Spinocerebellar ataxia type 19/22 mutations alter heterocomplex Kv4.3 channel function and gating in a dominant manner

The dominantly inherited cerebellar ataxias are a heterogeneous group of neurodegenerative disorders caused by Purkinje cell loss in the cerebellum. Recently, we identified loss-of-function mutations in the KCND3 gene as the cause of spinocerebellar ataxia type 19/22 (SCA19/22), revealing a previously unknown role for the voltage-gated potassium channel, Kv4.3, in Purkinje cell survival. However, how mutant Kv4.3 affects wild-type Kv4.3 channel functioning remains unknown. We provide evidence that SCA19/22-mutant Kv4.3 exerts a dominant negative effect on the trafficking and surface expression of wild-type Kv4.3 in the absence of its regulatory subunit, KChIP2. Notably, this dominant negative effect can be rescued by the presence of KChIP2. We also found that all SCA19/22-mutant subunits either suppress wild-type Kv4.3 current amplitude or alter channel gating in a dominant manner. Our findings suggest that altered Kv4.3 channel localization and/or functioning resulting from SCA19/22 mutations may lead to Purkinje cell loss, neurodegeneration and ataxia

Increased White Matter Inflammation in Aging- and Alzheimer's Disease Brain

Chronic neuroinflammation, which is primarily mediated by microglia, plays an essential role in aging and neurodegeneration. It is still unclear whether this microglia-induced neuroinflammation occurs globally or is confined to distinct brain regions. In this study, we investigated microglia activity in various brain regions upon healthy aging and Alzheimer's disease (AD)-related pathology in both human and mouse samples. In purified microglia isolated from aging mouse brains, we found a profound gene expression pattern related to pro-inflammatory processes, phagocytosis, and lipid homeostasis. Particularly in white matter microglia of 24-month-old mice, abundant expression of phagocytic markers including Mac-2, Axl, CD16/32, Dectin1, CD11c, and CD36 was detected. Interestingly, in white matter of human brain tissue the first signs of inflammatory activity were already detected during middle age. Thus quantification of microglial proteins, such as CD68 (commonly associated with phagocytosis) and HLA-DR (associated with antigen presentation), in postmortem human white matter brain tissue showed an age-dependent increase in immunoreactivity already in middle-aged people (53.2 +/- 2.0 years). This early inflammation was also detectable by non-invasive positron emission tomography imaging using [C-11]-(R)-PK11195, a ligand that binds to activated microglia. Increased microglia activity was also prominently present in the white matter of human postmortem early-onset AD (EOAD) brain tissue. Interestingly, microglia activity in the white matter of late-onset AD (LOAD) CNS was similar to that of the aged clinically silent AD cases. These data indicate that microglia-induced neuroinflammation is predominant in the white matter of aging mice and humans as well as in EOAD brains. This white matter inflammation may contribute to the progression of neurodegeneration, and have prognostic value for detecting the onset and progression of aging and neurodegeneration

Intrinsic DNA damage repair deficiency results in progressive microglia loss and replacement

The DNA excision repair protein Ercc1 is important for nucleotide excision, double strand DNA break, and interstrand DNA crosslink repair. In constitutiveErcc1-knockout mice, microglia display increased phagocytosis, proliferation and an enhanced responsiveness to lipopolysaccharide (LPS)-induced peripheral inflammation. However, the intrinsic effects ofErcc1-deficiency on microglia are unclear. In this study,Ercc1was specifically deleted from Cx3cr1-expressing cells and changes in microglia morphology and immune responses at different times after deletion were determined. Microglia numbers were reduced with approximately 50% at 2-12 months afterErcc1deletion. Larger and more ramified microglia were observed followingErcc1deletion both in vivo and in organotypic hippocampal slice cultures.Ercc1-deficient microglia were progressively lost, and during this period, microglia proliferation was transiently increased.Ercc1-deficient microglia were gradually replaced by nondeficient microglia carrying a functionalErcc1allele. In contrast to constitutiveErcc1-deficient mice, microglia-specific deletion ofErcc1did not induce microglia activation or increase their responsiveness to a systemic LPS challenge. Gene expression analysis suggested thatErcc1deletion in microglia induced a transient aging signature, which was different from a priming or disease-associated microglia gene expression profile.</p

