Accumulation of amyloid-β (Aβ) peptide and the hyperphosphorylation of tau protein are major hallmarks of Alzheimer's disease (AD). The causes of AD are not well known but a number of environmental and dietary factors are suggested to increase the risk of developing AD. Additionally, altered metabolism of iron may have a role in the pathogenesis of AD. We have previously demonstrated that cholesterol-enriched diet causes AD-like pathology with iron deposition in rabbit brain. However, the extent to which chelation of iron protects against this pathology has not been determined. In this study, we administered the iron chelator deferiprone in drinking water to rabbits fed with a 2% cholesterol diet for 12 weeks. We found that deferiprone (both at 10 and 50 mg/kg/day) significantly decreased levels of Aβ40 and Aβ42 as well as BACE1, the enzyme that initiates cleavage of amyloid-β protein precursor to yield Aβ. Deferiprone also reduced the cholesterol diet-induced increase in phosphorylation of tau but failed to reduce reactive oxygen species generation. While deferiprone treatment was not associated with any change in brain iron levels, it was associated with a significant reduction in plasma iron and cholesterol levels. These results demonstrate that deferiprone confers important protection against hypercholesterolemia-induced AD pathology but the mechanism(s) may involve reduction in plasma iron and cholesterol levels rather than chelation of brain iron. We propose that adding an antioxidant therapy to deferiprone may be necessary to fully protect against cholesterol-enriched diet-induced AD-like pathology.
Ischemia-reperfusion (I-R) injury is a cardinal pathophysiological hallmark of ischemic heart disease (IHD). Despite significant advances in the understanding of what causes I-R injury and hypoxia-reoxygenation (H-R) stress, viable molecular strategies that could be targeted for the treatment of the deleterious biochemical pathways activated during I-R remain elusive. The master hypoxamiR, microRNA-210 (miR-210), is a major determinant of protective cellular adaptation to hypoxia stress but exacerbates apoptotic cell death during cellular reoxygenation. While the hypoxia-induced transcriptional up-regulation of miR-210 is well delineated, the cellular mechanisms and molecular entities that regulate the transcriptional induction of miR-210 during the cellular reoxygenation phase have not been elucidated yet. Herein, in immortalized AC-16 cardiomyocytes, we delineated the indispensable role of the ubiquitously expressed transcription factor, NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) in H-R-induced miR-210 expression during cellular reoxygenation. Using dominant negative and dominant active expression vectors encoding kinases to competitively inhibit NF-κB activation, we elucidated NF-κB activation as a significant mediator of H-R-induced miR-210 expression. Ensuing molecular assays revealed a direct NF-κB-mediated transcriptional up-regulation of miR-210 expression in response to the H-R challenge that is characterized by the NF-κB-mediated reorchestration of the entire repertoire of histone modification changes that are a signatory of a permissive actively transcribed miR-210 promoter. Our study confers a novel insight identifying NF-κB as a potential novel molecular target to combat H-R-elicited miR-210 expression that fosters augmented cardiomyocyte cell death.
Alzheimer's disease (AD) is the most prevalent progressive neurodegenerative disorder and the most common form of dementia in the elderly. AD is histo-pathologically characterized by the accumulation of amyloid-beta (Aβ) peptide as extracellular neuritic plaques and the intracellular accumulation of hyperphosphorylated tau protein as neurofibrillary tangles (NFT). Emerging evidence from prospective and cross-sectional epidemiological studies have suggested that lower plasma Vitamin D3 levels are associated with a higher risk for developing AD. The excessive genesis and accumulation of the Aβ peptide is considered as a core pathological event that evokes and drives other neurodegenerative pathological signaling cascades in the etio-pathogenesis of AD. The aspartyl protease β-site APP-cleaving enzyme 1 (BACE1) catalyzes the rate-limiting step in the genesis of Aβ from the amyloid-beta precursor protein (AβPP). Recent studies have shown that Vitamin D3 supplementation decreases Aβ burden and age-related cognitive decline in rodents. However, the molecular mechanisms that underlie the salutary effects of Vitamin D3 have not been delineated. In this study, we determined the effects of calcitriol (1,25 dihydroxyvitamin D3), the most active endogenous metabolite of Vitamin D3, on the expression of BACE1 and Aβ genesis and delineated the underlying cellular and molecular mechanisms. Human SH-SY5Y neuroblastoma cells stably expressing the AβPP Swedish KM670/671NL double mutation (SH-SY5Y-APPSwe) and rat pheochromocytoma PC12 cells were treated with calcitriol (1,25 dihydroxyvitamin D3) and subsequent effects on BACE1 expression, BACE1 enzymatic activity, AβPP processing, and Aβ levels determined. Our study shows that calcitriol (1,25 dihydroxyvitamin D3) attenuates the basal expression of BACE1 and subsequently reduces Aβ genesis by decreasing the amyloidogenic processing of AβPP. Further delineation of the underlying mechanisms unveiled that the effects of calcitriol were contingent on Vitamin D Receptor (VDR) activation as RNAi-mediated knock-down of VDR expression significantly blunted the calcitriol-induced decrease in BACE1 expression and Aβ production. Our study highlights and delineates a novel mechanism through which calcitriol (1,25 dihydroxyvitamin D3) decreases BACE1 expression and activity that culminates in the mitigation of Aβ genesis.
