Autophagy Activation is Associated with Neuroprotection in Diabetes-associated Cognitive Decline

Huang-Lian-Jie-Du decoction drug-containing serum inhibits IL-1β secretion from D-glucose and PA induced BV2 cells via autophagy/NLRP3 signaling

ETHNOPHARMACOLOGICAL RELEVANCE

Huang-Lian-Jie-Du decoction (HLJDD), a famous traditional Chinese medicine prescription with heat-clearing and detoxifying effects, has been widely used to treat diabetes, dementia, stroke, and other diseases. However, the detailed mechanisms of HLJDD against type 2 diabetes associated cognitive dysfunction (DACD) through inhibiting interleukin-1β (IL-1β) mediated neuroinflammation remain to be further elucidated.

AIM OF THE STUDY

The aim of this study was to investigate the effect and potential mechanism of HLJDD on IL-1β secretion in a DACD model of BV2 cells induced by D-glucose and palmitic acid (PA).

MATERIALS AND METHOD

sUltra-performance liquid chromatography-quadrupole/electrostatic field orbital well high-resolution mass spectrometry technology was used to analyze the compounds in HLJDD drug-containing serum. The cytotoxicity was detected by cell counting kit-8. Enzyme-linked immunosorbent assay was used to measure the secretion of IL-1β in BV2 cells. Reactive oxygen species, glutathione, superoxide dismutase, and malondialdehyde kits were used to detect the intracellular oxidative stress levels. The autophagy level was determined by autophagy staining kit and transmission electron microscope. The expression levels of autophagy-related 7 (Atg7), P62, LC3, nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3(NLRP3), Caspase1, and IL-1β were detected by real-time PCR, immunofluorescence, and western blotting. The Atg7siRNA was transfected into BV2 cells to produce autophagy inhibitory effect. Then the effect of HLJDD drug-containing serum on IL-1β secretion in D-glucose and PA induced BV2 cells and the potential mechanism of autophagy-NLRP3 inflammasome activation were further observed.

RESULTS

Eighty-eight compounds were preliminarily identified in HLJDD drug-containing serum, among which geniposide, baicalin, palmatine, berberine, wogonoside, wogonin, and geniposidic acid were identified as the main prototype components of HLJDD into the blood. In this study, the DACD model of BV2 cells induced by high concentrations of glucose and PA was successfully constructed. HLJDD drug-containing serum significantly reduced the secretion of IL-1β and the activity of NLRP3 inflammasome with improving the oxidative stress level. Interestingly, the enhanced autophagy level was also found. After transfection of Atg7siRNA into BV2 cells, the effect of HLJDD drug-containing serum on autophagy promotion was reversed, but the inhibitory effects on IL-1β secretion, NLRP3 inflammasome activation, and oxidative stress were reduced.

CONCLUSIONS

These results indicated that the inhibition of HLJDD drug-containing serum on the IL-1β secretion in D-glucose and PA induced BV2 cells was related to autophagy promotion, the decreased NLRP3 inflammasome activation, and the improved oxidative stress. Moreover, the improvement of HLJDD drug-containing serum on IL-1β secretion, NLRP3 inflammasome activation, and oxidative stress were all closely associated with Atg7 mediated autophagy promotion. Geniposide, baicalin, palmatine, berberine, wogonoside, wogonin, and geniposidic acid may be the potential active ingredients of HLJDD drug-containing serum.

Fibroblast growth factor 21 alleviates diabetes-induced cognitive decline

Diabetes mellitus (DM) causes damage to the central nervous system, resulting in cognitive impairment. Fibroblast growth factor 21 (FGF21) exhibits the potential to alleviate neurodegeneration. However, the therapeutic effect of intracerebroventricular (i.c.v) FGF21 infusion on diabetes-induced cognitive decline (DICD) and its potential mechanisms remain unclear. In this study, the impact of FGF21 on DICD was explored, and 1H nuclear magnetic resonance (NMR)-based metabolomics plus 13C NMR spectroscopy in combine with intravenous [1-13C]-glucose infusion were used to investigate the underlying metabolic mechanism. Results revealed that i.c.v FGF21 infusion effectively improved learning and memory performance of DICD mice; neuron loss and apoptosis in hippocampus and cortex were significantly blocked, suggesting a potential neuroprotective role of FGF21 in DICD. Metabolomics results revealed that FGF21 modulated DICD metabolic alterations related to glucose and neurotransmitter metabolism, which are characterized by distinct recovered enrichment of [3-13C]-lactate, [3-13C]-aspartate, [4-13C]-glutamine, [3-13C]-glutamine, [4-13C]-glutamate, and [4-13C]- γ-aminobutyric acid (GABA) from [1-13C]-glucose. Moreover, diabetes-induced neuron injury and metabolic dysfunctions might be mediated by PI3K/AKT/GSK-3β signaling pathway inactivation in the hippocampus and cortex, which were activated by i.c.v injection of FGF21. These findings indicate that i.c.v FGF21 infusion exerts its neuroprotective effect on DICD by remodeling cerebral glucose and neurotransmitter metabolism by activating the PI3K/AKT/GSK-3β signaling pathway.

