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Background and purposeCerebral small vessel diseases (SVDs) are characterized by early white matter (WM) changes, whose pathological underpinnings are yet poorly understood. CADASIL is a monogenic and archetypal SVD, providing an ideal model for investigating these changes. Here, we used multicompartment microscopic diffusion imaging and relaxometry to elucidate microstructural changes underlying early WM abnormalities in CADASIL.MethodsWe acquired diffusion MRI data with a multiple-shell Q-space sampling strategy, and relaxometry T1 and T2 data, with a 160 and 80-μm isotropic resolution respectively,ex vivo, in CADASIL and control mice. Diffusion datasets were computed with the Neurite Orientation Dispersion and Density Imaging model to extract the neurite density index, the extracellular free water and the orientation dispersion index. Relaxometry datasets were computed with a 3-compartment myelin water imaging model to extract the myelin content. MRI metrics were compared between CADASIL and control mice using voxel and WM tract-based analyses and with electron microscopy analysis.ResultsWM in CADASIL mice displayed a widespread reduction in general fractional anisotropy, a large increase in extracellular free water, a reduction in the myelin content, but no reduction in neurite density. Electron microscopy analysis showed a ∽2-fold increase in the extracellular spaces and an elevation of the g-ratio indicative of myelin sheath thinning in CADASIL WM.ConclusionOur findings suggest that accumulation of interstitial fluid and myelin damage are 2 major factors underlying early WM changes in CADASIL. Advanced diffusion MRI and relaxometry are promising approaches to decipher the underpinnings of WM alterations in SVDs.

International audience; Aims: The objective of this study was to elucidate the early white matter changes in CADASIL small vessel disease.Methods: We used high-pressure freezing and freeze substitution (HPF/FS) in combination with high-resolution electron microscopy (EM), immunohistochemistry and confocal microscopy of brain specimens from control and CADASIL (TgNotch3R169C ) mice aged 4-15 months to study white matter lesions in the corpus callosum.Results: We first optimised the HPF/FS protocol in which samples were chemically prefixed, frozen in a sample carrier filled with 20% polyvinylpyrrolidone and freeze-substituted in a cocktail of tannic acid, osmium tetroxide and uranyl acetate dissolved in acetone. EM analysis showed that CADASIL mice exhibit significant splitting of myelin layers and enlargement of the inner tongue of small calibre axons from the age of 6 months, then vesiculation of the inner tongue and myelin sheath thinning at 15 months of age. Immunohistochemistry revealed an increased number of oligodendrocyte precursor cells, although only in older mice, but no reduction in the number of mature oligodendrocytes at any age. The number of Iba1 positive microglial cells was increased in older but not in younger CADASIL mice, but the number of activated microglial cells (Iba1 and CD68 positive) was unchanged at any age.Conclusion: We conclude that early WM lesions in CADASIL affect first and foremost the myelin sheath and the inner tongue, suggestive of a primary myelin injury. We propose that those defects are consistent with a hypoxic/ischaemic mechanism.

Background: Spontaneous deep intracerebral hemorrhage (ICH) is a devastating subtype of stroke without specific treatments. It has been thought that smooth muscle cell (SMC) degeneration at the site of arteriolar wall rupture may be sufficient to cause hemorrhage. However, deep ICHs are rare in some aggressive small vessel diseases that are characterized by significant arteriolar SMC degeneration. Here we hypothesized that a second cellular defect may be required for the occurrence of ICH. Methods: We studied a genetic model of spontaneous deep ICH using Col4a1 +/G498V and Col4a1 +/G1064D mouse lines that are mutated for the α1 chain of collagen type IV. We analyzed cerebroretinal microvessels, performed genetic rescue experiments, vascular reactivity analysis, and computational modeling. We examined postmortem brain tissues from patients with sporadic deep ICH. Results: We identified in the normal cerebroretinal vasculature a novel segment between arterioles and capillaries, herein called the transitional segment (TS), which is covered by mural cells distinct from SMCs and pericytes. In Col4a1 mutant mice, this TS was hypermuscularized, with a hyperplasia of mural cells expressing more contractile proteins, whereas the upstream arteriole exhibited a loss of SMCs. TSs mechanistically showed a transient increase in proliferation of mural cells during postnatal maturation. Mutant brain microvessels, unlike mutant arteries, displayed a significant upregulation of SM genes and Notch3 target genes, and genetic reduction of Notch3 in Col4a1 +/G498V mice protected against ICH. Retina analysis showed that hypermuscularization of the TS was attenuated, but arteriolar SMC loss was unchanged in Col4a1 +/G498V , Notch3 +/− mice. Moreover, hypermuscularization of the retinal TS increased its contractility and tone and raised the intravascular pressure in the upstream feeding arteriole. We similarly found hypermuscularization of the TS and focal arteriolar SMC loss in brain tissues from patients with sporadic deep ICH. Conclusions: Our results suggest that hypermuscularization of the TS, through increased Notch3 activity, is involved in the occurrence of ICH in Col4a1 mutant mice, by raising the intravascular pressure in the upstream feeding arteriole and promoting its rupture at the site of SMC loss. Our human data indicate that these 2 mutually reinforcing vascular defects may represent a general mechanism of deep ICH.

