Exogenous IGF-1 improves tau pathology and neuronal pyroptosis in high-fat diet mice with cognitive dysfunction

Exercise-mediated muscle-hypothalamus crosstalk: Improvement for cognitive dysfunction caused by disrupted circadian rhythm

In contemporary societal evolution, the increasing disruption of the natural sleep-wake cycle, attributable to factors such as shift work and overexposure to artificial light, has been paralleled by a marked escalation in the incidence of cognitive impairments and the prevalence of neurodegenerative diseases. Current management strategies for cognitive impairments include pharmacological and non-pharmacological interventions. Pharmacological interventions for cognitive impairments typically involve medications to manage cognitive symptoms and improve neurological functions. However, these drugs show limited long-term efficacy in slowing disease progression and may cause side effects. Given the widespread occurrence of cognitive dysfunction, it is crucial to develop accessible non-pharmacological interventions. Physical activity and exercise have emerged as pivotal lifestyle determinants known to exert a modulatory effect on the risk profile for cognitive dysfunction caused by disrupted circadian rhythms. The skeletal muscle, a dynamic tissue, undergoes a profound morphological and metabolic reconfiguration in response to physical exertion, along with the secretion of myokines. Additionally, the hypothalamus, particularly the ventromedial nuclei, arcuate nuclei, and the suprachiasmatic nucleus, have crucial functions in regulating physical activity, influencing energy metabolism, and managing circadian cycles. Nevertheless, the communication between the hypothalamus and skeletal muscle during exercise is not fully understood. This narrative review integrates current knowledge on the interaction between the hypothalamus and skeletal muscle during exercise, emphasizing its neuroendocrine effects and potential therapeutic implications for alleviating cognitive dysfunction associated with disrupted circadian rhythms.

IGF-1 Provides Protective Role in Arteriosclerotic Cerebral Small Vessel Disease

BACKGROUND

Hypertension and advanced age are risk factors for arteriosclerotic cerebral small vessel disease (cSVD), a common cause of vascular dementia in elderly individuals. Circulating IGF-1 (insulin-like growth factor 1) levels decrease with age and are linked to age-related cognitive impairment. This study assessed the relationship between serum IGF-1 and arteriosclerotic cSVD severity in patients and the therapeutic effects and underlying mechanisms of exogenous IGF-1 supplementation in a cSVD rat model.

METHODS

Serum and MR images were collected from healthy subjects (n=26) and patients with arteriosclerotic cSVD (n=86). Stroke-prone renovascular hypertensive rats were used as cSVD animal models and subjected to the Morris water maze test, magnetic resonance imaging, immunohistochemistry, and biochemical analysis. hCMEC/D3 cells were utilized to validate the underlying mechanisms in vitro.

RESULTS

Serum IGF-1 concentration was significantly reduced in patients and rats with arteriosclerotic cSVD. Lower serum IGF-1 was associated with an increased cSVD burden and cognitive impairment. Compared with cSVD rats, IGF-1-treated rats had lighter white matter lesions, greater global cerebral blood flow, greater cerebrovascular density, less blood-brain barrier leakage, and better cognitive function. In vitro, IGF-1 administration promoted endothelial proliferation, migration, tube formation, and barrier function. Mechanistically, IGF-1 exerts neuroprotective effects by activating the IGF-1R (IGF-1 receptor)/Wnt7b/β-catenin pathway in vivo and in vitro.

CONCLUSIONS

Low serum IGF-1 was associated with greater arteriosclerotic cSVD severity. IGF-1 treatment improved cerebral perfusion, blood-brain barrier integrity, and cognitive function in cSVD rats by activating the IGF-1R/Wnt7b/β-catenin pathway, suggesting a potential therapeutic strategy for patients with arteriosclerotic cSVD, particularly those with low IGF-1 levels.

