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Mutations in leucine-rich repeat kinase 2 (LRRK2) cause late-onset Parkinson's disease (PD), but the underlying pathophysiological mechanisms and the normal function of this large multidomain protein remain speculative. To address the role of this protein in vivo, we generated three different LRRK2 mutant mouse lines. Mice completely lacking the LRRK2 protein (knock-out, KO) showed an early-onset (age 6 weeks) marked increase in number and size of secondary lysosomes in kidney proximal tubule cells and lamellar bodies in lung type II cells. Mice expressing a LRRK2 kinase-dead (KD) mutant from the endogenous locus displayed similar early-onset pathophysiological changes in kidney but not lung. KD mutants had dramatically reduced full-length LRRK2 protein levels in the kidney and this genetic effect was mimicked pharmacologically in wild-type mice treated with a LRRK2-selective kinase inhibitor. Knock-in (KI) mice expressing the G2019S PD-associated mutation that increases LRRK2 kinase activity showed none of the LRRK2 protein level and histopathological changes observed in KD and KO mice. The autophagy marker LC3 remained unchanged but kidney mTOR and TCS2 protein levels decreased in KD and increased in KO and KI mice. Unexpectedly, KO and KI mice suffered from diastolic hypertension opposed to normal blood pressure in KD mice. Our findings demonstrate a role for LRRK2 in kidney and lung physiology and further show that LRRK2 kinase function affects LRRK2 protein steady-state levels thereby altering putative scaffold/GTPase activity. These novel aspects of peripheral LRRK2 biology critically impact ongoing attempts to develop LRRK2 selective kinase inhibitors as therapeutics for PD.

Human beta-amyloid precursor protein (APP) transgenic mice are commonly used to test potential therapeutics for Alzheimer's disease. We have characterized the dynamics of beta-amyloid (Abeta) generation and deposition following gamma-secretase inhibition with compound LY-411575 [N(2)-[(2S)-2-(3,5-difluorophenyl)-2-hydroxyethanoyl]-N(1)-[(7S)-5-methyl-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-yl]-L-alaninamide]. Kinetic studies in preplaque mice distinguished a detergent-soluble Abeta pool in brain with rapid turnover (half-lives for Abeta40 and Abeta42 were 0.7 and 1.7 h) and a much more stable, less soluble pool. Abeta in cerebrospinal fluid (CSF) reflected the changes in the soluble brain Abeta pool, whereas plasma Abeta turned over more rapidly. In brain, APP C-terminal fragments (CTF) accumulated differentially. The half-lives for gamma-secretase degradation were estimated as 0.4 and 0.1 h for C99 and C83, respectively. Three different APP transgenic lines responded very similarly to gamma-secretase inhibition regardless of the familial Alzheimer's disease mutations in APP. Amyloid deposition started with Abeta42, whereas Abeta38 and Abeta40 continued to turn over. Chronic gamma-secretase inhibition lowered amyloid plaque formation to a different degree in different brain regions of the same mice. The extent was inversely related to the initial amyloid load in the region analyzed. No evidence for plaque removal below baseline was obtained. gamma-Secretase inhibition led to a redistribution of intracellular Abeta and an elevation of CTFs in neuronal fibers. In CSF, Abeta showed a similar turnover as in preplaque animals demonstrating its suitability as marker of newly generated, soluble Abeta in plaque-bearing brain. This study supports the use of APP transgenic mice as translational models to characterize Abeta-lowering therapeutics.

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-beta40 peptide (Abeta40) to Abeta42 was significantly higher than that seen in APPwt mice or AD human brain. Genetically shifting the ratio of AbetaDutch40/AbetaDutch42 toward AbetaDutch42 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 Abeta 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 Abeta to vascular amyloid pathology and emphasizing the differing roles of Abeta40 and Abeta42 in vascular and parenchymal amyloid pathology.

