Lack of association of VEGF promoter polymorphisms with sporadic ALS

Roles of vascular endothelial growth factor in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal devastating neurodegenerative disorder, involving progressive degeneration of motor neurons in spinal cord, brainstem, and motor cortex. Riluzole is the only drug approved in ALS but it only confers a modest improvement in survival. In spite of a high number of clinical trials no other drug has proved effectiveness. Recent studies support that vascular endothelial growth factor (VEGF), originally described as a key angiogenic factor, also plays a key role in the nervous system, including neurogenesis, neuronal survival, neuronal migration, and axon guidance. VEGF has been used in exploratory clinical studies with promising results in ALS and other neurological disorders. Although VEGF is a very promising compound, translating the basic science breakthroughs into clinical practice is the major challenge ahead. VEGF-B, presenting a single safety profile, protects motor neurons from degeneration in ALS animal models and, therefore, it will be particularly interesting to test its effects in ALS patients. In the present paper the authors make a brief description of the molecular properties of VEGF and its receptors and review its different features and therapeutic potential in the nervous system/neurodegenerative disease, particularly in ALS.

ALS and oxidative stress: the neurovascular scenario

Oxidative stress and angiogenic factors have been placed as the prime focus of scientific investigations after an establishment of link between vascular endothelial growth factor promoter (VEGF), hypoxia, and amyotrophic lateral sclerosis (ALS) pathogenesis. Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter and mutant superoxide dismutase 1 (SOD1) which are characterised by atrophy and muscle weakness resulted in phenotype resembling human ALS in mice. This results in lower motor neurodegeneration thus establishing an important link between motor neuron degeneration, vasculature, and angiogenic molecules. In this review, we have presented human, animal, and in vitro studies which suggest that molecules like VEGF have a therapeutic, diagnostic, and prognostic potential in ALS. Involvement of vascular growth factors and hypoxia response elements also highlights the converging role of oxidative stress and neurovascular network for understanding and treatment of various neurodegenerative disorders like ALS.

Gene and protein therapies utilizing VEGF for ALS

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that is usually fatal within 2-5years. Unfortunately, the only treatment currently available is riluzole, which has a limited efficacy. As a redress, there is an expanding literature focusing on other potential treatments. One such potential treatment option utilizes the vascular endothelial growth factor (VEGF) family, which includes factors that are primarily associated with angiogenesis but are now increasingly recognized to have neurotrophic effects. Reduced expression of a member of this family, VEGF-A, in mice results in neurodegeneration similar to that of ALS, while treatment of animal models of ALS with either VEGF-A gene therapy or VEGF-A protein has yielded positive therapeutic outcomes. These basic research findings raise the potential for a VEGF therapy to be translated to the clinic for the treatment of ALS. This review covers the VEGF family, its receptors and neurotrophic effects as well as VEGF therapy in animal models of ALS and advances towards clinical trials.

Evolution of the VEGF-regulated vascular network from a neural guidance system

The vascular network is closely linked to the neural system, and an interdependence is displayed in healthy and in pathophysiological responses. How has close apposition of two such functionally different systems occurred? Here, we present a hypothesis for the evolution of the vascular network from an ancestral neural guidance system. Biological cornerstones of this hypothesis are the vascular endothelial growth factor (VEGF) protein family and cognate receptors. The primary sequences of such proteins are conserved from invertebrates, such as worms and flies that lack discernible vascular systems compared to mammals, but all these systems have sophisticated neuronal wiring involving such molecules. Ancestral VEGFs and receptors (VEGFRs) could have been used to develop and maintain the nervous system in primitive eukaryotes. During evolution, the demands of increased morphological complexity required systems for transporting molecules and cells, i.e., biological conductive tubes. We propose that the VEGF-VEGFR axis was subverted by evolution to mediate the formation of biological tubes necessary for transport of fluids, e.g., blood. Increasingly, there is evidence that aberrant VEGF-mediated responses are also linked to neuronal dysfunctions ranging from motor neuron disease, stroke, Parkinson's disease, Alzheimer's disease, ischemic brain disease, epilepsy, multiple sclerosis, and neuronal repair after injury, as well as common vascular diseases (e.g., retinal disease). Manipulation and correction of the VEGF response in different neural tissues could be an effective strategy to treat different neurological diseases.

Neurotrophic growth factors for the treatment of amyotrophic lateral sclerosis: where do we stand?

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that results in progressive loss of motoneurons, motor weakness and death within 3–5 years after disease onset. Therapeutic options remain limited despite substantial number of approaches that have been tested clinically. Many neurotrophic growth factors are known to promote the survival of neurons and foster regeneration in the central nervous system. Various neurotrophic factors have been investigated pre-clinically and clinically for the treatment of ALS. Although pre-clinical data appeared promising, no neurotrophic factors succeeded yet in a clinical phase III trial. In this review we discuss the rationale behind those factors, possible reasons for clinical failures, and argue for a renewal of hope in this powerful class of drugs for the treatment of ALS.

