Vesicular Glutamate Transporter Changes in the Cortical Default Mode Network During the Clinical and Pathological Progression of Alzheimer's Disease.

BACKGROUND: Altered glutamatergic neurotransmission may contribute to impaired default mode network (DMN) function in Alzheimer's disease (AD). Among the DMN hub regions, frontal cortex (FC) was suggested to undergo a glutamatergic plasticity response in prodromal AD, while the status of glutamatergic synapses in the precuneus (PreC) during clinical-neuropathological AD progression is not known. OBJECTIVE: To quantify vesicular glutamate transporter VGluT1- and VGluT2-containing synaptic terminals in PreC and FC across clinical stages of AD. METHODS: Unbiased sampling and quantitative confocal immunofluorescence of cortical VGluT1- and VGluT2-immunoreactive profiles and spinophilin-labeled dendritic spines were performed in cases with no cognitive impairment (NCI), mild cognitive impairment (MCI), mild-moderate AD (mAD), or moderate-severe AD (sAD). RESULTS: In both regions, loss of VGluT1-positive profile density was seen in sAD compared to NCI, MCI, and mAD. VGluT1-positive profile intensity in PreC did not differ across groups, while in FC it was greater in MCI, mAD, and sAD compared to NCI. VGluT2 measures were stable in PreC while FC had greater VGluT2-positive profile density in MCI compared to sAD, but not NCI or mAD. Spinophilin measures in PreC were lower in mAD and sAD compared to NCI, while in FC they were stable across groups. Lower VGluT1 and spinophilin measures in PreC, but not FC, correlated with greater neuropathology. CONCLUSION: Frank loss of VGluT1 in advanced AD relative to NCI occurs in both DMN regions. In FC, an upregulation of VGluT1 protein content in remaining glutamatergic terminals may contribute to this region's plasticity response in AD.

Methotrexate Inhibits T Cell Proliferation but Not Inflammatory Cytokine Expression to Modulate Immunity in People Living With HIV.

Inflammation associated with increased risk of comorbidities persists in people living with HIV (PWH) on combination antiretroviral therapy (ART). A recent placebo-controlled trial of low-dose methotrexate (MTX) in PWH found that numbers of total CD4 and CD8 T cells decreased in the low-dose MTX arm. In this report we analyzed T cell phenotypes and additional plasma inflammatory indices in samples from the trial. We found that cycling (Ki67+) T cells lacking Bcl-2 were reduced by MTX but plasma inflammatory cytokines were largely unaffected. In a series of in vitro experiments to further investigate the mechanisms of MTX activity, we found that MTX did not inhibit effector cytokine production but inhibited T cell proliferation downstream of mTOR activation, mitochondrial function, and cell cycle entry. This inhibitory effect was reversible with folinic acid, suggesting low-dose MTX exerts anti-inflammatory effects in vivo in PWH largely by blocking T cell proliferation via dihydrofolate reductase inhibition, yet daily administration of folic acid did not rescue this effect in trial participants. Our findings identify the main mechanism of action of this widely used anti-inflammatory medicine in PWH and may provide insight into how MTX works in the setting of other inflammatory conditions.

Loss of precuneus dendritic spines immunopositive for spinophilin is related to cognitive impairment in early Alzheimer's disease.

Precuneus (PreC) cortex is affected with amyloid plaques early in Alzheimer's disease (AD), and this pathology may be associated with alterations in PreC synapses and cognitive impairment. We quantified the spinophilin-immunoreactive (ir) dendritic spine density and the intensity of spinophilin immunofluorescence, the latter as a measure of relative protein levels of spinophilin, in PreC lamina III from 33 subjects with clinical diagnoses of no cognitive impairment (NCI), mild cognitive impairment (MCI), mild-moderate AD (mAD), or severe AD (sAD). Both measures of spinophilin were lower in mAD and sAD compared with NCI. The MCI group had higher protein levels of spinophilin compared with mAD and sAD, and higher spinophilin-ir dendritic spine density compared with sAD. Lower spinophilin-ir dendritic spine density and relative protein levels of spinophilin were associated with greater amyloid beta (Aß) plaque burden, detected with a derivative of Pittsburgh compound-B (6-CN-PiB), and worse cognitive performance. Clinical onset of AD is marked by the loss of PreC spinophilin-ir dendritic spines that is related to Aß pathology and may contribute to cognitive symptoms early in the disease.