Aggregates and Disrupted Dynein-Dependent Trafficking in ALS

Amyotrophic Lateral Sclerosis (ALS) is an adult-onset neuro-degenerative disease. The death of motor neurons leads to progressive paralysis of voluntary muscles, making patients unable to control their movements, and ultimately leads to paralysis of respiratory muscles and death. So far there is no effective treatment available. It is not clear how motor neurons die in ALS-patients. 10% of the ALS-cases are familial, and so far mutations in 6 genes have been identified in ALS-families. Mutations in the gene for SOD1 were the first to be discovered and account for up to 20% of familial ALS-cases. Most likely, mutant SOD1-protein is misfolded and accumulates in insoluble aggregates, that are toxic to motor neurons. In the studies described in this thesis, we use transgenic mice that express human mutant SOD1, and that develop paralysis and other pathological changes resembling ALS. We have studied changes in motor neurons in the spinal cord of these SOD1-ALS mice in great detail, and show that the appearance of aggregates is a very early phenomenon in these cells. In addition, motor neurons develop accumulations resembling a traffic jam, and a fragmented Golgi apparatus, an indication for disrupted cellular transport. Supporting cell-types, as astrocytes and microglia, are also affected in the spinal cord of SOD1-ALS mice. To study which cell-types are primarily responsible for the death of motor neurons, we developed transgenic mice with a restricted expression of mutant SOD1 in neurons. These mice develop similar pathological changes as SOD1-ALS mice, indicating that mutant SOD1 acting solely in neurons is sufficient to induce an ALS-like disease. Several studies have indicated that disruptions of axonal transport could cause motor neuron death. We have generated transgenic mice with a disruption of the retrograde microtubule motor dynein/dynactin, by expressing the dominant-negative linker protein BICD2-N in neurons. These mice have impaired retrograde axonal transport and develop cellular changes that resemble those found in SOD1-ALS-mice, like a disrupted Golgi apparatus and neurofilament accumulations. However, up to two years the mice are healthy and do not show any forms of paralysis. Moreover, if we cross these BICD2-N mice with SOD1-ALS mice, animals develop paralysis at a later age and survive longer, indicating that a disruption of retrograde transport could be beneficial for SOD1-linked ALS. Mutations in the gene for VAPB were most recently discovered in ALS-patients. We show that this relatively unknown protein is expressed at high levels in motor neurons in humans and mice and localizes to the Endoplasmic Reticulum. The ALS-linked mutation mislocalize

Intrinsic plasticity complements long-term potentiation in parallel fiber input gain control in cerebellar Purkinje cells

Synaptic gain control and information storage in neural networks are mediated by alterations in synaptic transmission, such as in long-term potentiation (LTP). Here,weshowusingboth in vitroandin vivo recordingsfromthe rat cerebellum that tetanization protocols for the induction of LTP at parallel fiber (PF)-to-Purkinje cell synapsescanalsoevokeincreases in intrinsic excitability. Thisformof intrinsic plasticity shares with LTP a requirement for the activation of protein phosphatases 1, 2A, and 2B for induction. Purkinje cell intrinsic plasticity resembles CA1 hippocampal pyramidal cell intrinsic plasticity in that it requires activity of protein kinase A(PKA) and casein kinase 2 (CK2) and is mediated by a downregulation of SK-type calcium-sensitive K conductances. In addition, Purkinje cell intrinsic plasticity similarly results in enhanced spine calcium signaling. However, there are fundamental differences: first, while in the hippocampus increases in excitability result in a higher probability for LTP induction, intrinsic plasticity in Purkinj

The ALS8 protein VAPB interacts with the ER-Golgi recycling protein YIF1A and regulates membrane delivery into dendrites