Neuroprotective Effect of Zishen Huoxue Decoction treatment on Vascular Dementia by activating PINK1/Parkin mediated Mitophagy in the Hippocampal CA1 Region

ETHNOPHARMACOLOGICAL RELEVANCE

Zishen Huoxue Decoction (ZSHXD) is a Traditional Chinese Medicine (TCM) prescription for the treatment of vascular dementia (VD). Although the clinical effects of ZSHXD have been demonstrated, the molecular mechanisms underlying the neuroprotective effects of ZSHXD remain unclear.

AIM OF THE STUDY

To explore whether the neuroprotective effect of Zishen Huoxue Decoction (ZSHXD) treatment is associated with the PINK1/Parkin pathway-mediated mitophagy in hippocampal CA1 region of 2-VO model rats.

MATERIALS AND METHODS

Seventy-two male SD rats were randomly divided into the sham group, model group, Donepezil (0.45 mg/kg) group, ZSHXD low dose group (8.9 g/kg), ZSHXD medium dose group (17.8 g/kg), and ZSHXD high dose group (35.6 g/kg). Two-vessel occlusion (2-VO) rat model is established to evaluate the therapeutic effect of ZSHXD pretreatment. Hematoxylin-eosin (HE) staining is conducted to detect the morphological changes of neurons and the number of normal neurons in the hippocampal CA1 region. Then, the mitochondrial function and structure were reflected by the mitochondrial membrane potential (MMP) levels and transmission electron microscopy (TEM). Meanwhile, the expression of mitophagy related proteins mediated by PINK1/Parkin was detected by western blot (WB). After that, malondialdehyde (MDA) and superoxide dismutase (SOD) levels were measured by Elisa. At last, the apoptosis-related proteins Caspase-3、Bax、Bcl-2 were measured by WB.

RESULTS

The results depict that ZSHXD has dose-dependently improved the cognitive function in 2-VO model rats. It has also been showed that ZSHXD can alleviate neuron damage, rescue the mitochondrial structural injury and dysfunction in hippocampal CA1 region. Besides, ZSHXD has increased the activity of SOD and decreased the activity of MDA. In addition, ZSHXD can inhibit apoptosis with Caspase-3, Bax decreasing and Bcl-2 increasing. Specially, the protection of ZSHXD showed in 2-VO model rats is along with the upregulation of PINK1, Parkin and LC3-Ⅱ/Ⅰ, and downregulation of p62 in the hippocampal CA1 region.

CONCLUSIONS

This study reveals that ZSHXD protects the 2-VO model rats from ischemic injury by activating the PINK1/Parkin-mediated mitophagy in the hippocampal CA1 region.

The role of autophagy in the treatment of type II diabetes and its complications: a review

Type II diabetes mellitus (T2DM) is a chronic metabolic disease characterized by prolonged hyperglycemia and insulin resistance (IR). Its incidence is increasing annually, posing a significant threat to human life and health. Consequently, there is an urgent requirement to discover effective drugs and investigate the pathogenesis of T2DM. Autophagy plays a crucial role in maintaining normal islet structure. However, in a state of high glucose, autophagy is inhibited, resulting in impaired islet function, insulin resistance, and complications. Studies have shown that modulating autophagy through activation or inhibition can have a positive impact on the treatment of T2DM and its complications. However, it is important to note that the specific regulatory mechanisms vary depending on the target organ. This review explores the role of autophagy in the pathogenesis of T2DM, taking into account both genetic and external factors. It also provides a summary of reported chemical drugs and traditional Chinese medicine that target the autophagic pathway for the treatment of T2DM and its complications.

mTOR-dependent TFEB activation and TFEB overexpression enhance autophagy-lysosome pathway and ameliorate Alzheimer's disease-like pathology in diabetic encephalopathy

BACKGROUND

Diabetic encephalopathy (DE) is a complication of type 2 diabetes mellitus (T2DM) that features Alzheimer's disease (AD)-like pathology, which can be degraded by the autophagy-lysosome pathway (ALP). Since transcription factor EB (TFEB) is a master regulator of ALP, TFEB-mediated ALP activation might have a therapeutic effect on DE, but this has yet to be investigated.

METHODS

We established T2DM mouse models and cultured HT22 cells under high-glucose (HG) conditions to confirm the role of ALP in DE. To further investigate this, both mice and HT22 cells were treated with 3-methyladenine (3-MA). We also analyzed the content of TFEB in the nucleus and cytoplasm to evaluate its role in ALP. To confirm the effect of TFEB activation at the post-translational level in DE, we used rapamycin to inhibit the mechanistic target of rapamycin (mTOR). We transduced both mice and cells with TFEB vector to evaluate the therapeutic effect of TFEB overexpression on DE. Conversely, we conducted TFEB knockdown to verify its role in DE in another direction.

RESULTS

We found that T2DM mice experienced compromised cognitive function, while HG-cultured HT22 cells exhibited increased cell apoptosis. Additionally, both T2DM mice and HG-cultured HT22 cells showed impaired ALP and heavier AD-like pathology. This pathology worsened after treatment with 3-MA. We also observed decreased TFEB nuclear translocation in both T2DM mice and HG-cultured HT22 cells. However, inhibiting mTOR with rapamycin or overexpressing TFEB increased TFEB nuclear translocation, enhancing the clearance of ALP-targeted AD-like pathology. This contributed to protection against neuronal apoptosis and alleviation of cognitive impairment. Conversely, TFEB knockdown lessened ALP-targeted AD-like pathology clearance and had a negative impact on DE.

