Yuxing Zhao

Effects of an enriched environment on myelin sheaths in the white matter of rats during normal aging: A stereological study

We found that an enriched environment (EE) could delay the loss of myelinated fibers in the white matter of rats during normal aging. However, the reasons for the protective effects of EE on the myelinated fibers were unclear. In this present study, via the use of stereological methods, we quantitatively investigated the myelin sheaths and the axons of myelinated fibers in the white matter of rats reared in an EE or a standard environment (SE) during the aging process. The results showed that an EE induced significant increases in the lengths of myelinated fibers, the axon volumes and the myelin sheath volumes of aging rats when compared with SE rats and that the enrichment effects, with the exception of the axon volumes, were sex- and age-independent. The mean diameter of the myelinated fibers, the mean perimeter of the myelin sheaths and the mean thicknesses of the myelin sheaths were not significantly changed. The EE-induced increase in myelinated fibers was mostly observed in those of smaller diameter (<1μm) with thinner myelin sheaths (<0.16μm), which had an optimal axon-fiber ratio (g=0.61). Our results suggest that EE-induced an increase in myelinated fibers in the white matter of aging rats primarily due to marked remyelination and some ongoing myelination.

Targeting thioredoxin-1 with siRNA exacerbates oxidative stress injury after cerebral ischemia/reperfusion in rats

Reactive oxygen species and their detrimental effects on the brain after transient ischemia/reperfusion (I/R) have been implicated in the pathogenesis of ischemic reperfusion injury. Thioredoxin-1 (Trx-1) is an endogenous antioxidant protein that has neuroprotective effects. We hypothesized that Trx-1 plays a crucial role in regulating cerebral I/R injury. To be able to test this, 190 Sprague-Dawley rats were subjected to transient middle cerebral artery occlusion (tMCAO) with Trx-1 siRNA (small interference RNA) injected 24 h prior to ischemia. At 24 h after tMCAO, we measured neurological deficits, infarct volume, and brain water content, and found that neurological dysfunction, brain infarct size, and brain edema were worse in the Trx-1 siRNA group than in the control group. Oxidative stress was evaluated by measuring superoxide dismutase activity and malondialdehyde level. The levels of Trx-1 and its cofactor, peroxiredoxin (Prdx), were significantly decreased after Trx-1 down-regulated. However, there is no significant difference in the Prdx mRNA level after administration of Trx-1 siRNA. In contrast, Prdx-SO3 protein levels were significantly increased in the Trx-1 siRNA group. We also investigated the specific role of nuclear factor erythroid 2-related factor 2 (Nrf2) in Trx-1 induction by knocking down Nrf2. Nrf2 siRNA injection decreased Trx-1 mRNA and protein expression. Our results suggest that the exacerbation of brain damage was associated with enhanced cerebral peroxidation in brain tissues. Moreover, these results revealed that Trx-1, which is more likely regulated by Nrf2, exerts a neuroprotective role probably through maintaining the reduction activity of Prdx1-4.

High-glucose induces tau hyperphosphorylation through activation of TLR9-P38MAPK pathway

ABSTRACT Diabetic encephalopathy (DE) is one of the most common complications of diabetes. The major pathological variations include neurofibrillary tangles (NFTs), which are caused by tau hyperphosphorylation, and senile plaques (SPs) consisting of amyloid &bgr;‐ protein(A&bgr;) deposits. In recent years, DE research studies have focused on exploring the activation of the inflammatory signaling pathway in immune cells. Toll‐like receptor 9 (TLR9) is well known to regulate the inflammatory reactions in immune processes. During the tau hyperphosphorylation process, TLR9 in microglia plays bidirectional roles. However, no studies have clearly demonstrated the relationship between TLR9 and tau hyperphosphorylation in neurons. Based on our experiments, we found significant increase in TLR9 expression in neurons and an increase in tau hyperphosphorylation in high‐glucose media. However, these alterations can be reversed by TLR9 inhibitor. Furthermore, we specifically inhibited the activation of P38mitogenactivated protein kinase(P38MAPK) and found an effective decrease in tau hyperphosphorylation. This effect is likely related to Unc93b1. Meanwhile, High glucose levels can induce neuronal apoptosis via the TLR9 signaling pathway. Our studies are the first to reveal that high glucose can regulate tau hyperphosphorylation and neuronal apoptosis via TLR9‐P38MAPK signaling pathway. These findings provide a new method for studying the mechanism underlying DE. HIGHLIGHTSHigh‐glucose regulates tau hyperphosphorylation through neuronal metabolic pathway mediated by TLR9.The mechanism relies on time‐dependent elevation of UNC93B1 stimulated high‐glucose.TLR9 signaling is involved in high‐glucose induced neuronal apoptosis.

