David T. Winkler

Aβ is targeted to the vasculature in a mouse model of hereditary cerebral hemorrhage with amyloidosis

The E693Q mutation in the amyloid beta precursor protein (APP) leads to cerebral amyloid angiopathy (CAA), with recurrent cerebral hemorrhagic strokes and dementia. In contrast to Alzheimer disease (AD), the brains of those affected by hereditary cerebral hemorrhage with amyloidosis–Dutch type (HCHWA-D) show few parenchymal amyloid plaques. We found that neuronal overexpression of human E693Q APP in mice (APPDutch mice) caused extensive CAA, smooth muscle cell degeneration, hemorrhages and neuroinflammation. In contrast, overexpression of human wild-type APP (APPwt mice) resulted in predominantly parenchymal amyloidosis, similar to that seen in AD. In APPDutch mice and HCHWA-D human brain, the ratio of the amyloid-β40 peptide (Aβ40) to Aβ42 was significantly higher than that seen in APPwt mice or AD human brain. Genetically shifting the ratio of AβDutch40/AβDutch42 toward AβDutch42 by crossing APPDutch mice with transgenic mice producing mutated presenilin-1 redistributed the amyloid pathology from the vasculature to the parenchyma. The understanding that different Aβ species can drive amyloid pathology in different cerebral compartments has implications for current anti-amyloid therapeutic strategies. This HCHWA-D mouse model is the first to develop robust CAA in the absence of parenchymal amyloid, highlighting the key role of neuronally produced Aβ to vascular amyloid pathology and emphasizing the differing roles of Aβ40 and Aβ42 in vascular and parenchymal amyloid pathology.

Brain homogenates from human tauopathies induce tau inclusions in mouse brain.

Filamentous inclusions made of hyperphosphorylated tau are characteristic of numerous human neurodegenerative diseases, including Alzheimer’s disease, tangle-only dementia, Pick disease, argyrophilic grain disease (AGD), progressive supranuclear palsy, and corticobasal degeneration. In Alzheimer’s disease and AGD, it has been shown that filamentous tau appears to spread in a stereotypic manner as the disease progresses. We previously demonstrated that the injection of brain extracts from human mutant P301S tau-expressing transgenic mice into the brains of mice transgenic for wild-type human tau (line ALZ17) resulted in the assembly of wild-type human tau into filaments and the spreading of tau inclusions from the injection sites to anatomically connected brain regions. Here we injected brain extracts from humans who had died with various tauopathies into the hippocampus and cerebral cortex of ALZ17 mice. Argyrophilic tau inclusions formed in all cases and following the injection of the corresponding brain extracts, we recapitulated the hallmark lesions of AGD, PSP and CBD. Similar inclusions also formed after intracerebral injection of brain homogenates from human tauopathies into nontransgenic mice. Moreover, the induced formation of tau aggregates could be propagated between mouse brains. These findings suggest that once tau aggregates have formed in discrete brain areas, they become self-propagating and spread in a prion-like manner.

Spontaneous Hemorrhagic Stroke in a Mouse Model of Cerebral Amyloid Angiopathy

A high risk factor for spontaneous and often fatal lobar hemorrhage is cerebral amyloid angiopathy (CAA). We now report that CAA in an amyloid precursor protein transgenic mouse model (APP23 mice) leads to a loss of vascular smooth muscle cells, aneurysmal vasodilatation, and in rare cases, vessel obliteration and severe vasculitis. This weakening of the vessel wall is followed by rupture and bleedings that range from multiple, recurrent microhemorrhages to large hematomas. Our results demonstrate that, in APP transgenic mice, the extracellular deposition of neuron-derived β-amyloid in the vessel wall is the cause of vessel wall disruption, which eventually leads to parenchymal hemorrhage. This first mouse model of CAA-associated hemorrhagic stroke will now allow development of diagnostic and therapeutic strategies.