CONCLUSION

Our findings suggest that impaired ALP is responsible for the aggravation of AD-like pathology in T2DM. We propose that mTOR-dependent TFEB activation and TFEB overexpression are promising therapeutic strategies for DE, as they enhance the clearance of ALP-targeted AD-like pathology and alleviate neuronal apoptosis. Our study provides insight into the underlying mechanisms of DE and offers potential avenues for the development of new treatments for this debilitating complication of T2DM. Video abstract.

Salidroside Alleviates Diabetic Cognitive Dysfunction Via B3galt2/F3/Contactin Signaling Pathway in Mice

Diabetes is frequently accompanied by cognitive impairment with insidious onset, and progressive cognitive and behavioral changes. β-1, 3-galactosyltransferase 2 (B3galt2) contributes to glycosylation, showing a clue for neuronal apoptosis, proliferation and differentiation. However, the role of B3galt2 in diabetic cognitive dysfunction (DCD) has not been investigated. In the present study, we aimed to explore the role of B3galt2 in DCD. Additionally, the potential therapeutic effects of salidroside on DCD was also explored. Diabetic C57BL/6J mice showed cognitive dysfunction together with down-regulated B3galt2. Overexpression of B3galt2 reversed the cognitive decline of diabetic C57BL/6J. Moreover, cognitive impairment was aggravated in B3galt2^+/- diabetic mice compared with C57BL/6J diabetic mice. Immunohistochemistry fluorescence indicated that B3galt2 and F3/Contactin were co-localized in the hippocampal regions. Importantly, the expression of F3/Contactin can be regulated by the manipulation of B3galt2, overexpression of which assuaged hippocampal neuronal damage, protected the synapsin, and reduced neuronal apoptosis in diabetic mice. Interestingly, SAL alleviated DCD and reversed the expression of B3galt2 in diabetic C57BL/6J mice. These findings indicate that inhibition of B3galt2/F3/Contactin pathway contributes to DCD, and participates in SAL reversed DCD.

Dietary Tyrosine Intake (FFQ) Is Associated with Locus Coeruleus, Attention and Grey Matter Maintenance: An MRI Structural Study on 398 Healthy Individuals of the Berlin Aging Study-II

BACKGROUND AND OBJECTIVE

It is documented that low protein and amino-acid dietary intake is related to poorer cognitive health and increased risk of dementia. Degradation of the neuromodulatory pathways, (comprising the cholinergic, dopaminergic, serotoninergic and noradrenergic systems) is observed in neurodegenerative diseases and impairs the proper biosynthesis of key neuromodulators from micro-nutrients and amino acids. How these micro-nutrients are linked to neuromodulatory pathways in healthy adults is less studied. The Locus Coeruleus-Noradrenergic System (LC-NA) is the earliest subcortical structure affected in Alzheimer's disease, showing marked neurodegeneration, but is also sensitive for age-related changes. The LC-NA system is critical for supporting attention and cognitive control, functions that are enhanced both by tyrosine administration and chronic tyrosine intake. The purpose of this study was to 1) investigate whether the dietary intake of tyrosine, the key precursor for noradrenaline (NA), is related to LC signal intensity 2) whether LC mediates the reported association between tyrosine intake and higher cognitive performance (measured with Trail Making Test - TMT), and 3) whether LC signal intensity relates to an objective measure of brain maintenance (BrainPAD).

METHODS

The analyses included 398 3T MRIs of healthy participants from the Berlin Aging Study II to investigate the relationship between LC signal intensity and habitual dietary tyrosine intake-daily average (HD-Tyr-IDA - measured with Food Frequency Questionnaire - FFQ). As a control procedure, the same analyses were repeated on other main seeds of the neuromodulators' subcortical system (Dorsal and Medial Raphe, Ventral Tegmental Area and Nucleus Basalis of Meynert). In the same way, the relationships between the five nuclei and BrainPAD were tested.

RESULTS

Results show that HD-Tyr-IDA is positively associated with LC signal intensity. Similarly, LC disproportionally relates to better brain maintenance (BrainPAD). Mediation analyses reveal that only LC, relative to the other nuclei tested, mediates the relationship between HD-Tyr-IDA I and performance in the TMT and between HD-Tyr-IDA and BrainPAD.

CONCLUSIONS

These findings provide the first evidence linking tyrosine intake with LC-NA system signal intensity and its correlation with neuropsychological performance. This study strengthens the role of diet for maintaining brain and cognitive health and supports the noradrenergic theory of cognitive reserve. Within this framework, adequate tyrosine intake might increase the resilience of LC-NA system functioning, by preventing degeneration and supporting noradrenergic metabolism required for LC function and neuropsychological performance.

The protective effects of Esculentoside A through AMPK in the triple transgenic mouse model of Alzheimer's disease

BACKGROUND

Neurofibrillary tangles comprising hyperphosphorylated tau are vital factors associated with the pathogenesis of Alzheimer's disease (AD). The elimination or reduction of hyperphosphorylated and abnormally aggregated tau is a valuable measure in AD therapy. Esculentoside A (EsA), isolated from Phytolacca esculenta, exhibits pharmacotherapeutic efficacy in mice with amyloid beta-induced AD. However, whether EsA affects tau pathology and its specific mechanism of action in AD mice remains unclear.