The discovery of two missense mutations (A53T and A30P) in the gene encoding the presynaptic protein alpha-synuclein (alphaSN) that are genetically linked to rare familial forms of Parkinson's disease and its accumulation in Lewy bodies and Lewy neurites has triggered several attempts to generate transgenic mice overexpressing human alphaSN. Analogous to a successful strategy for the production of transgenic animal models for Alzheimer's disease we generated mice expressing wildtype and the A53T mutant of human alphaSN in the nervous system under control of mouse Thy1 regulatory sequences. These animals develop neuronal alpha-synucleinopathy, striking features of Lewy pathology, neuronal degeneration and motor defects. Neurons in brainstem and motor neurons appeared particularly vulnerable. Motor neuron pathology included axonal damage and denervation of neuromuscular junctions, suggesting that alphaSN may interfere with a universal mechanism of synapse maintenance. Thy1-transgene expression of wildtype human alphaSN resulted in comparable pathological changes thus supporting a central role for mutant and wildtype alphaSN in familial and idiopathic forms of diseases with neuronal alpha-synucleinopathy and Lewy pathology. The mouse models provide means to address fundamental aspects of alpha-synucleinopathy and to test therapeutic strategies.

An early role of amyloid-β peptide (Aβ) aggregation in Alzheimer's disease pathogenesis is well established. However, the contribution of intracellular or extracellular forms of Aβ to the neurodegenerative process is a subject of considerable debate. We here describe transgenic mice expressing Aβ1–40(APP47) and Aβ1–42(APP48) with a cleaved signal sequence to insert both peptides during synthesis into the endoplasmic reticulum. Although lower in transgene mRNA, APP48 mice reach a higher brain Aβ concentration. The reduced solubility and increased aggregation of Aβ1–42may impair its degradation. APP48 mice develop intracellular Aβ lesions in dendrites and lysosomes. The hippocampal neuron number is reduced already at young age. The brain weight decreases during aging in conjunction with severe white matter atrophy. The mice show a motor impairment. Only very few Aβ1–40lesions are found in APP47 mice. Neither APP47 nor APP48 nor the bigenic mice develop extracellular amyloid plaques. While intracellular membrane expression of Aβ1–42in APP48 mice does not lead to the AD-typical lesions, Aβ aggregates develop within cells accompanied by considerable neurodegeneration.

The role of neuropeptides and the significance of peptidergic mechanisms in neurodegenerative diseases are still unclear. In the periphery, nerve injury results in dramatic changes in the expression of neuropeptides. An important question regards to what extent similar changes occur, and similar mechanisms operate, after lesions and/or degeneration in the brain. The purpose of this work is, therefore, to study neuropeptides with regard to their presence and distribution in the APP23 mouse (HuAPP(751) K670M/N671L under the murine Thy-1 promoter), a model for Alzheimer's disease, or cerebral amyloidosis, using the immunohistochemical technique. In addition, tyrosine hydroxylase and acetylcholinesterase were analyzed. This study shows marked neuropeptide changes in the hippocampal formation and the ventral cortex, whereas the dorsolateral neocortex was less affected. There was a considerable variation with regard to peptide expression among animals of the same age which was related to the variation in Abeta deposition. Dystrophic and varicose fibers containing galanin, neuropeptide Y, enkephalin, and especially cholecystokinin were commonly seen in close proximity to amyloid plaques. In addition, generalized changes were observed, such as increases of enkephalin and neuropeptide Y in stratum lacunosum moleculare and of neuropeptide Y, enkephalin, and dynorphin in mossy fibers. In contrast, cholecystokinin was decreased in mossy fibers. Comparatively small differences were observed between wild-type and transgenic mice with regard to tyrosine hydroxylase (noradrenergic but also dopaminergic fibers) and acetylcholine esterase (mainly cholinergic fibers). The increase of neuropeptides in dystrophic fibers in this model may represent a response to nerve injury caused by the amyloid accumulation and may reflect attempts to counteract degeneration by initiating protective and/or regenerative processes.