The vesicle-associated membrane protein (VAMP) associated protein B (VAPB) is an integral membrane protein localized to the endoplasmic reticulum (ER). The P56S mutation in VAPB has been linked to motor neuron degeneration in amyotrophic lateral sclerosis type 8 (ALS8) and forms ER-like inclusions in various model systems. However, the role of wild-type and mutant VAPB in neurons is poorly understood. Here, we identified Yip1-interacting factor homologue A (YIF1A) as a new VAPB binding partner and important component in the early secretory pathway. YIF1A interacts with VAPB via its transmembrane regions, recycles between the ER and Golgi and is mainly localized to the ER–Golgi intermediate compartments (ERGICs) in rat hippocampal neurons. VAPB strongly affects the distribution of YIF1A and is required for intracellular membrane trafficking into dendrites and normal dendritic morphology. When VAPB-P56S is present, YIF1A is recruited to the VAPB-P56S clusters and loses its ERGIC localization. These data suggest that both VAPB and YIF1A are important for ER-to-Golgi transport and that missorting of YIF1A may contribute to VAPB-associated motor neuron disease

Neuron-specific expression of mutant superoxide dismutase is sufficient to induce amyotrophic lateral sclerosis in transgenic mice

Mutations in superoxide dismutase (SOD1) cause amyotrophic lateral sclerosis (ALS), an adult-onset progressive paralytic disease characterized by loss of motor neurons, and cause an ALS-like disease when expressed in mice. Recent data have suggested that motor neuron degeneration results from toxic actions of mutant SOD1 operating in both motor neurons and their neighboring glia, raising the question whether mutant SOD1 expression selectively in neurons is

The Journal of Physiology SK2 channel expression and function in cerebellar Purkinje cells

Abstract Small-conductance calcium-activated K + channels (SK channels) regulate the excitability of neurons and their responsiveness to synaptic input patterns. SK channels contribute to the afterhyperpolarization (AHP) following action potential bursts, and curtail excitatory postsynaptic potentials (EPSPs) in neuronal dendrites. Here we review evidence that SK2 channels are expressed in rat cerebellar Purkinje cells during development and throughout adulthood, and play a key role in diverse cellular processes such as the regulation of the spike firing frequency and the modulation of calcium transients in dendritic spines. In Purkinje cells as well as in other types of neurons, SK2 channel plasticity seems to provide an important mechanism allowing these cells to adjust their intrinsic excitability and to alter the probabilities for the induction of synaptic learning correlates, such as long-term potentiation (LTP)

Regulated expression of ADAMTS family members in follicles and cumulus oocyte complexes:evidence for specific and redundant patterns during ovulation

Protease cascades are essential for many biological events, including the LH-induced process of ovulation. ADAMTS1 (a disintegrin and metalloproteinase with thrombospondin-like repeats-1) is expressed and hormonally regulated in the ovary by LH and the progesterone receptor. To determine whether other family members might be expressed and regulated in the rodent ovary, those closely related to ADAMTS1 (ADAMTS4 and ADAMTS5) were analyzed in the mouse ovary by reverse transcription-polymerase chain reaction as well as by Western blot, immunohistochemical, and immunocytochemical analyses using highly specific antibodies. Prior to ovulation, ADAMTS4 and ADAMTS5 were coexpressed in granulosa cells of most follicles, whereas ADAMTS5 was also present in granulosa cells of atretic follicles. Following ovulation, ADAMTS1 and ADAMTS4 (but not ADAMTS5) were expressed in multiple cell types, including those within the highly vascular ovulation cone that marks the site of follicle rupture, endothelial cells of newly forming corpora lutea, and cumulus cells within the ovulated cumulus cell-oocyte complex (COC). Versican, a substrate for ADAMTS1 and ADAMTS4, colocalized with these proteases and hylauronan on the cumulus cell surface. To further characterize induction of these proteases and associated molecules, COCs and granulosa cells were isolated from preovulatory follicles and treated with FSH. In expanded COCs and differentiated granulosa cells, FSH induced expression of ADAMTS4 and versican message and protein, whereas increased levels of ADAMTS1 protein was observed in the media of granulosa cells where it was stabilized by heparin in this in vitro system. These studies provide the first evidence that ADAMTS1, ADAMTS4, and ADAMTS5 are expressed in spatiotemporal patterns that suggest distinct as well as some overlapping functions that relate to the broad expression pattern of versican in granulosa cells of small follicles, expanded COCs, and endothelial cells of the mouse ovary