Microglia activation and inflammation in hippocampus attenuates memory and mood functions during experimentally induced diabetes in rat

Diabetes Mellitus Impairs Blood-Brain Barrier Integrality and Microglial Reactivity

Diabetes mellitus (DM), a chronic metabolic disorder that adversely affects the blood-brain barrier (BBB) and microglial function in the central nervous system (CNS), contributing to neuronal damage and neurodegenerative diseases. However, the underlying molecular mechanisms linking diabetes to BBB dysfunction and microglial dysregulation remain poorly understood. Here, we assessed the impacts of diabetes on BBB and microglial reactivity and investigated its mechanisms. We found diabetes severely disrupted the BBB integrity and microglial response to vascular injury. We also revealed a potential relationship between BBB disruption and impaired microglial function, whereby increasing BBB permeability led to a downregulation of microglial P2RY12 expression, thereby impairing microglial protection against cerebrovascular injury. Understanding these mechanisms may contribute to the developing of therapeutic strategies for diabetes-related neurological complications.

Alzheimer's Disease, Obesity, and Type 2 Diabetes: Focus on Common Neuroglial Dysfunctions (Critical Review and New Data on Human Brain and Models)

BACKGROUND/OBJECTIVES

Obesity, type 2 diabetes (T2D), and Alzheimer's disease (AD) are pathologies that affect millions of people worldwide. They have no effective therapy and are difficult to prevent and control when they develop. It has been known for many years that these diseases have many pathogenic aspects in common. We highlight in this review that neuroglial cells (astroglia, oligodendroglia, and microglia) play a vital role in the origin, clinical-pathological development, and course of brain neurodegeneration. Moreover, we include the new results of a T2D-AD mouse model (APP+PS1 mice on a high-calorie diet) that we are investigating.

METHODS

Critical bibliographic revision and biochemical neuropathological study of neuroglia in a T2D-AD model.

RESULTS

T2D and AD are not only "connected" by producing complex pathologies in the same individual (obesity, T2D, and AD), but they also have many common pathogenic mechanisms. These include insulin resistance, hyperinsulinemia, hyperglycemia, oxidative stress, mitochondrial dysfunction, and inflammation (both peripheral and central-or neuroinflammation). Cognitive impairment and AD are the maximum exponents of brain neurodegeneration in these pathological processes. both due to the dysfunctions induced by metabolic changes in peripheral tissues and inadequate neurotoxic responses to changes in the brain. In this review, we first analyze the common pathogenic mechanisms of obesity, T2D, and AD (and/or cerebral vascular dementia) that induce transcendental changes and responses in neuroglia. The relationships between T2D and AD discussed mainly focus on neuroglial responses. Next, we present neuroglial changes within their neuropathological context in diverse scenarios: (a) aging involution and neurodegenerative disorders, (b) human obesity and diabetes and obesity/diabetes models, (c) human AD and in AD models, and (d) human AD-T2D and AD-T2D models. An important part of the data presented comes from our own studies on humans and experimental models over the past few years. In the T2D-AD section, we included the results of a T2D-AD mouse model (APP+PS1 mice on a high-calorie diet) that we investigated, which showed that neuroglial dysfunctions (astrocytosis and microgliosis) manifest before the appearance of amyloid neuropathology, and that the amyloid pathology is greater than that presented by mice fed a normal, non-high-caloric diet A broad review is finally included on pharmacological, cellular, genic, and non-pharmacological (especially diet and lifestyle) neuroglial-related treatments, as well as clinical trials in a comparative way between T2D and AD. These neuroglial treatments need to be included in the multimodal/integral treatments of T2D and AD to achieve greater therapeutic efficacy in many millions of patients.

CONCLUSIONS

Neuroglial alterations (especially in astroglia and microglia, cornerstones of neuroinflammation) are markedly defining brain neurodegeneration in T2D and A, although there are some not significant differences between each of the studied pathologies. Neuroglial therapies are a very important and p. promising tool that are being developed to prevent and/or treat brain dysfunction in T2D-AD. The need for further research in two very different directions is evident: (a) characterization of the phenotypic changes of astrocytes and microglial cells in each region of the brain and in each phase of development of each isolated and associated pathology (single-cell studies are mandatory) to better understand the pathologies and define new therapeutic targets; (b) studying new therapeutic avenues to normalize the function of neuroglial cells (preventing neurotoxic responses and/or reversing them) in these pathologies, as well as the phenotypic characteristics in each moment of the course and place of the neurodegenerative process.

