Retinal mid-peripheral capillary free zones are enlarged in cognitively unimpaired older adults at high risk for Alzheimer's disease.

BACKGROUND: Compared to standard neuro-diagnostic techniques, retinal biomarkers provide a probable low-cost and non-invasive alternative for early Alzheimer's disease (AD) risk screening. We have previously quantified the periarteriole and perivenule capillary free zones (mid-peripheral CFZs) in cognitively unimpaired (CU) young and older adults as novel metrics of retinal tissue oxygenation. There is a breakdown of the inner retinal blood barrier, pericyte loss, and capillary non-perfusion or dropout in AD leading to potential enlargement of the mid-peripheral CFZs. We hypothesized the mid-peripheral CFZs will be enlarged in CU older adults at high risk for AD compared to low-risk individuals. METHODS: 20 × 20° optical coherence tomography angiography images consisting of 512 b-scans, 512 A-scans per b-scan, 12-µm spacing between b-scans, and 5 frames averaged per each b-scan location of the central fovea and of paired major arterioles and venules with their surrounding capillaries inferior to the fovea of 57 eyes of 37 CU low-risk (mean age: 66 years) and 50 eyes of 38 CU high-risk older adults (mean age: 64 years; p = 0.24) were involved in this study. High-risk participants were defined as having at least one APOE e4 allele and a positive first-degree family history of AD while low-risk participants had neither of the two criteria. All participants had Montreal Cognitive Assessment scores ≥ 26. The mid-peripheral CFZs were computed in MATLAB and compared between the two groups. RESULTS: The periarteriole CFZ of the high-risk group (75.8 ± 9.19 µm) was significantly larger than that of the low-risk group (71.3 ± 7.07 µm), p = 0.005, Cohen's d = 0.55. The perivenule CFZ of the high-risk group (60.4 ± 8.55 µm) was also significantly larger than that of the low-risk group (57.3 ± 6.40 µm), p = 0.034, Cohen's d = 0.42. There were no significant differences in foveal avascular zone (FAZ) size, FAZ effective diameter, and vessel density between the two groups, all p > 0.05. CONCLUSIONS: Our results show larger mid-peripheral CFZs in CU older adults at high risk for AD, with the potential for the periarteriole CFZ to serve as a novel retinal vascular biomarker for early AD risk detection.

The Expression of Activin Receptor-Like Kinase 1 (ACVRL1/ALK1) in Hippocampal Arterioles Declines During Progression of Alzheimer's Disease.

Cerebral amyloid angiopathy (CAA) in Alzheimer's disease (AD)-deposition of beta amyloid (Aß) within the walls of cerebral blood vessels-typically accompanies Aß buildup in brain parenchyma and causes abnormalities in vessel structure and function. We recently demonstrated that the immunoreactivity of activin receptor-like kinase 1 (ALK1), the type I receptor for circulating BMP9/BMP10 (bone morphogenetic protein) signaling proteins, is reduced in advanced, but not early stages of AD in CA3 pyramidal neurons. Here we characterize vascular expression of ALK1 in the context of progressive AD pathology accompanied by amyloid angiopathy in postmortem hippocampi using immunohistochemical methods. Hippocampal arteriolar wall ALK1 signal intensity was 35% lower in AD patients (Braak and Braak Stages IV and V [BBIV-V]; clinical dementia rating [CDR1-2]) as compared with subjects with early AD pathologic changes but either cognitively intact or with minimal cognitive impairment (BBIII; CDR0-0.5). The intensity of Aß signal in arteriolar walls was similar in all analyzed cases. These data suggest that, as demonstrated previously for specific neuronal populations, ALK1 expression in blood vessels is also vulnerable to the AD pathophysiologic process, perhaps related to CAA. However, cortical arterioles may remain responsive to the ALK1 ligands, such as BMP9 and BMP10 in early and moderate AD.

Methionine Sulfoxide Reductase-B3 Risk Allele Implicated in Alzheimer's Disease Associates with Increased Odds for Brain Infarcts.

Genome-wide association studies identified a single nucleotide polymorphism (SNP) in the MSRB3 gene encoding Methionine Sulfoxide Reductase-B3 (MsrB3) to be associated with the risk for low hippocampal volume and late onset Alzheimer's disease (AD). Subsequently, we identified AD-associated abnormal patterns of neuronal and vascular MsrB3 expression in postmortem hippocampi. The present study investigated the relationship between the MSRB3 SNP rs61921502, G (minor/risk allele) and MRI measures of brain injury including total brain volume, hippocampal volume, and white matter hyperintensities using linear regression models; the presence of brain infarcts using logistic regression models; and the incidence of stroke, dementia, and AD using Cox proportional hazards models in 2,038 Framingham Heart Study Offspring participants with MRI administered close to examination cycle 7 (1998-2001). Participants with neurological conditions that impede evaluation of vascular pathology by MRI, i.e., brain tumors, multiple sclerosis, and major head trauma, were excluded from the study. When adjusted for age and age squared at MRI exam, sex, and presence of Apolipoproteinɛ4 allele (APOE4), individuals with MSRB3 rs61921502 minor allele had increased odds for brain infarcts on MRI compared to those with no minor allele. However, in stratified analyses, MSRB3 rs61921502 minor allele was significantly associated with increased odds for MRI brain infarcts only in the absence of APOE4.