PURPOSE

To investigate the roles and mechanisms of EsA in cognitive decline and tau pathology in a triple transgenic AD (3 × Tg-AD) mouse model.

METHODS

EsA (5 and 10 mg/kg) was administered via intraperitoneal injection to 8-month-old AD mice for eight consecutive weeks. Y-maze and novel object recognition tasks were used to evaluate the cognitive abilities of mice. Potential signaling pathways and targets in EsA-treated AD mice were assessed using quantitative proteomic analysis. The NFT levels and hippocampal synapse numbers were investigated using Gallyas-Braak silver staining and transmission electron microscopy, respectively. Western blotting and immunofluorescence assays were used to measure the expression of tau-associated proteins.

RESULTS

EsA administration attenuated memory and recognition deficits and synaptic damage in AD mice. Isobaric tags for relative and absolute quantitation proteomic analysis of the mouse hippocampus revealed that EsA modulated the expression of some critical proteins, including brain-specific angiogenesis inhibitor 3, galectin-1, and Ras-related protein 24, whose biological roles are relevant to synaptic function and autophagy. Further research revealed that EsA upregulated AKT/GSK3β activity, in turn, inhibited tau hyperphosphorylation and promoted autophagy to clear abnormally phosphorylated tau. In hippocampus-derived primary neurons, inhibiting AMP-activated protein kinase (AMPK) activity through dorsomorphin could eliminate the effect of EsA, as revealed by increased tau hyperphosphorylation, downregulated activity AKT/GSK3β, and blocked autophagy.

CONCLUSIONS

To our knowledge, this study is the first to demonstrate that EsA attenuates cognitive decline by targeting the pathways of both tau hyperphosphorylation and autophagic clearance in an AMPK-dependent manner and it shows a high reference value in AD pharmacotherapy research.

Fluoride-Induced Cortical Toxicity in Rats: the Role of Excessive Endoplasmic Reticulum Stress and Its Mediated Defective Autophagy

The cerebral cortex is closely associated with learning and memory, and fluoride is capable of inducing cortical toxicity, but its mechanism is unclear. This study aimed to investigate the role of endoplasmic reticulum stress and autophagy in fluoride-induced cortical toxicity. Rats exposed to sodium fluoride (NaF) were used as an in vivo model. The results showed that NaF exposure impaired the learning and memory capacities and increased urinary fluoride levels in rats. In addition, NaF exposure induced excessive endoplasmic reticulum stress and associated apoptosis, as evidenced by elevated IRE1α, GRP78, cleaved caspase-12, and cleaved caspase-3, as well as defective autophagy, as evidenced by increased expression of Beclin1, LC3-II, and p62 in cortical areas. Importantly, the endoplasmic reticulum stress inhibitor 4-phenylbutyric acid (4-PBA) alleviated endoplasmic reticulum stress as well as defective autophagy, thus confirming the critical role of endoplasmic reticulum stress and autophagy in fluoride-induced cortical toxicity. Taken together, these results suggest that excessive endoplasmic reticulum stress and its mediated defective autophagy lead to fluoride-induced cortical toxicity. This provides new insights into the mechanisms of fluoride-induced neurotoxicity and a new theoretical basis for the prevention and treatment of fluoride-induced neurotoxicity.

Mechanism underlying linezolid-induced peripheral neuropathy in multidrug-resistant tuberculosis

Multidrug-resistant tuberculosis (MDR-TB) remains a main global health concern as there is no comprehensive therapeutic intervention yet and numerous adverse effects follow the therapeutic process. In recent years, linezolid has been frequently used for treating MDR-TB. However, peripheral neuropathy associated with linezolid has reduced patient compliance. The current study explored the mechanism underlying linezolid-induced peripheral neuropathy in MDR-TB. Autophagy plays a neuroprotective role against peripheral nerve injury. We hypothesized that autophagy might also play a neuroprotective role against linezolid-induced peripheral neuropathy. In this study, we collected 12 questionnaires from MDR-TB patients in our hospital, and 10 of them developed linezolid-induced pain. The pain is mainly concentrated in the feet and accompanied by numbness. Subsequently, we used Sprague-Dawley (SD) rats and Schwann cells (SCs) to explore the mechanism. We found that linezolid causes a sparse arrangement of sciatic nerve tissue with associated loss of neurons, myelin sheaths, and down-regulation of LC3B expression. These results were also confirmed by in vitro experiments, showing that linezolid inhibited the proliferation of SCs. And the expression of P-AKT and P62 was elevated, and the expression of LC3B declined compared with the control group. Moreover, chloroquine (CQ), an autophagy inhibitor, also exhibited experimental results similar to linezolid. In summary, we conclude that linezolid-induced peripheral neuropathy is associated with the inhibition of autophagy flux.

Huang-Lian-Jie-Du decoction attenuates cognitive dysfunction of rats with type 2 diabetes by regulating autophagy and NLRP3 inflammasome activation

ETHNOPHARMACOLOGICAL RELEVANCE

Huang-Lian-Jie-Du decoction (HLJDD) is a traditional Chinese formula that is efficacious in treating diabetes mellitus, Alzheimer's disease, and diabetic encephalopathy; the underlying mechanisms of HLJDD in diabetes-associated cognitive dysfunction remain unclear.