VEGF up-regulation by G93A superoxide dismutase and the role of malate-aspartate shuttle inhibition

A gain of interaction of the amyotrophic lateral sclerosis (ALS)-linked G93A-superoxide dismutase-1 (G93A-hSOD1) with cytosolic malate dehydrogenase (cytMDH), a key enzyme in the malate-aspartate shuttle, diverts neurons towards anaerobic metabolism. Changes in vascular endothelial growth factor (VEGF) are reported in ALS and hypoxia. Here we report that expression of G93A-hSOD1 fused with green fluorescent protein in NSC-34 cells enhanced VEGF expression and levels of VEGF and its upstream regulator hypoxia-inducible factor (HIF-1alpha). G93A-hSOD1 expressing cells were unable to further up-regulated VEGF in response to Co(2+) and H(2)O(2). Amino-oxyacetate that inhibits the malate-aspartate shuttle caused a similar increase in VEGF mRNA and impaired response to H(2)O(2) in WT-hSOD1 expressing cells. Interruption of the G93A-hSOD1/cytMDH interaction reduced VEGF expression in G93A-hSOD1 expressing cells and restored their ability to up-regulate VEGF in response to Co(2+) and H(2)O(2). These results demonstrate that the ALS-linked G93A hSOD1 mutation impairs VEGF regulation compatible with the inhibition of neuronal malate-aspartate shuttle.

Role and therapeutic potential of VEGF in the nervous system

The development of the nervous and vascular systems constitutes primary events in the evolution of the animal kingdom; the former provides electrical stimuli and coordination, while the latter supplies oxygen and nutrients. Both systems have more in common than originally anticipated. Perhaps the most striking observation is that angiogenic factors, when deregulated, contribute to various neurological disorders, such as neurodegeneration, and might be useful for the treatment of some of these pathologies. The prototypic example of this cross-talk between nerves and vessels is the vascular endothelial growth factor or VEGF. Although originally described as a key angiogenic factor, it is now well established that VEGF also plays a crucial role in the nervous system. We describe the molecular properties of VEGF and its receptors and review the current knowledge of its different functions and therapeutic potential in the nervous system during development, health, disease and in medicine.

VEGF genetic variability is associated with increased risk of developing Alzheimer's disease

Specific polymorphisms within the vascular endothelial growth factor (VEGF) gene promoter region are of particular interest: VEGF variability has been associated with increased risk of developing a wide variety of disorders from diabetes to neurodegenerative diseases, suggesting functions not confined to its originally described vascular effects. A hypothetical loss of the VEGF-mediated neuroprotective effect has been proposed as a cause of neurodegenerative disorders. An impaired regulation of VEGF expression has been also reported in Alzheimer's disease (AD) pathogenesis. Recently, VEGF gene promoter polymorphisms have been associated with an increased risk for AD in the Italian population. Conversely, two subsequent studies failed to find a positive association between VEGF variability and greater risk for AD. To better clarify this issue, a meta-analysis of all published association studies has been performed. Overall, polymorphic variants within VEGF gene promoter confer greater risk for AD at least in the Italian population; the meta-analysis provides evidence of a role of the functional variant C(-2578)A in the pathogenesis of the disease, although the pooled odds ratio obtained represents a modest effect. These findings provide new evidence for an additional candidate genetic risk factor for AD that can be tested in further studies.

Targeting angiogenin in therapy of amyotropic lateral sclerosis

BACKGROUND

Missense heterozygous mutations in the coding region of angiogenin (ANG) gene, encoding a 14 kDa angiogenic RNase, were recently found in patients of amyotropic lateral sclerosis (ALS). Functional analyses have shown that these are loss-of-function mutations, implying that angiogenin deficiency is associated with ALS pathogenesis and that increasing ANG expression or angiogenin activity could be a novel approach for ALS therapy.

OBJECTIVE

Review the evidence showing the involvement of angiogenin in motor neuron physiology and function, and provide a rationale for targeting angiogenin in ALS therapy.

METHODS

Review the current understanding of the mechanism of angiogenin action in connection with ALS genetics, pathogenesis and therapy.

CONCLUSION

ANG is the first gene whose loss-of-function mutations are associated with ALS pathogenesis. Therapeutic modulation of angiogenin level and activity in the spinal cord, either by systemic delivery of angiogenin protein or through retrograde transport of ANG-encoding viral particles, may be beneficial for ALS patients.

Genetics of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) was first described by Charcot in 1869 as what we would now call a sporadic disease-a disease believed to occur without a strong genetic influence. Only within the past 10 years has it been possible to fully explore genetic influence on disorders that seem to occur sporadically but likely result from the convergence of multiple genetic and environmental factors. This article reviews the genetics of familial ALS and summarizes current investigations of genetic influence in sporadic ALS. Genetic study clearly offers the potential for identification of molecular targets that would allow development of rational therapies for various forms of ALS, but much work remains.

A strategy for developing effective amyotropic lateral sclerosis pharmacotherapy: from clinical trials to novel pharmacotherapeutic strategies

BACKGROUND

The pathomechanism of sporadic amyotropic lateral sclerosis is not clearly understood, although a proportion of familial amyotropic lateral sclerosis is caused by superoxide dismutase 1 mutations. Theories based on studies of human post-mortem tissue, research on animal models and in vitro work have been proposed for the pathogenesis of amyotropic lateral sclerosis, but the pathogenesis is not the same between sporadic and familial amyotropic lateral sclerosis.

