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Metformin activated autophagy in SH-SY5Y cells. A) Treatment of metformin for 24 h increased microtubule-associated protein light chain II (LC3-II) levels. However, treatment of 3MA (5 mM, 24 h) alone or 1 h of pretreatment of 3MA (5 mM) before metformin incubation (10 mM, 24 h) did not show any increase in LC3-II levels. B) Electron microscopic (EM) analysis of autophasic vesicles in vehicle or metformin (10 mM, 24 h) treated SH-SY5Y cells (n = 5/group). Metformin treated group (middle panel) shows more autophagosomes compared to those in vehicle treated group (left panel). Two squares represented as a, b in the middle panel are magnified and shown in the right panel to confirm accumulated autophagosomes in metformin treated group. Scale bars represent 2 m and 1 m in the middle and right panel, respectively.
Source publication
The evidence of strong pathological associations between type 2 diabetes and Alzheimer's disease (AD) has increased in recent years. Contrary to suggestions that anti-diabetes drugs may have potential for treating AD, we demonstrate here that the insulin sensitizing anti-diabetes drug metformin (Glucophage®) increased the generation of amyloid-β (A...
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Methods
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Methods
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Citations
... To induce IR, cells were incubated with 100 nM insulin (INS) for 24 h following 5 days of differentiation with RA. This method of high-insulin-induced IR has previously been demonstrated in SH-SY5Y cells and other cell types (Amine et al., 2021;Mayer & Belsham, 2010;Tian et al., 2019;Vlavcheski et al., 2020). 2 mM Metformin was used to induce the phosphorylation of AMPK T172 (Benito-Cuesta et al., 2021;Lu et al., 2016;Son et al., 2016). A Trypan blue exclusion assay was conducted for both HI and MET treatments over 24 h to determine cell viability with these treatments as described by Strober (2015). ...
... To establish the effective dose of MET, we exposed cells to either 2 mM or 5 mM MET, doses used in previous studies (Benito-Cuesta et al., 2021;Lu et al., 2016;Son et al., 2016), for 24 h. Cells exposed to 2 mM or 5 mM MET showed no reduction in viability compared to the vehicle-treated control cells, as determined by the Trypan Blue Exclusion assay (Figure 1e; one-way ANOVA p = 0.9382) and both doses showed equivalent increases in AMPK T172 phosphorylation status (Figure 1f; one-way ANOVA p = 0.0142, post hoc ctl-2mM p = 0.0153, post hoc ctl-5mM p = 0.007, post hoc 2mM-5mM p = 0.2529). ...
Insulin resistance (IR) is associated with reductions in neuronal proteins often observed with Alzheimer's disease (AD), however, the mechanisms through which IR promotes neurodegeneration/AD pathogenesis are poorly understood. Metformin (MET), a potent activator of the metabolic regulator AMPK is used to treat IR but its effectiveness for AD is unclear. We have previously shown that chronic AMPK activation impairs neurite growth and protein synthesis in SH‐SY5Y neurons, however, AMPK activation in IR was not explored. Therefore, we examined the effects of MET‐driven AMPK activation with and without IR. Retinoic acid‐differentiated SH‐SY5Y neurons were treated with: (1) Ctl: 24 h vehicle followed by 24 h Vehicle; (2) HI: 100 nM insulin (24 h HI followed by 24 h HI); or (3) MET: 24 h vehicle followed by 24 h 2 mM metformin; (4) HI/MET: 24 h 100 nM insulin followed by 24 h 100 nM INS+2 mM MET. INS and INS/MET groups saw impairments in markers of insulin signaling (Akt S473, mTOR S2448, p70s6k T389, and IRS‐1S636) demonstrating IR was not recovered with MET treatment. All treatment groups showed reductions in neuronal markers (post‐synaptic marker HOMER1 mRNA content and synapse marker synaptophysin protein content). INS and MET treatments showed a reduction in the content of the mature neuronal marker NeuN that was prevented by INS/MET. Similarly, increases in cell size/area, neurite length/area observed with INS and MET, were prevented with INS/MET. These findings indicate that IR and MET impair neuronal markers through distinct pathways and suggest that MET is ineffective in treating IR‐driven impairments in neurons.
