Low-glucose-sensitive TRPC6 dysfunction drives hypoglycemia-induced cognitive impairment in diabetes

Hypoglycemia and Alzheimer Disease Risk: The Possible Role of Dasiglucagon

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by memory impairment and cognitive dysfunctions. It has been shown that hypoglycemia can adversely affect AD neuropathology. It is well-known that chronic hyperglycemia in type 2 diabetes (T2D) is regarded as a potential risk factor for the development and progression of AD. However, the effect of recurrent hypoglycemia on the pathogenesis of AD was not deeply discussed, and how recurrent hypoglycemia affects AD at cellular and molecular levels was not intensely interpreted by the previous studies. The underlying mechanisms for hypoglycaemia-induced AD are diverse such as endothelial dysfunction, thrombosis, and neuronal injury that causing tau protein hyperphosphorylation and the accumulation of amyloid beta (Aβ) in the brain neurons. Of note, the glucagon hormone, which controls blood glucose, can also regulate the cognitive functions. Glucagon increases blood glucose by antagonizing the metabolic effect of insulin. Therefore, glucagon, through attenuation of hypoglycemia, may prevent AD neuropathology. Glucagon/GLP-1 has been shown to promote synaptogenesis, hippocampal synaptic plasticity, and learning and memory, while attenuating amyloid and tau pathologies. Therefore, activation of glucagon receptors in the brain may reduce AD neuropathology. A recent glucagon receptor agonist dasiglucagon which used in the management of hypoglycemia may be effective in preventing hypoglycemia and AD neuropathology. This review aims to discuss the potential role of dasiglucagon in treating hypoglycemia in AD, and how this drug reduce AD neuropathology.

Potential risk factors for mild cognitive impairment among patients with type 2 diabetes experiencing hypoglycemia

AIMS

This study examined the association between hypoglycemia and mild cognitive impairment (MCI) among patients with type 2 diabetes mellitus (T2DM) and identified risk factors for MCI in patients with hypoglycemia.

METHODS

In this retrospective study, 328 patients with T2DM were screened in 2019 and followed up in 2022. Cognitive performance was assessed using the Montreal Cognitive Assessment (MoCA). The diagnosis of MCI was based on established criteria. Risk ratio (RR) with 95 % confidence intervals (CI) was calculated to estimate the risk of MCI. Univariate and multivariate logistic regression analyses were conducted to identify risk factors for MCI in those with hypoglycemia.

RESULTS

Patients with hypoglycemia had lower cognitive performance 3 years later. The RR of MCI was 2.221 (95 % CI 1.269-3.885). Multivariate logistic analysis showed that low grip strength, existing diabetic retinopathy (DR), and multiple hypoglycemia episodes were associated with higher odds of MCI in patients with hypoglycemia (adjusted odds ratio [OR] 0.909 [95 % CI 0.859-0.963]), 3.078 [95 % CI 1.158-12.358], and 4.642 [95 % CI 1.284-16.776], respectively, all P < 0.05).

CONCLUSIONS

Hypoglycemia increased MCI risk among patients with T2DM. Low grip strength, DR, and multiple hypoglycemia episodes may be potential risk factors for hypoglycemia-associated MCI.

CaMKK2 as an emerging treatment target for bipolar disorder

Current pharmacological treatments for bipolar disorder are inadequate and based on serendipitously discovered drugs often with limited efficacy, burdensome side-effects, and unclear mechanisms of action. Advances in drug development for the treatment of bipolar disorder remain incremental and have come largely from repurposing drugs used for other psychiatric conditions, a strategy that has failed to find truly revolutionary therapies, as it does not target the mood instability that characterises the condition. The lack of therapeutic innovation in the bipolar disorder field is largely due to a poor understanding of the underlying disease mechanisms and the consequent absence of validated drug targets. A compelling new treatment target is the Ca2+-calmodulin dependent protein kinase kinase-2 (CaMKK2) enzyme. CaMKK2 is highly enriched in brain neurons and regulates energy metabolism and neuronal processes that underpin higher order functions such as long-term memory, mood, and other affective functions. Loss-of-function polymorphisms and a rare missense mutation in human CAMKK2 are associated with bipolar disorder, and genetic deletion of Camkk2 in mice causes bipolar-like behaviours similar to those in patients. Furthermore, these behaviours are ameliorated by lithium, which increases CaMKK2 activity. In this review, we discuss multiple convergent lines of evidence that support targeting of CaMKK2 as a new treatment strategy for bipolar disorder.