Objective CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy), caused by dominant mutations in the NOTCH3 receptor, is the most aggressive small vessel disease of the brain. A key feature of its pathogenesis is accumulation of the extracellular domain of NOTCH3 receptor (Notch3ECD ) in small vessels, with formation of characteristic extracellular deposits termed granular osmiophilic material (GOM). Here, we investigated the therapeutic potential of a mouse monoclonal antibody (5E1) that specifically recognizes Notch3ECD . Methods The binding affinity of 5E1 toward purified NOTCH3 was assessed using Octet analysis. The ability of 5E1 to bind Notch3ECD deposits in brain vessels and its effects on disease-related phenotypes were evaluated in the CADASIL mouse model, which overexpresses a mutant rat NOTCH3. Notch3ECD and GOM deposition, white matter lesions, and cerebral blood flow deficits were assessed at treatment initiation (10 weeks) and study completion (30 weeks) using quantitative immunohistochemistry, electron microscopy, and laser-Doppler flowmetry. Results 5E1 antibody bound recombinant rat NOTCH3 with an average affinity of 317nM. A single peripheral injection of 5E1 robustly decorated Notch3ECD deposits in the brain vasculature. Chronic administration of 5E1 did not attenuate Notch3ECD or GOM deposition and was not associated with perivascular microglial activation. It also failed to halt the development of white matter lesions. Despite this, 5E1 treatment markedly protected against impaired cerebral blood flow responses to neural activity and topical application of vasodilators and normalized myogenic responses of cerebral arteries. Interpretation This study establishes immunotherapy targeting Notch3ECD as a new avenue for disease-modifying treatment in CADASIL that warrants further development. Ann Neurol 2018;84:246-259.

CADASIL (Cerebral Autosomal Dominant Arteriopathy With Subcortical Infarcts and Leukoencephalopathy), the most frequent genetic cause of stroke and vascular dementia, is caused by highly stereotyped mutations in the NOTCH3 receptor, which is predominantly expressed in vascular smooth muscle. The well-established TgNotch3 R169C mouse model develops characteristic features of the human disease, with deposition of NOTCH3 and other proteins, including TIMP3 (tissue inhibitor of metalloproteinase 3), on brain vessels, as well as reduced maximal dilation, and attenuated myogenic tone of cerebral arteries, but without elevated blood pressure. Increased TIMP3 levels were recently shown to be a major determinant of altered myogenic tone. In this study, we investigated the contribution of TIMP3 and Notch3 signaling to the impairment of maximal vasodilator capacity caused by the archetypal R169C mutation. Maximally dilated cerebral arteries in TgNotch3 R169C mice exhibited a decrease in lumen diameter over a range of physiological pressures that occurred before myogenic tone deficits. This defect was not prevented by genetic reduction of TIMP3 in TgNotch3 R169C mice and was not observed in mice overexpressing TIMP3. Knock-in mice with the R169C mutation ( Notch3 R170C/R170C ) exhibited similar reductions in arterial lumen, and both TgNotch3 R169C and Notch3 R170C/R170C mice showed increased cerebral artery expression of Notch3 target genes. Reduced maximal vasodilation was prevented by conditional reduction of Notch activity in smooth muscle of TgNotch3 R169C mice and mimicked by conditional activation of Notch3 in smooth muscle, an effect that was blood pressure–independent. We conclude that increased Notch3 activity mediates reduction in maximal dilator capacity of cerebral arteries in CADASIL and may contribute to reductions in cerebral blood flow.