... Chronic hyperglycemia is a hallmark of diabetes and is closely associated with complications in various tissues and organs, such as the kidneys, nerves, skin, and eyes. It has been reported that the concentration of glucose in diabetic patients' aqueous humor increases with their blood glucose levels [24]. In this study, D-glucose was used to simulate the HG environment in vitro. ...
Purpose
The aim of this study is to explore whether metformin (MET) protects the human lens epithelial cells (HLECs) from high glucose-induced senescence and to identify the underlying mechanisms.
Methods
A cellular senescence model was established by treating HLE-B3 cells with D-glucose and then intervened with MET. Concentrations of high glucose (HG) and MET were detected using CCK-8 and western blot. qRT-PCR, western blot, and senescence-associated β-galactosidase (SA-β-gal) were performed to verify the protective effect of MET on senescent HLE-B3 cells. Additionally, western blot and qRT-PCR were conducted to detect the effects of MET on autophagy-related markers p62 and LC3, as well as SIRT1.
Results
In vitro, we observed apparent senescence in human lens epithelial cells (HLECs) under high glucose conditions. This was characterized by increased senescence-associated genes p21 and p53. However, the addition of MET significantly reduced the occurrence of HLECs senescence. We also observed that high glucose inhibited both autophagy and SIRT1, which could be restored by MET. Moreover, we verified that the anti-senescence effect of MET was mediated by SIRT1 using SIRT1 activators and inhibitors.
Conclusion
We have demonstrated that autophagy and SIRT1 activity are inhibited in HLE-B3 cells using the HG induced senescence model. Furthermore, our results showed that MET can delay senescence by activating SIRT1 and autophagy. These findings suggest that MET may be a promising candidate for alleviating cataract development and provide a direction for further investigation into the underlying molecular mechanisms.
... Metformin also stimulates caspase-3 to increase the cleavage of Tau proteins and disrupts synaptic communication (Barini et al. 2016). Metformin-induced accumulation of autophagosomes leads to increased γ-secretase activity and Aβ generation (Son et al. 2016). Although most of the data on the use of metformin in dementia / AD with or without T2DM are promising, it should be noted that the effect of metformin might depend on complex underlying pathological processes. ...
Alzheimer’s disease (AD) and Type 2 diabetes mellitus (T2DM) are two of the most common age-related diseases. There is accumulating evidence of an overlap in the pathophysiological mechanisms of these two diseases. Studies have demonstrated insulin pathway alternation may interact with amyloid-β protein deposition and tau protein phosphorylation, two essential factors in AD. So attention to the use of anti-diabetic drugs in AD treatment has increased in recent years. In vitro, in vivo, and clinical studies have evaluated possible neuroprotective effects of anti-diabetic different medicines in AD, with some promising results. Here we review the evidence on the therapeutic potential of insulin, metformin, Glucagon-like peptide-1 receptor agonist (GLP1R), thiazolidinediones (TZDs), Dipeptidyl Peptidase IV (DPP IV) Inhibitors, Sulfonylureas, Sodium-glucose Cotransporter-2 (SGLT2) Inhibitors, Alpha-glucosidase inhibitors, and Amylin analog against AD. Given that many questions remain unanswered, further studies are required to confirm the positive effects of anti-diabetic drugs in AD treatment. So to date, no particular anti-diabetic drugs can be recommended to treat AD.
... The long-held notion that AMPK promotes autophagy has led to numerous studies examining the potential therapeutic applications of AMPK-activating agents, such as metformin, for various diseases. However, conflicting results have emerged, with some studies showing adverse effects in Alzheimer's disease patients and mouse models [50][51][52][53] , while others demonstrating clear benefits in ameliorating diabetesrelated complications. These inconsistent outcomes may be related to the dual role of AMPK in regulating autophagy. ...