Dementia in Diabetes: The Role of Hypoglycemia

Hypoglycemia, a common consequence of diabetes treatment, is associated with severe morbidity and mortality and has become a major barrier to intensifying antidiabetic therapy. Severe hypoglycemia, defined as abnormally low blood glucose requiring the assistance of another person, is associated with seizures and comas, but even mild hypoglycemia can cause troubling symptoms such as anxiety, palpitations, and confusion. Dementia generally refers to the loss of memory, language, problem-solving, and other cognitive functions, which can interfere with daily life, and there is growing evidence that diabetes is associated with an increased risk of both vascular and non-vascular dementia. Neuroglycopenia resulting from a hypoglycemic episode in diabetic patients can lead to the degeneration of brain cells, with a resultant cognitive decline, leading to dementia. In light of new evidence, a deeper understating of the relationship between hypoglycemia and dementia can help to inform and guide preventative strategies. In this review, we discuss the epidemiology of dementia among patients with diabetes, and the emerging mechanisms thought to underlie the association between hypoglycemia and dementia. Furthermore, we discuss the risks of various pharmacological therapies, emerging therapies to combat hypoglycemia-induced dementia, as well as risk minimization strategies.

Calpain-TRPC6 signaling pathway contributes to propofol-induced developmental neurotoxicity in rats

Growing animal studies suggest a risk of neuronal damage following early childhood exposure to anesthesia and sedation drugs including propofol. Inhibition of transient receptor potential canonical 6 (TRPC6) degradation has been shown to protect neurons from neuronal damage induced by multiple brain injury models. Our aim was to investigate whether calpain-TRPC6 pathway is a target in propofol-induced neurotoxicity. Postnatal day (PND) 7 rats were exposed to five bolus injections of 25 mg/kg propofol or 10 % intralipid at hourly intervals. Neuronal injury was assessed by the expression pattern of TUNEL staining and cleaved-caspase-3. The Morris water maze test was used to evaluate learning and memory functions in later life. Pretreatments consisting of intracerebroventricular injections of a TRPC6 agonist, TRPC6 inhibitor, or calpain inhibitor were used to confirm the potential role of the calpain-TRPC6 pathway in propofol-induced neurotoxicity. Prolonged exposure to propofol induced neuronal injury, downregulation of TRPC6, and enhancement of calpain activity in the cerebral cortex up to 24 h after anesthesia. It also induced long-term behavioral disorders, manifesting as longer escape latency at PND40 and PND41 and as fewer platform-crossing times and less time spent in the target quadrant at PND42. These propofol-induced effects were attenuated by treatment with the TRPC6 agonist and exaggerated by the TRPC6 inhibitor. Pretreatment with the calpain inhibitor alleviated the propofol-induced TRPC6 downregulation and neuronal injury in the cerebral cortex. In conclusion, our data suggest that a calpain-TRPC6 signaling pathway contributes to propofol-induced acute cortical neuron injury and long-term behavioral disorders in rats.

Transient receptor potential channel 6 knockdown prevents high glucose-induced Müller cell pyroptosis

BACKGROUND

Transient receptor potential channel 6 (TRPC6) is reported to be involved in the pathogenesis of diabetic complications, but its role in diabetic retinopathy (DR) remains unknown. The aim of our study was to determine the role and mechanism of TRPC6 in DR.