Angiotensin-(1–7) administration attenuates Alzheimer’s disease-like neuropathology in rats with streptozotocin-induced diabetes via Mas receptor activation

Diabetes mellitus (DM) is associated with cognitive deficits and an increased risk of Alzheimers disease (AD). Recently, a newly identified heptapeptide of the renin-angiotensin system (RAS), angiotensin-(1-7) [Ang-(1-7)], was found to protect against brain damage. This study investigated the effects of Ang-(1-7) on diabetes-induced cognitive deficits. Sprague-Dawley rats were randomly divided into four groups. Diabetes was induced via single i.p. streptozotocin (STZ) injections. Ten weeks after diabetes induction, rats in each group received an intracerebral-ventricular (ICV) infusion of either vehicle, Ang-(1-7) alone, or Ang-(1-7)+A779 daily for two weeks. At the end of the study, Morris water maze (MWM) tests were performed to test cognitive functions before the rats were euthanized. Ang-(1-7) treatment significantly reduced escape latencies in diabetic rats in acquisition trials and markedly enhanced platform area crossing frequency and time spent in the target quadrant in probe trials (3.0±0.39 vs. 1.0±0.33, 39.39±1.11% vs. 25.62±3.07%, respectively, P<0.01). Ang-(1-7) treatment ameliorated damage to the ultrastructure of hippocampal synapses, reduced the expression of hippocampal phospho-tau at Ser396 (P<0.01), Ser404 (P<0.01) and Ser202/Thr205 (P<0.05), and decreased amyloid-β oligomer and both soluble and insoluble β-amyloid peptide 1-42 (Aβ 1-42) and Aβ 1-40 levels (P<0.01). These protective effects were significantly reversed by the co-administration of A779. These findings show that Ang-(1-7) is a promising therapeutic target for diabetes-induced cognitive impairment. The neuroprotective effects of Ang-(1-7) were mainly through Mas receptor (MasR) activation.

Ghrelin ameliorates nerve growth factor Dysmetabolism and inflammation in STZ-induced diabetic rats

Diabetic encephalopathy is characterized by cognitive impairment and neuroinflammation, deficient neurotrophic support, and neuronal and synaptic loss. Ghrelin, a 28 amino acid peptide, is associated with neuromodulation and cognitive improvement, which has been considered as a potential protective agent for several neurodegenerative diseases. Here we sought to investigate the role of ghrelin in preventing diabetic-related neuropathology. We found that ghrelin attenuated astrocytic activation and reduced levels of interleukin-6 and tumor necrosis factor-α in streptozotocin-induced diabetic rats. In addition, ghrelin inhibited p38 mitogen-associated protein kinase activation. The upregulation of nerve growth factor (NGF) precursor and matrix metalloproteinase (MMP)-9 and downregulation of mature NGF and MMP-7 in the diabetic brain were reversed by ghrelin. Treatment with ghrelin elevated synaptophysin expression and synaptic density in diabetic rats. Taken together, our results demonstrate that ghrelin ameliorates diabetes-related neurodegeneration by preventing NGF dysmetabolism and synaptic degeneration through regulating MMP levels as well as inhibiting neuroinflammation.

The effect of exercise, resveratrol or their combination on Sarcopenia in aged rats via regulation of AMPK/Sirt1 pathway.

