel for Oxidative Stress Sensing.

Transient receptor potential (TRP) channel is a superfamily of cation channels located on the cell membrane. TRP channels are classified into seven subfamilies based on the amino acid sequence homology,and transient receptor potential melastatin 2(TRPM2) is the second member of the TRPM subfamily. More evidences have revealed the important roles of TRPM2 in physiological and pathological events such as release of insulin from pancreatic Β-cells,inflammatory cytokines production from cells,and oxidative stress-induced cell death. As a cellular sensor for oxidative stress channel,TRPM2 is activated by a variety of factors. TRPM2 is a potential therapeutic target for oxidative stress-related diseases.

Effects of exposure to high glucose on primary cultured hippocampal neurons: involvement of intracellular ROS accumulation.

Recent studies showed that hyperglycemia is the main trigger of diabetic cognitive impairment and can cause hippocampus abnormalities. The goal of this study is to explore the effects of different concentrations of high glucose for different exposure time on cell viability as well as intracellular reactive oxygen species (ROS) generation of primary cultured hippocampal neurons. Hippocampal neurons were exposed to different concentrations of high glucose (50, 75, 100, 125, and 150 mM) for 24, 48, 72 and 96 h. Cell viability and nuclear morphology were evaluated by MTT and Hoechst assays, respectively. Intracellular ROS were monitored using the fluorescent probe DCFH-DA. The results showed that, compared with control group, the cell viability of all high glucose-treated groups decreased significantly after 72 h and there also was a significant increase of apoptotic nuclei in high glucose-treated groups from 72 to 96 h. Furthermore, 50 mM glucose induced a peak rise in ROS generation at 24 h and the intracellular ROS levels of 50 mM glucose group were significantly higher than the corresponding control group from 6 to 72 h. These results suggest that hippocampal neurons could be injured by high glucose exposure and the neuronal injury induced by high glucose is potentially mediated through intracellular ROS accumulation.

[Effect of ginsenoside Rb1 on insulin signal transduction pathway in hippocampal neurons of high-glucose-fed rats].

OBJECTIVE: To study the effect of ginsenoside Rb1 on GSKbeta/IDE signal transduction pathway and Abeta protein secretion in hippocampal neurons of high glucose-treated rats. METHOD: Hippocampal neurons of 24 h-old newly born SD rats were primarily cultured, inoculated in culture medium under different conditions, and then divided into the normal group, the high glucose group, the LiCl group and the Rb1 group. After being cultured for 72 h, the expressions of their phosphorylated GSK3beta, total GSK3beta and IDE protein were detected by Western blotting analysis. The mRNA expressions of GSK3beta and IDE were determined by RT-PCR. The ELISA assay was used to detect the secretion of Abeta protein in cell supernatant. RESULT: Compared with the normal group, the high glucose group showed increase in the p/tGSK3beta protein ratio and the secretion of Abeta protein and decrease in IDE protein and mRNA (P < 0.05). Compared with the high glucose group, both Rb1 and LiCl groups showed decrease in the p/tGSK3beta protein ratio and the expression of Abeta protein and increase in IDE protein and mRNA expression (P < 0.05). Compared with the LiCl group, the Rb1 group showed no significant difference in the expressions of p/tGSK3beta protein, IDE protein, mRNA and Abeta protein expression. In addition, the GSK3beta mRNA expression of the four groups had no significant difference. CONCLUSION: Ginsenoside Rb1 may reduce the secretion of Abeta protein in hippocampal neurons by reducing the phosphorylation of GSK3beta, down-regulating the ratio of pGSK3beta/GSK3beta and upregulating the expression of IDE.

Haplotype-resolved chromosome-level genome assembly of Ehretia macrophylla.

Ehretia macrophylla Wall, known as wild loquat, is an ecologically, economically, and medicinally significant tree species widely grown in China, Japan, Vietnam, and Nepal. In this study, we have successfully generated a haplotype-resolved chromosome-scale genome assembly of E. macrophylla by integrating PacBio HiFi long-reads, Illumina short-reads, and Hi-C data. The genome assembly consists of two haplotypes, with sizes of 1.82 Gb and 1.58 Gb respectively, and contig N50 lengths of 28.11 Mb and 21.57 Mb correspondingly. Additionally, 99.41% of the assembly was successfully anchored into 40 pseudo-chromosomes. We predicted 58,886 protein-coding genes, of which 99.60% were functionally annotated from databases. We furthermore detected 2.65 Gb repeat sequences, 659,290 rRNAs, 4,931 tRNAs and 4,688 other ncRNAs. The high-quality assembly of the genome offers a solid basis for furthering the fields of molecular breeding and functional genomics of E. macrophylla.

Signaling pathways involved in endoplasmic reticulum stress-induced neuronal apoptosis.

In eukaryotic cells, the endoplasmic reticulum (ER) is a very critical site for synthesis, folding, modification of protein, and calcium homeostasis. The ER responds to factors that perturb ER function such as the accumulation of unfolded proteins (ER stress) by activating unfolded protein response to relieve the stress. However, chronic or unresolved ER stress can induce neuronal apoptosis by activating c-Jun N-terminal kinase (JNK), glycogen synthase kinase 3/3ß (GSK3/3ß), CAAT/enhancer binding protein homologous protein (CHOP), and caspase-12 pathway. Research related to ER stress will provide therapeutic implications in neurological diseases.

Insulin-degrading enzyme: Roles and pathways in ameliorating cognitive impairment associated with Alzheimer's disease and diabetes.