METHODS

High glucose was used to construct a DR cell model using rat retinal Müller cells (rMC-1). Intracellular Ca²⁺, reactive oxygen species (ROS) and cell pyroptosis were evaluated by flow cytometry. Protein levels of NLRP3, pro-caspase-1, active caspase-1, gasdermin D (GSDMD), GSDMD-N, TRPC6 and H3K27ac were detected by Western blot. mRNA levels of EP300 and TRPC6 were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR). Levels of IL-1β and IL-18 were estimated by enzyme linked immunosorbent assay (ELISA). The interaction between EP300 and TRPC6 was validated by a chromatin immunoprecipitation assay.

RESULTS

The knockdown of TRPC6 reduced inflammation and cell pyroptosis in HG induced rMC-1 cells, whereas overexpression of TRPC6 had the opposite effects. The inhibition of ROS and NLRP3 reversed TRPC6-mediated cell pyroptosis in the DR cell model. In addition, EP300 increased the expression of H3K27ac and TRPC6 to promote cell pyroptosis, which was suppressed by the knockdown of TRPC6.

CONCLUSIONS

Our study revealed a novel EP300/H3K27ac/TRPC6 signaling pathway that may contribute to HG induced Müller cell pyroptosis. TRPC6 played a novel role in Müller cell pyroptosis triggered by HG, and may be a potential target for DR treatment in the future.

The Impact of Intermittent Hypoxia on Metabolism and Cognition

Intermittent hypoxia (IH), one of the primary pathologies of sleep apnea syndrome (SAS), exposes cells throughout the body to repeated cycles of hypoxia/normoxia that result in oxidative stress and systemic inflammation. Since SAS is epidemiologically strongly correlated with type 2 diabetes/insulin resistance, obesity, hypertension, and dyslipidemia included in metabolic syndrome, the effects of IH on gene expression in the corresponding cells of each organ have been studied intensively to clarify the molecular mechanism of the association between SAS and metabolic syndrome. Dementia has recently been recognized as a serious health problem due to its increasing incidence, and a large body of evidence has shown its strong correlation with SAS and metabolic disorders. In this narrative review, we first outline the effects of IH on the expression of genes related to metabolism in neuronal cells, pancreatic β cells, hepatocytes, adipocytes, myocytes, and renal cells (mainly based on the results of our experiments). Next, we discuss the literature regarding the mechanisms by which metabolic disorders and IH develop dementia to understand how IH directly and indirectly leads to the development of dementia.

Impairment of Mitochondrial Respiration in Metabolic Diseases: An Overview

Mitochondrial dysfunction has emerged as a central pathomechanism in the setting of obesity and diabetes mellitus, linking these intertwined pathologies that share insulin resistance as a common denominator. High-resolution respirometry (HRR) is a state-of-the-art research method currently used to study mitochondrial respiration and its impairment in health and disease. Tissue samples, cells or isolated mitochondria are exposed to various substrate-uncoupler-inhibitor-titration protocols, which allows the measurement and calculation of several parameters of mitochondrial respiration. In this review, we discuss the alterations of mitochondrial bioenergetics in the main dysfunctional organs that contribute to the development of the obese and diabetic phenotypes in both animal models and human subjects. Herein we review data regarding the impairment of oxidative phosphorylation as integrated mitochondrial function assessed by means of HRR. We acknowledge the critical role of this method in determining the alterations in oxidative phosphorylation occurring in the early stages of metabolic pathologies. We conclude that there is a mutual two-way relationship between mitochondrial dysfunction and insulin insensitivity that characterizes these diseases.

Recurrent Hypoglycemia Impaired Vascular Function in Advanced T2DM Rats by Inducing Pyroptosis

Background

Hypoglycemia is a dangerous side effect of intensive glucose control in diabetes. Even though it leads to adverse cardiovascular events, the effects of hypoglycemia on vascular biology in diabetes have not been adequately studied.

Methods

Aged Sprague-Dawley rats were fed a high-fat diet and given streptozotocin to induce type 2 diabetes mellitus (T2DM). Acute and recurrent hypoglycemia were then induced by glucose via insulin administration. Vascular function, oxidative stress, and pyroptosis levels in aortic tissue were assessed by physiological and biochemical methods.