AIM OF THE STUDY

This study investigated the neuroprotective effects of HLJDD on cognitive function, and the possible underlying mechanisms in type 2 diabetes mellitus (T2DM) in a rat model of cognitive impairment.

MATERIALS AND METHODS

Twelve active ingredients in HLJDD were detected using high-performance liquid chromatography analysis. An animal model of cognitive dysfunction in T2DM was induced via a high-sugar and high-fat diet combined with a low dose of streptozotocin. Sprague-Dawley rats were randomly divided into six groups: control, T2DM, metformin (0.34 g/kg/day), and HLJDD groups (3, 1.5, and 0.75 g/kg/day). All treatments were intragastrically administrated for nine continuous weeks after the development of T2DM. Body weight, food and water intake, fasting blood glucose, insulin sensitivity, and blood lipid levels were measured. Spatial learning and memory of the rats were assessed using the Morris water maze test. Hematoxylin and eosin and Nissl staining were performed to evaluate neuronal morphology and vitality. Glutathione, malondialdehyde, and superoxide dismutase levels were measured to determine the level of oxidative stress in the hippocampus. Transmission electron microscopy was performed to observe the synaptic morphology and structure of hippocampal neurons. IL-1β levels in the hippocampus and cerebrospinal fluid were determined. The protein expression of NLRP3, cleaved caspase-1, mature IL-1β, ATG7, P62, LC3, and brain-derived neurotrophic factor (BDNF) was determined using western blotting and immunofluorescence analysis.

RESULTS

HLJDD attenuated cognitive dysfunction in rats with T2DM as shown by the decreased escape latency, increased times crossing the platform and time spent in the target quadrant in the Morris water maze test (P < 0.05), improvement in hippocampal histopathological changes, and an elevated level of cell vitality. HLJDD treatment also reduced blood glucose and lipid levels, ameliorated oxidative stress, and downregulated IL-1β expression in the hippocampus and cerebrospinal fluid (P < 0.05). Moreover, HLJDD enhanced BDNF, ATG7, and LC3 protein expression and significantly inhibited the expression of P62, NLRP3, cleaved caspase-1, and mature IL-1β in the hippocampal CA1 region (P < 0.05). Immunofluorescence results further confirmed that the fluorescence intensity of NLRP3 and P62 in the hippocampus decreased after HLJDD intervention (P < 0.05).

CONCLUSIONS

HLJDD ameliorated cognitive dysfunction in T2DM rats. The neuroprotective effect is exerted via the modulation of glucose and lipid metabolism, upregulation of autophagy, and inhibition of NLRP3 inflammasome signaling pathway.

Abnormal Vacuole Membrane Protein-1 Expression in Parkinson’s Disease Patients

Background

Parkinson’s disease (PD) is pathologically characterized by progressive dopaminergic (DAergic) neuron loss in the substantia nigra pars compacta (SNpc) and accumulation of intracytoplasmic α-synuclein-containing Lewy bodies. Autophagy has been identified as a critical component in the development and progression of PD. Several autophagy genes have been identified as being altered in PD. One of those genes, vacuole membrane protein-1 (VMP1), an autophagy protein localized in the endoplasmic reticulum (ER) in DAergic neurons, has been shown to cause motor disorder, severe loss of DAergic neurons, and autophagy flux disturbance in the VMP1 knockout mouse model.

Objective

To evaluate for the first time the alteration on the expression of the VMP1 gene and its clinical correlations in peripheral blood mononuclear cells (PBMCs) of a relatively large sample of PD patients.

Methods

We assessed the VMP1 mRNA levels in PD patients (n = 229) and healthy controls (HC) (n = 209) using real-time quantitative PCR (RT-qPCR), and the VMP1 protein levels in PD patients (n = 27) and HC (n = 27) using Western blot (WB). Then, we analyzed the VMP1 expression levels and clinical features of PD patients.

Results

Our findings revealed that VMP1 levels in the PD group were significantly lower than in the HC group (RT-qPCR p < 0.01 and WB p < 0.001). The VMP1 expression was significantly lower as the disease progressed, which could be ameliorated by administering DAergic receptor agonists. Moreover, receiver operating characteristic (ROC) curve analysis showed that VMP1 mRNA and protein level area under the curves (AUCs) were 64.5%, p < 0.01, and 83.4%, p < 0.01, respectively.

Conclusion

This case-control study demonstrates that peripheral VMP1 level altered in PD patients and may serve as a potential endogenous diagnostic marker of PD.

Autophagy and Diabetic Encephalopathy: Mechanistic Insights and Potential Therapeutic Implications

Diabetic Encephalopathy (DE) is one of the complications of diabetes mellitus (DM) in the central nervous system. Up to now, the mechanisms of DE are not fully discussed by the field. Autophagy is an intracellular degradation pathway crucial to maintain cellular homeostasis by clearing damaged organelles, pathogens, and unwanted protein aggregates. Increasing evidence has demonstrated that autophagy might play an essential role in DE progress. In this review, we summarize the current evidence on autophagy dysfunction under the condition of DE, and provide novel insights of possibly biological mechanisms linking autophagy impairment to DE, as well as discuss autophagy-targeted therapies as potential treatments for DE.