CADASIL is a genetic paradigm of cerebral small vessel disease caused by NOTCH3 mutations that stereotypically lead to the extracellular deposition of NOTCH3 ectodomain (Notch3(ECD) ) on the vessels. TIMP3 and vitronectin are two extracellular matrix proteins that abnormally accumulate in Notch3(ECD) -containing deposits on brain vessels of mice and patients with CADASIL. Herein, we investigated whether increased levels of TIMP3 and vitronectin are responsible for aspects of CADASIL disease phenotypes. Timp3 and vitronectin expression were genetically reduced in TgNotch3(R169C) mice, a well-established preclinical model of CADASIL. A mouse overexpressing human TIMP3 (TgBAC-TIMP3) was developed. Disease-related phenotypes, including cerebral blood flow deficits, white matter lesions and Notch3(ECD) deposition, were evaluated between 6 and 20 months of age. Cerebral blood flow responses to neural activity (functional hyperemia), topical application of vasodilators, and decreases in blood pressure (CBF autoregulation) were similarly reduced in TgNotch3(R169C) and TgBAC-TIMP3 mice, and myogenic responses of brain arteries were likewise attenuated. These defects were rescued in TgNotch3(R169C) mice by haploinsufficiency of Timp3, although the number of white matter lesions was unaffected. In contrast, haploinsufficiency or loss of vitronectin in TgNotch3(R169C) mice ameliorated white matter lesions, although cerebral blood flow responses were unchanged. Amelioration of cerebrovascular reactivity or white matter lesions in these mice was not associated with reduced Notch3(ECD) deposition in brain vessels. Elevated levels of TIMP3 and vitronectin, acting downstream of Notch3(ECD) deposition, play a role in CADASIL, producing divergent influences on early cerebral blood flow deficits and later white matter lesions. This article is protected by copyright. All rights reserved.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and a phenotypically similar recessive condition (CARASIL) have emerged as important genetic model diseases for studying the molecular pathomechanisms of cerebral small vessel disease (SVD). CADASIL, the most frequent and intensely explored monogenic SVD, is characterized by a severe pathology in the cerebral vasculature including the mutation-induced aggregation of the Notch3 extracellular domain (Notch3ECD) and the formation of protein deposits of insufficiently determined composition in vessel walls. To identify key molecules and pathways involved in this process, we quantitatively determined the brain vessel proteome from CADASIL patient and control autopsy samples (n = 6 for each group), obtaining 95 proteins with significantly increased abundance. Intriguingly, high-temperature requirement protein A1 (HTRA1), the extracellular protease mutated in CARASIL, was found to be strongly enriched (4.9-fold, p = 1.6 × 10-3) and to colocalize with Notch3ECD deposits in patient vessels suggesting a sequestration process. Furthermore, the presence of increased levels of several HTRA1 substrates in the CADASIL proteome was compatible with their reduced degradation as consequence of a loss of HTRA1 activity. Indeed, a comparison with the brain vessel proteome of HTRA1 knockout mice (n = 5) revealed a highly significant overlap of 18 enriched proteins (p = 2.2 × 10-16), primarily representing secreted and extracellular matrix factors. Several of them were shown to be processed by HTRA1 in an in vitro proteolysis assay identifying them as novel substrates. Our study provides evidence for a loss of HTRA1 function as a critical step in the development of CADASIL pathology linking the molecular mechanisms of two distinct SVD forms.