IGF1 enhances memory function in obese mice and stabilizes the neural structure under insulin resistance via AKT-GSK3β-BDNF signaling

Obesity is a prevalent metabolic disorder linked to insulin resistance, hyperglycemia, increased adiposity, chronic inflammation, and cognitive dysfunction. Recent research has focused on developing therapeutic strategies to mitigate cognitive impairment associated with obesity. Insulin growth factor-1 (IGF1) deficiency is linked to insulin resistance, glucose intolerance, and the progression of obesity-related central nervous system (CNS) disorders. In this study, we investigated the neuroprotective effects of IGF1 in two obesity models: diet-induced obesity (high-fat diet mice) and genetic obesity (ob/ob mice which is genetically deficient in leptin), and in vitro Neuro2A neuronal cells and primary cortical neurons under insulin resistance conditions. We performed RNA sequencing analysis using the cortex of high-fat diet mice injected with IGF1. Also, we detected cytokine levels in blood of high-fat diet mice injected with IGF1. In addition, we conducted the Barnes maze test as a spatial memory function test and open field test as an anxiety behavior test in ob/ob mice. We measured the levels of proteins and mRNAs related to insulin signaling, including synaptic density proteins in brain cortex of ob/ob mice. Our results showed that IGF1 injection enhanced spatial memory function and synaptic plasticity in obese mice. Furthermore, in vitro data demonstrated that IGF1 treated neurons revealed enhanced neural complexity and improved neurite outgrowth under insulin resistance condition through the AKT-GSK3β-BDNF pathway related to antidepressant, cognitive function and anti-apoptotic mechanisms. Therefore, our results provided that IGF1 have potential to alleviate cognitive impairment by promoting synaptic plasticity and neural complexity in the obese brain.

Forkhead box P1 transcriptionally activates IGF-1 to lighten ox-LDL-induced endothelial cellular senescence by inactivating NLRP3 inflammasome

Endothelial cell (EC) senescence is a major contributor in atherosclerosis (AS) development. Herein, the role of forkhead box P transcription factor 1 (FOXP1) and insulin-like growth factor (IGF)-1 in regulating EC senescence during AS progression was investigated. The mRNA and protein expressions were assessed using qRT-PCR and western blot. IL-1β and IL-18 secretion levels were analyzed by ELISA. Cell viability and pyroptosis were determined by MTT assay and flow cytometry, respectively. SA β-Gal staining was used to measure cell senescence. Tube formation assay was adopted to detect the angiogenesis ability. Dual-luciferase reporter and ChIP assays were used to investigate the relationship between FOXP1 and IGF‑1. ox-LDL stimulation significantly reduced FOXP1 and IGF-1 expression levels in human aortic endothelial cells (HAECs). FOXP1 or IGF-1 overexpression both mitigated ox-LDL-induced cellular senescence and NLRP3 activation in HAECs. It was subsequently revealed that FOXB1 transcriptionally activated IGF-1 expression in HAECs by binding to IGF-1 promoter. Rescue experiments demonstrated that IGF-1 silencing abolished the inhibitory impact of FOXP1 overexpression on ox-LDL-induced cellular senescence and NLRP3 activation in HAECs. FOXP1 transcriptionally activated IGF-1 to lighten ox-LDL-induced endothelial cellular senescence by inactivating NLRP3 inflammasome.

Human umbilical cord mesenchymal stem cell-derived extracellular vesicles harboring IGF-1 improve ovarian function of mice with premature ovarian insufficiency through the Nrf2/HO-1 pathway

OBJECTIVE

Premature ovarian insufficiency (POI) is a disease with medical, psychological and reproductive implications, but its common therapies have limited efficacy and a likelihood of complications. This study delves into the therapeutic role of human umbilical cord mesenchymal stem cell-derived extracellular vesicles (hUC-MSCs-EVs) in POI mice through the insulin-like growth factor 1 (IGF-1)/nuclear factor E2 related factor 2 (Nrf2)/heme oxygenase-1 (HO-1)/autophagy pathway.