An extract of Hibiscus sabdariffa improves short-term memory in rats with experimental diabetic hyperglycemia

BACKGROUND

Calyxes of Hibiscus sabdariffa (Hs) contain anthocyanins, that normalize blood glucose levels (BGL) in diabetic patients. Diabetes also causes memory alterations, which could hypothetically decrease with the consumption of Hs.

OBJECTIVES

To investigate the effect of dietary supplementation with a Hs extract on working memory and BGL in rats.

METHODS

Diabetic hyperglycemia (DHG) was induced with streptozotocin (STZ, 55 mg/kg i.p.) in Wistar rats. After 72 h DHG was confirmed, and the consumption of Hs extract began (50 mg/Kg/day). BGL and body weight (BW) were measured at 10, 20 and 30 days after DHG induction in controls and treated animals. Learning and short-term memory were evaluated after 30 days with Novel Object Recognition Test (NOR) and Barnes Maze (BM). The gross hippocampal structure was histologically analyzed.

RESULTS

STZ-treated animals presented low BW and persistent DHG (BGL <300 mg/dL). Diabetic animals consuming the Hs extract had a dual response: some showed BGL comparable to controls, while others had levels comparable to diabetic animals not consuming extract. Diabetic animals that consumed the Hs extract had a better performance in NOR and BM than the diabetic animals not consuming the extract. At the histological level, hippocampal morphological differences were observed between diabetic animals that consumed the extract and those that did not.

DISCUSSION

The Hs extract used here could be a good co-adjuvant in the treatment of DHG, aimed at mitigating memory deficits and high BGL. These beneficial effects could be attributed to the anthocyanin content in the extract.

Neuroprotective compounds alter the expression of genes coding for proteins related to mitochondrial function in activated microglia

A hallmark of neuroinflammatory disorders is mitochondrial dysfunction. Nevertheless, the transcriptional changes underlying this alteration are not well-defined. Microglia activation, a decrease in mitochondrion biogenesis and a subsequent alteration of the redox are common factors in diseases coursing with neuroinflammation. In the last two decades, components of the adenosinergic system have been proposed as potential therapeutic targets to combat neuroinflammation. In this research, we analyzed by RNAseq the gene expression in activated microglia treated with an adenosine A2A receptor antagonist, SCH 582561, and/or an A3 receptor agonist, 2-Cl-IB-MECA, since these receptors are deeply related to neurodegeneration and inflammation. The analysis was focused on genes related to inflammation and REDOX homeostasis. It was detected that in the three conditions (microglia treated with 2-Cl-IB-MECA, SCH 582561, and their combination) more than 40 % of the detected genes codified by the mitochondrial genome were differentially expressed (FDR < 0.05) (14/34, 16/34, and 13/34) respectively, being almost all of them (>85 %) upregulated in the microglia treated with adenosinergic compounds. Also, we analyzed the differential expression of genes related to mitochondrial function and oxidative stress codified by the nuclear genome. Additionally, we evaluated the oxygen consumption rate (OCR) of mitochondria in microglia treated with LPS and IFN-γ, both alone and in combination with adenosinergic compounds. The data showed an improvement in mitochondrial function with the antagonist of the adenosine A2A receptor, compared to the effects of pro-inflammatory stimulus, confirming a functional effect consistent with the RNAseq data.

Progress in the Pathogenesis of Diabetic Encephalopathy: The Key Role of Neuroinflammation

Diabetic encephalopathy (DE) is a severe complication that occurs in the central nervous system (CNS) and leads to cognitive impairment. DE involves various pathophysiological processes, and its pathogenesis is still unclear. This review summarised current research on the pathogenesis of diabetic encephalopathy, which involves neuroinflammation, oxidative stress, iron homoeostasis, blood-brain barrier disruption, altered gut microbiota, insulin resistance, etc. Among these pathological mechanisms, neuroinflammation has been focused on. This paper summarises some of the molecular mechanisms involved in neuroinflammation, including the Mammalian Target of Rapamycin (mTOR), Lipocalin-2 (LCN-2), Pyroptosis, Advanced Glycosylation End Products (AGEs), and some common pro-inflammatory factors. In addition, we discuss recent advances in the study of potential therapeutic targets for the treatment of DE against neuroinflammation. The current research on the pathogenesis of DE is progressing slowly, and more research is needed in the future. Further study of neuroinflammation as a mechanism is conducive to the discovery of more effective treatments for DE in the future.