Protective Effects of Chaya against Mitochondrial and Synaptic Toxicities in the Type 2 Diabetes Mouse Model TallyHO

The purpose of our study is to determine the protective effects of the chaya leaf against mitochondrial abnormalities and synaptic damage in the Type 2 diabetes (T2D) mouse model, TallyHO (TH). The TH mouse is a naturally occurring polygenic mouse model of diabetes that mimics many characteristics of human Type 2 diabetes. Only male TH mice develop hyperglycemia and moderate obesity. Female mice display moderate obesity but do not manifest overt diabetes. In this study, we evaluated three groups of mice over a period of 11 weeks: (1) the experimental group of TH diabetic mice fed with chaya chow; (2) a diabetic control group of TH diabetic mice fed with regular chow; and (3) a non-diabetic control group of SWR/J mice fed with regular chow. Body mass and fasting blood glucose were assessed weekly. Brain and other peripheral tissues were collected. Using qRT-PCR and immunoblotting analyses, we measured the mRNA abundance and protein levels of mitochondrial biogenesis, mitochondrial dynamics, autophagy/mitophagy, and synaptic genes. Using immunofluorescence analysis, we measured the regional immunoreactivities of mitochondrial and synaptic proteins. Using biochemical methods, we assessed mitochondrial function. We found increased body mass and fasting glucose levels in the TH diabetic mice relative to the non-diabetic control SWRJ mice. In chaya chow-fed TH diabetic mice, we found significantly reduced body mass and fasting glucose levels. Mitochondrial fission genes were increased and fusion, biogenesis, autophagy/mitophagy, and synaptic genes were reduced in the TH mice; however, in the chaya chow-fed TH diabetic mice, mitochondrial fission genes were reduced and fusion, biogenesis, autophagy/mitophagy, and synaptic genes were increased. Mitochondrial function was defective in the diabetic TH mice; however, it was rescued in the chaya chow-fed TH mice. These observations strongly suggest that chaya chow reduces the diabetic properties, mitochondrial abnormalities, and synaptic pathology in diabetic, TH male mice. Our data strongly indicates that chaya can be used as natural supplemental diet for prediabetic and diabetic subjects and individuals with metabolic disorders.

High intensity interval training ameliorates cognitive impairment in T2DM mice possibly by improving PI3K/Akt/mTOR Signaling-regulated autophagy in the hippocampus

Exercise can improve cognitive impairment in type 2 diabetes mellitus (T2DM). However, the underlying mechanisms are not clear, and the optimal exercise modes for cognitive benefits are controversial. The aim of this study was to investigate the effects of high-intensity interval training (HIIT) and moderate-intensity interval training (MICT) on cognitive function and the PI3K/Akt/mTOR pathway as well as autophagy in T2DM mice. The results showed that 8 weeks of HIIT and MICT intervention could improve the spatial learning and memory ability of T2DM mice, as determined by the Morris water maze (MWM) test. Both HIIT and MICT similarly improved autophagy, as evidenced by increased Beclin1 and LC3 II/I ratios and decreased p62. Meanwhile, HIIT and MICT inhibited excessive activation of the PI3K/Akt/mTOR pathway in the hippocampus. HIIT induced a larger reduction in mTOR activity than MICT. This study suggests that both HIIT and MICT can alleviate cognitive decline induced by T2DM, improve autophagy in the hippocampus, and downregulate the excessive activation of the PI3K/Akt/mTOR signaling pathway, with similar effects.

The effect of cordycepin on brain oxidative stress and protein expression in streptozotocin-induced diabetic mice

Diabetes mellitus (DM) is characterized by metabolic disorders and psychological deficits, including cognitive decline. Here, we investigated the effect of cordycepin on oxidative stress and protein expression in the brains of diabetic mice. Twenty-four mice were divided into four groups, one comprising untreated healthy mice (N); one comprising healthy mice treated with cordycepin (24 mg/kg body weight) (N+Cor); one comprising untreated DM mice; and one comprising DM mice treated with cordycepin (24 mg/kg body weight) (DM+Cor). After 14 days of treatment, cognitive behavior was assessed using the novel object recognition (NOR) test. The brain levels of oxidative stress markers (glutathione, catalase, and superoxide dismutase) were examined using the respective detection kits. Protein expression in brain tissues was assessed by liquid chromatography with tandem mass spectrometry (LC-MS/MS); the functions of the identified proteins were annotated by PANTHER, while major protein-protein interactions were assessed using STITCH. We found that cordycepin treatment significantly decreased body weight and food and water intake in the DM+Cor group compared with that in the DM group; however, no differences in blood glucose levels were found between the two groups. Cordycepin treatment significantly reversed cognitive decline in diabetic mice in the NOR test and ameliorated antioxidant defenses. Additionally, we identified ULK1 isoform 2, a protein associated with cognitive function via the activated AMPK and autophagic pathways, as being uniquely expressed in the DM+Cor group. Our findings provide novel insights into the cellular mechanisms underlying how cordycepin improves cognitive decline in diabetic mice.

