Ras p21 protein promotes survival and fiber outgrowth of cultured embryonic neurons

Although evidence obtained with the PC12 cell line has suggested a role for the ras oncogene proteins in the signal transduction of nerve growth factor-mediated fiber outgrowth, little is known about the signal transduction mechanisms involved in the neuronal response to neurotrophic factors in nontransformed cells. We report here that the oncogene protein T24-ras, when introduced into the cytoplasm of freshly dissociated chick embryonic neurons, promotes the in vitro survival and neurite outgrowth of nerve growth factor-responsive dorsal root ganglion neurons, brain-derived neurotrophic factor-responsive nodose ganglion neurons, and ciliary neuronotrophic factor-responsive ciliary ganglion neurons. The proto-oncogene product c-Ha-ras also promotes neuronal survival, albeit less strongly. No effect could be observed with truncated counterparts of T24-ras and c-Ha-ras lacking the 23 C-terminal amino acids including the membrane-anchoring, palmityl-accepting cysteine. These results suggest a generalized involvement of ras or ras-like proteins in the intracellular signal transduction pathway for neurotrophic factors

Rat ciliary neurotrophic factor (CNTF)

The structure of the rat ciliary neurotrophic factor (CNTF) gene and the regulation of CNTF mRNA levels in cultured glial cells were investigated. The rat mRNA is encoded by a simple two-exon transcription unit. Sequence analysis of the region upstream of the transcription start-site did not reveal a typical TATA-box consensus sequence. Low levels of CNTF mRNA were detected in cultured Schwann cells, and CNTF mRNA was not increased by a variety of treatments. Three-week-old astrocyte-enriched cell cultures from new-born rat brain contained easily detectable CNTF mRNA. In astrocyte-enriched cultures, upregulation of CNTF mRNA levels was observed after treatment with IFN-. CNTF mRNA levels were down-regulated in these cells by treatments that elevate intracellular cyclic AMP and by members of the fibroblast growth factor (FGF) family. The implications of these results for potential in vivo functions of CNTF are discusse

Downregulation of genes with a function in axon outgrowth and synapse formation in motor neurones of the VEGF(delta/delta) mouse model of amyotrophic lateral sclerosis

Background: Vascular endothelial growth factor (VEGF) is an endothelial cell mitogen that stimulates vasculogenesis. It has also been shown to act as a neurotrophic factor in vitro and in vivo. Deletion of the hypoxia response element of the promoter region of the gene encoding VEGF in mice causes a reduction in neural VEGF expression, and results in adult-onset motor neurone degeneration that resembles amyotrophic lateral sclerosis (ALS). Investigating the molecular pathways to neurodegeneration in the VEGF(delta/delta) mouse model of ALS may improve understanding of the mechanisms of motor neurone death in the human disease. Results: Microarray analysis was used to determine the transcriptional profile of laser captured spinal motor neurones of transgenic and wild-type littermates at 3 time points of disease. 324 genes were significantly differentially expressed in motor neurones of presymptomatic VEGF(delta/delta) mice, 382 at disease onset, and 689 at late stage disease. Massive transcriptional downregulation occurred with disease progression, associated with downregulation of genes involved in RNA processing at late stage disease. VEGF(delta/delta) mice showed reduction in expression, from symptom onset, of the cholesterol synthesis pathway, and genes involved in nervous system development, including axonogenesis, synapse formation, growth factor signalling pathways, cell adhesion and microtubule-based processes. These changes may reflect a reduced capacity of VEGF(delta/delta) mice for maintenance and remodelling of neuronal processes in the face of demands of neural plasticity. The findings are supported by the demonstration that in primary motor neurone cultures from VEGF(delta/delta) mice, axon outgrowth is significantly reduced compared to wild-type littermates. Conclusions: Downregulation of these genes involved in axon outgrowth and synapse formation in adult mice suggests a hitherto unrecognized role of VEGF in the maintenance of neuronal circuitry. Dysregulation of VEGF may lead to neurodegeneration through synaptic regression and dying-back axonopathy