International audience; Mutations in the α1 (COL4A1) or α2 (COL4A2) chains of collagen type IV, a major component of the vascular basement membrane, cause intracerebral haemorrhages with variable expressivity and reduced penetrance by mechanisms that remain poorly understood. Here we sought to investigate the cellular mechanisms of COL4A1-related intracerebral haemorrhage and identify a marker for haemorrhage risk stratification. A combination of histological, immunohistochemical, and electron microscopy analyses were used to analyse the brain parenchyma, cerebrovasculature, and retinal vessels of mice expressing the disease-causing COL4A1 p.G498V mutation. Mutant mice developed cerebral microhaemorrhages and macroscopic haemorrhages (macrohaemorrhages), the latter with reduced penetrance, mimicking the human disease. Microhaemorrhages that occurred in early postnatal life were associated with a transient, generalized increase in blood-brain barrier permeability at the level of capillaries. Macrohaemorrhages, which occurred later in life, originated from deep brain arteries with focal loss of smooth muscle cells. Similar smooth muscle cell loss was detected in retinal arteries, and a time-course analysis of arterial lesions showed that smooth muscle cells are recruited normally in arterial wall during development, but undergo progressive apoptosis-mediated degeneration. By assessing in parallel the extent of these retinal arterial lesions and the presence/absence of macrohaemorrhages, we found that the arterial lesion load in the retina is strongly correlated with the burden of macrohaemorrhages. We conclude that microhaemorrhages and macrohaemorrhages are driven by two distinct mechanisms. Moreover, smooth muscle cell degeneration is a critical factor underlying the partial penetrance of COL4A1-related macrohaemorrhages, and retinal imaging is a promising tool for identifying high-risk patients. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy), caused by dominant mutations in the NOTCH3 receptor, is the most aggressive small vessel disease of the brain. A key feature of its pathogenesis is accumulation of the extracellular domain of NOTCH3 receptor (Notch3The binding affinity of 5E1 toward purified NOTCH3 was assessed using Octet analysis. The ability of 5E1 to bind Notch35E1 antibody bound recombinant rat NOTCH3 with an average affinity of 317nM. A single peripheral injection of 5E1 robustly decorated Notch3This study establishes immunotherapy targeting Notch3

Background and Purpose— Cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy, the most common heritable small vessel disease of the brain, is caused by dominant mutations in the NOTCH3 receptor that stereotypically lead to age-dependent Notch3 ECD deposition in the vessels. NOTCH3 loss of function has been demonstrated for few mutations. However, whether this finding applies to all mutations and whether a loss-of-function mechanism drives the manifestations of the disease remain yet unknown. This study investigated the in vivo functionality of the Arg169Cys archetypal mutation. Methods— We used mice with constitutive or conditional reduction of NOTCH3 activity, mice harboring the Arg169Cys mutation at the endogenous Notch3 locus ( Notch3 Arg170Cys ), and mice overexpressing the Arg169Cys NOTCH3 mutant ( TgPAC-Notch3 R169C ) on either a Notch3 wild-type or a null background. NOTCH3 activity was monitored in the brain arteries by measuring the expression of NOTCH3 target genes using real-time polymerase chain reaction. Notch3 ECD deposits were assessed by immunohistochemistry. Brain parenchyma was analyzed for vacuolation and myelin debris in the white matter and infarcts. Results— We identified a subset of genes appropriate to detect NOTCH3 haploinsufficiency in the adult. Expression of these genes was unaltered in Notch3 Arg170Cys mice, despite marked Notch3 ECD deposits. Elimination of wild-type NOTCH3 did not influence the onset and burden of white matter lesions in 20-month-old TgPAC-Notch3 R169C mice, and 20-month-old Notch3-null mice exhibited neither infarct nor white matter changes. Conclusions— These data provide strong evidence that cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy can develop without impairment of NOTCH3 signaling and argue against a loss of NOTCH3 function as a general driving mechanism for white matter lesions in cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy.