Epidemiological studies have suggested a positive correlation between saturated fat intake and the risk for developing Alzheimer's disease (AD). While diets-enriched in the saturated free fatty acid (sFFA) palmitate has been shown to induce cognitive dysfunction and AD-like pathology, polyunsaturat ed fatty acids (PUFA) such as linoleate have been suggested to protect against AD in mouse models. However, the underlying cellular and molecular mechanisms that mediate the deleterious effects of palmitate or the protective effects of linoleate remain to be characterized. We fed 9-month-old cohorts of triple transgenic AD mice (3xTg-AD) and their-matched controls with a palmitate-enriched/linoleate-deficient diet for three months and determined the impact of the diet on oxidative stress, Bace1 promoter transactivation status, and amyloid-β (Aβ) burden. The palmitate-enriched/linoleate-deficient diet causes a profound increase in oxidative stress burden characterized by significant oxidative damage to lipids, proteins, and nucleic acids concomitant with deficits in the endogenous antioxidant defense capacity in the hippocampi of 3xTg-AD mice. These effects were also associated with increased NF-κB transcriptional activity resulting in NF-κB-mediated transactivation of the Bace1 promoter that culminated in higher BACE1 expression and activity, and Aβ production. Our study unveils a novel mechanism by which a diet enriched in the sFFA palmitate and deficient in the PUFA linoleate exacerbates AD-like pathology involving signaling cross-talk between oxidative stress and NF-κB activation as a critical underlying factor in upregulating BACE1 activity and increasing Aβ burden.
Several studies showed that insulin-like growth factor-1 (IGF-1) and leptin reduce ß-amyloid (Aß) production. Of relevance, both IGF-1 and leptin expression levels are reduced in Alzheimer's disease (AD) brains. IGF-1 expression is known to involve the JAK/STAT pathway and the expression of leptin is regulated by the mammalian target of rapamycin complex 1 (mTORC1). While IGF-1 activates mTORC1, leptin has been shown to modulate JAK/STAT pathway. We have previously shown that Aß reduces leptin by inhibiting the mTORC1 pathway, and Aß was also suggested to inhibit the JAK/STAT signaling pathway. However, the extent to which Aß may reduce the expression of IGF-1 by inhibiting the JAK/STAT pathways has not been determined. Additionally, the ability of treatment with IGF-1 or leptin to prevent Aß-induced inhibition of mTORC1 or JAK/STAT and subsequently reduce leptin or IGF-1 expression is not known. In this study, organotypic slices from adult rabbit hippocampus were incubated with Aß42 for 72h in presence or absence of leptin or IGF-1. We demonstrate that incubation of organotypic slices from adult rabbit hippocampus with Aß42 down regulates IGF-1 expression by inhibiting JAK2/STAT5 pathway. Leptin treatment reverses these Aß42 effects by increasing the activation of JAK2/STAT5. We also show that IGF-1 increases the expression of leptin via the activation of mTORC1 signaling and reverses the Aß42-induced attenuation in leptin expression. Our results demonstrate for the first time that Aß42 regulates IGF-1 expression and that leptin and IGF-1 rescue one another from down regulation by Aß42. Our study provides a valuable insight into the leptin/IGF-1/Aß interplay that may be relevant to the pathophysiology of AD.
The aspartyl protease β-site AβPP-cleaving enzyme 1 (BACE1) catalyzes the rate-limiting step in Aβ production, a peptide at the nexus of neurodegenerative cascades in Alzheimer Disease (AD). The adipocytokine leptin has been demonstrated to reduce Aβ production and decrease BACE1 activity and expression levels. However, the signaling cascades involved in the leptin-induced mitigation in Aβ levels and BACE1 expression levels have not been elucidated. We have demonstrated that the transcription factor nuclear factor - kappa B (NF-κB) positively regulates BACE1 transcription. NF-κB activity is tightly regulated by the mammalian sirtuin SIRT1. Multiple studies have cogently evinced that leptin activates the metabolic master regulator SIRT1. In this study, we determined the extent to which SIRT1 expression and activity regulate the leptin-induced attenuation in BACE1 expression and Aβ levels in cultured human neuroblastoma SH-SY5Y cells. This study also elucidated and delineated the signal transduction pathways involved in the leptin induced mitigation in BACE1 expression. Human neuroblastoma SH-SY5Y cells were grown in Dulbecco's modified Eagle's medium:Ham's F12 with Glutamax (1:1; v/v), 10% fetal bovine serum, and 1% antibiotic/antimycotic mix. Cells were maintained at 37°C in a saturated humidity atmosphere containing 95% air and 5% CO 2. After having reached 80% confluence, cells were incubated with vehicle (control), 10nM leptin, 400μM Sirtinol, and 10nM leptin + 400μM Sirtinol, for 24h at 37°C in cell medium. Our results demonstrate for the first time that leptin attenuates the activation and transcriptional activity of NF-κB by reducing the acetylation of the p65 subunit in a SIRT1-dependent manner. Furthermore, our data shows that leptin reduces the NF-κB - mediated transcription of BACE1 and consequently reduces Amyloid-β genesis. Our study provides a valuable insight and a novel mechanism by which leptin reduces BACE1 expression and Amyloid-β production and may help design potential therapeutic interventions.
