Sensory stimulation evokes a local, vasodilation-mediated blood flow increase to the activated brain region, which is referred to as functional hyperemia. Spontaneous vasomotion is a change in... Show moreSensory stimulation evokes a local, vasodilation-mediated blood flow increase to the activated brain region, which is referred to as functional hyperemia. Spontaneous vasomotion is a change in arteriolar diameter that occurs without sensory stimulation, at low frequency (similar to 0.1 Hz). These vessel diameter changes are a driving force for perivascular soluble waste clearance, the failure of which has been implicated in neurodegenerative disease. Stimulus-evoked vascular reactivity is known to propagate along penetrating arterioles to pial arterioles, but it is unclear whether spontaneous vasomotion propagates similarly. We therefore imaged both stimulus-evoked and spontaneous changes in pial arteriole diameter in awake, head-fixed mice with 2-photon microscopy. By cross-correlating different regions of interest (ROIs) along the length of imaged arterioles, we assessed vasomotion propagation. We found that both during rest and during visual stimulation, one-third of the arterioles showed significant propagation (i.e., a wave), with a median (interquartile range) wave speed of 405 (323) mu m/s at rest and 345 (177) mu m/s during stimulation. In a second group of mice, with GCaMP expression in their vascular smooth muscle cells, we also found spontaneous propagation of calcium signaling along pial arterioles. In summary, we demonstrate that spontaneous vasomotion propagates along pial arterioles like stimulus-evoked vascular reactivity. Show less
Perivascular spaces (PVS) are compartments surrounding cerebral blood vessels that become visible on MRI when enlarged. Enlarged PVS (EPVS) are commonly seen in patients with cerebral small vessel... Show morePerivascular spaces (PVS) are compartments surrounding cerebral blood vessels that become visible on MRI when enlarged. Enlarged PVS (EPVS) are commonly seen in patients with cerebral small vessel disease (CSVD) and have been suggested to reflect dysfunctional perivascular clearance of soluble waste products from the brain. In this study, we investigated histopathological correlates of EPVS and how they relate to vascular amyloid-beta (A beta) in cerebral amyloid angiopathy (CAA), a form of CSVD that commonly co-exists with Alzheimer's disease (AD) pathology. We used ex vivo MRI, semi-automatic segmentation and validated deep-learning-based models to quantify EPVS and associated histopathological abnormalities. Severity of MRI-visible PVS during life was significantly associated with severity of MRI-visible PVS on ex vivo MRI in formalin fixed intact hemispheres and corresponded with PVS enlargement on histopathology in the same areas. EPVS were located mainly around the white matter portion of perforating cortical arterioles and their burden was associated with CAA severity in the overlying cortex. Furthermore, we observed markedly reduced smooth muscle cells and increased vascular A beta accumulation, extending into the WM, in individually affected vessels with an EPVS. Overall, these findings are consistent with the notion that EPVS reflect impaired outward flow along arterioles and have implications for our understanding of perivascular clearance mechanisms, which play an important role in the pathophysiology of CAA and AD. Show less
Munting, L.P.; Derieppe, M.; Suidgeest, E.; Hirschler, L.; Osch, M.J.P. van; Senneville, B.D. de; Weerd, L. van der 2021
Impaired cerebrovascular function is an early biomarker for cerebral amyloid angiopathy (CAA), a neurovascular disease characterized by amyloid-b accumulation in the cerebral vasculature, leading... Show moreImpaired cerebrovascular function is an early biomarker for cerebral amyloid angiopathy (CAA), a neurovascular disease characterized by amyloid-b accumulation in the cerebral vasculature, leading to stroke and dementia. The transgenic Swedish Dutch Iowa (Tg-SwDI) mouse model develops cerebral microvascular amyloid-b deposits, but whether this leads to similar functional impairments is incompletely understood. We assessed cerebrovascular function longitudinally in Tg-SwDI mice with arterial spin labeling (ASL)-magnetic resonance imaging (MRI) and laser Doppler flowmetry (LDF) over the course of amyloid-b deposition. Unexpectedly, TgSwDI mice showed similar baseline perfusion and cerebrovascular reactivity estimates as agematched wild-type control mice, irrespective of modality (ASL or LDF) or anesthesia (isoflurane or urethane and a-chloralose). Hemodynamic changes were, however, observed as an effect of age and anesthesia. Our findings contradict earlier results obtained in the same model and question to what extent microvascular amyloidosis as seen in Tg-SwDI mice is representative of cerebrovascular dysfunction observed in CAA patients. Show less
Gravesteijn, G.; Munting, L.P.; Overzier, M.; Mulder, A.A.; Hegeman, I.; Derieppe, M.; ... ; Oberstein, S.A.J.L. 2019
CADASIL is a NOTCH3-associated cerebral small vessel disease. A pathological ultrastructural disease hallmark is the presence of NOTCH3-protein containing deposits called granular osmiophilic... Show moreCADASIL is a NOTCH3-associated cerebral small vessel disease. A pathological ultrastructural disease hallmark is the presence of NOTCH3-protein containing deposits called granular osmiophilic material (GOM), in small arteries. How these GOM deposits develop over time and what their role is in disease progression is largely unknown. Here, we studied the progression of GOM deposits in humanized transgenic NOTCH3(Arg182Cys) mice, compared them to GOM deposits in patient material, and determined whether GOM deposits in mice are associated with a functional CADASIL phenotype. We found that GOM deposits are not static, but rather progress in ageing mice, both in terms of size and aspect. We devised a GOM