This is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
A progressive defect in the energy generation pathway is implicated in multiple aging-related diseases, including cardiovascular conditions and Alzheimer's Disease (AD). However, evidence of the pathogenesis of cardiac dysfunction in AD and the associations between the two organ diseases need further elucidation. This study aims to characterize cellular defects resulting in decreased cardiac function in AD-model. 5XFAD mice, a strain expressing five mutations in human APP and PS1 that shows robust Aβ production with visible plaques at 2 months and were used in this study as a model of AD. 5XFAD mice and wild-type (WT) counterparts were subjected to echocardiography at 2-, 4-, and 6-month, and 5XFAD had a significant reduction in cardiac fractional shortening and ejection fraction compared to WT. Additionally, 5XFAD mice had decreased observed electrical signals demonstrated as decreased R, P, T wave amplitudes. In isolated cardiomyocytes, 5XFAD mice showed decreased fraction shortening, rate of shortening, as well as the degree of transient calcium influx. To reveal the mechanism by which AD leads to cardiac systolic dysfunction, the immunoblotting analysis showed increased activation of AMP-activated protein kinase (AMPK) in 5XFAD left ventricular and brain tissue, indicating altered energy metabolism. Mito Stress Assays examining mitochondrial function revealed decreased basal and maximal oxygen consumption rate, as well as defective pyruvate dehydrogenase activity in the 5XFAD heart and brain. Cellular inflammation was provoked in the 5XFAD heart and brain marked by the increase of reactive oxygen species accumulation and upregulation of inflammatory mediator activities. Finally, AD pathological phenotype with increased deposition of Aβ and defective cognitive function was observed in 6-month 5XFAD mice. In addition, elevated fibrosis was observed in the 6-month 5XFAD heart. The results implicated that AD led to defective mitochondrial function, and increased inflammation which caused the decrease in contractility of the heart.
Introduction: Metformin activates AMP-activated protein kinase (AMPK) to improve cardiac function during ischemia and reperfusion (I/R). We reported that Sestrin2 (Sesn2) is associated with AMPK and maintains oxidative phosphorylation (OXPHOS) under I/R stress. The role of age-related Sesn2-AMPK signaling in the beneficial actions of metformin on ischemic insults remains unknown. Hypothesis: Metformin maintains mitochondrial integrity and limits cardiac damage caused by ischemic insults through the Sesn2-AMPK signaling pathway. Methods: Young (3-6 months) and aged (22-24 months) C57BL/6J wild type mice, and 3 months of Sesn2 f/f and cardiomyocyte-specific Sesn2 knockout (cSesn2 -/- ) C57BL/6J mice were subjected to 45 minutes of ischemia followed by 2 mM metformin injection 5 minutes before 24-hour of reperfusion. Cardiac function and myocardial infarction were determined with echocardiography and 2,3,5-triphenyl tetrazolium chloride staining. Immunoblotting determines the mechanism of metformin in modulating Sesn2 to preserve mitochondrial OXPHOS components. The Seahorse XF Analyzer examined the mitochondrial respiratory functions. Results: Metformin administration can significantly improve cardiac function and reduce myocardial infarction size during I/R conditions in both young and aged wild-type C57BL/6J mice. Intriguingly, the beneficial effects of metformin administration on cardiac function and myocardial infarction were significantly blunted in the cSesn2 -/- versus Sesn2 f/f C57BL/6J mice. The immunoblotting showed metformin treatment augmented mitochondrial OXPHOS Complex II levels in young/aged wild type, and Sesn2 f/f but not cSesn2 -/- heart during I/R stress. Moreover, the mitochondrial respiration data displayed that metformin treatment improved the respiration rate of mitochondrial states 2 and 3μ in the isolated cardiomyocytes from Sens2 f/f but not from cSesn2 -/- mouse hearts under I/R stress conditions. Conclusions: Metformin can stabilize age-related Sesn2 levels in cardiomyocytes and improve cardiac function under I/R stress through maintaining mitochondrial integrity. Metformin is a potential therapeutic drug for ischemic heart disease in the elderly.
