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Microglial dysregulation, pertaining to impairment in phagocytosis, clearance and containment of amyloid-β (Aβ), and activation of neuroinflammation, has been posited to contribute to the pathogenesis of Alzheimer's disease (AD). Detailed cellular mechanisms that are disrupted during the disease course to display such impairment in microglia, however, remain largely undetermined. We hypothesize that loss of hematopoietic cell kinase (HCK), a phagocytosis-regulating member of the Src family tyrosine kinases that mediate signals from triggering receptor expressed on myeloid cells 2 and other immunoreceptors, impairs microglial homeostasis and Aβ clearance, leading to the accelerated buildup of Aβ pathology and cognitive decline during the early stage of neuropathological development. To elucidate the pivotal role of HCK in AD, we generated a constitutive knockout of HCK in the Tg2576 mouse model of AD. We found that HCK deficiency accelerated cognitive decline along with elevated Aβ level and plaque burden, attenuated microglial Aβ phagocytosis, induced iNOS expression in microglial clusters, and reduced pre-synaptic protein at the hippocampal regions. Our findings substantiate that HCK plays a prominent role in regulating microglial neuroprotective functions and attenuating early AD neuropathology.

Background Copper (Cu) is an essential metal mediating a variety of vital biological reactions with its redox property. Its dyshomeostasis has been associated with accelerated cognitive decline and neurodegenerative disorders, such as Alzheimer’s disease (AD). However, underlying neurotoxic mechanisms elicited by dysregulated Cu remain largely elusive. We and others previously demonstrated that exposure to Cu in drinking water significantly exacerbated pathological hallmarks of AD and pro-inflammatory activation of microglia, coupled with impaired phagocytic capacity, in mouse models of AD. Methods In the present study, we extended our investigation to evaluate whether chronic Cu exposure to wild-type (WT) and J20 mouse model of AD perturbs homeostatic dynamics of microglia and contributes to accelerated transformation of microglia towards degenerative phenotypes that are closely associated with neurodegeneration. We further looked for evidence of alterations in the microglial morphology and spatial memory of the Cu-exposed mice to assess the extent of the Cu toxicity. Results We find that chronic Cu exposure to pre-pathological J20 mice upregulates the translation of degenerative genes and represses homeostatic genes within microglia even in the absence amyloid-beta plaques. We also observe similar expression signatures in Cu-exposed WT mice, suggesting that excess Cu exposure alone could lead to perturbed microglial homeostatic phenotypes and contribute to accelerated cognitive decline. Conclusion Our findings highlight the risk of chronic Cu exposure on cognitive decline and altered microglia activation towards degenerative phenotypes. These changes may represent one of the key mechanisms linking Cu exposure or its dyshomeostasis to an increased risk for AD.

Emerging evidence have posited that dysregulated microglia impair clearance and containment of amyloid-β (Aβ) species in the brain, resulting in aberrant buildup of Aβ and onset of Alzheimer's disease (AD). Hematopoietic cell kinase (Hck) is one of the key regulators of phagocytosis among the Src family tyrosine kinases (SFKs) in myeloid cells, and its expression is found to be significantly altered in AD brains. However, the role of Hck signaling in AD pathogenesis is unknown. We employed pharmacological inhibition and genetic ablation of Hck in BV2 microglial cells and J20 mouse model of AD, respectively, to evaluate the impact of Hck deficiency on Aβ-stimulated microglial phagocytosis, Aβ clearance, and resultant AD-like neuropathology. Our in vitro data reveal that pharmacological inhibition of SFKs/Hck in BV2 cells and genetic ablation of their downstream kinase, spleen tyrosine kinase (Syk), in primary microglia significantly attenuate Aβ oligomers-stimulated microglial phagocytosis. Whereas in Hck-deficient J20 mice, we observed exacerbated Aβ plaque burden, reduced microglial coverage, containment, and phagocytosis of Aβ plaques, and induced iNOS expression in plaque-associated microglial clusters. These multifactorial changes in microglial activities led to attenuated PSD95 levels in hippocampal DG and CA3 regions, but did not alter the postsynaptic dendritic spine morphology at the CA1 region nor cognitive function of the mice. Hck inhibition thus accelerates early stage AD-like neuropathology by dysregulating microglial function and inducing neuroinflammation. Our data implicate that Hck pathway plays a prominent role in regulating microglial neuroprotective function during the early stage of AD development.

Chronic exposure to copper and its dyshomeostasis have been linked to accelerated cognitive decline and potentially increasing risk for Alzheimer's disease (AD). We and others have previously demonstrated that exposure to copper through drinking water significantly increased parenchymal amyloid-beta (Aβ) plaques and decreased endothelial low-density lipoprotein receptor-related protein 1 (LRP1) in mouse models of AD. In this study, we determined the underlying mechanisms that microRNA critically mediated the copper-induced loss of endothelial LRP1. In human primary microvascular endothelial cells (MVECs), microRNA-200b-3p, -200c-3p, and -205-5p were significantly elevated within the 24-h exposure to copper and returned to baseline after 48-h postexposure, which corresponded with the temporal change of LRP1 expression in these cells. Transient expression of synthetic microRNA-200b-3p, -200c-3p, or -205-5p on MVECs significantly decreased endothelial LRP1, and cotreatment of synthetic antagomirs effectively prevented the loss of LRP1 during copper exposure, collectively supporting the key regulatory role of these microRNAs in copper-induced loss of LRP1. In mice, a significant reduction of LRP1 in cortical vasculature was evident following 9 months exposure to 1.3 ppm copper in drinking water, although the levels of cortical microRNA-205-5p, -200b-3p, and -200c-3p were only marginally elevated. This, however, correlated with increased vascular accumulation of Aβ and impairment of spatial memory, indicating that copper exposure has the pivotal role in the vascular damage and development of cognitive decline.