Nonenzymatic function of DPP4 in diabetes-associated mitochondrial dysfunction and cognitive impairment

Dipeptidyl peptidase-4 (DPP4) has been proven to exert its functions by both enzymatic and nonenzymatic pathways. The nonenzymatic function of DPP4 in diabetes-associated cognitive impairment remains unexplored. We determined DPP4 protein concentrations or its enzymatic activity in type 2 diabetic patients and db/db mice and tested the impact of the non-enzymatic function of DPP4 on mitochondrial dysfunction and cognitive impairment both in vivo and in vitro. The results show that increased DPP4 activity was an independent risk factor for incident mild cognitive impairment (MCI) in type 2 diabetic patients. In addition, DPP4 was highly expressed in the hippocampus of db/db mice and contributed to mitochondria dysfunction and cognitive impairment. Mechanistically, DPP4 might bind to PAR2 in the hippocampus and trigger GSK-3β activation, which downregulates peroxisome proliferator-activated receptor gamma coactivator 1 alpha expression and leads to mitochondria dysfunction, thereby promoting cognitive impairment in diabetes. Our findings indicate that the nonenzymatic function of DPP4 might promote mitochondrial dysfunction and cognitive impairment in diabetes.

Normobaric Oxygen (NBO) Therapy Reduces Cerebral Ischemia/Reperfusion Injury through Inhibition of Early Autophagy

Objectives

Normobaric oxygen (NBO) therapy has great clinical potential in the treatment of ischemic stroke, but its underlying mechanism is unknown. Our study aimed to investigate the role of autophagy during the application of NBO on cerebral ischemia/reperfusion injury.

Methods

Male Sprague Dawley rats received 2 hours of middle cerebral artery occlusion (MCAO), followed by 2, 6, or 24 hours of reperfusion. At the beginning of reperfusion, rats were randomly given NBO (95% O₂) or room air (21% O₂) for 2 hours. In some animals, 3-methyladenine (3-MA, autophagy inhibitor) was administered 10 minutes before reperfusion. The severity of the ischemic injury was determined by infarct volume, neurological deficit, and apoptotic cell death. Western blotting was used to determine the protein expression of autophagy and apoptosis, while mRNA expression of apoptotic molecules was detected by real-time PCR.

Results

NBO treatment after ischemia/reperfusion significantly decreased infarct volume and neurobehavioral defects. The increased expression of the autophagy markers, including microtubule-associated protein 1A light chain 3 (LC3) and Beclin 1, after ischemia/reperfusion was reversed by NBO, while promoting Sequestosome 1 (p62/SQSTM1) expression. In addition, NBO reduced cerebral apoptosis in association with alleviated BAX expression and increased BCL-2 expression. 3-MA reduced autophagy and apoptotic death but did not further improve NBO-attenuated ischemic damage.

Conclusion

NBO induced remarkable neuroprotection from ischemic injury, which was correlated with blocked autophagy activity.

The mTOR/NF-κB Pathway Mediates Neuroinflammation and Synaptic Plasticity in Diabetic Encephalopathy

Diabetic encephalopathy, a severe complication of diabetes mellitus, is characterized by neuroinflammation and aberrant synaptogenesis in the hippocampus leading to cognitive decline. Mammalian target of rapamycin (mTOR) is associated with cognition impairment. Nuclear factor-κB (NF-κB) is a transcription factor of proinflammatory cytokines. Although mTOR has been ever implicated in processes occurring in neuroinflammation, the role of this enzyme on NF-κB signaling pathway remains unclear in diabetic encephalopathy. In the present study, we investigated whether mTOR regulates the NF-κB signaling pathway to modulate inflammatory cytokines and synaptic plasticity in hippocampal neurons. In vitro model was constructed in mouse HT-22 hippocampal neuronal cells exposed to high glucose. With the inhibition of mTOR or NF-κB by either chemical inhibitor or short-hairpin RNA (shRNA)-expressing lentivirus-vector, we examined the effects of mTOR/NF-κB signaling on proinflammatory cytokines and synaptic proteins. The diabetic mouse model induced by a high-fat diet combined with streptozotocin injection was administrated with rapamycin (mTOR inhibitor) and PDTC (NF-κB inhibitor), respectively. High glucose significantly increased mTOR phosphorylation in HT-22 cells. While inhibiting mTOR by rapamycin or shmTOR significantly suppressed high glucose-induced activation of NF-κB and its regulators IKKβ and IκBα, suggesting mTOR is the upstream regulator of NF-κB. Furthermore, inhibiting NF-κB by PDTC and shNF-κB decreased proinflammatory cytokines expression (IL-6, IL-1β, and TNF-α) and increased brain-derived neurotrophic factor (BDNF) and synaptic proteins (synaptophysin and PSD-95) in HT-22 cells under high glucose conditions. Besides, the mTOR and NF-κB inhibitors improved cognitive decline in diabetic mice. The inhibition of mTOR and NF-κB suppressed mTOR/NF-κB signaling pathway, increased synaptic proteins, and improved ultrastructural synaptic plasticity in the hippocampus of diabetic mice. Activating mTOR/NF-κB signaling pathway regulates the pathogenesis of diabetic encephalopathy, such as neuroinflammation, synaptic proteins loss, and synaptic ultrastructure impairment. The findings provide the implication that mTOR/NF-κB is potential new drug targets to treat diabetic encephalopathy.