Introduction: Sirtuin 1 (SIRT1) is a nicotinamide adenine dinucleotide-dependent histone deacetylase. We revealed that the pressure-overload-induced SIRT1 can exacerbate cardiac systolic dysfunction. But the mechanisms by which SIRT1 undermines cardiac function under pathological conditions remain unclear. Hypothesis: SIRT1 induced by pathological hypotrophy disturbs mitochondrial dynamics homeostasis resulting in an exacerbated cardiac dysfunction. Methods: Wild-type littermates SIRT1 f/f (3-5 months) and inducible cardiomyocyte-specific SIRT1 knockout (icSIRT1 -/- ) (3-5 months) C57BL/6J mice were subjected to transverse aortic constriction (TAC) surgery for six weeks. Echocardiography assessed cardiac functions and CODA tail-cuff system measured blood pressure. The mitochondrial dynamics were examined by immunoblotting and transmission electron microscopy (TEM). Results: The echocardiography showed that there were significant reductions in ejection fraction (EF) and fractional shortening (FS) of the SIRT1 f/f mice after 6-weeks of TAC-induced pressure overload. The diastolic and systolic blood pressure were increased in SIRT1 f/f mice during TAC surgery. Intriguingly, icSIRT1 -/- versus SIRT1 f/f demonstrated significant resistance to pathological hypertrophy caused by TAC-induced pressure overload as determined with echocardiography and blood pressure measurements. The immunoblotting revealed that the six weeks of TAC surgery caused significantly higher levels of the mitochondrial fusion protein, mitofusin 2 (MFN2), in SIRT1 f/f versus icSIRT1 -/- hearts. In addition, TEM data showed more elongated mitochondria in SIRT1 f/f versus icSIRT1 -/- hearts, indicating a critical role of SIRT1 in maintaining mitochondrial dynamic homeostasis under pathological stress conditions. Metabolomics and proteomics showed that SIRT1 regulates carnitine palmitoyltransferase-1 and long-chain acyl CoA dehydrogenase to modulate fatty acid metabolism in response to TAC-induced stress. Conclusions: Cardiomyocyte SIRT1 plays a key role in cardiac mitochondrial dynamics during pathological stress conditions. Inhibition of SIRT1 activity could be a good strategy to ameliorate pressure overload-induced hypertrophy.
Introduction: Activated protein C (APC) is a blood serine protease that has been shown to have neuroprotective function via its downstream signaling cascade. However, there is no study has investigated how the lack of APC signaling is associated with Alzheimer’s disease (AD)-related neuronal changes. Hypothesis: Diminished APC signaling is related to AD-associated biomarkers and behavioral symptoms. APC ameliorates these symptoms via the activation of the protein kinase B (Akt) signaling pathway which inhibits glycogen synthase kinase 3β (GSK3β) and tau hyperphosphorylation. Methods: Immunofluorescence imaging and proteomic analysis were performed on EPCR R84A/R84A mice, which had blunted APC activity due to mutated endothelial protein C receptor (EPCR), for examining amyloid β (Aβ) deposition. A rodent model of AD, 5xFAD mice, were subjected to either one-time or chronic daily APC injection (100 μg/kg/d i.p.). Morris's water maze test was performed to assess spatial memory and learning. The tissue of the hippocampus and cortex were collected for transcriptomic and proteomic analysis. Results: EPCR R84A/R84A mice showed greater hippocampal and cortical deposition of Aβ comparing to EPCR WT/WT counterparts. This result indicates defective APC signaling might contribute to the development of Aβ accumulation and insoluble plaque formation. A one-time injection of APC significantly activated AKT through phosphorylating the Ser 473 site, as well as inhibited AKT’s downstream target, GSK3β, via phosphorylation at Ser 9 in both wild-type and 5 x FAD mice. Downregulation of GSK3β activity is associated with decreased tau phosphorylation at Ser 202 /Thr 205 but not Ser 396 , indicating a reduction in the hyperphosphorylated form of tau that is prone to neurofibrillary tangle formation. Additionally, chronic APC administration for 3 months was observed to attenuate the cognitive deficits seen in 5 x FAD mice. Conclusions: APC has a crucial neuroprotective role because dampened APC signaling is related to AD-associated neuronal changes. APC has the downstream effect of Akt activation, which in turn inhibits GSK3β and the hyperphosphorylation of tau, ameliorating both the histological and behavioral markers seen in AD.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.