beta-Site APP-cleaving enzyme (BACE) initiates the processing of the amyloid precursor protein (APP) leading to the generation of beta-amyloid, the main component of Alzheimer's disease senile plaques. BACE (Asp2, memapsin 2) is a type I transmembrane aspartyl protease and is responsible for the beta-secretase cleavage of APP producing different endoproteolytic fragments referred to as the carboxy-terminal C99, C89 and the soluble ectodomain sAPPbeta. Here we describe two transgenic mouse lines expressing human BACE in the brain. Overexpression of BACE augments the amyloidogenic processing of APP as demonstrated by decreased levels of full-length APP and increased levels of C99 and C89 in vivo. In mice expressing huBACE in addition to human APP wild-type or carrying the Swedish mutation, the induction of APP processing characterized by elevated C99, C89 and sAPPbeta, results in increased brain levels of beta-amyloid peptides Abeta40 and Abeta42 at steady-state.

Lesions can affect the nervous system in many different ways and lead to more or less serious consequences. Our approach has over a period of 15 years been to study the effect of injury on dorsal root ganglion (DRG) neurons projecting into the sciatic nerve and to the dorsal horn of the spinal cord. The most simple approach is to completely transect the sciatic nerve and study the consequences of this injury in the parent cell bodies in the DRGs. This model may have some significance for our understanding of the mechanisms underlying pain that emerges in some patients after various types of surgical procedures, so called neuropathic pain (see 1). It has also been suggested that this model may be relevant for studying neurodegeneration (see refs. in 2). Our work on DRGs has led us to ask questions to what extent the changes we see in DRG neurons occur also in other neuronal systems. In fact, peptide regulation occurs in several systems in the brain in response to nerve injury (see 3). We have then turned our attention to established neurodegenerative diseases. In particular, we have analysed some mouse models for Alzheimer’s disease (AD), as will be described below.

The presynaptic protein alpha-synuclein is a prime suspect for contributing to Lewy pathology and clinical aspects of diseases, including Parkinson's disease, dementia with Lewy bodies, and a Lewy body variant of Alzheimer's disease. alpha-Synuclein accumulates in Lewy bodies and Lewy neurites, and two missense mutations (A53T and A30P) in the alpha-synuclein gene are genetically linked to rare familial forms of Parkinson's disease. Under control of mouse Thy1 regulatory sequences, expression of A53T mutant human alpha-synuclein in the nervous system of transgenic mice generated animals with neuronal alpha-synucleinopathy, features strikingly similar to those observed in human brains with Lewy pathology, neuronal degeneration, and motor defects, despite a lack of transgene expression in dopaminergic neurons of the substantia nigra pars compacta. Neurons in brainstem and motor neurons appeared particularly vulnerable. Motor neuron pathology included axonal damage and denervation of neuromuscular junctions in several muscles examined, suggesting that alpha-synuclein interfered with a universal mechanism of synapse maintenance. Thy1 transgene expression of wild-type human alpha-synuclein resulted in similar pathological changes, thus supporting a central role for mutant and wild-type alpha-synuclein in familial and idiotypic forms of diseases with neuronal alpha-synucleinopathy and Lewy pathology. These mouse models provide a means to address fundamental aspects of alpha-synucleinopathy and test therapeutic strategies.

