Amyloid Triggers Extensive Cerebral Angiogenesis Causing Blood Brain Barrier Permeability and Hypervascularity in Alzheimer's Disease

Evidence of reduced blood-brain barrier (BBB) integrity preceding other Alzheimer's disease (AD) pathology provides a strong link between cerebrovascular angiopathy and AD. However, the “Vascular hypothesis”, holds that BBB leakiness in AD is likely due to hypoxia and neuroinflammation leading to vascular deterioration and apoptosis. We propose an alternative hypothesis: amyloidogenesis promotes extensive neoangiogenesis leading to increased vascular permeability and subsequent hypervascularization in AD. Cerebrovascular integrity was characterized in Tg2576 AD model mice that overexpress the human amyloid precursor protein (APP) containing the double missense mutations, APPsw, found in a Swedish family, that causes early-onset AD. The expression of tight junction (TJ) proteins, occludin and ZO-1, were examined in conjunction with markers of apoptosis and angiogenesis. In aged Tg2576 AD mice, a significant increase in the incidence of disrupted TJs, compared to age matched wild-type littermates and young mice of both genotypes, was directly linked to an increased microvascular density but not apoptosis, which strongly supports amyloidogenic triggered hypervascularity as the basis for BBB disruption. Hypervascularity in human patients was corroborated in a comparison of postmortem brain tissues from AD and controls. Our results demonstrate that amylodogenesis mediates BBB disruption and leakiness through promoting neoangiogenesis and hypervascularity, resulting in the redistribution of TJs that maintain the barrier and thus, provides a new paradigm for integrating vascular remodeling with the pathophysiology observed in AD. Thus the extensive angiogenesis identified in AD brain, exhibits parallels to the neovascularity evident in the pathophysiology of other diseases such as age-related macular degeneration

Angiogenesis not apoptosis induces alterations in tight junction immunoreactivity in Tg2576 mice.

<p>Representative confocal micrographs of TJs (ZO-1), double stained for markers of angiogenesis or apoptosis in aged wild-type and Tg2576 mice. All vessels stained for CD105 regardless of the TJ expression pattern. White arrowheads point to regions of TJ abnormality in the vasculature. Double staining of blood vessels with ZO-1 (red) and CD105 (green) in wild-type (A). and Tg2576 (B) neocortex. Double staining of vessels with ZO-1 (red) and caspase 3 (green) in wild-type (C) and Tg2576 (D) neocortex. Caspase-3 staining did not colocalize with ZO-1 staining indicating an absence of apoptosis in the vasculature. Results are representative of three separate experiments of three mice per group of brain tissues examined. Scale bar represents 20 µm.</p

Microvascular Density is increased in Aged Tg2576 and in Human patients with AD.

<p>The MVD, by CD105 staining, in the cerebrovasculature and CD105 protein expression were quantified in aged and young Tg2576 and wild-type. (A) Aged Tg2576 mice had a significantly higher MVD compared to age-matched wild-type (***p<0.001). Aged Tg2576 were had a significantly higher MVD compared to young Tg2576 (Aged wild-type, n = 5; aged Tg2576, n = 4; young wild-type, n = 4; young Tg2576, n = 3; *p<0.05). Although not significant, young Tg2576 mice trended to a higher average MVD compared to wild-type. (B) Aged Tg2576 mice had a significantly increased CD105 protein levels in the cortex compared to age-matched wild-type (wild-type, n = 5; Tg2576, n = 6; ***p<0.001). (C) Aged Tg2576 mice had a significantly increased CD105 protein levels in the hippocampus compared to age-matched wild-type (n = 7, *p<0.05). (D) The cortex of the AD patient had a significantly increased MVD, as measured by % area occupied by laminin staining, compared to the ND patient (n = 4, *p<0.05). (E) The hippocampus of the AD patient had a significantly increased MVD, as measured by % area occupied by laminin staining, compared to the ND patient (n = 4, ***p<0.001). Representative images of immunohistochemical staining for laminin in the cortex of the ND patient (F) and the AD patient (G). Scale bar represents 95 µm. Values represent mean ± SEM.</p

Tg2576 AD mice have cerebral tight junction pathology.

<p>Representative confocal micrographs of cerebral blood vessels from aged Tg2576 and wild-type mice immunolabeled for either occludin or ZO-1 (red) and counterstained for DNA (blue) with TOTO-3. Blood vessels, imaged in the neocortex and hippocampus, which exhibited strong, continuous and linear occludin (A and C) or ZO-1 (E and G) expression were considered normal, as demonstrated in the wild-type. Abnormal occludin (B and F) and ZO-1 (D and H) staining displayed punctate (white arrowheads), discontinuous or interrupted (hollow white arrows), as seen in the Tg2576 cerebrovasculature. Results are representative from three mice per group from three separate experiments. Scale bar represents 20 µm.</p

Epigenetic Control of the Immune Escape Mechanisms in Malignant Carcinomas▿

Downregulation of the transporter associated with antigen processing 1 (TAP-1) has been observed in many tumors and is closely associated with tumor immunoevasion mechanisms, growth, and metastatic ability. The molecular mechanisms underlying the relatively low level of transcription of the tap-1 gene in cancer cells are largely unexplained. In this study, we tested the hypothesis that epigenetic regulation plays a fundamental role in controlling tumor antigen processing and immune escape mechanisms. We found that the lack of TAP-1 transcription in TAP-deficient cells correlated with low levels of recruitment of the histone acetyltransferase, CBP, to the TAP-1 promoter. This results in lower levels of histone H3 acetylation at the TAP-1 promoter, leading to a decrease in accessibility of the RNA polymerase II complex to the TAP-1 promoter. These observations suggest that CBP-mediated histone H3 acetylation normally relaxes the chromatin structure around the TAP-1 promoter region, allowing transcription. In addition, we found a hitherto-unknown mechanism wherein interferon gamma up-regulates TAP-1 expression by increasing histone H3 acetylation at the TAP-1 promoter locus. These findings lie at the heart of understanding immune escape mechanisms in tumors and suggest that the reversal of epigenetic codes may provide novel immunotherapeutic paradigms for intervention in cancer