Vascular signal transducer and activator of transcription-3 promotes angiogenesis and neuroplasticity long-term after stroke

BACKGROUND: Poststroke angiogenesis contributes to long-term recovery after stroke. Signal transducer and activator of transcription-3 (Stat3) is a key regulator for various inflammatory signals and angiogenesis. It was the aim of this study to determine its function in poststroke outcome. METHODS AND RESULTS: We generated a tamoxifen-inducible and endothelial-specific Stat3 knockout mouse model by crossbreeding Stat3(floxed/KO) and Tie2-Cre(ERT2) mice. Cerebral ischemia was induced by 30 minutes of middle cerebral artery occlusion. We demonstrated that endothelial Stat3 ablation did not alter lesion size 2 days after ischemia but did worsen functional outcome at 14 days and increase lesion size at 28 days. At this late time point vascular Stat3 expression and phosphorylation were still increased in wild-type mice. Gene array analysis of a CD31-enriched cell population of the neurovascular niche showed that endothelial Stat3 ablation led to a shift toward an antiangiogenic and axon growth-inhibiting micromilieu after stroke, with an increased expression of Adamts9. Remodeling and glycosylation of the extracellular matrix and microglia proliferation were increased, whereas angiogenesis was reduced. CONCLUSIONS: Endothelial Stat3 regulates angiogenesis, axon growth, and extracellular matrix remodeling and is essential for long-term recovery after stroke. It might serve as a potent target for stroke treatment after the acute phase by fostering angiogenesis and neuroregeneration

Relationships of peripheral IGF-1, VEGF and BDNF levels to exercise-related changes in memory, hippocampal perfusion and volumes in older adults

Animal models point towards a key role of brain-derived neurotrophic factor (BDNF), insulin-like growth factor-I (IGF-I) and vascular endothelial growth factor (VEGF) in mediating exercise-induced structural and functional changes in the hippocampus. Recently, also platelet derived growth factor-C (PDGF-C) has been shown to promote blood vessel growth and neuronal survival. Moreover, reductions of these neurotrophic and angiogenic factors in old age have been related to hippocampal atrophy, decreased vascularization and cognitive decline. In a 3-month aerobic exercise study, forty healthy older humans (60 to 77years) were pseudo-randomly assigned to either an aerobic exercise group (indoor treadmill, n=21) or to a control group (indoor progressive-muscle relaxation/stretching, n=19). As reported recently, we found evidence for fitness-related perfusion changes of the aged human hippocampus that were closely linked to changes in episodic memory function. Here, we test whether peripheral levels of BDNF, IGF-I, VEGF or PDGF-C are related to changes in hippocampal blood flow, volume and memory performance. Growth factor levels were not significantly affected by exercise, and their changes were not related to changes in fitness or perfusion. However, changes in IGF-I levels were positively correlated with hippocampal volume changes (derived by manual volumetry and voxel-based morphometry) and late verbal recall performance, a relationship that seemed to be independent of fitness, perfusion or their changes over time. These preliminary findings link IGF-I levels to hippocampal volume changes and putatively hippocampus-dependent memory changes that seem to occur over time independently of exercise. We discuss methodological shortcomings of our study and potential differences in the temporal dynamics of how IGF-1, VEGF and BDNF may be affected by exercise and to what extent these differences may have led to the negative findings reported here

A two-stage genome-wide association study of sporadic amyotrophic lateral sclerosis

