Studies of pathology and pharmacology of diabetic encephalopathy with KK-Ay mouse model

True or false? Alzheimer's disease is type 3 diabetes: Evidences from bench to bedside

Globally, Alzheimer's disease (AD) is the most widespread chronic neurodegenerative disorder, leading to cognitive impairment, such as aphasia and agnosia, as well as mental symptoms, like behavioral abnormalities, that place a heavy psychological and financial burden on the families of the afflicted. Unfortunately, no particular medications exist to treat AD, as the current treatments only impede its progression.The link between AD and type 2 diabetes (T2D) has been increasingly revealed by research; the danger of developing both AD and T2D rises exponentially with age, with T2D being especially prone to AD. This has propelled researchers to investigate the mechanism(s) underlying this connection. A critical review of the relationship between insulin resistance, Aβ, oxidative stress, mitochondrial hypothesis, abnormal phosphorylation of Tau protein, inflammatory response, high blood glucose levels, neurotransmitters and signaling pathways, vascular issues in AD and diabetes, and the similarities between the two diseases, is presented in this review. Grasping the essential mechanisms behind this detrimental interaction may offer chances to devise successful therapeutic strategies.

Bridging metabolic syndrome and cognitive dysfunction: role of astrocytes

Metabolic syndrome (MetS) and cognitive dysfunction pose significant challenges to global health and the economy. Systemic inflammation, endocrine disruption, and autoregulatory impairment drive neurodegeneration and microcirculatory damage in MetS. Due to their unique anatomy and function, astrocytes sense and integrate multiple metabolic signals, including peripheral endocrine hormones and nutrients. Astrocytes and synapses engage in a complex dialogue of energetic and immunological interactions. Astrocytes act as a bridge between MetS and cognitive dysfunction, undergoing diverse activation in response to metabolic dysfunction. This article summarizes the alterations in astrocyte phenotypic characteristics across multiple pathological factors in MetS. It also discusses the clinical value of astrocytes as a critical pathologic diagnostic marker and potential therapeutic target for MetS-associated cognitive dysfunction.

The role of neurovascular coupling dysfunction in cognitive decline of diabetes patients

Neurovascular coupling (NVC) is an important mechanism to ensure adequate blood supply to active neurons in the brain. NVC damage can lead to chronic impairment of neuronal function. Diabetes is characterized by high blood sugar and is considered an important risk factor for cognitive impairment. In this review, we provide fMRI evidence of NVC damage in diabetic patients with cognitive decline. Combined with the exploration of the major mechanisms and signaling pathways of NVC, we discuss the effects of chronic hyperglycemia on the cellular structure of NVC signaling, including key receptors, ion channels, and intercellular connections. Studying these diabetes-related changes in cell structure will help us understand the underlying causes behind diabetes-induced NVC damage and early cognitive decline, ultimately helping to identify the most effective drug targets for treatment.

Function and therapeutic value of astrocytes in diabetic cognitive impairment

Diabetic cognitive impairment (DCI) is a complex complication of diabetes in the central nervous system, and its pathological mechanism is still being explored. Astrocytes are abundant glial cells in central nervous system that perform diverse functions in health and disease. Accumulating excellent research has identified astrocyte dysfunction in many neurodegenerative diseases (such as Alzheimer's disease, aging and Parkinson's disease), and summarized and discussed its pathological mechanisms and potential therapeutic value. However, the contribution of astrocytes to DCI has been largely overlooked. In this review, we first systematically summarized the effects and mechanisms of diabetes on brain astrocytes, and found that the diabetic environment (such as hyperglycemia, advanced glycation end products and cerebral insulin resistance) mediated brain reactive astrogliosis, which was specifically reflected in the changes of cell morphology and the remodeling of signature molecules. Secondly, we emphasized the contribution and potential targets of reactive astrogliosis to DCI, and found that reactive astrogliosis-induced increased blood-brain barrier permeability, glymphatic system dysfunction, neuroinflammation, abnormal cell communication and cholesterol metabolism dysregulation worsened cognitive function. In addition, we summarized effective strategies for treating DCI by targeting astrocytes. Finally, we discuss the application of new techniques in astrocytes, including single-cell transcriptome, in situ sequencing, and prospected new functions, new subsets and new targets of astrocytes in DCI.