Glial glutamate transporter, GLT-1, is the major Na(+)-driven glutamate transporter to control glutamate levels in synapses and prevent glutamate-induced excitotoxicity implicated in neurodegenerative disorders including Alzheimer's disease (AD). Significant functional loss of GLT-1 has been reported to correlate well with synaptic degeneration and severity of cognitive impairment among AD patients, yet the underlying molecular mechanism and its pathological consequence in AD are not well understood. Here, we find the temporal decrease in GLT-1 levels in the hippocampus of the 3xTg-AD mouse model and that the pharmacological upregulation of GLT-1 significantly ameliorates the age-dependent pathological tau accumulation, restores synaptic proteins, and rescues cognitive decline with minimal effects on Aβ pathology. In primary neuron and astrocyte coculture, naturally secreted Aβ species significantly downregulate GLT-1 steady-state and expression levels. Taken together, our data strongly suggest that GLT-1 restoration is neuroprotective and Aβ-induced astrocyte dysfunction represented by a functional loss of GLT-1 may serve as one of the major pathological links between Aβ and tau pathology.

Alzheimer's disease (AD) is a leading cause of dementia among elderly. Yet, its etiology remains largely unclear. In this review, we summarize studies that associate systemic infection and neuroinflammation with AD, while highlighting that early-life or life-long exposure to infectious agents predisposes one to develop AD at a later age.

The rs1061170T/C variant encoding the Y402H change in complement factor H (CFH) has been identified by genome-wide association studies as being significantly associated with age-related macular degeneration (AMD). However, the precise mechanism by which this CFH variant impacts the risk of AMD remains largely unknown. Oxidative stress plays an important role in many aging diseases, including cardiovascular disease and AMD. A large amount of oxidized phospholipids (oxPLs) are generated in the eye because of sunlight exposure and high oxygen content. OxPLs bind to the retinal pigment epithelium and macrophages and strongly activate downstream inflammatory cascades. We hypothesize that CFH may impact the risk of AMD by modulating oxidative stress. Here we demonstrate that CFH binds to oxPLs. The CFH 402Y variant of the protective rs1061170 genotype binds oxPLs with a higher affinity and exhibits a stronger inhibitory effect on the binding of oxPLs to retinal pigment epithelium and macrophages. In addition, plasma from non-AMD subjects with the protective genotype has a lower level of systemic oxidative stress measured by oxPLs per apolipoprotein B (oxPLs/apoB). We also show that oxPL stimulation increases expression of genes involved in macrophage infiltration, inflammation, and neovascularization in the eye. OxPLs colocalize with CFH in drusen in the human AMD eye. Subretinal injection of oxPLs induces choroidal neovascularization in mice. In addition, we show that the CFH risk allele confers higher complement activation and cell lysis activity. Together, these findings suggest that CFH influences AMD risk by modulating oxidative stress, inflammation, and abnormal angiogenesis.

There is currently no FDA-approved therapy for treating patients with geographic atrophy (GA), a late stage of age-related macular degeneration (AMD). Cell transplantation has the potential to restore vision in these patients. This review discusses how recent advancement in induced pluripotent stem (iPS) cells provides a promising therapy for GA treatment. Recent advances in stem cell biology have demonstrated that it is possible to derive iPS cells from human somatic cells by introducing reprogramming factors. Human retinal pigment epithelium (RPE) cells and photoreceptors can be derived from iPS cells by defined factors. Studies show that transplanting these cells can stabilize or recover vision in animal models. However, cell derivation protocols and transplantation procedures still need to be optimized. Much validation has to be done before clinical-grade, patient-derived iPS can be applied for human therapy. For now, RPE cells and photoreceptors derived from patient-specific iPS cells can serve as a valuable tool in elucidating the mechanism of pathogenesis and drug discovery for GA.

The aim of this study was to correlate the taxonomy of grapefruit, pummelo, orange, lime and lemon with fruit juice-mediated cytotoxicity, modulation of epithelial permeability and P-glycoprotein (P-gp)-mediated efflux using 0-50% juice concentrations. Lime and lemon juices at 30% enhanced the absorption of [14C]-mannitol across Caco-2 cell monolayers by six- and eight-fold, respectively, but grapefruit and pummelo juices did not modulate the paracellular [14C]-mannitol transport even at 50%. Orange juice at 30% increased mannitol absorption to a comparable level as lime juice, but had minimal effects on TEER. All five juices did not modulate the passive diffusional pathway as exemplified by their negligible effects on [3H]-propranolol absorption. Grapefruit, pummelo and orange juices showed P-gp inhibitory activity by reducing rhodamine-123 (R-123) efflux and elevating R-123 cellular accumulation, but lime and lemon juices did not. Lime and lemon juices at >or=30% were cytotoxic towards Caco-2 cells. Grapefruit and pummelo juices at 10% did not affect Caco-2 cell viability, but they enhanced cell growth at concentrations of >or=30%. Orange juice increased cell viability only at lower concentrations. On the basis of these data, lime and lemon juices could be regarded as a group distinct from grapefruit and pummelo juices, while orange juice appeared to belong to a bridging group. This grouping was consistent with the categorization of the citrus fruits according to their dominant flavonoid pattern and taxonomy.