Cerebral small vessel disease (SVD) is a leading cause of stroke and dementia. CADASIL, an inherited SVD, alters cerebral artery function, compromising blood flow to the working brain. TIMP3 (tissue inhibitor of metalloproteinase 3) accumulation in the vascular extracellular matrix in CADASIL is a key contributor to cerebrovascular dysfunction. However, the linkage between elevated TIMP3 and compromised cerebral blood flow (CBF) remains unknown. Here, we show that TIMP3 acts through inhibition of the metalloprotease ADAM17 and HB-EGF to regulate cerebral arterial tone and blood flow responses. In a clinically relevant CADASIL mouse model, we show that exogenous ADAM17 or HB-EGF restores cerebral arterial tone and blood flow responses, and identify upregulated voltage-dependent potassium channel (KV) number in cerebral arterial myocytes as a heretofore-unrecognized downstream effector of TIMP3-induced deficits. These results support the concept that the balance of TIMP3 and ADAM17 activity modulates CBF through regulation of myocyte KV channel number. DOI: http://dx.doi.org/10.7554/eLife.17536.001, eLife digest There are currently no effective treatments or cures for small blood vessel diseases of the brain, which lead to strokes and subsequent decreases in mental abilities. Normally, smooth muscle cells that surround the vessels relax or contract to regulate blood flow and ensure the right amount of oxygen and nutrients reaches the different regions of the brain. In a syndrome called CADASIL, which is the most common form of inherited small vessel disease, a genetic mutation causes the smooth muscle cells to weaken over time. The accumulation of several proteins – including one called TIMP3 – around the smooth muscle cells plays a key role in the smooth muscle cell weakening seen in CADASIL. Capone et al. have now studied mice that display the symptoms of CADASIL to investigate how TIMP3 decreases blood flow through blood vessels in the brain. This revealed that TIMP3 inactivates another protein called ADAM17. The latter protein is normally responsible for starting a signaling pathway that helps smooth muscle cells to regulate blood flow according to the needs of the brain cells. Artificially adding more ADAM17 to the brains of the CADASIL mice reduced their symptoms of small vessel disease. Using smooth muscle cells freshly isolated from the brains of CADASIL mice, Capone et al. also demonstrated that abnormal TIMP3-ADAM17 signaling increases the number of voltage-dependent potassium channels in the membrane of the muscle cells. Having too many of these channels impairs the flow of blood through vessels in the brain. Further experiments are needed to investigate whether correcting TIMP3-ADAM17 signaling could prevent strokes in people with inherited CADASIL. It also remains to be seen whether similar signaling mechanisms are at play in other small vessel diseases. DOI: http://dx.doi.org/10.7554/eLife.17536.002

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), caused by dominant mutations in the NOTCH3 receptor in vascular smooth muscle, is a genetic paradigm of small vessel disease (SVD) of the brain. Recent studies using transgenic (Tg)Notch3R169C mice, a genetic model of CADASIL, revealed functional defects in cerebral (pial) arteries on the surface of the brain at an early stage of disease progression. Here, using parenchymal arterioles (PAs) from within the brain, we determined the molecular mechanism underlying the early functional deficits associated with this Notch3 mutation. At physiological pressure (40 mmHg), smooth muscle membrane potential depolarization and constriction to pressure (myogenic tone) were blunted in PAs from TgNotch3R169C mice. This effect was associated with an ∼60% increase in the number of voltage-gated potassium (KV) channels, which oppose pressure-induced depolarization. Inhibition of KV1 channels with 4-aminopyridine (4-AP) or treatment with the epidermal growth factor receptor agonist heparin-binding EGF (HB-EGF), which promotes KV1 channel endocytosis, reduced KV current density and restored myogenic responses in PAs from TgNotch3R169C mice, whereas pharmacological inhibition of other major vasodilatory influences had no effect. KV1 currents and myogenic responses were similarly altered in pial arteries from TgNotch3R169C mice, but not in mesenteric arteries. Interestingly, HB-EGF had no effect on mesenteric arteries, suggesting a possible mechanistic basis for the exclusive cerebrovascular manifestation of CADASIL. Collectively, our results indicate that increasing the number of KV1 channels in cerebral smooth muscle produces a mutant vascular phenotype akin to a channelopathy in a genetic model of SVD.