Autophagy maintains cellular homeostasis during low energy states. According to the current understanding, glucose-depleted cells induce autophagy through AMPK, the primary energy-sensing kinase, to acquire energy for survival. However, contrary to the prevailing concept, our study demonstrates that AMPK inhibits ULK1, the kinase responsible for autophagy initiation, thereby suppressing autophagy. We found that glucose starvation suppresses amino acid starvation-induced stimulation of ULK1-Atg14-Vps34 signaling via AMPK activation. During an energy crisis caused by mitochondrial dysfunction, the LKB1-AMPK axis inhibits ULK1 activation and autophagy induction, even under amino acid starvation. Despite its inhibitory effect, AMPK protects the ULK1-associated autophagy machinery from caspase-mediated degradation during energy deficiency, preserving the cellular ability to initiate autophagy and restore homeostasis once the stress subsides. Our findings reveal that dual functions of AMPK, restraining abrupt induction of autophagy upon energy shortage while preserving essential autophagy components, are crucial to maintain cellular homeostasis and survival during energy stress.
... In contrast, in another study, metformin was associated with decreased cognitive performance and increased expression of depressive-like behavior [260]. Thus, the data regarding the effects of metformin on cognitive activities are inconsistent [261,262]. ...
... Metformin also enhanced spatial memory in DM mice by decreasing the p-Tau and β-amyloid plaque load in the hippocampus with reduced neuronal cell death [257]. In contrast, other studies have indicated that metformin activated β-amyloid generation by β-and γ-secretases and autophagy activation [261]. Metformin induced abnormal accumulation of autophagosomes by inhibiting mTOR, thus inducing accumulation of β-amyloid [261]. ...
... In contrast, other studies have indicated that metformin activated β-amyloid generation by β-and γ-secretases and autophagy activation [261]. Metformin induced abnormal accumulation of autophagosomes by inhibiting mTOR, thus inducing accumulation of β-amyloid [261]. In another rodent study, metformin activated β-secretase and β-amyloid precursor protein (APP), which led to the accumulation of β-amyloid (Aβ) in the cortex [263]. ...
Diabetes mellitus (DM) is a metabolic disease that activates several molecular pathways involved in neurodegenerative disorders. Metformin, an anti-hyperglycemic drug used for treating DM, has the potential to exert a significant neuroprotective role against the detrimental effects of DM. This review discusses recent clinical and laboratory studies investigating the neuroprotective properties of metformin against DM-induced neurodegeneration and the roles of various molecular pathways, including mitochondrial dysfunction, oxidative stress, inflammation, apoptosis, and its related cascades. A literature search was conducted from January 2000 to December 2022 using multiple databases including Web of Science, Wiley, Springer, PubMed, Elsevier Science Direct, Google Scholar, the Core Collection, Scopus, and the Cochrane Library to collect and evaluate peer-reviewed literature regarding the neuroprotective role of metformin against DM-induced neurodegenerative events. The literature search supports the conclusion that metformin is neuroprotective against DM-induced neuronal cell degeneration in both peripheral and central nervous systems, and this effect is likely mediated via modulation of oxidative stress, inflammation, and cell death pathways.
... Moreover, studies report that inhibiting the mTOR pathway could significantly reduce Aβ-induced microglial toxicity [127]. However, Aβ plaques were found to be increased in 5 × FAD mouse brains after treatment with metformin, a commonly used mTOR inhibitor [167]. Altogether, strategies aimed at modulating microglial activation seem encouraging; however, the efficacy in humans largely remains to be evaluated. ...