Cognitive dysfunction and increased phosphorylated tau are associated with reduced O-GlcNAc signaling in an aging mouse model of metabolic syndrome

Metabolic syndrome (MetS), characterized by hyperglycemia, obesity, and hyperlipidemia, can increase the risk of developing late-onset dementia. Recent studies in patients and mouse models suggest a putative link between hyperphosphorylated tau, a component of Alzheimer's disease-related dementia (ADRD) pathology, and cerebral glucose hypometabolism. Impaired glucose metabolism reduces glucose flux through the hexosamine metabolic pathway triggering attenuated O-linked N-acetylglucosamine (O-GlcNAc) protein modification. The goal of the current study was to investigate the link between cognitive function, tau pathology, and O-GlcNAc signaling in an aging mouse model of MetS, agouti KKAy+/- . Male and female C57BL/6, non-agouti KKAy-/- , and agouti KKAy+/- mice were aged 12-18 months on standard chow diet. Body weight, blood glucose, total cholesterol, and triglyceride were measured to confirm the MetS phenotype. Cognition, sensorimotor function, and emotional reactivity were assessed for each genotype followed by plasma and brain tissue collection for biochemical and molecular analyses. Body weight, blood glucose, total cholesterol, and triglyceride levels were significantly elevated in agouti KKAy+/- mice versus C57BL/6 controls and non-agouti KKAy-/- . Behaviorally, agouti KKAy+/- revealed impairments in sensorimotor and cognitive function versus age-matched C57BL/6 and non-agouti KKAy-/- mice. Immunoblotting demonstrated increased phosphorylated tau accompanied with reduced O-GlcNAc protein expression in hippocampal-associated dorsal midbrain of female agouti KKAy+/- versus C57BL/6 control mice. Together, these data demonstrate that impaired cognitive function and AD-related pathology are associated with reduced O-GlcNAc signaling in aging MetS KKAy+/- mice. Overall, our study suggests that interaction of tau pathology with O-GlcNAc signaling may contribute to MetS-induced cognitive dysfunction in aging.

The gut microbiota-astrocyte axis: Implications for type 2 diabetic cognitive dysfunction

BACKGROUND

Diabetic cognitive dysfunction (DCD) is one of the most insidious complications of type 2 diabetes mellitus, which can seriously affect the ability to self-monitoring of blood glucose and the quality of life in the elderly. Previous pathological studies of cognitive dysfunction have focused on neuronal dysfunction, characterized by extracellular beta-amyloid deposition and intracellular tau hyperphosphorylation. In recent years, astrocytes have been recognized as a potential therapeutic target for cognitive dysfunction and important participants in the central control of metabolism. The disorder of gut microbiota and their metabolites have been linked to a series of metabolic diseases such as diabetes mellitus. The imbalance of intestinal flora has the effect of promoting the occurrence and deterioration of several diabetes-related complications. Gut microbes and their metabolites can drive astrocyte activation.

AIMS

We reviewed the pathological progress of DCD related to the "gut microbiota-astrocyte" axis in terms of peripheral and central inflammation, intestinal and blood-brain barrier (BBB) dysfunction, systemic and brain energy metabolism disorders to deepen the pathological research progress of DCD and explore the potential therapeutic targets.

CONCLUSION

"Gut microbiota-astrocyte" axis, unique bidirectional crosstalk in the brain-gut axis, mediates the intermediate pathological process of neurocognitive dysfunction secondary to metabolic disorders in diabetes mellitus.

Effects of diabetes on microglial physiology: a systematic review of in vitro, preclinical and clinical studies