Neuroprotective Effects of ZiBuPiYin Recipe on db/db Mice via PI3K-Akt Signaling Pathway by Activating Grb2

Background

Diabetes-associated cognitive decline (DACD) is one of the nervous system dysfunctions induced by diabetes mellitus with cognitive impairment as the major symptom. In a previous preliminary proteomic study, we found that endoplasmic reticulum processing and PI3K-Akt signaling pathway might be impaired in DACD pathogenesis. In addition, growth factor receptor-bound protein 2 might be a crucial protein as a molecular target of the neuroprotective effects of ZiBuPiYin recipe (ZBPYR).

Methods

In this study, 6-8 weeks aged db/db mice were treated with excipients or ZBPYR for 6 weeks. Body weight and RBG were recorded weekly. Oral glucose tolerance and insulin tolerance tests were used to assess insulin sensitivity. Morris water maze (MWM) tests were used to assess memory function. The expression of Grb2, Gab2, Akt, and GSK3β in mouse hippocampus and cerebral cortex were analyzed by Western blotting.

Results

ZBPYR not only significantly reduced RGB and improved glucose tolerance and insulin resistance, but also improved spatial cognition in DACD mice. The expression of Grb2 and Gab2 in hippocampus and cerebral cortex of db/db mice was upregulated after treated with ZBPYR, and then affected the PI3K/Akt signaling pathway, and inhibited GSK3β overactivity.

Conclusions

This study showed that ZBPYR could enhance the memory and learning ability of db/db mice. Such neuroprotective effect might be related to the activation of Grb2-PI3K/Akt signaling which might provide a novel therapeutic target for the clinical treatment of DACD.

RNA-binding protein HuR suppresses senescence through Atg7 mediated autophagy activation in diabetic intervertebral disc degeneration

Objectives

Diabetes is a risk factor for intervertebral disc degeneration (IVDD). Studies have demonstrated that diabetes may affect IVDD through transcriptional regulation; however, whether post‐transcriptional regulation is involved in diabetic IVDD (DB‐IVDD) is still unknown. This study was performed to illustrate the role of HuR, an RNA‐binding protein, in DB‐IVDD development and its mechanism.

Materials and Methods

The expression of HuR was evaluated in nucleus pulposus (NP) tissues from diabetic IVDD patients and in high glucose‐treated NP cells. Senescence and autophagy were assessed in HuR over‐expressing and downregulation NP cells. The mRNAs that were regulated by HuR were screened, and immunoprecipitation was applied to confirm the regulation of HuR on targeted mRNAs.

Results

The results showed that the expression of HuR was decreased in diabetic NP tissues and high glucose‐treated NP cells. Downregulation of HuR may lead to increased senescence in high glucose‐treated NP cells, while autophagy activation attenuates senescence in HuR deficient NP cells. Mechanistic study showed that HuR prompted Atg7 mRNA stability via binding to the AU‐rich elements. Furthermore, overexpression of Atg7, but not HuR, may ameliorate DB‐IVDD in rats in vivo.

Conclusions

In conclusion, HuR may suppress senescence through autophagy activation via stabilizing Atg7 in diabetic NP cells; while Atg7, but not HuR, may serve as a potential therapeutic target for DB‐IVDD.

Potential Biochemical Mechanisms of Brain Injury in Diabetes Mellitus

The goal of this review was to summarize current biochemical mechanisms of and risk factors for diabetic brain injury. We mainly summarized mechanisms published in the past three years and focused on diabetes induced cognitive impairment, diabetes-linked Alzheimer’s disease, and diabetic stroke. We think there is a need to conduct further studies with increased sample sizes and prolonged period of follow-ups to clarify the effect of DM on brain dysfunction. Additionally, we also think that enhancing experimental reproducibility using animal models in conjunction with application of advanced devices should be considered when new experiments are designed. It is expected that further investigation of the underlying mechanisms of diabetic cognitive impairment will provide novel insights into therapeutic approaches for ameliorating diabetes-associated injury in the brain.

Exogenous fibroblast growth factor 1 ameliorates diabetes-induced cognitive decline via coordinately regulating PI3K/AKT signaling and PERK signaling

BACKGROUND

Diabetes induces central nervous system damage, leading to cognitive decline. Fibroblast growth factor 1 (FGF1) has dual function of neuroprotection and normalizing hyperglycemia. To date, the precise mechanisms and potential treating strategies of FGF1 for diabetes-induced cognitive decline (DICD) hasn't been fully elucidated.

METHODS

In this study, db/db mice were used as DICD animal model. We found that diabetes remarkably suppressed FGF1 expression in hippocampus. Thus, exogenous FGF1 had been treated for db/db mice and SH-SY5Y cells.

RESULTS

FGF1 significantly ameliorates DICD with better spatial learning and memory function. Moreover, FGF1 blocked diabetes-induced morphological structure change, neuronal apoptosis and Aβ1-42 deposition and synaptic dysfunction in hippocampus. But normalizing glucose may not the only contributed factor for FGF1 treating DICD with evidencing that metformin-treated db/db mice has a inferior cognitive function than that in FGF1 group. Current mechanistic study had found that diabetes inhibits cAMP-response element binding protein (CREB) activity and subsequently suppresses brain derived neurotrophic factor (BDNF) level via coordinately regulating PERK signaling and PI3K/AKT signaling in hippocampus, which were reversed by FGF1.

CONCLUSION

We conclude that FGF1 exerts its neuroprotective role and normalizing hyperglycemia effect, consequently ameliorates DICD, implying FGF1 holds a great promise to develop a new treatment for DICD. Video abstract.