Stimulation of autophagy reduces neurodegeneration in a mouse model of human tauopathy

The accumulation of insoluble proteins is a pathological hallmark of several neurodegenerative disorders. Tauopathies are caused by the dysfunction and aggregation of tau protein and an impairment of cellular protein degradation pathways may contribute to their pathogenesis. Thus, a deficiency in autophagy can cause neurodegeneration, while activation of autophagy is protective against some proteinopathies. Little is known about the role of autophagy in animal models of human tauopathy. In the present report, we assessed the effects of autophagy stimulation by trehalose in a transgenic mouse model of tauopathy, the human mutant P301S tau mouse, using biochemical and immunohistochemical analyses. Neuronal survival was evaluated by stereology. Autophagy was activated in the brain, where the number of neurons containing tau inclusions was significantly reduced, as was the amount of insoluble tau protein. This reduction in tau aggregates was associated with improved neuronal survival in the cerebral cortex and the brainstem. We also observed a decrease of p62 protein, suggesting that it may contribute to the removal of tau inclusions. Trehalose failed to activate autophagy in the spinal cord, where it had no impact on the level of sarkosyl-insoluble tau. Accordingly, trehalose had no effect on the motor impairment of human mutant P301S tau transgenic mice. Our findings provide direct evidence in favour of the degradation of tau aggregates by autophagy. Activation of autophagy may be worth investigating in the context of therapies for human tauopathies.

Cystatin C modulates cerebral |[beta]|-amyloidosis

The CST3 Thr25 allele of CST3, which encodes cystatin C, leads to reduced cystatin C secretion and conveys susceptibility to Alzheimers disease. Here we show that overexpression of human cystatin C in brains of APP-transgenic mice reduces cerebral amyloid-β deposition and that cystatin C binds amyloid-β and inhibits its fibril formation. Our results suggest that cystatin C concentrations modulate cerebral amyloidosis risk and provide an opportunity for genetic risk assessment and therapeutic interventions.

Rapamycin attenuates the progression of tau pathology in P301S tau transgenic mice.

Altered autophagy contributes to the pathogenesis of Alzheimer’s disease and other tauopathies, for which curative treatment options are still lacking. We have recently shown that trehalose reduces tau pathology in a tauopathy mouse model by stimulation of autophagy. Here, we studied the effect of the autophagy inducing drug rapamycin on the progression of tau pathology in P301S mutant tau transgenic mice. Rapamycin treatment resulted in a significant reduction in cortical tau tangles, less tau hyperphosphorylation, and lowered levels of insoluble tau in the forebrain. The favourable effect of rapamycin on tau pathology was paralleled by a qualitative reduction in astrogliosis. These effects were visible with early preventive or late treatment. We further noted an accumulation of the autophagy associated proteins p62 and LC3 in aged tangle bearing P301S mice that was lowered upon rapamycin treatment. Thus, rapamycin treatment defers the progression of tau pathology in a tauopathy animal model and autophagy stimulation may constitute a therapeutic approach for patients suffering from tauopathies.

Mechanisms of cerebrovascular amyloid deposition. Lessons from mouse models.

Abstract: Cerebrovascular deposition of amyloid is a frequent observation in Alzheimers disease patients. It can also be detected sporadically in normal aged individuals and is further found in familial diseases linked to specific gene mutations. The source and mechanism of this pathology are still unknown. It has been suggested that amyloidogenic proteins are derived from blood, the vessel wall itself, or from the central nervous system. in this article evidence is reviewed for and against each of these hypotheses, including new data obtained from transgenic mouse models. in app23 transgenic mice that develop cerebral amyloid angiopathy (CAA) in addition to amyloid plaques, the transport and drainage of neuronally produced amyloid‐β (aβ) seem to be responsible for CAA rather than vascular aβ production or blood uptake. although a number of mechanisms may contribute to CAA in humans, these results suggest that a neuronal source of aβ is sufficient to induce vascular amyloid deposition. The possibility to cross genetically defined mouse models of CAA with other mutant mice now has the potential to identify molecular mechanisms of CAA.