METHODS

hUC-MSCs were transfected with lentiviral short hairpin RNA of IGF-1 before EV extraction. Cyclophosphamide (CTX)-induced POI mouse models were administrated with hUC-MSCs-EVs. Mouse ovarian granulosa cells (GCs) were induced with CTX, then treated with hUC-MSCs-EVs and ML385. Ovarian histopathological changes were observed, changes in follicle number at all levels were counted and serum sex hormones were evaluated, as well as LC3II/I and Beclin-1 expression. GCs were subject to detection of proliferation, deaths, oxidative stress, and Nrf2 nuclear translocation.

RESULTS

After CTX exposure, mice showed thinner GCs layer in the ovary, reduced number of GCs and follicles at all levels, disturbed serum sex hormones, enhanced oxidative stress and autophagy, and downregulated ovarian IGF-1; whereas, hUC-MSCs-EVs upregulated IGF-1 to improve the ovarian function. hUC-MSCs-EVs carrying IGF-1 activated Nrf2/HO-1 signaling to inhibit CTX-induced excessive autophagy of GCs, but this ameliorative effect was partially weakened by inhibiting Nrf2/HO-1 signaling. hUC-MSCs-EVs inhibited excessive autophagy of GCs and improved ovarian function of CTX-induced mice through IGF-1/Nrf2/HO-1 pathway.

CONCLUSION

hUC-MSCs-EVs activate the Nrf2/HO-1 signaling by carrying IGF-1, which in turn inhibits excessive autophagy and damage of GCs, thus improving ovarian function in POI mice.

Resveratrol protects against a high-fat diet-induced neuroinflammation by suppressing mitochondrial fission via targeting SIRT1/PGC-1α

Various health issues have emerged due to consuming high-fat diets (HFD), particularly the detrimental impact they have on mitochondrial dynamics and subsequet cognition functions. Specially, mitochondrial fission can serve as an upstream signal in the regulation of cortical inflammation and neural pyroptosis. Our study was designed to verify the existence of neuroinflammation in the pathogenesis of HFD-induced cognitive dysfunction and demonstrated that resveratrol (RSV) attenuated neural deficits via regulation of cortical mitochondrial fission. A total of 50 male Sprague Dawley rats were randomly divided into five groups: control (Cont, 26 weeks on normal rodent diet); high-fat diet (HFD); dietary adjustments (HFD + ND); resveratrol intervention (HFD + R); joint intervention (HFD + ND + R) for 26 weeks. The spatial learning and memory function, spine density, NLRP3 inflammasome associated protein, mRNA and protein expression involved in mitochondrial dynamics and SIRT1/PGC-1α signaling pathway in brain were measured. Furthermore, reactive oxygen species (ROS) accumulation and resultant mitochondrial membrane potential (MMP) alteration in PC12 cells exposed to palmitic acid (PA) or Drp1 inhibitor (Mdivi-1) were detected to reflect mitochondrial function. The findings suggested that prolonged treatment of RSV improved cognitive deficits and neuronal damage induced by HFD, potentially attributed to activation of the SIRT1/PGC-1α axis. We further indicated that the activation of the NLRP3 inflammasome in PA (200 μM) treated PC12 cells could be inhibited by Mdivi-1. More importantly, Mdivi-1 (10 μM) reduced intracellular ROS levels and enhanced MMP by reversing Drp1-mediated aberrant mitochondrial fission. To summarize, those results clearly indicated that a HFD inhibited the SIRT1/PGC-1α pathway, which contributed to an imbalance in mitochondrial dynamics and the onset of NLRP3-mediated pyroptosis. This effect was mitigated by the RSV possibly through triggering the SIRT1/PGC-1α axis, prevented aberrant mitochondrial fission and thus inhibited the activation of the NLRP3 inflammatory pathway.

High-fat diet induces cognitive impairment through repression of SIRT1/AMPK-mediated autophagy

AIMS

Recent evidence suggests an association between a high-fat diet (HFD) and cognitive decline. HFD may reduce synaptic plasticity and cause tau hyperphosphorylation, but the mechanisms involved remain unclear. The purpose of this study was to explore whether Sirtuin1 (SIRT1)/AMP-activated protein kinase (AMPK) pathway was involved in this pathogenic effect in the HFD exposed mice.