classification system, reflecting size, morphology and electron density. Six-month-old mice showed mostly early stage GOM, whereas older mice and patient vessels showed predominantly advanced stage GOM, but also early stage GOM. Mutant mice did not develop the most severe GOM stage seen in patient material. This absence of end-stage GOM in mice was associated with an overall lack of histological vascular pathology, which may explain why the mice did not reveal functional deficits in cerebral blood flow, cognition and motor function. Taken together, our data indicate that GOM progress over time, and that new GOM deposits are continuously being formed. The GOM staging system we introduce here allows for uniform GOM deposit classification in future mouse and human studies, which may lead to more insight into a potential association between GOM stage and CADASIL disease severity, and the role of GOM in disease progression. Show less
Munting, L.P.; Derieppe, M.P.P.; Suidgeest, E.; Senneville, B.D. de; Wells, J.A.; Weerd, L. van der 2019
Arterial spin labeling (ASL)-MRI can noninvasively map cerebral blood flow (CBF) and cerebrovascular reactivity (CVR), potential biomarkers of cognitive impairment and dementia. Mouse models of... Show moreArterial spin labeling (ASL)-MRI can noninvasively map cerebral blood flow (CBF) and cerebrovascular reactivity (CVR), potential biomarkers of cognitive impairment and dementia. Mouse models of disease are frequently used in translational MRI studies, which are commonly performed under anesthesia. Understanding the influence of the specific anesthesia protocol used on the measured parameters is important for accurate interpretation of hemodynamic studies with mice. Isoflurane is a frequently used anesthetic with vasodilative properties. Here, the influence of three distinct isoflurane protocols was studied with pseudo-continuous ASL in two different mouse strains. The first protocol was a free-breathing set-up with medium concentrations, the second a free-breathing set-up with low induction and maintenance concentrations, and the third a set-up with medium concentrations and mechanical ventilation. A protocol with the vasoconstrictive anesthetic medetomidine was used as a comparison. As expected, medium isoflurane anesthesia resulted in significantly higher CBF and lower CVR values than medetomidine (median whole-brain CBF of 157.7 vs 84.4 mL/100 g/min and CVR of 0.54 vs 51.7% in C57BL/6 J mice). The other two isoflurane protocols lowered the CBF and increased the CVR values compared with medium isoflurane anesthesia, without obvious differences between them (median whole-brain CBF of 138.9 vs 131.7 mL/100 g/min and CVR of 10.0 vs 9.6%, in C57BL/6 J mice). Furthermore, CVR was shown to be dependent on baseline CBF, regardless of the anesthesia protocol used. Show less
Moursel, L.G.; Munting, L.P.; Graaf, L.M. van der; Duinen, S.G. van; Goumans, M.J.T.H.; Ueberham, U.; ... ; Weerd, L. van der 2018
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... Show moreHereditary 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 beta (A beta) peptide. Transforming growth factor beta 1 (TGF beta 1) is a key player in vascular fibrosis and in the formation of angiopathic vessels in transgenic mice. Therefore, we investigated whether the TGF beta pathway is involved in HCHWA-D pathogenesis in human postmortem brain tissue from frontal and occipital lobes. Components of the TGF pathway were analyzed with quantitative RT-PCR. TGF beta 1 and TGF beta Receptor 2 (TGFBR2) gene expression levels were significantly increased in HCHWA-D in comparison to the controls, in both frontal and occipital lobes. TGF beta-induced pro-fibrotic target genes were also upregulated. We further assessed pathway activation by detecting phospho-SMAD2/3 (pSMAD2/3), a direct TGF beta 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 TGF beta 1 in HCHWA-D, as was found previously in AD with CAA pathology. We discuss the possible origins and implications of the TGF beta pathway deregulation in the microvasculature in HCHWA-D. These findings identify the TGF beta pathway as a potential biomarker of disease progression and a possible target of therapeutic intervention in HCHWA-D. Show less
The cerebral blood flow (CBF) is a potential biomarker for neurological disease. However, the arterial transit time (ATT) of the labeled blood is known to potentially affect CBF quantification.... Show moreThe cerebral blood flow (CBF) is a potential biomarker for neurological disease. However, the arterial transit time (ATT) of the labeled blood is known to potentially affect CBF quantification. Furthermore, ATT could be an interesting biomarker in itself, as it may reflect underlying macro and microvascular pathologies. Currently, no optimized magnetic resonance imaging (MRI) sequence exists to measure ATT in mice. Recently, time-encoded labeling schemes have been implemented in rats and humans, enabling ATT mapping with higher signal-to-noise ratio (SNR) and shorter scan time than multi-delay arterial spin labeling (ASL). In this study, we show that time-encoded pseudo-continuous arterial spin labeling (te-pCASL) also enables transit time measurements in mice. As an optimal design that takes the fast blood flow in mice into account, time encoding with 11 sub-boli of 50 ms is proposed to accurately probe the inflow of labeled blood. For perfusion imaging, a separate, traditional pCASL scan was employed. From the six studied brain regions, the hippocampus showed the shortest ATT (169 +/- 11 ms) and the auditory/visual cortex showed the longest (284 +/- 16 ms). Furthermore, ATT was found to be preserved in old wild-type mice. In a mouse with an induced carotid artery occlusion, prolongation of ATT was shown. In conclusion, this study shows the successful implementation of te-pCASL in mice, making it possible, for the first time, to measure ATT in mice in a time-efficient manner. Show less