Thrombolysis induces cerebral hemorrhage in a mouse model of cerebral amyloid angiopathy

We studied the impact of cerebral amyloid angiopathy on tissue plasminogen activator‐induced cerebral hemorrhages in APP23 transgenic mice. Results show that the intravenous administration of tissue plasminogen activator in APP23 mice leads to an increase in cerebral amyloid angiopathy‐associated microhemorrhages and can provoke parenchymal and subarachnoidal hematomas. We conclude that cerebral amyloid angiopathy is a risk factor for cerebral hemorrhage caused by tissue plasminogen activator administration in mice and stress the need for more comprehensive studies of the relation between cerebral amyloid angiopathy and tissue plasminogen activator‐induced cerebral hemorrhages in elderly and Alzheimers disease patients.

Highly potent soluble amyloid-β seeds in human Alzheimer brain but not cerebrospinal fluid

The soluble fraction of brain samples from patients with Alzheimers disease contains highly biologically active amyloid-β seeds. In this study, we sought to assess the potency of soluble amyloid-β seeds derived from the brain and cerebrospinal fluid. Soluble Alzheimers disease brain extracts were serially diluted and then injected into the hippocampus of young, APP transgenic mice. Eight months later, seeded amyloid-β deposition was evident even when the hippocampus received subattomole amounts of brain-derived amyloid-β. In contrast, cerebrospinal fluid from patients with Alzheimers disease, which contained more than 10-fold higher levels of amyloid-β peptide than the most concentrated soluble brain extracts, did not induce detectable seeding activity in vivo. Similarly, cerebrospinal fluid from aged APP-transgenic donor mice failed to induce cerebral amyloid-β deposition. In comparison to the soluble brain fraction, cerebrospinal fluid largely lacked N-terminally truncated amyloid-β species and exhibited smaller amyloid-β-positive particles, features that may contribute to the lack of in vivo seeding by cerebrospinal fluid. Interestingly, the same cerebrospinal fluid showed at least some seeding activity in an in vitro assay. The present results indicate that the biological seeding activity of soluble amyloid-β species is orders of magnitude greater in brain extracts than in the cerebrospinal fluid.

TREX1 C-terminal frameshift mutations in the systemic variant of retinal vasculopathy with cerebral leukodystrophy

AbstractRetinal vasculopathy with cerebral leukodystrophy (RVCL) is an adult-onset disorder caused by C-terminal heterozygous frameshift (fs) mutations in the human 3′–5′ DNA exonuclease TREX1. Hereditary systemic angiopathy (HSA) is considered a variant of RVCL with systemic involvement of unknown genetic cause, described in a unique family so far. Here we describe the second case of RVCL with systemic involvement, characterized by cerebral calcifications and pseudotumoral lesions, retinopathy, osteonecrosis, renal and hepatic failure. The genetic screening of TREX1 in this patient revealed the novel heterozygous T270fs mutation on the C-terminal region. On the same gene, we found the V235fs mutation, formerly shown in RVCL, in one patient previously reported with HSA. These mutations lead to important alterations of the C-terminal of the protein, with the loss of the transmembrane helix (T270fs) and the insertion of a premature stop codon, resulting in a truncated protein (V235fs). Functional analysis of T270fs-mutated fibroblasts showed a prevalent localization of the protein in the cytosol, rather than in the perinuclear region. RVCL with systemic involvement is an extremely rare condition, whose diagnosis is complex due to multiorgan manifestations, unusual radiological and histopathological findings, not easily attributable to a single disease. It should be suspected in young adults with systemic microangiopathy involving retina, liver, kidney, bones and brain. Here we confirm the causative role played by TREX1 autosomal dominant fs mutations disrupting the C-terminal of the protein, providing a model for the study of stroke in young adults.