OBJECTIVE/METHODS

Drug candidates were tested using superoxide dismutase 1 mutant mice. Although the candidates were shown to be effective in mice, clinical trials in humans have failed to identify any truly effective pharmacotherapies in sporadic amyotropic lateral sclerosis, with only riluzole providing a modest improvement in survival. Ongoing or planned trials are exploring the value of antiglutamatergic drugs, antioxidants, neurotrophic factors, anti-inflammatory drugs and anti-aggregation drugs.

RESULTS/CONCLUSIONS

A combination of drugs acting on different mechanisms is needed for effective therapy. Moreover, gene expression profiling and genome-wide association studies, together with inhibitory RNA techniques, are helpful for developing new pharmacotherapeutic strategies including gene therapy. It is also likely that the recently advanced generation of induced pluripotent stem cells will lead to the development of cell therapy for amyotropic lateral sclerosis. In addition to finding effective therapies, research is also needed in order to detect early disease markers since pharmacotherapy is most beneficial when given early in the course of sporadic amyotropic lateral sclerosis.

VEGF and ALS

In amyotrophic lateral sclerosis (ALS), an adult-onset progressive degeneration of motor neurons occurring as sporadic and familial disease, there is emerging evidence for and against the role of vascular endothelial growth factor (VEGF), an endothelial cell mitogen crucial for angiogenesis, in its etiopathogenesis. Our understanding of the role of VEGF in ALS has come from studies of both experimental models and human cases. In this article, I have examined in detail the in vitro and in vivo evidence for and against VEGF in ALS, concluding that more compelling evidence is required before we can conclusively link VEGF to ALS in humans.

Amyotrophic lateral sclerosis: from current developments in the laboratory to clinical implications

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive degeneration of motor neurons occurring both as a sporadic and a familial disease. The etiology of ALS remains unknown, but one fifth of instances are due to specific gene defects, the best characterized of which is point mutations in the gene coding for Cu/Zn superoxide dismutase (SOD1). Because sporadic and familial ALS affect the same neurons with similar pathology, it is hoped that understanding these gene defects will help in devising therapies effective in both forms. A wealth of evidence has been collected in rodents made transgenic for mutant SOD1, which represent the best available models for familial ALS. Mutant SOD1 likely induces selective vulnerability of motor neurons through a combination of several mechanisms, including protein misfolding, mitochondrial dysfunction, oxidative damage, cytoskeletal abnormalities and defective axonal transport, excitotoxicity, inadequate growth factor signaling, and inflammation. Damage within motor neurons is enhanced by noxious signals originating from nonneuronal neighboring cells, where mutant SOD1 induces an inflammatory response that accelerates disease progression. The clinical implication of these findings is that promising therapeutic approaches can be derived from multidrug treatments aimed at the simultaneous interception of damage in both motor neurons and nonmotor neuronal cells.

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 ( approximately 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.

Amyotrophic lateral sclerosis: all roads lead to Rome

Amyotrophic lateral sclerosis (ALS) is the most frequent adult-onset motor neuron disease characterized by degeneration of upper and lower motor neurons, generalized weakness and muscle atrophy. Most cases of ALS appear sporadically but some forms of the disease result from mutations in the gene encoding the antioxidant enzyme Cu/Zn superoxide dismutase (SOD1). Several other mutated genes have also been found to predispose to ALS including, among others, one that encodes the regulator of axonal retrograde transport dynactin. As all roads lead to the proverbial Rome, we discuss here how distinct molecular pathways may converge to the same final result that is motor neuron death. We critically review the basic research on SOD1-linked ALS to propose a pioneering model of a 'systemic' form of the disease, causally involving multiple cell types, either neuronal or non-neuronal. Contrasting this, we also postulate that other neuron-specific defects, as those triggered by dynactin dysfunction, may account for a primary motor neuron disease that would represent 'pure' neuronal forms of ALS. Identifying different disease subtypes is an unavoidable step toward the understanding of the physiopathology of ALS and will hopefully help to design specific treatments for each subset of patients.

ALS: a disease of motor neurons and their nonneuronal neighbors

Amyotrophic lateral sclerosis is a late-onset progressive neurodegenerative disease affecting motor neurons. The etiology of most ALS cases remains unknown, but 2% of instances are due to mutations in Cu/Zn superoxide dismutase (SOD1). Since sporadic and familial ALS affects the same neurons with similar pathology, it is hoped that therapies effective in mutant SOD1 models will translate to sporadic ALS. Mutant SOD1 induces non-cell-autonomous motor neuron killing by an unknown gain of toxicity. Selective vulnerability of motor neurons likely arises from a combination of several mechanisms, including protein misfolding, mitochondrial dysfunction, oxidative damage, defective axonal transport, excitotoxicity, insufficient growth factor signaling, and inflammation. Damage within motor neurons is enhanced by damage incurred by nonneuronal neighboring cells, via an inflammatory response that accelerates disease progression. These findings validate therapeutic approaches aimed at nonneuronal cells.