TGFβ pathway deregulation and abnormal phospho‐SMAD2/3 staining in 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) pathology, caused by the E22Q mutation in the amyloid β (Aβ) peptide. Transforming growth factor β1 (TGFβ1) is a key player in vascular fibrosis and in the formation of angiopathic vessels in transgenic mice. Therefore, we investigated whether the TGFβ pathway is involved in HCHWA‐D pathogenesis in human postmortem brain tissue from frontal and occipital lobes. Components of the TGFβ pathway were analyzed with quantitative RT‐PCR. TGFβ1 and TGFβ Receptor 2 (TGFBR2) gene expression levels were significantly increased in HCHWA‐D in comparison to the controls, in both frontal and occipital lobes. TGFβ‐induced pro‐fibrotic target genes were also upregulated. We further assessed pathway activation by detecting phospho‐SMAD2/3 (pSMAD2/3), a direct TGFβ down‐stream signaling mediator, using immunohistochemistry. We found abnormal pSMAD2/3 granular deposits specifically on HCHWA‐D angiopathic frontal and occipital vessels. We graded pSMAD2/3 accumulation in angiopathic vessels and found a positive correlation with the CAA load independent of the brain area. We also observed pSMAD2/3 granules in a halo surrounding occipital vessels, which was specific for HCHWA‐D. The result of this study indicates an upregulation of TGFβ1 in HCHWA‐D, as was found previously in AD with CAA pathology. We discuss the possible origins and implications of the TGFβ pathway deregulation in the microvasculature in HCHWA‐D. These findings identify the TGFβ pathway as a potential biomarker of disease progression and a possible target of therapeutic intervention in HCHWA‐D.

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.…”

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 .…”

“…Brain tissue from eight D‐CAA patients, genetically tested for the presence of the mutation (NM_000484.3(APP):c.2077G>C), was used in this study as summarized in Table . In addition to the two cases previously described for the presence of calcifications (in ; cases H2 and H14), six additional patients presenting a known range of CAA severity (based on ) were selected (H5, H6, H7, H8, H9 and H10 as shown in Table ).…”

“…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 (9,10). 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 (9).…”

“…We previously reported an upregulation of the TGFβ pathway in HCHWA-D post-mortem brain tissue (9,10). 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 (9). Since, it is known that TGFβ is a key factor in peripheral vascular calcifications (13,40), we investigated the correlation between TGFβ regulation and calcification in individual vessels.…”