Alzheimer’s disease (AD) is the most common progressive and irreversible neurodegeneration characterized by the impairment of memory and cognition. Despite years of studies, no effective treatment and prevention strategies are available yet. Identifying new AD therapeutic targets is crucial for better elucidating the pathogenesis and establishing a valid treatment of AD. Growing evidence suggests that microglia play a critical role in AD. Microglia are resident macrophages in the central nervous system (CNS), and their core properties supporting main biological functions include surveillance, phagocytosis, and the release of soluble factors. Activated microglia not only directly mediate the central immune response, but also participate in the pathological changes of AD, including amyloid-beta (Aβ) aggregation, tau protein phosphorylation, synaptic dissection, neuron loss, memory function decline, etc. Based on these recent findings, we provide a new framework to summarize the role of microglia in AD memory impairment. This evidence suggests that microglia have the potential to become new targets for AD therapy.
... In addition, studies indicated that metformin ameliorated arthritis through inhibition of osteoclastogenesis by suppressing the STAT3 and AMPK pathway and the expression of proinflammatory cytokines [18,19]. However, current studies showed that metformin, as an autophagy modulator, is widely involved in various tissues protection, including the heart [20], kidney [21], and brain [22], but no such evidence has been proven yet for bone. Therefore, we hypothesized that metformin could inhibit osteoclast formation and activation by regulating autophagy during osteoclastogenesis in ovariectomized mice. ...
Background
Postmenopausal bone loss, mainly caused by excessive bone resorption mediated by osteoclasts, has become a global public health burden. Metformin, a hypoglycemic drug, has been reported to have beneficial effects on maintaining bone health. However, the role and underlying mechanism of metformin in ovariectomized (OVX)-induced bone loss is still vague.
Results
In this study, we demonstrated for the first time that metformin administration alleviated bone loss in postmenopausal women and ovariectomized mice, based on reduced bone resorption markers, increased bone mineral density (BMD) and improvement of bone microstructure. Then, osteoclast precursors administered metformin in vitro and in vivo were collected to examine the differentiation potential and autophagical level. The mechanism was investigated by infection with lentivirus-mediated BNIP3 or E2F1 overexpression. We observed a dramatical inhibition of autophagosome synthesis and osteoclast formation and activity. Treatment with RAPA, an autophagy activator, abrogated the metformin-mediated autophagy downregulation and inhibition of osteoclastogenesis. Additionally, overexpression of E2F1 demonstrated that reduction of OVX-upregulated autophagy mediated by metformin was E2F1 dependent. Mechanistically, metformin-mediated downregulation of E2F1 in ovariectomized mice could downregulate BECN1 and BNIP3 levels, which subsequently perturbed the binding of BECN1 to BCL2. Furthermore, the disconnect between BECN1 and BCL2 was shown by BNIP3 overexpression.
Conclusion
In summary, we demonstrated the effect and underlying mechanism of metformin on OVX-induced bone loss, which could be, at least in part, ascribed to its role in downregulating autophagy during osteoclastogenesis via E2F1-dependent BECN1 and BCL2 downregulation, suggesting that metformin or E2F1 inhibitor is a potential agent against postmenopausal bone loss.
... Similarly, positive effects of lithium on behaviours of the AD patients have been demonstrated in recent studies [139][140] . Although latrepirdine had been found to alleviate neuropathic Aβ via restoring autophagy impairment in vivo [141] , clinical trials showed that this drug did not improve cognitive dysfunction, and two ongoing studies were terminated (NCT00912288 and NCT00838110). These differences in efficacy between animal models and AD patients may infer that latrepirdine has other functions unrelated to autophagy. ...
Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder. The major pathological changes in AD progression are the generation and accumulation of amyloid-beta (Aβ) peptides as well as the presence of abnormally hyperphosphorylated tau proteins in the brain. Autophagy is a conserved degradation pathway that eliminates abnormal protein aggregates and damaged organelles. Previous studies have suggested that autophagy plays a key role in the production and clearance of Aβ peptides to maintain a steady-state of Aβ peptides levels. However, a growing body of evidence suggests that autophagy is significantly impaired in the pathogenesis of AD, especially in Aβ metabolism. Therefore, this article reviews the latest studies concerning the mechanisms of autophagy, the metabolism of Aβ peptides, and the defective autophagy in the production and clearance of Aβ peptides. Here, we also summarize the established and new strategies for targeting autophagy in vivo and through clinical AD trials to identify gaps in our knowledge and to generate further questions.
... Reducing mTOR levels and signaling by removing one copy of the mTOR gene led to increased induction of autophagy and improvement in AD-like changes, including cognition and pathological defects (Caccamo et al., 2014). Therefore, the restoration or promotion of autophagy function has been proposed as a promising method for delaying age-related diseases, including AD. Potential strategies included pharmacological treatments using mTORC1 inhibitors (rapamycin (Kaeberlein & Galvan, 2019), rapamycin analogs (Fanoudi et al., 2018), memantine (Son et al., 2016), latrepirdine (Steele & Gandy, 2013), and resveratrol (Kou & Chen, 2017)), activating AMPK (resveratrol (Kou & Chen, 2017), metformin (Piskovatska et al., 2020), RSvA314 (vingtdeux et al., 2011), and RSvA405 (Sarkar et al., 2005)), inhibiting inositol monophosphatase (lithium and (Sarkar et al., 2005)), other pathways (GTM-1, carbamazepine), and non-drug methods (Escobar et al., 2019) such as caloric restriction, physical exercise, etc. Besides aiming signal pathways for autophagy, an acidification disorder was observed in lysosomes of senescent cells. ...
Age is the strongest risk factor for Alzheimer’s disease (AD). In recent years, the relationship between aging and AD has been widely studied, with anti-aging therapeutics as the treatment for AD being one of the mainstream research directions. Therapeutics targeting senescent cells have shown improvement in AD symptoms and cerebral pathological changes, suggesting that anti-aging strategies may be a promising alternative for AD treatment. Nanoparticles represent an excellent approach for efficiently crossing the blood-brain barrier (BBB) to achieve better curative function and fewer side effects. Thereby, nanoparticles-based anti-aging treatment may exert potent anti-AD therapeutic efficacy. This review discusses the relationship between aging and AD and the application and prospect of anti-aging strategies and nanoparticle-based therapeutics in treating AD.
... Metformin (Met) is a common hypoglycemic drug that can reduce oxidative stress in diabetic nephropathy by activating autophagy (Ren et al., 2020). In addition, it can also exert a protective effect in the brain (Son et al., 2016) and heart (Xie et al., 2011) by activating autophagy. Autophagy is a dynamic process, during which the damaged proteins or organelles are wrapped by autophagy vesicles in a bilayer membrane structure to form autophagosomes, which then fuse with lysosomes to generate autolysosomes, resulting in the degradation of the wrapped contents (Klionsky et al., 2012). ...
Intervertebral disc degeneration (IVDD) is a complex process involving many factors, among which excessive senescence of nucleus pulposus cells (NPCs) is considered to be the main factor. Our previous study found that metformin may inhibit senescence in nucleus pulposus cells; however, its working mechanism is still largely unknown. In the current study, we found that metformin may inactivate cGAS-STING pathway during oxidative stress. Knock-down of STING may further suppress senescence, indicating metformin may exert its effect through cGAS-STING pathway. Damaged DNA is a major inducer of the activation of cGAS-STING pathway. Mechanistically, our study showed that DNA damage was reduced during metformin treatment; however, suppression of autophagy by 3-methyladenine (3MA) may compromise the effect of metformin on DNA damage. The in vivo study also showed that 3MA may recede the therapeutic effect of metformin on IVDD. Taken together, our results reveal that metformin may suppress senescence via inactivating the cGAS-STING pathway through autophagy, implying the new application of metformin in cGAS-STING pathway related diseases.