METHODS

C57BL/6 mice at 12 months of age were fed a standard (9% kcal fat) or high-fat (60% kcal fat) diet for 22 weeks, and Neuro-2a (N2a) cells were treated with normal culture medium or a palmitic acid (PA) medium (100uM) for 40 h. After that, cognitive function was tested by Morris water maze (MWM). The levels of proteins involved in SIRT1/AMPK pathway and autophagy were measured using western blotting and immunofluorescence. We also assessed the phosphorylation of tau protein and synapse.

RESULTS

The mice presented impaired learning and memory abilities. We further found decreased levels of synaptophysin (Syn) and brain-derived neurotrophic factor (BDNF), increased tau46 and phosphorylated tau protein, and damaged neurons in mice after HFD or in N2a cells treated with PA medium. Moreover, HFD can also reduce the expression of SIRT1, inhibit AMPK phosphorylation, and block autophagic flow in both mice and cells. After treating the cells with the SIRT1 agonist SRT1720, SIRT1/AMPK pathway and autophagy-related proteins were partially reversed and the number of PA-induced positive cells was alleviated in senescence-associated β-galactosidase (SA-β-gal) staining.

CONCLUSIONS

HFD may inhibit the expression of SIRT1/AMPK pathway and disrupt autophagy flux, and result in tau hyperphosphorylation and synaptic dysfunction during aging, which ultimately lead to cognitive decline.

Insulin-like growth factor 1 in heat stress-induced neuroinflammation: novel perspective about the neuroprotective role of chromium

Heat stress (HS) can cause a series of stress responses, resulting in numerous negative effects on the body, such as the diminished food intake, carcass quality and reproductive capacity. In addition to the negative effects on the peripheral system, HS leads to central nervous system (CNS) disorders given its toll on neuroinflammation. This neuroinflammatory process is mainly mediated by microglia and astrocytes, which are involved in the activation of glial cells and the secretion of cytokines. While the regulation of inflammatory signaling has a close relationship with the expression of heat shock protein 70 (Hsp70), HS-induced neuroinflammation is closely related to the activation of the TLR4/NF-κB pathway. Moreover, oxidative stress and endoplasmic reticulum (ER) stress are key players in the development of neuroinflammation. Chromium (Cr) has been widely shown to have neuroprotective effects in both humans and animals, despite the lack of mechanistic evidence. Evidence has shown that Cr supplementation can increase the levels of insulin-like growth factor 1 (IGF-1), a major neurotrophic factor with anti-inflammatory and antioxidant effects. This review highlights recent advances in the attenuating effects and potential mechanisms of Cr-mediated IGF-1 actions on HS-induced neuroinflammation, providing presently existing evidence supporting the neuroprotective role of Cr.

The role of pyroptosis in cognitive impairment

Cognitive impairment is a major global disease, manifests as a decline in cognitive functioning and endangers the health of the population worldwide. The incidence of cognitive impairment has increased rapidly with an increasingly aging population. Although the mechanisms of cognitive impairment have partly been elucidated with the development of molecular biological technology, treatment methods are very limited. As a unique form of programmed cell death, pyroptosis is highly pro-inflammatory and is closely associated with the incidence and progression of cognitive impairment. In this review, we discuss the molecular mechanisms of pyroptosis briefly and the research progress on the relationship between pyroptosis and cognitive impairment and its potential therapeutic values, to provide a reference for research in the field of cognitive impairment.