International audience; Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, or CADASIL, one of the most common inherited small vessel diseases of the brain, is characterized by a progressive loss of vascular smooth muscle cells and extracellular matrix accumulation. The disease is caused by highly stereotyped mutations within the extracellular domain of the NOTCH3 receptor (Notch3(ECD)) that result in an odd number of cysteine residues. While CADASIL-associated NOTCH3 mutations differentially affect NOTCH3 receptor function and activity, they all are associated with early accumulation of Notch3(ECD)-containing aggregates in small vessels. We still lack mechanistic explanation to link NOTCH3 mutations with small vessel pathology. Herein, we hypothesized that excess Notch3(ECD) could recruit and sequester functionally important proteins within small vessels of the brain. We performed biochemical, nano-liquid chromatography-tandem mass spectrometry and immunohistochemical analyses, using cerebral and arterial tissue derived from patients with CADASIL and mouse models of CADASIL that exhibit vascular lesions in the end- and early-stage of the disease, respectively. Biochemical fractionation of brain and artery samples demonstrated that mutant Notch3(ECD) accumulates in disulphide cross-linked detergent-insoluble aggregates in mice and patients with CADASIL. Further proteomic and immunohistochemical analyses identified two functionally important extracellular matrix proteins, tissue inhibitor of metalloproteinases 3 (TIMP3) and vitronectin (VTN) that are sequestered into Notch3(ECD)-containing aggregates. Using cultured cells, we show that increased levels or aggregation of Notch3 enhances the formation of Notch3(ECD)-TIMP3 complex, promoting TIMP3 recruitment and accumulation. In turn, TIMP3 promotes complex formation including NOTCH3 and VTN. In vivo, brain vessels from mice and patients with CADASIL exhibit elevated levels of both insoluble cross-linked and soluble TIMP3 species. Moreover, reverse zymography assays show a significant elevation of TIMP3 activity in the brain vessels from mice and patients with CADASIL. Collectively, our findings lend support to a Notch3(ECD) cascade hypothesis in CADASIL disease pathology, which posits that aggregation/accumulation of Notch3(ECD) in the brain vessels is a central event, promoting the abnormal recruitment of functionally important extracellular matrix proteins that may ultimately cause multifactorial toxicity. Specifically, our results suggest a dysregulation of TIMP3 activity, which could contribute to mutant Notch3(ECD) toxicity by impairing extracellular matrix homeostasis in small vessels.

Objective— Notch3 is critically important for the structure and myogenic response of distal arteries, particularly of cerebral arteries. However, signaling pathways acting downstream of Notch3 remain largely unknown. Methods and Results— Transcriptome analysis using tail arteries of Notch3-null mice identified a core set of 17 novel Notch3-regulated genes confirmed in tail or brain arteries. Postnatal deletion of RBP-Jκ in smooth muscle cells recapitulated the structural, functional, and molecular defects of brain arteries induced by Notch3 deficiency. Transient in vivo blockade of the Notch pathway with γ-secretase inhibitors uncovered, in addition to Notch3 , 6 immediate responders, including the voltage-gated potassium channel Kv1.5, which opposes to myogenic constriction of brain arteries, and the glutamate receptor–interacting protein 2 (Grip2) with no previously established role in the cerebrovasculature. We identified a vascular smooth muscle cell isoform of Grip2 . We showed that Notch3–RBP-Jκ specifically regulates this isoform. Finally, we found that cerebral arteries of Grip2 mutant mice, which express an N-terminally truncated Grip2 protein, exhibited selective attenuation of pressure-induced contraction. Conclusion— Our data provide insight into how Notch3 signals in the brain arteries, establishing the postnatal requirement of smooth muscle RBP-Jκ in this context. Notch3-regulated transcriptome provides potential for modulating myogenic response in the cerebrovasculature.

Introduction Small vessel disease (SVD) of the brain is a leading cause of age- and hypertension-related cognitive decline and disability. Cerebral white matter changes are a consistent manifestation of SVD on neuroimaging, progressing silently for many years before becoming clinically evident. The pathogenesis of these changes remains poorly understood, despite their importance. In particular, their pathological correlate at early stages remains largely undefined. Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL), caused by dominant mutations of the NOTCH3 receptor, is regarded as a paradigm for the most common form of sporadic SVD. In this study, we used immunohistochemistry, confocal microscopy and electron microscopy, together with qualitative and quantitative analyses to assess oligodendroglial, axon and myelin damage in TgPAC-Notch3R169C mice, a model of preclinical CADASIL. Results The principal cerebral white matter changes in TgPAC-Notch3R169C mice are microvacuoles (≤1 μm diameter) in the myelin sheaths associated with focal myelin degradation and occurring in the absence of oligodendrocyte loss. Half the damaged myelin sheaths still contain an apparently intact axon. Clearance of myelin debris appears inefficient, as demonstrated by the significant but mild microglial reaction, with occasional myelin debris either contacted or internalized by microglial cells. Conclusion Our findings suggest that segmental intramyelinic oedema is an early, conspicuous white matter change in CADASIL. Brain white matter intramyelinic oedema is consistently found in patients and mouse models with compromised ion and water homeostasis. These data provide a starting point for novel mechanistic studies to investigate the pathogenesis of SVD-related white matter changes. Electronic supplementary material The online version of this article (doi:10.1186/2051-5960-2-49) contains supplementary material, which is available to authorized users.