The role of vascular endothelial growth factor (VEGF)-B, a close relative of the angiogenic growth factor VEGF-A, has remained something of a mystery. A new study suggests that VEGF-B protects motor neurons from apoptosis in a rodent model of amyotrophic lateral sclerosis (ALS), but doesn’t provoke the unwanted vascularization that is a worrisome side effect of VEGF-A treatment. Writing in yesterday’s Journal of Neuroscience, joint first authors Koen Poesen and Diether Lambrechts, of the Flanders Institute for Biotechnology (VIB) in Leuven, Belgium, suggest that VEGF-B has potential as a mitigator of ALS symptoms.

The researchers chose to investigate VEGF-B because of the important role VEGF-A, also known simply as VEGF, plays in ALS. In 2001, Peter Carmeliet, also at VIB and principal investigator on the current study, and colleagues discovered that reduced VEGF-A expression in the spinal cord led to ALS-like symptoms (see Oosthuyse et al., 2001 and ARF related news story). Since then scientists have found that excess VEGF-A delays neurodegeneration and extends survival of a mouse model of ALS (Wang et al., 2007; Azzouz et al., 2004; and see ARF related news story), and that a mutation in the VEGF-A promoter is associated with risk for ALS in men (Lambrechts et al., 2008). “It was logical to also consider analyzing the other VEGF family members,” Carmeliet said.

Unlike VEGF-A, VEGF-B shows little angiogenic activity, and its role has been “enigmatic,” Carmeliet said. VEGF-B knockout mice are viable and fertile, exhibiting relatively subtle cardiac defects (Bellomo et al., 2000). However, VEGF-B has been shown to block apoptosis in retinal and brain neurons (Li et al., 2008). The current study is the first to link VEGF-B to motor neuron degeneration.

The researchers crossed VEGF-B-null mice with mice expressing mutant human superoxide dismutase 1 (SOD1), which causes about 20 percent of familial ALS cases. Such mice are a common model for the disease. The mSOD1 mice lacking VEGF-B failed a rotarod test two weeks before control mSOD1 mice, suggesting that VEGF-B plays a protective role. Similarly, mSOD1 mice with a kinase-dead version of the VEGF-B receptor VEGFR-1 failed the rotarod test nine days earlier than their littermates with active VEGFR-1.

The scientists also found that motor neurons from wild-type rat and mouse embryos survived longer in culture when treated with VEGF-B. The cell survival was similar to murine cultures treated with other growth factors. Growing mouse motor neurons with a feeder layer of astrocytes, the researchers then discovered that VEGF-B was neuroprotective as long as the neurons themselves had the proper receptor; VEGFR-1 in the astrocytes was unimportant. This suggests that VEGF-B exerts its protective effect directly on motor neurons.

Could VEGF-B turn into a potential therapy for ALS? Currently, there is no treatment for the disease, which destroys motor neurons and gradually paralyzes patients. Carmeliet’s results hint that VEGF-B might protect motor neurons in vivo. The scientists tested this hypothesis by giving VEGF-B to rats carrying mutant SOD1. Poesen and colleagues used surgically implanted osmotic minipumps to deliver recombinant mouse VEGF-B to the left lateral brain ventricle at a dose equivalent to 0.2 micrograms per kilogram per day. Treatment began with 60-day-old rats, before the onset of symptoms. Compared to rats receiving only artificial cerebrospinal fluid, the VEGF-B rats survived 15 days longer. They also took 11 more days to fail the rotarod test, although this effect was not statistically significant.

Carmeliet speculates that there might be a more pronounced effect with higher doses of VEGF-B. The recombinant protein is expensive because it’s tricky to make; it sticks together and often folds improperly. Had he the funds, Carmeliet said, he would have tested doses 10-fold, or even 100-fold higher than what was used in the study.

Nevertheless, the current study suggests that VEGF-B, while not essential for normal neural function, springs into action to protect neurons that are injured or diseased. Carmeliet thinks it likely acts by inhibiting apoptosis of the damaged cells, allowing them to function for longer before giving out. VEGF-B could still have a role in healthy animals, and that role remains unclear. “Things tend to have some function,” said David Greenberg of the Buck Institute for Aging in Novato, California. He speculates that VEGF-B’s function might overlap with VEGF-A’s.

“This is a very comprehensive study; the results are very solid,” said Kunlin Jin, also of the Buck Institute. “It opens a new avenue for the treatment of neurodegeneration.” A clinical trial of VEGF-A as therapy for ALS is due to begin in Belgium this autumn, Carmeliet said, under the direction of Wim Robberecht, also at the Flanders Institute, and Neuronova, a biopharmaceutical company in Stockholm, Sweden. However, in contrast to VEGF-B, VEGF-A has side effects, including angiogenesis and potential weakening or perforation of the blood-brain barrier, which may limit its use. In a follow-up study, Carmeliet plans to test a combined treatment with both growth factors, which he suspects might be effective at lower levels of VEGF-A, thus minimizing side effects.

Carmeliet notes that VEGF-B has gotten little attention compared to VEGF-A. A PubMed search finds thousands of VEGF-A papers, but only a couple of hundred on VEGF-B. “Because it doesn’t have the same angiogenic potential, everyone has lost interest in this gene,” he said. “I hope that this paper will prime some interest in the field so that people will study this molecule in more detail.”—Amber Dance

Amber Dance is a freelance writer living in Los Angeles.

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  1. VEGF-B, a New Hope for ALS?
    More than 10 years ago, when I joined Dr. Ulf Eriksson’s laboratory in Stockholm as a postdoctoral fellow to try to delineate the biological function of VEGF-B by phenotyping VEGF-B deficient mice, I was excited.