ABSTRACT Sarcopenia is an age‐related syndrome characterized by progressive loss of muscle mass and function. Exercise is an important strategy to prolong life and increase muscle mass, and resveratrol has been shown a variety beneficial effects on skeletal muscle. In the present study, we investigated the potential efficacy of using short‐term exercise (six weeks), resveratrol (150 mg/kg/day), or combined exercise + resveratrol (150 mg/kg/day) on gastrocnemius muscle mass, grip strength, cross‐sectional area and microscopic morphology in aged rats, and explored the potential mechanism at the apoptosis level. Six months old SD rats were used as young control group and 24 months old SD rats were adopted as aged group. After six weeks intervention, the data provide evidence that exercise, resveratrol or their combination significantly increase the relative grip strength and muscle mass in aged rats (P < 0.05). Electron microscopy discovered a significant increase in sarcomere length, I‐band and H‐zone in aged rats (P < 0.05), and exercise, resveratrol or their combination significantly reduced the increasement (P < 0.05). Moreover, light microscopy revealed a significant increase on Ferets diameter and cross‐sectional area (CSA) in aged rats (P < 0.05), but exercise and resveratrol did not show significant effects on them (P > 0.05). Furthermore, exercise, resveratrol or their combination significantly increased the expression of p‐AMPK and SIRT1, decreased the expression of acetyl P53 and Bax/Bcl‐2 ratio in aged rats (P < 0.05). These findings show that aged rats show significant changes in gastrocnemius muscle morphology and ultrastructure, and the protective effects of exercise, resveratrol and their combination are probably associated with anti‐apoptotic signaling pathways through activation of AMPK/Sirt1. HighlightsExercise, resveratrol or combination increased muscle mass and function in aged rats.Exercise and resveratrol ameliorated ultrastructure of muscle fibrils in aged rats.Exercise and resveratrol prevented muscle apoptosis via AMPK/Sirt1 activation.

Metformin attenuates diabetes-induced tau hyperphosphorylation in vitro and in vivo by enhancing autophagic clearance

&NA; Diabetes mellitus (DM) can increase the risk of Alzheimers disease (AD) in patients. However, no effective approaches are available to prevent its progression and development. Recently, autophagy dysfunction was identified to be involved in the pathogenesis of neurodegenerative diseases. This study was designed to investigate the effect of metformin on hyperphosphorylated tau proteins in diabetic encephalopathy (DE) by regulating autophagy clearance. db/db mice were randomly divided into four groups, db/+ mice were used as control group. Twelve‐week old male db/db mice received consecutive intraperitoneal injection of 200 mg/kg/d metformin or (and) 10 mg/kg/d chloroquine for eight weeks. Morris water maze (MWM) tests were performed to test cognitive functions before the mice were euthanized. Metformin attenuated cognitive impairment in db/db mice, reduced hyperphosphorylated tau proteins, restored the impaired autophagy in diabetic mice, all of which were reversed by inhibiting of autophagy activity. In high glucose‐cultured HT22 cells, metformin increased autophagy in a dose‐dependent manner. Besides, metformin enhanced autophagy activity in an AMPK dependent manner. These data show that metformin may reduce tauopathy and improve cognitive impairment in db/db mice by modulating autophagy through the AMPK dependent pathway. These findings highlight metformin as a new therapeutic strategy for the treatment of DE.

Protective Effects of Sulforaphane on Cognitive Impairments and AD-like Lesions in Diabetic Mice are Associated with the Upregulation of Nrf2 Transcription Activity

Type 2 diabetes mellitus (T2DM)-associated oxidative stress contributes to cognitive deficiencies and Alzheimers disease (AD). Sulforaphane (SFN) is a pharmacological activator of Nrf2 that provokes Nrf2-mediated intracellular defenses, including antioxidant and anti-inflammatory responses, under oxidative stress (OS) conditions. This study investigated the effects of SFN on DM-related cognitive decline and its potential mechanisms. Morris water maze (MWM) tests showed that SFN (1 mg/kg i.p. for 28 days) mitigated the cognitive decline of db/db mice, a transgenic mouse model of T2DM. Accordingly, immunoblotting and immunohistochemistry analyses showed that SFN decreased the levels of amyloid-β (Aβ) oligomers and Aβ 1-42 plaques as well as phospho-tau at Ser396 and Thr231 in the DM mouse hippocampus. This protective effect of SFN might be due to the activation of Nrf2-regulated antioxidant defense deficiencies in the DM mice, as SFN increased the Nrf2 nuclear accumulation and the downstream expression of the antioxidases HO-1 and NQO1 and reduced the levels of the reactive oxygen/nitrogen species (ROS/RNS) in DM mouse brains. Our results confirm that SFN has potential as a therapeutic agent to protect T2DM patients from cognitive deficiencies and AD-like pathological lesions related to the upregulation of Nrf2-regulated antioxidant defenses.