The cause of sporadic amyotrophic lateral sclerosis (ALS) is largely unknown, but genetic factors are thought to play a significant role in determining susceptibility to motor neuron degeneration. To identify genetic variants altering risk of ALS, we undertook a two-stage genome-wide association study (GWAS): we followed our initial GWAS of 545 066 SNPs in 553 individuals with ALS and 2338 controls by testing the 7600 most associated SNPs from the first stage in three independent cohorts consisting of 2160 cases and 3008 controls. None of the SNPs selected for replication exceeded the Bonferroni threshold for significance. The two most significantly associated SNPs, rs2708909 and rs2708851 [odds ratio (OR) = 1.17 and 1.18, and P-values = 6.98 x 10–7 and 1.16 x 10–6], were located on chromosome 7p13.3 within a 175 kb linkage disequilibrium block containing the SUNC1, HUS1 and C7orf57 genes. These associations did not achieve genome-wide significance in the original cohort and failed to replicate in an additional independent cohort of 989 US cases and 327 controls (OR = 1.18 and 1.19, P-values = 0.08 and 0.06, respectively). Thus, we chose to cautiously interpret our data as hypothesis-generating requiring additional confirmation, especially as all previously reported loci for ALS have failed to replicate successfully. Indeed, the three loci (FGGY, ITPR2 and DPP6) identified in previous GWAS of sporadic ALS were not significantly associated with disease in our study. Our findings suggest that ALS is more genetically and clinically heterogeneous than previously recognized. Genotype data from our study have been made available online to facilitate such future endeavors

A transgene carrying an A2G missense mutation in the SMN gene modulates phenotypic severity in mice with severe (type I) spinal muscular atrophy

5q spinal muscular atrophy (SMA) is a common autosomal recessive disorder in humans and the leading genetic cause of infantile death. Patients lack a functional survival of motor neurons (SMN1) gene, but carry one or more copies of the highly homologous SMN2 gene. A homozygous knockout of the single murine Smn gene is embryonic lethal. Here we report that in the absence of the SMN2 gene, a mutant SMN A2G transgene is unable to rescue the embryonic lethality. In its presence, the A2G transgene delays the onset of motor neuron loss, resulting in mice with mild SMA. We suggest that only in the presence of low levels of full-length SMN is the A2G transgene able to form partially functional higher order SMN complexes essential for its functions. Mild SMA mice exhibit motor neuron degeneration, muscle atrophy, and abnormal EMGs. Animals homozygous for the mutant transgene are less severely affected than heterozygotes. This demonstrates the importance of SMN levels in SMA even if the protein is expressed from a mutant allele. Our mild SMA mice will be useful in (a) determining the effect of missense mutations in vivo and in motor neurons and (b) testing potential therapies in SMA

Large-scale pathways-based association study in amyotrophic lateral sclerosis

Sporadic amyotrophic lateral sclerosis (ALS), a devastating neurodegenerative disease, most likely results from complex genetic and environmental interactions. Although a number of association studies have been performed in an effort to find genetic components of sporadic ALS, most of them resulted in inconsistent findings due to a small number of genes investigated in relatively small sample sizes, while the replication of results was rarely attempted. Defects in retrograde axonal transport, vesicle trafficking and xenobiotic metabolism have been implicated in neurodegeneration and motor neuron death both in human disease and animal models. To assess the role of common genetic variation in these pathways in susceptibility to sporadic ALS, we performed a pathway-based candidate gene case-control association study with replication. Furthermore, we determined reliability of whole genome amplified DNA in a large-scale association study. In the first stage of the study, 1277 putative functional and tagging SNPs in 134 genes spanning 8.7 Mb were genotyped in 822 British sporadic ALS patients and 872 controls using whole genome amplified DNA. To detect variants with modest effect size and discriminate among false positive findings 19 SNPs showing a trend of association in the initial screen were genotyped in a replication sample of 580 German sporadic ALS patients and 361 controls. We did not detect strong evidence of association with any of the genes investigated in the discovery sample (lowest uncorrected P-value 0.00037, lowest permutation corrected P-value 0.353). None of the suggestive associations was replicated in a second sample, further excluding variants with moderate effect size. We conclude that common variation in the investigated pathways is unlikely to have a major effect on susceptibility to sporadic ALS. The genotyping efficiency was only slightly decreased (∼1%) and genotyping quality was not affected using whole genome amplified DNA. It is reliable for large scale genotyping studies of diseases such as ALS, where DNA sample collections are limited because of low disease prevalence and short survival time. © 2007 The Author(s)