Brain Transcriptomic Analysis of Hereditary Cerebral Hemorrhage With Amyloidosis-Dutch Type

Abstract

Hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D) is an early onset hereditary form of cerebral amyloid angiopathy (CAA) caused by a point mutation resulting in an amino acid change (NP_000475.1:p.Glu693Gln) in the amyloid precursor protein (APP). Post-mortem frontal and occipital cortical brain tissue from nine patients and nine age-related controls was used for RNA sequencing to identify biological pathways affected in HCHWA-D. Although previous studies indicated that pathology is more severe in the occipital lobe in HCHWA-D compared to the frontal lobe, the current study showed similar changes in gene expression in frontal and occipital cortex and the two brain regions were pooled for further analysis. Significantly altered pathways were analyzed using gene set enrichment analysis (GSEA) on 2036 significantly differentially expressed genes. Main pathways over-represented by down-regulated genes were related to cellular aerobic respiration (including ATP synthesis and carbon metabolism) indicating a mitochondrial dysfunction. Principal up-regulated pathways were extracellular matrix (ECM)–receptor interaction and ECM proteoglycans in relation with an increase in the transforming growth factor beta (TGFβ) signaling pathway. Comparison with the publicly available dataset from pre-symptomatic APP-E693Q transgenic mice identified overlap for the ECM–receptor interaction pathway, indicating that ECM modification is an early disease specific pathomechanism.

Different microvascular alterations underlie microbleeds and microinfarcts

“…First, our findings provide evidence for a scenario in which microbleeds happen in unhealthy enlarged CAA-affected vessels due to Aβ-induced degeneration of SMCs, fibrin(ogen) buildup, extensive vessel wall remodeling, and loss of Aβ locally. 28,29 Second, our findings provide evidence that microinfarcts happen in intact CAA-affected arterioles that are characterized by extensive Aβ buildup, loss of SMCs, and luminal narrowing. Our findings also fit well with early observations of fibrinoid necrotic vessels and microaneurysms in brains with CAA-related hemorrhages 27 and more recently reported associations between microbleeds and fibrin(ogen) in patients with CAA.…”

“…This is in line with recent transcriptomic studies in patients with hereditary CAA (Dutch-type) that found upregulation of extracellular matrix-related pathways and transforming growth factor β-induced profibrotic genes. 28,29 Second, our findings provide evidence that microinfarcts happen in intact CAA-affected arterioles that are characterized by extensive Aβ buildup, loss of SMCs, and luminal narrowing. These vessels likely predispose to hypoperfusion and/or occlusions.…”

Osteopontin and phospho‐SMAD2/3 are associated with calcification of vessels in D‐CAA, an hereditary cerebral amyloid angiopathy

“…Alternatively, as the arterial system was not distinguished from the venous system, the fibrosis of veins and venules (usually spared from amyloid deposition) might contribute to the number of Col1‐positive vessels. Both scenarios involve an early stage fibrosis of the vessel wall because of ECM remodeling regulated by TGFβ as proposed in our previous work .…”

“…Finally, ECM‐related pathways are known to be upregulated in D‐CAA . In particular Col1, which is a pro‐fibrotic gene induced by TGFβ1 signaling and an OPN binder, was found upregulated in D‐CAA and in an earlier study significantly increased quantities of Col1 were associated with vascular amyloid deposition .…”

“…In the current study, we investigated if vascular calcification in HCHWA‐D is linked to expression of several factors known to promote calcification, independent of CAA itself, namely transforming growth factor β (TGFβ), osteopontin (OPN) and collagen1 (Col1), as detailed below. We previously reported an upregulation of the TGFβ pathway in HCHWA‐D post‐mortem brain tissue . In particular, we described in angiopathic vessels a correlation between CAA severity and the accumulation of phosphoSMAD2/3 (pSMAD2/3), a direct TGFβ1 downstream signaling factor .…”