    Who would not be excited? VEGF-A was then, and still is, right in the spotlight of the medical research field. Loss of even a single allele of VEGF-A caused early embryonic lethality in mice (1,2). VEGF-B, as a newly discovered VEGF-A homolog at that time, might prove to be equally, if not more, important, I thought.

    However, the subsequent journey to reveal the biological function of VEGF-B has been largely full of disappointments. As a VEGF-A homolog, VEGF-B failed to produce most of the functionality of VEGF-A, for example, inducing new blood vessel growth and blood vessel permeability, etc. Further, loss of VEGF-B does not seem to matter greatly, since VEGF-B-null mice appear largely healthy (3). Years of work investigating the function of VEGF-B had mostly led to negative findings.

    Is VEGF-B a redundant molecule? This was suspected.

    I am happy to say that perhaps now is the time to answer that question with greater confidence.

    The answer is no.

    Even though VEGF-B does not seem to be critically required in normal physiology (3), VEGF-B plays an important role in diseased conditions, such as in amyotrophic lateral sclerosis (ALS), as recently reported by Dr. Pater Carmeliet’s group (4). In an ALS mouse model, VEGF-B deficiency accelerated the onset of this devastating disease and shortened the lifespan of the diseased animals (4). On the contrary, VEGF-B186 protein treatment not only slowed down motor neuron degeneration in ALS rats but also increased their lifespan (4). More importantly, VEGF-B186 does so without affecting the vascular system, in contrast to VEGF-A. Indeed, it is also recently reported that VEGF-B167 protein treatment protected challenged neurons in both the retina and brain without interfering with the blood vessel system (5). Based on these findings, may we now have another good reason to be optimistic in the battle against ALS?

    As for most scientific findings, many questions follow.

    In this study from Dr. Carmeliet’s group (4), VEGF-B186 protein was administered to the ALS rats approximately 30 days before onset of the disease and rescued motor neurons from apoptosis. This supports the theory that VEGF-B186 has a therapeutic value in the prevention of ALS. However, it is highly desirable to know whether VEGF-B186 could do so when administered after the onset of the disease, a situation that is more clinically relevant.

    Since VEGF-B167, as compared with VEGF-B186, is the naturally more abundant isoform of VEGF-B expressed in the neural system and in most other organs (6), and since both systemic and topical delivery of VEGF-B167 protein protected the retina, brain, and heart in pathological conditions (5,7), there is a good reason to test whether this naturally more abundant isoform of VEGF-B protein could also save motor neurons from dying, and if so what efficacy will exist as compared with VEGF-B186.

    Given its unique nature of being “inert” in most conditions (8), and therefore having a unique safety profile, together with its potent neuroprotective effects, it would not be surprising to soon note an aggressive research effort to investigate the therapeutic potential of VEGF-B gene and cell therapy in treating different types of neurodegenerative diseases, such as ALS.

    References:

    . Heterozygous embryonic lethality induced by targeted inactivation of the VEGF gene. Nature. 1996 Apr 4;380(6573):439-42. PubMed.

    . Abnormal blood vessel development and lethality in embryos lacking a single VEGF allele. Nature. 1996 Apr 4;380(6573):435-9. PubMed.

    . Vascular endothelial growth factor-B-deficient mice display an atrial conduction defect. Circulation. 2001 Jul 17;104(3):358-64. PubMed.

    . Novel role for vascular endothelial growth factor (VEGF) receptor-1 and its ligand VEGF-B in motor neuron degeneration. J Neurosci. 2008 Oct 15;28(42):10451-9. PubMed.

    . VEGF-B inhibits apoptosis via VEGFR-1-mediated suppression of the expression of BH3-only protein genes in mice and rats. J Clin Invest. 2008 Mar;118(3):913-23. PubMed.

    . Isoform-specific expression of VEGF-B in normal tissues and tumors. Growth Factors. 2001;19(1):49-59. PubMed.

    . Reevaluation of the role of VEGF-B suggests a restricted role in the revascularization of the ischemic myocardium. Arterioscler Thromb Vasc Biol. 2008 Sep;28(9):1614-20. PubMed.

    . Novel VEGF family members: VEGF-B, VEGF-C and VEGF-D. Int J Biochem Cell Biol. 2001 Apr;33(4):421-6. PubMed.

References

News Citations

  1. New Gene Suspect for ALS
  2. Viral VEGF Treats Mouse ALS

Paper Citations

  1. . Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter causes motor neuron degeneration. Nat Genet. 2001 Jun;28(2):131-8. PubMed.
  2. . Vascular endothelial growth factor overexpression delays neurodegeneration and prolongs survival in amyotrophic lateral sclerosis mice. J Neurosci. 2007 Jan 10;27(2):304-7. PubMed.
  3. . VEGF delivery with retrogradely transported lentivector prolongs survival in a mouse ALS model. Nature. 2004 May 27;429(6990):413-7. PubMed.
  4. . Meta-analysis of vascular endothelial growth factor variations in amyotrophic lateral sclerosis: increased susceptibility in male carriers of the -2578AA genotype. J Med Genet. 2009 Dec;46(12):840-6. PubMed.
  5. . Mice lacking the vascular endothelial growth factor-B gene (Vegfb) have smaller hearts, dysfunctional coronary vasculature, and impaired recovery from cardiac ischemia. Circ Res. 2000 Feb 4;86(2):E29-35. PubMed.
  6. . VEGF-B inhibits apoptosis via VEGFR-1-mediated suppression of the expression of BH3-only protein genes in mice and rats. J Clin Invest. 2008 Mar;118(3):913-23. PubMed.

Further Reading

Primary Papers

  1. . Novel role for vascular endothelial growth factor (VEGF) receptor-1 and its ligand VEGF-B in motor neuron degeneration. J Neurosci. 2008 Oct 15;28(42):10451-9. PubMed.