Friend or foe: role of pathological tau in neuronal death

Neuronal death is one of the most common pathological hallmarks of diverse neurological diseases, which manifest varying degrees of cognitive or motor dysfunction. Neuronal death can be classified into multiple forms with complicated and unique regulatory signaling pathways. Tau is a key microtubule-associated protein that is predominantly expressed in neurons to stabilize microtubules under physiological conditions. In contrast, pathological tau always detaches from microtubules and is implicated in a series of neurological disorders that are characterized by irreversible neuronal death, such as necrosis, apoptosis, necroptosis, pyroptosis, ferroptosis, autophagy-dependent neuronal death and phagocytosis by microglia. However, recent studies have also revealed that pathological tau can facilitate neuron escape from acute apoptosis, delay necroptosis through its action on granulovacuolar degeneration bodies (GVBs), and facilitate iron export from neurons to block ferroptosis. In this review, we briefly describe the current understanding of how pathological tau exerts dual effects on neuronal death by acting as a double-edged sword in different neurological diseases. We propose that elucidating the mechanism by which pathological tau affects neuronal death is critical for exploring novel and precise therapeutic strategies for neurological disorders.

sTREM2 and GFAP Mediated the Association of IGF-1 Signaling Biomarkers with Alzheimer's Disease Pathology

Defects in insulin-like growth factor 1 (IGF-1) signaling is a key contributor to Alzheimer's disease (AD). However, the mechanism of how IGF-1 signaling relates to AD remained unclear. Here, we investigated the association of IGF-1 signaling associated biomarkers with AD pathology, sTREM2, and GFAP. Finally, insulin-like growth factor binding protein 2 (IGFBP-2) was associated with AD pathology, and the association was partly medicated by sTREM2 (Aβ 42, β= 0.794, p = 0.016; T-tau, β= 0.291, p <  0.001; P-tau181, β= 0.031, p <  0.001) and GFAP (T-tau, β= 0.427, p <  0.001; P-tau181, β= 0.044, p <  0.001). It suggested that sTREM2 and GFAP mediated the relationship between IGF-1 signaling and AD pathology.

Research Progress of Pyroptosis in Alzheimer's Disease

Alzheimer's disease (AD) is a disease characterized by insidious and progressive neurodegeneration, with clinical syndromes of memory and visuospatial skills damage. The pathogenic mechanism of AD is complex in which neural inflammation and neuron death play important roles. Pyroptosis, an inflammatory programmed cell death, has been reported to be involved in neuron death. Pyroptosis is executed by the protein family of gasdermins which punch pores on plasma membrane when activated by the upstream signals including the activation of NLRP3 and caspases, and subsequently triggers the inflammatory cascades featured by the release of interleukin (IL) -1β and IL-18. Herein, we summarized the current research on the roles of neuron pyroptosis in AD, aiming to provide a comprehensive view of the molecular mechanisms underlying AD pathogenesis and potential therapeutic targets for AD.

Late-Life Obesity Associated with Tau Pathology in Cognitively Normal Individuals: The CABLE Study

BACKGROUND

Existed evidence suggests that midlife obesity increases the risk of Alzheimer's disease (AD), while there is an inverse association between AD and obesity in late life. However, the underlying metabolic changes of AD pathological proteins attributed to obesity in two life stages were not clear.

OBJECTIVE

To investigate the associations of obesity types and obesity indices with AD biomarkers in cerebrospinal fluid (CSF) in different life stages.

METHODS

We recruited 1,051 cognitively normal individuals (61.94±10.29 years, 59.66%male) from the Chinese Alzheimer's Biomarker and LifestylE (CABLE) study with CSF detections for amyloid-β 42 (Aβ 42), total-tau (T-tau), and phosphorylated tau (P-tau). We utilized body mass index, waist circumference, waist-to-height ratio, and metabolic risk factors to determine human obesity types. Multiple linear models and interaction analyses were run to assess the impacts of obesity on AD biomarkers.

RESULTS

The metabolically unhealthy obesity or healthy obesity might exert a reduced tau pathology burden (p <  0.05). Individuals with overweight, general obesity, and central obesity presented lower levels of tau-related proteins in CSF than normal controls (p <  0.05). Specially, for late-life individuals, higher levels of obesity indices were associated with a lower load of tau pathology as measured by CSF T-tau and T-tau/Aβ 42 (p <  0.05). No similar significant associations were observed in midlife.

CONCLUSION

Collectively, late-life general and central obesity seems to be associated with the reduced load of tau pathology, which further consolidates the favorable influence of obesity in specific life courses for AD prevention.