Diabetes mellitus is a heterogeneous chronic metabolic disorder characterized by the presence of hyperglycemia, commonly preceded by a prediabetic state. The excess of blood glucose can damage multiple organs, including the brain. In fact, cognitive decline and dementia are increasingly being recognized as important comorbidities of diabetes. Despite the largely consistent link between diabetes and dementia, the underlying causes of neurodegeneration in diabetic patients remain to be elucidated. A common factor for almost all neurological disorders is neuroinflammation, a complex inflammatory process in the central nervous system for the most part orchestrated by microglial cells, the main representatives of the immune system in the brain. In this context, our research question aimed to understand how diabetes affects brain and/or retinal microglia physiology. We conducted a systematic search in PubMed and Web of Science to identify research items addressing the effects of diabetes on microglial phenotypic modulation, including critical neuroinflammatory mediators and their pathways. The literature search yielded 1327 records, including 18 patents. Based on the title and abstracts, 830 papers were screened from which 250 primary research papers met the eligibility criteria (original research articles with patients or with a strict diabetes model without comorbidities, that included direct data about microglia in the brain or retina), and 17 additional research papers were included through forward and backward citations, resulting in a total of 267 primary research articles included in the scoping systematic review. We reviewed all primary publications investigating the effects of diabetes and/or its main pathophysiological traits on microglia, including in vitro studies, preclinical models of diabetes and clinical studies on diabetic patients. Although a strict classification of microglia remains elusive given their capacity to adapt to the environment and their morphological, ultrastructural and molecular dynamism, diabetes modulates microglial phenotypic states, triggering specific responses that include upregulation of activity markers (such as Iba1, CD11b, CD68, MHC-II and F4/80), morphological shift to amoeboid shape, secretion of a wide variety of cytokines and chemokines, metabolic reprogramming and generalized increase of oxidative stress. Pathways commonly activated by diabetes-related conditions include NF-κB, NLRP3 inflammasome, fractalkine/CX3CR1, MAPKs, AGEs/RAGE and Akt/mTOR. Altogether, the detailed portrait of complex interactions between diabetes and microglia physiology presented here can be regarded as an important starting point for future research focused on the microglia-metabolism interface.

MiR-146a-5p Contributes to Microglial Polarization Transitions Associated With AGEs

M1/M2 polarization transitions of microglial phenotypes determine the states of neuroinflammation, which is critical in the pathophysiology of diabetic encephalopathy. This study aims to investigate the effects of advanced glycation end products (AGEs) on the microglial polarization state, the role of miR-146a-5p in the regulation of microglial polarization, and the underlying signaling pathways. BV-2 cells were incubated with N-ε-carboxymethyl lysine (CML), one kind of Advanced Glycation End Products (AGEs), to induce polarization. CD11b and iNOS and CD206 and Arg-1 were used to evaluate M1 and M2 microglia, respectively. The mRNA and protein expression levels of miR-146a-5p, transcription factor NF-κB, and inflammasome NLRP3 were measured. High and low expression of miR-146a-5p in the BV-2 cell line was generated by lentivirus transfection technology. RAGE, TLR-4, and NF-κB antagonists were applied to evaluate the underlying signaling pathways. Compared with the control group, CML upregulated the M1 phenotype and downregulated the M2 phenotype. These effects were reversed by overexpression of miR-146a. Furthermore, the expression of inflammasome NLRP3 and NF-κB was upregulated in the CML group and was reduced after miR-146a overexpression. And then overexpression of miR-146a effects was reversed by inhibition miR-146a expression. An NF-κB antagonist (PDTC), a RAGE antagonist (FPS-ZMI), and a TLR-4 antagonist (TLI-095) all reversed the polarization state induced by CML. In summary, CML induced polarization transitions to M1 phenotype and promoted inflammasome NLRP3 expression in BV-2 cells. The RAGE or TLR-4/miR-146a/NLRP3/NF-кB pathway might participate in the regulation of CML-induced BV-2 polarization.

Exploring the Protective Effect of ShenQi Compound on Skeletal Muscle in Diabetic Macrovasculopathy Mice

OBJECTIVE

ShenQi compound (SQC) is a traditional herbal formula, which has been used to treat Type 2 diabetes mellitus (T2DM) and complications for years. The aim of this study was to explore the preventive and protective effects of SQC recipe on the skeletal muscle of diabetic macrovasculopathy mice, which provides a theoretical basis for the clinical use of this formula.

METHODS

We evaluated the effect of SQC in a diabetic vasculopathy mouse model by detecting a series of blood indicators (blood glucose, lipids and insulin) and performing histological observations. Meanwhile, we explored the molecular mechanism of SQC treatment on skeletal muscle by genome expression profiles.

RESULTS

The results indicated that SQC could effectively improve blood glucose, serum lipids (total cholesterol (TC), Triglyceride (TG), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C)) and insulin (INS) levels in diabetic vasculopathy mice, as well as alleviating skeletal muscle tissue damage for diabetic macrovasculopathy. Meanwhile, compared with rosiglitazone, SQC showed a better effect on blood glucose fluctuation. Moreover, the gene microarray analysis indicated that SQC might improve T2DM by affecting biological functions related to cell death and cell adhesion. Moreover, 7 genes (Celsr2, Rilpl1, Dlx6as, 2010004M13Rik, Anapc13, Gm6097, Ddx39b) might be potential therapeutic targets of SQC.