High glucose-induced complement component 3 up-regulation via RAGE-p38MAPK-NF-κB signalling in astrocytes: In vivo and in vitro studies

Diabetes is considered as a risk for cognitive decline, which is characterized by neurodegenerative alteration and innate immunity activation. Recently, complement 3 (C3), the critical central component of complement system, has been reported to play a key role in neurodegenerative alterations under pathological condition. Receptor for advanced glycation end products (RAGE) activation is confirmed to mediate several inflammatory cytokines production. However, whether C3 activation participates in the diabetic neuropathology and whether this process is regulated by RAGE activation remains unknown. The present study aimed to investigate the role of C3 in streptozotocin‐induced diabetic mice and high glucose‐induced primary astrocytes and the underlying modulatory mechanisms. The decreased synaptophysin density and increased C3 deposition at synapses were observed in the diabetic brain compared to the control brain. Furthermore, the elevated C3 was co‐localized with GFAP‐positive astrocytes in the diabetic brain slice in vivo and high glucose‐induced astrocytes culture in vitro. Diabetes/high glucose‐induced up‐regulation of C3 expression at gene, protein and secretion levels, which were attenuated by pre‐treatment with RAGE, p38MAPK and NF‐κB inhibitors separately. These results demonstrate that high glucose induces C3 up‐regulation via RAGE‐ p38MAPK‐NF‐κB signalling in vivo and in vitro, which might be associated with synaptic protein loss.

High glucose-induced defective thrombospondin-1 release from astrocytes via TLR9 activation contributes to the synaptic protein loss

Abstract Diabetes, characterized by chronic hyperglycemia, is known to induce synaptic degeneration in the brain, thereby resulting in cognitive dysfunction. Thrombospondin‐1(TSP‐1), the secreted protein produced by astrocytes, plays a crucial role in promoting synapse formation. Toll‐like receptor 9 (TLR9) has been widely known to initiate the innate immune response. We recently reported TLR9 activation in neurons results in tau hyperphosphorylation induced by HG in vitro. Its activation has been also considered to mediate oxidative stress and astrocytic dysfunction under pathological circumstance. However, whether astrocytic TSP‐1 alteration plays a role in synaptic protein loss under high glucose condition and whether TLR9 activation is involved in this process have not been reported. In this study, we found that primary mouse astrocytes incubated in high glucose (30 mM) induced a significant decreased TSP‐1 secretion and increased intracellular contents of TSP‐1 without affecting transcription level. Addition of conditioned medium from high glucose (30 mM) treated astrocytes to the primary neurons exhibited reduced synaptic proteins expression, which was attenuated by treatment with exogenous rTSP‐1. In addition, we demonstrated that TLR9 activation along with reactive oxygen species (ROS) generation in astrocytes was induced by high glucose (30 mM). Furthermore, we explored the relationship between TLR9 activation and TSP‐1 production. Both TLR9 deficiency and the antioxidant N‐acetyl‐L‐cysteine treatment improved altered intra‐ and extracellular TSP‐1 levels under high glucose condition. Together, our findings suggest that high glucose (30 mM) impairs TSP‐1 secretion from astrocytes, which depends on astrocytic dysfunction associated with TLR9 activation mediated ROS signaling, ultimately contributing to the synaptic proteins loss. HighlightsHigh glucose (30 mM) impaired TSP‐1 secretion from astrocytes, resulting in neuronal synaptic proteins loss.High glucose (30 mM) induced TLR9 activation and ROS generation in astrocytes.Defective TSP‐1 secretion from astrocytes was mediated by TLR9‐ROS signaling. Abbreviations: CNS: Central nervous system; TSP‐1: Thrombospondin‐1; HG: High glucose; TLR9: Toll like receptor 9; DAMPs: damage associated molecular patterns; SD: Standard deviations; ELISA: Enzyme‐linked immune sorbent assay; ACM: Astrocyte conditioned medium; SYP: Synaptophysin; SYN‐1: Synapsin‐1; NAC: N‐acetyl‐L‐cysteine; ROS: Reactive oxygen species.