Accumulation of amyloid-ß in the central nervous system is a common feature of Alzheimer's disease (AD) and diabetes-related cognitive impairment. Since the insulin-degrading enzyme (IDE) can break down amyloid-ß plaques, there is considerable interest in using this enzyme to treat both neurological disorders. In this review, we have summarized the pre-clinical and clinical research on the potential application of IDE for the improvement of cognitive impairment. Furthermore, we have presented an overview of the main pathways that can be targeted to mitigate the progression of AD and the cognitive impairment caused by diabetes.

Naofucong Ameliorates High Glucose Induced Hippocampal Neuron Injury Through Suppressing P2X7/NLRP1/Caspase-1 Pathway.

P2X7/NLRP1/caspase-1 mediated neuronal injury plays an important role in diabetic cognitive impairment and eventually inflammatory cascade reaction. Chinese herbal compound Naofucong has been mainly used to treat cognitive disorders in Traditional Chinese Medicine The present study aimed to investigate whether its neuroprotective effects might be related to the inhibition of P2X7R/NLRP1/caspase-1 mediated neuronal injury or not. In this study, high glucose-induced HT22 hippocampal neurons were used to determine Naofucong-containing serum neuronal protective effects. Lentiviruses knock out of TXNIP and P2X7R was used to determine that protective effects of Naofucong was related to inflammatory response and P2X7/NLRP1/caspase-1 mediated neuronal injury. NAC was also used to inhibit oxidative stress, so as to determine that oxidative stress is an important starting factor for neuronal injury of HT22 cells cultured with high glucose. Naofucong decreased apoptosis, IL-1ß and IL-18 levels in high glucose-induced HT22 hippocampal neuron cells. Naofucong suppressed NLRP1/caspase-1 mediated neuronal injury, and P2X7 was involved in process. HT22 cells cultured in high glucose had an internal environment with elevated oxidative stress, which could promote neuronal injury. The current study demonstrated that Naofucong could significantly improve high glucose-induced HT22 hippocampal neuron injury, which might be related to suppress P2X7R/NLRP1/caspase-1 pathway, which provides novel evidence to support the future clinical use of Naofucong.

Nao-Fu-Cong ameliorates diabetic cognitive dysfunction by inhibition of JNK/CHOP/Bcl2-mediated apoptosis in vivo and in vitro.

Chinese herbal compound Nao-Fu-Cong (NFC) has been mainly used to treat cognitive disorders in Traditional Chinese Medicine (TCM). The present study aimed to investigate whether its neuroprotective effects might be related to the inhibition of JNK/CHOP/Bcl2-mediated apoptosis pathway or not. We randomly assigned STZ (60 mg·kg-1)-induced diabetic rats into control group, diabetic model group and NFC groups (low-dose, medium-dose and high-dose). The primary culture of hippocampal neurons were transferred into different culture media on the third day. The cells were then divided into control group, high-glucose group, NFC (low-dose, medium-dose and high-dose) groups, CHOP si-RNA intervention group, JNK pathway inhibitor SP600125 group and oxidative stress inhibitor N-acetylcysteine (NAC) group. NFC significantly improved the cognitive function of diabetic rats, and had neuroprotective effect on hippocampal neurons cultured in high glucose. Further research results showed that NFC could reduce the apoptosis of hippocampal neurons in rats with diabetic cognitive dysfunction. NFC had inhibitory effects on CHOP/JNK apoptosis pathway induced by high glucose, and also decreased the levels of ROS and increased the mitochondrial membrane potential. These suggested that the neuroprotective effect of NFC might be related to the inhibition of CHOP and JNK apoptotic signaling pathways, and the cross pathway between oxidative stress and mitochondrial damage pathway.

Effect of Chinese herbal compound Naofucong () on the inflammatory process induced by high glucose in BV-2 cells.

OBJECTIVE: To determine the effect of medicated serum of Chinese herbal compound Naofucong (, NFC) on the microglia BV-2 cells viability and the transcription and expression of interleukin-6 (IL-6) and tumor necrosis factor α (TNF-α) in microglia BV-2 cells to further explore the mechanisms underlying the protective effect of NFC on inflammatory process induced by high glucose. METHODS: The microglia BV-2 cells incubated in vitro were divided into different groups: the control group (25 mmol/L glucose), the model group (75 mmol/L glucose), high glucose media containing different dose medicated serum of NFC. After being cultured for 24 h, changes in IL-6 and TNF-α were measured by quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay. The expression of surface marker CD11b of activated microglia was measured by confocal laser scanning microscope and Western blot. Nuclear factor-κB (NF-κB) p-p65 expression was analyzed by Western blot. RESULTS: The model group obviously increased the expression of microglial surface marker CD11b and NF-κB p-p65 (all P<0.01), induced a signifificant up-regulation of release and the mRNA expression of IL-6 and TNF-α (P<0.01 or P<0.05). The medicated serum of NFC could obviously down-regulate the transcription and expression of surface marker CD11 b and NF-κB p-p65 (all P<0.01), and inhibit the mRNA and protein expression (P<0.01 or P<0.05) of inflflammatory cytokines, such as IL-6 and TNF-α, in microglia BV-2 cells cultured with high glucose for 24 h. CONCLUSIONS: The inhibition of microglial activation and IL-6 and TNF-α expression induced by high glucose may at least partly explain NFC therapeutic effects on diabetes-associated cognitive decline diseases. Its underlying mechanism could probably be related to the inhibition of NFC on NF-κB phosphorylation.