CONCLUSION

All these results indicate that SQC is an effective preventive and protective drug for skeletal muscle in diabetic macrovasculopathy, and could alleviate skeletal muscle tissue damage through affecting biological functions related to cell death and cell adhesion.

Treatment with an Angiopoietin-1 mimetic peptide promotes neurological recovery after stroke in diabetic rats

Aim

Vasculotide (VT), an angiopoietin‐1 mimetic peptide, exerts neuroprotective effects in type one diabetic (T1DM) rats subjected to ischemic stroke. In this study, we investigated whether delayed VT treatment improves long‐term neurological outcome after stroke in T1DM rats.

Methods

Male Wistar rats were induced with T1DM, subjected to middle cerebral artery occlusion (MCAo) model of stroke, and treated with PBS (control), 2 µg/kg VT, 3 µg/kg VT, or 5.5 µg/kg VT. VT treatment was initiated at 24 h after stroke and administered daily (i.p) for 14 days. We evaluated neurological function, lesion volume, vascular and white matter remodeling, and inflammation in the ischemic brain. In vitro, we evaluated the effects of VT on endothelial cell capillary tube formation and inflammatory responses of primary cortical neurons (PCN) and macrophages.

Results

Treatment of T1DM‐stroke with 3 µg/kg VT but not 2 µg/kg or 5.5 µg/kg significantly improves neurological function and decreases infarct volume and cell death compared to control T1DM‐stroke rats. Thus, 3 µg/kg VT dose was employed in all subsequent in vivo analysis. VT treatment significantly increases axon and myelin density, decreases demyelination, decreases white matter injury, increases number of oligodendrocytes, and increases vascular density in the ischemic border zone of T1DM stroke rats. VT treatment significantly decreases MMP9 expression and decreases the number of M1 macrophages in the ischemic brain of T1DM‐stroke rats. In vitro, VT treatment significantly decreases endothelial cell death and decreases MCP‐1, endothelin‐1, and VEGF expression under high glucose (HG) and ischemic conditions and significantly increases capillary tube formation under HG conditions when compared to non‐treated control group. VT treatment significantly decreases inflammatory factor expression such as MMP9 and MCP‐1 in macrophages subjected to LPS activation and significantly decreases IL‐1β and MMP9 expression in PCN subjected to ischemia under HG conditions.

Conclusion

Delayed VT treatment (24 h after stroke) significantly improves neurological function, promotes vascular and white matter remodeling, and decreases inflammation in the ischemic brain after stroke in T1DM rats.

Studies of pathology and pharmacology of diabetic encephalopathy with KK-Ay mouse model

AIMS

Pathogenesis of diabetic encephalopathy (DE) is not completely understood until now. The purposes of this study were to illustrate the changes in morphology, function, and important transporters in neurons and glia during DE, as well as to reveal the potential therapeutic effects of medicines and the diet control on DE.

METHODS

Spontaneous obese KK-Ay mice were used to investigate diabetes-induced cognitive disorder, the morphology, function, and protein expression changes in impact animal and the cell level studies. The new drug candidate PHPB, donepezil, and low-fat food were used to observe the therapeutic effects.

RESULTS

KK-Ay mice at 5 months of age showed typical characteristics of type 2 diabetes mellitus (T2DM） and appeared significant cognitive deficits. Morphological study showed microtubule-associated protein 2 (MAP2) expression was increased in hippocampal neurons and glial fibrillary acidic protein (GFAP) expression decreased in astrocytes. Meanwhile, the vesicular glutamate transporter 1 (vGLUT1) expression was increased and glucose transporter 1 (GLUT1) decreased, and the expression of brain-derived neurotrophic factor (BDNF) and glial cell-derived neurotrophic factor (GDNF) was also reduced in KK-Ay mice. Microglia were activated, and IL-1β and TNF-α were increased obviously in the brains of the KK-Ay mice. Most of the above changes in the KK-Ay mice at 5 months of age could be relieved by diet intervention (DR) or by treatment of donepezil or new drug candidate PHPB.

CONCLUSION

KK-Ay mouse is a useful animal model for studying DE. The alterations of morphology, structure, and function of astrocyte and microglia in KK-Ay mice might be rescued by DR and by treatment of medicine. The proteins we reported in this study could be used as biomarkers and the potential drug targets for DE study and treatment.