Neurogenesis in HD mice prolongs life

HD Lighthouse Contributing Editor's Comment: The Lighthouse has been following the research of Dr. Steven Goldman and his team ever since we heard about it at the ASENT conference in March 2005. Contributing editor Ann Covalt explained the research in detail last year and it's worth rereading since this line of research is so important and her explanation is so clear. HDL: Trophic Factors Generate Functioning New Neurons for Brain Repair

In summary, the earlier research, conducted in rats, showed that it was possible to induce hibernating stem cells to develop into medium spiny neurons (the ones affected by HD) which would then migrate over to the damaged part of the striatum and establish themselves as functioning neurons. The next step in the research was to conduct experiments to see if this technique would work as a treatment for an HD mouse model.

The next step has been completed and the landmark results are reported in a new journal article. The introduction of genes for the neurotrophic factor BDNF and the polypeptide noggin into the brain through an adenoviral vector does indeed prolong health and increase lifespan by 17 percent in the R6/2 mouse. These exciting results were achieved after only one treatment.

The treatment works by generating new neurons. The researchers concluded this was the mechanism because when they added an inhibitor of mitosis, the good results were suppressed. BDNF alone generates new neurons but the addition of noggin, which stops the progenitor cells from becoming glial cells (as some would otherwise do) doubles the numbers of neurons.

The new neurons also have the HD gene but they are new cells which are not overwhelmed by challenges presented by the HD protein. Remember that brain cells are able to cope for years before symptoms appear.

This technique boosts a natural process. The brain already responds to HD by generating new neurons although not enough to keep countering the damage. Many of the stem cells die probably because there's a reduction in BDNF which protects them and some develop into glial cells instead. By introducing BDNF the cells are protected and with noggin, they don't develop into glial cells.

Obtaining these kinds of results is good news in and of itself. However, the authors argue that it is reasonable to expect even better results with multiple treatments. They got this result will just a small increase of new cells and it seems likely that the pool of progenitor cells is still greater in the mice (see Batista 2006). They note that research by Curtis and colleagues (2003) shows that there is an abundant, potentially functional pool of these progenitor cells in human beings as well.

There's some evidence to believe that the technique would work in people. The Lighthouse has already covered an experiment by Claude Gravel and colleagues (2005) which showed that introducing the BDNF gene through an adenoviral vector stimulates the growth of functional medium spiny neurons in primates.

Why do I consider this to be a landmark study important to HD families?

1. This is a very significant extension of health and survival with potential for better results with subsequent treatments.
   
   
2. This potential treatment is independent from other treatment strategies we've been covering on the Lighthouse such as increasing cellular energy (through CoQ10 and creatine and perhaps new analogs), restoring gene transcription through HDAC inhibitors, and caspase inhibition. As the authors point out, their neurogenesis strategy could be a significant addition to the combination treatment approach that the researchers are already working towards.
   
   
3. Once we can stop Huntington's Disease, we need a technique for brain restoration. Based on research with the HD mice, we can expect some improvements when that happens but more will be needed for some patients. This looks like a feasible strategy.

Resources and references:

You can download a free copy of the 2007 Goldman article here: http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1978427&blobtype=pdf

Read Ann Covalt's earlier update on Goldman's earlier research here: http://www.hdlighthouse.org/research/bdnf/updates/1255bdnf.php

Read about the Gravel study with primates here: http://www.hdlighthouse.org/research/brain/updates/1202bdnf.php

C Batista,T Kippin, S Willaime-Morawek M K Shimabukuro, W Akamatsu, and D van der Kooy, "A Progressive and Cell Non-Autonomous Increase in Striatal Neural Stem Cells in the Huntington's Disease R6/2 Mouse," The Journal of Neuroscience, October 11, 2006, 26(41):10452-10460.

You can download a free copy of the Batista article here: http://www.jneurosci.org/cgi/reprint/26/41/10452

M Curtis, E Penney, A Pearson, W van Roon-Mom, N Butterworth, M Dragunow, B Connor, and R Faull, "Increased cell proliferation and neurogenesis in the adult human Huntington's disease brain," Proceedings of the National Academy of Sciences July 22, 2003 vol. 100 | no. 15, 9023-9027.

You can download a free copy of the Curtis article here: http://www.pnas.org/cgi/reprint/100/15/9023

-- Marsha L. Miller, Ph.D.
Posted to the HDL: 09-22-2007

Induction of neostriatal neurogenesis slows disease progression in a transgenic murine model of Huntington disease

Sung-Rae Cho, Abdelatif Benraiss, Eva Chmielnicki, Amer Samdani, Aris Economides, and Steven A. Goldman

Dr. Benraiss, another member of the research team, shown here at a recent HDF conference.

Ependymal overexpression of brain-derived neurotrophic factor (BDNF) stimulates neuronal addition to the adult striatum, from subependymal progenitor cells. Noggin, by suppressing subependymal gliogenesis and increasing progenitor availability, potentiates this process. We asked whether BDNF/Noggin overexpression might be used to recruit new striatal neurons in R6/2 huntingtin transgenic mice. R6/2 mice injected with adenoviral BDNF and adenoviral Noggin (AdBDNF/AdNoggin) recruited BrdU(+)betaIII-tubulin(+) neurons, which developed as DARPP-32(+) and GABAergic medium spiny neurons that expressed either enkephalin or substance P and extended fibers to the globus pallidus. Only AdBDNF/AdNoggin-treated R6/2 mice harbored migrating doublecortin-defined neuroblasts in their striata, and the new neurons expressed p27 as a marker of mitotic quiescence after parenchymal integration. AdBDNF/AdNoggin-treated R6/2 mice sustained their rotarod performance and open-field activity and survived longer than did AdNull-treated and untreated controls. Neither motor performance nor survival improved in R6/2 mice treated only with AdBDNF, and intraventricular infusion of the mitotic inhibitor Ara-C completely blocked the performance and survival effects of AdBDNF/AdNoggin, suggesting that the benefits of AdBDNF/AdNoggin derived from neuronal addition. Thus, BDNF and Noggin induced striatal neuronal regeneration, delayed motor impairment, and extended survival in R6/2 mice, suggesting a new therapeutic strategy in Huntington disease.

# # #

Source: Journal of Clinical Investigation 2007 Sep 20; [Epub ahead of print]