Immunohistochemical Analysis of Activin Receptor-Like Kinase 1 (ACVRL1/ALK1) Expression in the Rat and Human Hippocampus: Decline in CA3 During Progression of Alzheimer's Disease.

The pathophysiology of Alzheimer's disease (AD) includes signaling defects mediated by the transforming growth factor ß-bone morphogenetic protein-growth and differentiation factor (TGFß-BMP-GDF) family of proteins. In animal models of AD, administration of BMP9/GDF2 improves memory and reduces amyloidosis. The best characterized type I receptor of BMP9 is ALK1. We characterized ALK1 expression in the hippocampus using immunohistochemistry. In the rat, ALK1 immunoreactivity was found in CA pyramidal neurons, most frequently and robustly in the CA2 and CA3 fields. In addition, there were sporadic ALK1-immunoreactive cells in the stratum oriens, mainly in CA1. The ALK1 expression pattern in human hippocampus was similar to that of rat. Pyramidal neurons within the CA2, CA3, and CA4 were strongly ALK1-immunoreactive in hippocampi of cognitively intact subjects with no neurofibrillary tangles. ALK1 signal was found in the axons of alveus and fimbria, and in the neuropil across CA fields. Relatively strongest ALK1 neuropil signal was observed in CA1 where pyramidal neurons were occasionally ALK1-immunoractive. As in the rat, horizontally oriented neurons in the stratum oriens of CA1 were both ALK1- and GAD67-immunoreactive. Analysis of ALK1 immunoreactivity across stages of AD pathology revealed that disease progression was characterized by overall reduction of the ALK1 signal in CA3 in advanced, but not early, stages of AD. These data suggest that the CA3 pyramidal neurons may remain responsive to the ALK1 ligands, e.g., BMP9, during initial stages of AD and that ALK1 may constitute a therapeutic target in early and moderate AD.

Methionine Sulfoxide Reductase-B3 (MsrB3) Protein Associates with Synaptic Vesicles and its Expression Changes in the Hippocampi of Alzheimer's Disease Patients.

Genome-wide association studies (GWAS) identified susceptibility loci associated with decreased hippocampal volume, and found hippocampal subfield-specific effects at MSRB3 (methionine sulfoxide reductase-B3). The MSRB3 locus was also linked to increased risk for late onset Alzheimer's disease (AD). In this study, we uncovered novel sites of MsrB3 expression in CA pyramidal layer and arteriolar walls by using automated immunohistochemistry on hippocampal sections from 23 individuals accompanied by neuropathology reports and clinical dementia rating scores. Controls, cognitively intact subjects with no hippocampal neurofibrillary tangles, exhibited MsrB3 signal as distinct but rare puncta in CA1 pyramidal neuronal somata. In CA3, however, MsrB3-immunoreactivity was strongest in the neuropil of the pyramidal layer. These patterns were replicated in rodent hippocampi where ultrastructural and immunohistofluorescence analysis revealed MsrB3 signal associated with synaptic vesicles and colocalized with mossy fiber terminals. In AD subjects, the number of CA1 pyramidal neurons with frequent, rather than rare, MsrB3-immunoreactive somatic puncta increased in comparison to controls. This change in CA1 phenotype correlated with the occurrence of AD pathological hallmarks. Moreover, the intensity of MsrB3 signal in the neuropil of CA3 pyramidal layer correlated with the signal pattern in neurons of CA1 pyramidal layer that was characteristic of cognitively intact individuals. Finally, MsrB3 signal in the arteriolar walls in the hippocampal white matter decreased in AD patients. This characterization of GWAS-implicated MSRB3 protein expression in human hippocampus suggests that patterns of neuronal and vascular MsrB3 protein expression reflect or underlie pathology associated with AD.

Pyruvate Occupancy in the Carboxyl Transferase Domain of Pyruvate Carboxylase Facilitates Product Release from the Biotin Carboxylase Domain through an Intermolecular Mechanism.