Characterizing microglial gene expression in a model of secondary progressive multiple sclerosis

Multiple sclerosis (MS) is the most common inflammatory, demyelinating and neurodegenerative disease of the central nervous system in young adults. Chronic-relapsing experimental autoimmune encephalomyelitis (crEAE) in Biozzi ABH mice is an experimental model of MS. This crEAE model is characterized by an acute phase with severe neurological disability, followed by remission of disease, relapse of neurological disease and remission that eventually results in a chronic progressive phase that mimics the secondary progressive phase (SPEAE) of MS. In both MS and SPEAE, the role of microglia is poorly defined. We used a crEAE model to characterize microglia in the different phases of crEAE phases using morphometric and RNA sequencing analyses. At the initial, acute inflammation phase, microglia acquired a pro-inflammatory phenotype. At the remission phase, expression of standard immune activation genes was decreased while expression of genes associated with lipid metabolism and tissue remodeling were increased. Chronic phase microglia partially regain inflammatory gene sets and increase expression of genes associated with proliferation. Together, the data presented here indicate that microglia obtain different features at different stages of crEAE and a particularly mixed phenotype in the chronic stage. Understanding the properties of microglia that are present at the chronic phase of EAE will help to understand the role of microglia in secondary progressive MS, to better aid the development of therapies for this phase of the disease

Impairment of mitochondria dynamics by human A53T alpha-synuclein and rescue by NAP (davunetide) in a cell model for Parkinson's disease

The formation of oligomers and aggregates of overexpressed or mutant alpha-synuclein play a role in the degeneration of dopaminergic neurons in Parkinson's disease by causing dysfunction of mitochondria, reflected in their disturbed mobility and production of ROS. The mode of action and mechanisms underlying this mitochondrial impairment is still unclear. We have induced stable expression of wild-type, A30P or A53T alpha-synuclein in neuronally differentiated SH-SY5Y neuroblastoma cells and studied anterograde and retrograde mitochondrial trafficking in this cell model for Parkinson's disease. In contrast to wild-type and A30P, A53T alpha-synuclein significantly inhibited mitochondrial trafficking, at first retrogradely and in a later stage anterogradely. Accordingly, A53T alpha-synuclein also caused the highest increase in ROS production in the dysmobilized mitochondria in comparison to wild-type or A30P alpha-synuclein. Treatment with NAP, the eight amino acid peptide identified as the active component of activity-dependent neuroprotective protein (ADNP), completely annihilated the adverse effects of A53T on mitochondrial dynamics. Our results reveal that A53T alpha-synuclein (oligomers or aggregates) leads to the inhibition of mitochondrial trafficking, which can be rescued by NAP, suggesting the involvement of microtubule disruption in the pathophysiology of Parkinson's disease

Priming of microglia in a DNA-repair deficient model of accelerated aging

AbstractAging is associated with reduced function, degenerative changes, and increased neuroinflammation of the central nervous system (CNS). Increasing evidence suggests that changes in microglia cells contribute to the age-related deterioration of the CNS. The most prominent age-related change of microglia is enhanced sensitivity to inflammatory stimuli, referred to as priming. It is unclear if priming is due to intrinsic microglia ageing or induced by the ageing neural environment. We have studied this in Ercc1 mutant mice, a DNA repair-deficient mouse model that displays features of accelerated aging in multiple tissues including the CNS. In Ercc1 mutant mice, microglia showed hallmark features of priming such as an exaggerated response to peripheral lipopolysaccharide exposure in terms of cytokine expression and phagocytosis. Specific targeting of the Ercc1 deletion to forebrain neurons resulted in a progressive priming response in microglia exemplified by phenotypic alterations. Summarizing, these data show that neuronal genotoxic stress is sufficient to switch microglia from a resting to a primed state