Results

Hypoglycemia was associated with a marked decrease in vascular function, elevated oxidative stress, and elevated pyroptosis levels in the thoracic aorta. The changes in oxidative stress and pyroptosis were greater in rats with recurrent hypoglycemia than in those with acute hypoglycemia.

Conclusions

Hypoglycemia impaired vascular function in aged rats with T2DM by inducing pyroptosis. The extent of injury increased with the duration of blood glucose fluctuation.

Recurrent moderate hypoglycemia accelerates the progression of cognitive deficits through impairment of TRPC6/GLUT3 pathway in diabetic APP/PS1 mice

Currently, the most effective strategy for dealing with Alzheimer’s disease (AD) is delaying the onset of dementia. Severe hypoglycemia is strongly associated with dementia; however, the effects of recurrent moderate hypoglycemia (RH) on the progression of cognitive deficits in patients with diabetes with genetic susceptibility to AD remain unclear. Here, we report that insulin-controlled hyperglycemia slightly aggravated AD-type pathologies and cognitive impairment; however, RH significantly increased neuronal hyperactivity and accelerated the progression of cognitive deficits in streptozotocin-induced (STZ-induced) diabetic APP/PS1 mice. Glucose transporter 3–mediated (GLUT3-mediated) neuronal glucose uptake was not significantly altered under hyperglycemia but was markedly reduced by RH, which induced excessive mitochondrial fission in the hippocampus. Overexpression of GLUT3, specifically in the dentate gyrus (DG) area of the hippocampus, enhanced mitochondrial function and improved cognitive deficits. Activation of the transient receptor potential channel 6 (TRPC6) increased GLUT3-mediated glucose uptake in the brain and alleviated RH-induced cognitive deficits, and inactivation of the Ca²⁺/AMPK pathway was responsible for TRPC6-induced GLUT3 inhibition. Taken together, RH impairs brain GLUT3-mediated glucose uptake and further provokes neuronal mitochondrial dysfunction by inhibiting TRPC6 expression, which then accelerates progression of cognitive deficits in diabetic APP/PS1 mice. Avoiding RH is essential for glycemic control in patients with diabetes, and TRPC6/GLUT3 represents potent targets for delaying the onset of dementia in patients with diabetes.

Hypoglycemia, Vascular Disease and Cognitive Dysfunction in Diabetes: Insights from Text Mining-Based Reconstruction and Bioinformatics Analysis of the Gene Networks

Hypoglycemia has been recognized as a risk factor for diabetic vascular complications and cognitive decline, but the molecular mechanisms of the effect of hypoglycemia on target organs are not fully understood. In this work, gene networks of hypoglycemia and cardiovascular disease, diabetic retinopathy, diabetic nephropathy, diabetic neuropathy, cognitive decline, and Alzheimer's disease were reconstructed using ANDSystem, a text-mining-based tool. The gene network of hypoglycemia included 141 genes and 2467 interactions. Enrichment analysis of Gene Ontology (GO) biological processes showed that the regulation of insulin secretion, glucose homeostasis, apoptosis, nitric oxide biosynthesis, and cell signaling are significantly enriched for hypoglycemia. Among the network hubs, INS, IL6, LEP, TNF, IL1B, EGFR, and FOS had the highest betweenness centrality, while GPR142, MBOAT4, SLC5A4, IGFBP6, PPY, G6PC1, SLC2A2, GYS2, GCGR, and AQP7 demonstrated the highest cross-talk specificity. Hypoglycemia-related genes were overrepresented in the gene networks of diabetic complications and comorbidity; moreover, 14 genes were mutual for all studied disorders. Eleven GO biological processes (glucose homeostasis, nitric oxide biosynthesis, smooth muscle cell proliferation, ERK1 and ERK2 cascade, etc.) were overrepresented in all reconstructed networks. The obtained results expand our understanding of the molecular mechanisms underlying the deteriorating effects of hypoglycemia in diabetes-associated vascular disease and cognitive dysfunction.