Advancing the understanding of diabetic encephalopathy through unravelling pathogenesis and exploring future treatment perspectives

Diabetic encephalopathy (DE), a significant micro-complication of diabetes, manifests as neurochemical, structural, behavioral, and cognitive alterations. This condition is especially dangerous for the elderly because aging raises the risk of neurodegenerative disorders and cognitive impairment, both of which can be made worse by diabetes. Despite its severity, diagnosis of this disease is challenging, and there is a paucity of information on its pathogenesis. The pivotal roles of various cellular pathways, activated or influenced by hyperglycemia, insulin sensitivity, amyloid accumulation, tau hyperphosphorylation, brain vasculopathy, neuroinflammation, and oxidative stress, are widely recognized for contributing to the potential causes of diabetic encephalopathy. We also reviewed current pharmacological strategies for DE encompassing a comprehensive approach targeting metabolic dysregulations and neurological manifestations. Antioxidant-based therapies hold promise in mitigating oxidative stress-induced neuronal damage, while anti-diabetic drugs offer neuroprotective effects through diverse mechanisms, including modulation of insulin signaling pathways and neuroinflammation. Additionally, tissue engineering and nanomedicine-based approaches present innovative strategies for targeted drug delivery and regenerative therapies for DE. Despite significant progress, challenges remain in translating these therapeutic interventions into clinical practice, including long-term safety, scalability, and regulatory approval. Further research is warranted to optimize these approaches and address remaining gaps in the management of DE and associated neurodegenerative disorders.

Transcranial photobiomodulation improves insulin therapy in diabetic microglial reactivity and the brain drainage system

The dysfunction of microglia in the development of diabetes is associated with various diabetic complications, while traditional insulin therapy is insufficient to rapidly restore the function of microglia. Therefore, the search for new alternative methods of treating diabetes-related dysfunction of microglia is urgently needed. Here, we evaluate the effects of transcranial photobiomodulation (tPBM) on microglial function in diabetic mice and investigate its mechanism. We find tPBM treatment effectively improves insulin therapy on microglial morphology and reactivity. We also show that tPBM stimulates brain drainage system through activation of meningeal lymphatics, which contributes to the removal of inflammatory factor, and increase of microglial purinergic receptor P2RY12. Besides, the energy expenditure and locomotor activity of diabetic mice are also improved by tPBM. Our results demonstrate that tPBM can be an efficient, non-invasive method for the treatment of microglial dysfunction caused by diabetes, and also has the potential to prevent diabetic physiological disorders.

Impaired Insulin Signaling Alters Mediators of Hippocampal Synaptic Dynamics/Plasticity: A Possible Mechanism of Hyperglycemia-Induced Cognitive Impairment

Alzheimer's disease (AD) is a neurological condition that affects the elderly and is characterized by progressive and irreversible neurodegeneration in the cerebral cortex [...].

Cognitive dysfunction in diabetes: abnormal glucose metabolic regulation in the brain

Cognitive dysfunction is increasingly recognized as a complication and comorbidity of diabetes, supported by evidence of abnormal brain structure and function. Although few mechanistic metabolic studies have shown clear pathophysiological links between diabetes and cognitive dysfunction, there are several plausible ways in which this connection may occur. Since, brain functions require a constant supply of glucose as an energy source, the brain may be more susceptible to abnormalities in glucose metabolism. Glucose metabolic abnormalities under diabetic conditions may play an important role in cognitive dysfunction by affecting glucose transport and reducing glucose metabolism. These changes, along with oxidative stress, inflammation, mitochondrial dysfunction, and other factors, can affect synaptic transmission, neural plasticity, and ultimately lead to impaired neuronal and cognitive function. Insulin signal triggers intracellular signal transduction that regulates glucose transport and metabolism. Insulin resistance, one hallmark of diabetes, has also been linked with impaired cerebral glucose metabolism in the brain. In this review, we conclude that glucose metabolic abnormalities play a critical role in the pathophysiological alterations underlying diabetic cognitive dysfunction (DCD), which is associated with multiple pathogenic factors such as oxidative stress, mitochondrial dysfunction, inflammation, and others. Brain insulin resistance is highly emphasized and characterized as an important pathogenic mechanism in the DCD.