Protein structure, ligand binding, and catalytic turnover contributes to the governance of catalytic events occurring at spatially distinct domains in multifunctional enzymes. Coordination of these catalytic events partially rests on the ability of spatially discrete active sites to communicate with other allosteric and active sites on the same polypeptide chain (intramolecular) or on different polypeptide chains (intermolecular) within the holoenzyme. Often, communication results in long-range effects on substrate binding or product release. For example, pyruvate binding to the carboxyl transferase (CT) domain of pyruvate carboxylase (PC) increases the rate of product release in the biotin carboxylase (BC) domain. In order to address how CT domain ligand occupancy is "sensed" by other domains, we generated functional, mixed hybrid tetramers using the E218A (inactive BC domain) and T882S (low pyruvate binding, low activity) mutant forms of PC. The apparent Ka pyruvate for the pyruvate-stimulated release of Pi catalyzed by the T882S:E218A[1:1] hybrid tetramer was comparable to the wild-type enzyme and nearly 10-fold lower than that for the T882S homotetramer. In addition, the ratio of the rates of oxaloacetate formation to Pi release for the WT:T882S[1:1] and E218A:T882S[1:1] hybrid tetramer-catalyzed reactions was 0.5 and 0.6, respectively, while the T882S homotetramer exhibited a near 1:1 coupling of the two domains, suggesting that the mechanisms coordinating catalytic events is more complicated that we initially assumed. The results presented here are consistent with an intermolecular communication mechanism, where pyruvate binding to the CT domain is "sensed" by domains on a different polypeptide chain within the tetramer.

Subcellular Changes in Bridging Integrator 1 Protein Expression in the Cerebral Cortex During the Progression of Alzheimer Disease Pathology.

Genome-wide association studies have established BIN1 (Bridging Integrator 1) as the most significant late-onset Alzheimer disease (AD) susceptibility locus after APOE We analyzed BIN1 protein expression using automated immunohistochemistry on the hippocampal CA1 region in 19 patients with either no, mild, or moderate-to-marked AD pathology, who had been assessed by Clinical Dementia Rating and CERAD scores. We also examined the amygdala, prefrontal, temporal, and occipital regions in a subset of these patients. In non-demented controls without AD pathology, BIN1 protein was expressed in white matter, glia, particularly oligodendrocytes, and in the neuropil in which the BIN1 signal decorated axons. With increasing severity of AD, BIN1 in the CA1 region showed: 1) sustained expression in glial cells, 2) decreased areas of neuropil expression, and 3) increased cytoplasmic neuronal expression that did not correlate with neurofibrillary tangle load. In patients with AD, both the prefrontal cortex and CA1 showed a decrease in BIN1-immunoreactive (BIN1-ir) neuropil areas and increases in numbers of BIN1-ir neurons. The numbers of CA1 BIN1-ir pyramidal neurons correlated with hippocampal CERAD neuritic plaque scores; BIN1 neuropil signal was absent in neuritic plaques. Our data provide novel insight into the relationship between BIN1 protein expression and the progression of AD-associated pathology and its diagnostic hallmarks.

Age-related trends in red spruce foliar plasticity in relation to declining productivity.

Phenotypic plasticity in needle morphology with increasing tree size and age was investigated by comparing four age classes of red spruce (Picea rubens Sarg.) ranging from juvenile (3-12 years old) to mature (over 100 years old). With increase in tree age there were significant increases in leaf mass per unit area (LMA), mesophyll and vascular bundle area as a percentage of total needle cross-sectional area, and stomatal density. Within the vascular bundle, both xylem cross-sectional area and tracheid lumen area increased significantly, whereas air space as a percentage of total cross-sectional area decreased. These morphological changes were associated with a significant decrease in photosynthetic capacity and stomatal conductance, and an increase in (13)C enrichment. Although both photosynthetic capacity and whole-tree conductance decreased significantly between age classes 3 and 12 years, they did not differ between age classes 53 and 127 years, even though needle (13)C enrichment was significantly greater in the 127-year age class. Thus there appear to be compensatory mechanisms that maintain photosynthetic capacity as trees increase in size and vascular complexity, which in red spruce and other species, may affect leaf hydraulic conductance. Although increased LMA may contribute to reduced photosynthetic capacity in red spruce, similar relationships are not seen in other conifers.

Notch/Delta signaling constrains reengineering of pro-T cells by PU.1.

PU.1 is essential for early stages of mouse T cell development but antagonizes it if expressed constitutively. Two separable mechanisms are involved: attenuation and diversion. Dysregulated PU.1 expression inhibits pro-T cell survival, proliferation, and passage through beta-selection by blocking essential T cell transcription factors, signaling molecules, and Rag gene expression, which expression of a rearranged T cell antigen receptor transgene cannot rescue. However, Bcl2 transgenic cells are protected from this attenuation and may even undergo beta-selection, as shown by PU.1 transduction of defined subsets of Bcl2 transgenic fetal thymocytes with differentiation in OP9-DL1 and OP9 control cultures. The outcome of PU.1 expression in these cells depends on Notch/Delta signaling. PU.1 can efficiently divert thymocytes toward a myeloid-like state with multigene regulatory changes, but Notch/Delta signaling vetoes diversion. Gene expression analysis distinguishes sets of critical T lineage regulatory genes with different combinatorial responses to PU.1 and Notch/Delta signals, suggesting particular importance for inhibition of E proteins, Myb, and/or Gfi1 (growth factor independence 1) in diversion. However, Notch signaling only protects against diversion of cells that have undergone T lineage specification after Thy-1 and CD25 up-regulation. The results imply that in T cell precursors, Notch/Delta signaling normally acts to modulate and channel PU.1 transcriptional activities during the stages from T lineage specification until commitment.