Accumulation of amyloid-beta (Abeta) peptide and deposition of hyperphosphorylated tau protein are two major pathological hallmarks of Alzheimer's disease (AD). We have shown that cholesterol-enriched diets and its metabolite 27-hydroxycholesterol (27-OHC) increase Abeta and phosphorylated tau levels. However, the mechanisms by which cholesterol and 27-OHC regulate Abeta production and tau phosphorylation remain unclear. Leptin, an adipocytokine involved in cell survival and in learning, has been demonstrated to regulate Abeta production and tau hyperphosphorylation in transgenic mice for AD. However, the involvement of leptin signaling in cholesterol and cholesterol metabolites-induced Abeta accumulation and tau hyperphosphorylation are yet to be examined. In this study, we determined the effect of high cholesterol diet and 27-OHC on leptin expression levels and the extent to which leptin treatment affects 27-OHC-induced AD-like pathology. Our results show that feeding rabbits a 2% cholesterol-enriched diet for 12 weeks reduces the levels of leptin by approximately 80% and incubating organotypic slices from adult rabbit hippocampus with 27-OHC reduced leptin levels by approximately 30%. 27-OHC induces a 1.5-fold increase in Abeta (40) and a 3-fold increase in Abeta (42) and in phosphorylated tau. Treatment with leptin reversed the 27-OHC-induced increase in Abeta and phosphorylated tau by decreasing the levels of BACE-1 and GSK-3beta respectively. Our results suggest that cholesterol-enriched diets and cholesterol metabolites induce AD-like pathology by altering leptin signaling. We propose that leptin administration may prevent the progression of sporadic forms of AD that are related to increased cholesterol and oxidized cholesterol metabolite levels.
The plasma membrane protein STRA6 is thought to mediate uptake of retinol from its blood carrier retinol-binding protein (RBP) into cells and to function as a surface receptor that, upon binding of holo-RBP, activates a JAK/STAT cascade. It was suggested that STRA6 signaling underlies insulin resistance induced by elevated serum levels of RBP in obese animals. To investigate these activities in vivo, we generated and analyzed Stra6-null mice. We show that the contribution of STRA6 to retinol uptake by tissues in vivo is small and that, with the exception of the eye, ablation of Stra6 has only a modest effect on retinoid homeostasis and does not impair physiological functions that critically depend on retinoic acid in the embryo or in the adult. However, ablation of Stra6 effectively protects mice from RBP-induced suppression of insulin signaling. Thus one biological function of STRA6 in tissues other than the eye appears to be the coupling of circulating holo-RBP levels to cell signaling, in turn regulating key processes such as insulin response.Background: STRA6 transports retinol into cells and activates cell signaling.Results: Ablation of Stra6 does not impair vitamin A homeostasis in tissues other than the eye but protects mice against RBP-induced insulin resistance.Conclusion: One major function of STRA6 is to control cell signaling.Significance: The data point at a new function for vitamin A and its blood carrier RBP. The plasma membrane protein STRA6 is thought to mediate uptake of retinol from its blood carrier retinol-binding protein (RBP) into cells and to function as a surface receptor that, upon binding of holo-RBP, activates a JAK/STAT cascade. It was suggested that STRA6 signaling underlies insulin resistance induced by elevated serum levels of RBP in obese animals. To investigate these activities in vivo, we generated and analyzed Stra6-null mice. We show that the contribution of STRA6 to retinol uptake by tissues in vivo is small and that, with the exception of the eye, ablation of Stra6 has only a modest effect on retinoid homeostasis and does not impair physiological functions that critically depend on retinoic acid in the embryo or in the adult. However, ablation of Stra6 effectively protects mice from RBP-induced suppression of insulin signaling. Thus one biological function of STRA6 in tissues other than the eye appears to be the coupling of circulating holo-RBP levels to cell signaling, in turn regulating key processes such as insulin response. Background: STRA6 transports retinol into cells and activates cell signaling. Results: Ablation of Stra6 does not impair vitamin A homeostasis in tissues other than the eye but protects mice against RBP-induced insulin resistance. Conclusion: One major function of STRA6 is to control cell signaling. Significance: The data point at a new function for vitamin A and its blood carrier RBP.