Therapeutic effect of implanted and non-invasive vagus nerve stimulation on heroin-induced anxiety

Substance addiction causes anxiety, which in turn reinforces the maintaining of substance use, resulting in a vicious circle. And this circle is one of the reasons why addiction is so hard to cure. However, there is no treatment involved in addiction-induced anxiety at present. We tested whether VNS (vagus nerve stimulation) can improve heroin-induced anxiety, and made a comparison between nVNS (transcervical vagus nerve stimulation) and taVNS (transauricular vagus nerve stimulation) on therapeutic effect. Mice were subjected to nVNS or taVNS before heroin administration. By observing c-Fos expression in the NTS (nucleus of the solitary tract), we assessed vagal fiber activation. Using the OFT (open field test) and the EPM (elevated cross maze test), we evaluated the anxiety-like behaviors of the mice. Using immunofluorescence, we observed the proliferation and activation of microglia in the hippocampus. And ELISA was used to measure the levels of proinflammatory factors in the hippocampus. Both nVNS and taVNS significantly increased the expression of c-Fos in the nucleus of solitary tract, suggesting the feasibility of nVNS and taVNS. The anxiety level of heroin-treated mice was significantly increased, microglia in the hippocampus was significantly proliferated and activated, and the proinflammatory factors (IL-1β, IL-6, TNF-α) in the hippocampus were significantly up-regulated. Crucially, both nVNS and taVNS reversed the above changes caused by heroin addiction. SIGNIFICANCE: It was confirmed that the therapeutic effect of VNS on heroin-induced anxiety may be an effective treatment method to break the "addiction-anxiety" cycle and provides some insights for subsequent treatment of addiction.

Relations of hippocampal subfields atrophy patterns with memory and biochemical changes in end stage renal disease

End-stage renal disease (ESRD) results in hippocampal volume reduction, but the hippocampal subfields atrophy patterns cannot be identified. We explored the volumes and asymmetry of the hippocampal subfields and their relationships with memory function and biochemical changes. Hippocampal global and subfields volumes were derived from 33 ESRD patients and 46 healthy controls (HCs) from structural MRI. We compared the volume and asymmetric index of each subfield, with receiver operating characteristic curve analysis to evaluate the differentiation between ESRD and HCs. The relations of hippocampal subfield volumes with memory performance and biochemical data were investigated in ESRD group. ESRD patients had smaller hippocampal subfield volumes, mainly in the left CA1 body, left fimbria, right molecular layer head, right molecular layer body and right HATA. The right molecular layer body exhibited the highest accuracy for differentiating ESRD from HCs, with a sensitivity of 80.43% and specificity of 72.73%. Worse learning process (r = 0.414, p = 0.032), immediate recall (r = 0.396, p = 0.041) and delayed recall (r = 0.482, p = 0.011) was associated with left fimbria atrophy. The left fimbria volume was positively correlated with Hb (r = 0.388, p = 0.05); the left CA1 body volume was negatively correlated with Urea (r = - 0.469, p = 0.016). ESRD patients showed global and hippocampal subfields atrophy. Left fimbria atrophy was related to memory function. Anemia and Urea level may be associated with the atrophy of left fimbria and CA1 body, respectively.

Diabetic Encephalopathy in a Preclinical Experimental Model of Type 1 Diabetes Mellitus: Observations in Adult Female Rat

Patients affected by diabetes mellitus (DM) show diabetic encephalopathy with an increased risk of cognitive deficits, dementia and Alzheimer's disease, but the mechanisms are not fully explored. In the male animal models of DM, the development of cognitive impairment seems to be the result of the concomitance of different processes such as neuroinflammation, oxidative stress, mitochondrial dysfunction, and aberrant synaptogenesis. However, even if diabetic encephalopathy shows some sex-dimorphic features, no observations in female rats have been so far reported on these aspects. Therefore, in an experimental model of type 1 DM (T1DM), we explored the impact of one month of pathology on memory abilities by the novel object recognition test and on neuroinflammation, synaptogenesis and mitochondrial functionality. Moreover, given that steroids are involved in memory and learning, we also analysed their levels and receptors. We reported that memory dysfunction can be associated with different features in the female hippocampus and cerebral cortex. Indeed, in the hippocampus, we observed aberrant synaptogenesis and neuroinflammation but not mitochondrial dysfunction and oxidative stress, possibly due to the results of locally increased levels of progesterone metabolites (i.e., dihydroprogesterone and allopregnanolone). These observations suggest specific brain-area effects of T1DM since different alterations are observed in the cerebral cortex.