Vascular endothelial growth factor (VEGF) is an endothelial cell specific mitogen that has been implicated in hypoxia-mediated angiogenesis under physiological and pathological conditions. We used the middle cerebral artery occlusion model (MCAO) in the rat to investigate VEGF mRNA and protein localization, and VEGFR-1 mRNA and VEGFR-2 mRNA expression in cerebral ischemia. By nonradioactive in situ hybridization we observed upregulation of VEGF mRNA and VEGFR-1 mRNA, but not of VEGFR-2 mRNA in the hemisphere ipsilateral to MCA occlusion. VEGF mRNA was upregulated in the periphery of the ischemic area commencing 3 hours (h) after onset of MCAO, reached a peak after 24 h, and remained expressed at lower levels until 7 days (d) after MCAO. Double labelling experiments revealed that the majority of VEGF expressing cells in the penumbra and within the infarct were immunoreactive for Ox-42, lba-1, and Ed1, but not for GFAP and neurofilament proteins, suggesting that microglial cells/macrophages are the major cell type expressing VEGF. Since VEGF was also expressed in Ox-42 immunoreactive cells distant from the infarct (e.g. in the corpus callosum and hippocampus), activated microglial cells expressing VEGF may migrate towards the ischemic stimulus. VEGF protein was also detected on capillaries within the peri-ischemic area, suggesting that VEGF produced and secreted by microglial cells/macrophages binds to its receptors on nearby vascular endothelial cells and initiates an angiogenic response which counterbalances tissue hypoxia. Accordingly, apoptosis of neuroectodermal cells in the penumbra was highly depressed after the onset of angiogenesis. The spatial and temporal correlation between the induction of angiogenesis with VEGF and VEGFR-1 expression suggests that the ischemic upregulation of VEGF represents a physiological response of the brain to counterbalance hypoxia/ischemia in order to protect neuroectodermal tissue.

The vascular endothelial growth factor (VEGF) has been shown to be upregulated in acute hypoxia. Although an increase in blood vessel number has been described in severe chronic brain hypoxia, it is unclear whether VEGF is upregulated in this condition. We therefore investigated male inbred Wistar rats, which were exposed for 9 to 13 weeks to decreasing amounts of oxygen, down to 7% O2 (15%: 15 days; 12%, 10%, respectively; 8%: 1 day, 3 weeks, respectively; 7%: 4 weeks). The expression of VEGF was studied by Northern analysis and in situ hybridization in frozen sections of cerebral cortex, hippocampus and cerebellum in six chronic hypoxic and two control rats. We found a marked upregulation of VEGF mRNA in all brain regions investigated, being strongest in cerebral cortex and cerebellum. Our results suggest a potential role of VEGF for vascular growth and vascular permeability observed in chronic cerebral hypoxia.

α-Synuclein (αSN) in human is tightly linked both neuropathologically and genetically to Parkinson's disease (PD) and related disorders. Disease-causing properties in vivo of the wildtype mouse ortholog (mαSN), which carries a threonine at position 53 like the A53T human mutant version that is genetically linked to PD, were never reported. To this end we generated mouse lines that express mαSN in central neurons at levels reaching up to six-fold compared to endogenous mαSN. Unlike transgenic mice expressing human wildtype or mutant forms of αSN, these mαSN transgenic mice showed pronounced ubiquitin immunopathology in spinal cord and brainstem. Isoelectric separation of mαSN species revealed multiple isoforms including two Ser129-phosphorylated species in the most severely affected brain regions. Neuronal Ser129-phosphorylated αSN occurred in granular and small fibrillar aggregates and pathological staining patterns in neurites occasionally revealed a striking ladder of small alternating segments staining either for Ser129-phosphorylated αSN or ubiquitin but not both. Axonal degeneration in long white matter tracts of the spinal cord, with breakdown of myelin sheaths and degeneration of neuromuscular junctions with loss of integrity of the presynaptic neurofilament network in mαSN transgenic mice, was similar to what we have reported for mice expressing human αSN wildtype or mutant forms. In hippocampal neurons, the mαSN protein accumulated and was phosphorylated but these neurons showed no ubiquitin immunopathology. In contrast to the early-onset motor abnormalities and muscle weakness observed in mice expressing human αSN, mαSN transgenic mice displayed only end-stage phenotypic alterations that manifested alongside with neuropathology. Altogether these findings show that increased levels of wildtype mαSN does not induce early-onset behavior changes, but drives end-stage pathophysiological changes in murine neurons that are strikingly similar to those evoked by expression of human wildtype or mutant forms.