Activation of Glucagon-Like Peptide-1 Receptor Ameliorates Cognitive Decline in Type 2 Diabetes Mellitus Through a Metabolism-Independent Pathway

Background

Patients with hypertension and diabetes mellitus are susceptible to dementia, but regular therapy fails to reduce the risk of dementia. Glucagon‐like peptide‐1 receptor agonists have neuroprotective effects in experimental studies. We aimed to assess the effect of liraglutide, a glucagon‐like peptide‐1 receptor agonist, on cognitive function and whether its effect was associated with metabolic changes in patients with type 2 diabetes mellitus.

Methods and Results

Fifty patients with type 2 diabetes mellitus were recruited in this prospective study. All patients underwent cognitive assessment and brain activation monitoring by functional near‐infrared spectroscopy. At 12 weeks, patients in the glucagon‐like peptide‐1 group acquired better scores in all cognitive tests and showed remarkable improvement in memory and attention (P=0.040) test compared with the control group after multivariable adjustment. Compared with the control group, liraglutide significantly increased activation of the dorsolateral prefrontal cortex and orbitofrontal cortex brain regions (P=0.0038). After liraglutide treatment, cognitive scores were significantly correlated with changes in these activating brain regions (P<0.05), but no correlation was observed between the changes in cognitive function and changes of body mass index, blood pressure, and glycemic levels.

Conclusions

We concluded that liraglutide improves cognitive decline in patients with type 2 diabetes mellitus. This beneficial effect is independent of its hypoglycemic effect and weight loss. The optimal intervention should be targeted to cognitive decline in the early stages of dementia.

Registration

URL: https://www.ClinicalTrials.gov; Unique identifier: NCT03707171.

Canonical transient receptor potential channels and their modulators: biology, pharmacology and therapeutic potentials

Canonical transient receptor potential channels (TRPCs) are nonselective, high calcium permeability cationic channels. The TRPCs family includes TRPC1, TRPC2, TRPC3, TRPC4, TRPC5, TRPC6, and TRPC7. These channels are widely expressed in the cardiovascular and nervous systems and exist in many other human tissues and cell types, playing several crucial roles in the human physiological and pathological processes. Hence, the emergence of TRPCs modulators can help investigate these channels’ applications in health and disease. It is worth noting that the TRPCs subfamilies have structural and functional similarities, which presents a significant difficulty in screening and discovering of TRPCs modulators. In the past few years, only a limited number of selective modulators of TRPCs were detected; thus, additional research on more potent and more selective TRPCs modulators is needed. The present review focuses on the striking desired therapeutic effects of TRPCs modulators, which provides intel on the structural modification of TRPCs modulators and further pharmacological research. Importantly, TRPCs modulators can significantly facilitate future studies of TRPCs and TRPCs related diseases.

Novel Mechanistic Insights and Potential Therapeutic Impact of TRPC6 in Neurovascular Coupling and Ischemic Stroke

Ischemic stroke is one of the most disabling diseases and a leading cause of death globally. Despite advances in medical care, the global burden of stroke continues to grow, as no effective treatments to limit or reverse ischemic injury to the brain are available. However, recent preclinical findings have revealed the potential role of transient receptor potential cation 6 (TRPC6) channels as endogenous protectors of neuronal tissue. Activating TRPC6 in various cerebral ischemia models has been found to prevent neuronal death, whereas blocking TRPC6 enhances sensitivity to ischemia. Evidence has shown that Ca2+ influx through TRPC6 activates the cAMP (adenosine 3',5'-cyclic monophosphate) response element-binding protein (CREB), an important transcription factor linked to neuronal survival. Additionally, TRPC6 activation may counter excitotoxic damage resulting from glutamate release by attenuating the activity of N-methyl-d-aspartate (NMDA) receptors of neurons by posttranslational means. Unresolved though, are the roles of TRPC6 channels in non-neuronal cells, such as astrocytes and endothelial cells. Moreover, TRPC6 channels may have detrimental effects on the blood-brain barrier, although their exact role in neurovascular coupling requires further investigation. This review discusses evidence-based cell-specific aspects of TRPC6 in the brain to assess the potential targets for ischemic stroke management.