Society for Neuroscience Conference 2014 Continued


Let me emphasize that the huge number of posters and talks at the SfN conference made it impossible to attend all of them, so my recollections here are some of the high points that I was able to take in. There is a lot of terrific science going on out there and these conferences are windows into it.

One poster described a feeding study in rats. One group of rats received a diet rich in omega-3 fatty acids, which are found in fish oils and soy. Another group was fed a standard laboratory diet that tends to skim on the omega-3 fatty acids. In the brains of the omega-3-fed rats, the expression off the gene that encodes Brain Derived Neurotropic Factor or BDNF increased significantly.

This is significant because BDNF promotes the survival of nerve cells (neurons) by playing a role in the growth, maturation (differentiation), and maintenance of these cells. In the brain, BDNF protein is active at the connections between nerve cells (synapses), where cell-to-cell communication occurs. The synapses can change and adapt over time in response to experience, a characteristic called synaptic plasticity, and BDNF regulates synaptic plasticity, which is important for learning and memory.

When these researchers examined why the BDNF gene was unregulated in rats fed the omega-3-rich diet, they discovered that the starting point of the gene, which is called the promoter was nice and clear. In the standard diet rats, the promoter of the BDNF gene was chemically modified with methyl (-CH3) groups. In the absence of the methyl groups, the transcription factor CTCF was able to bind and increase the rate of transcription. If the promoter was chemically modified with methyl groups, then a protein called MeCP2 bound to the promoter and prevented expression of BDNF.

This group looked further and discovered that the omega-3-rich diet seemed to influence the expression of BDNF by means of the balance of reduced and oxidized versions of electron carriers in cells, in particular, the ratio of NAD+ to NADH. NAD is a major electron carrier in cells and the ratio of NAD+, the oxidized version of this molecule, to the reduced version of this molecule, NADH, is a measure of the energy charge of the cell and how well-fed the individual is. More importantly, NAD is a substrate for another regulator of gene expression called Sirtuins.

Sirtuins are protein deacetylases, but they are unusual deacetylases since many of them they do not simply hydrolyze acetyl-lysine residues. Instead they couple lysine deacetylation to NAD hydrolysis. This hydrolysis produces O-acetyl-ADP-ribose, which is the deacetylated substrate and nicotinamide, which is an inhibitor of sirtuin activity. The dependence of sirtuins on NAD links their enzymatic activity directly to the energy status of the cell via the cellular NAD:NADH ratio.

The fact that a diet high in omega-3 fatty acids affects the NAD/NADH ratio is significant for Alzheimer’s disease because the sirtuin, SIRT1, deacetylates and coactivates the promoter for the gene that encodes the retinoic acid receptor beta gene, which subsequently upregulates the expression of alpha-secretase (ADAM10). Alpha-secretase is able to suppress beta-amyloid production. ADAM10 activation by SIRT1 also induces the Notch signaling pathway, which is known to repair neuronal damage in the brain. All of this begins with a dietary factor that actually protects the brain from Alzheimer’s disease by profound changes in gene expression.

Another poster from an Italian group used the 5XFAD mouse model of Alzheimer’s disease to test a growth factor called “painless Nerve Growth Factor” on mice with protein plaque formation in their brains. The growth factor was given by placing droplets of the growth factor in the noses of the mice while they were anesthetized. The results were stunning. Normally, 5XFAD mice get plaques quickly in their brains and lots of them. However, the growth factor was able to rescue the onset of behavioral deficits and reduces, although not eliminate, plaque formation. Other brain-specific pathologies found in these mice were reduced, such as astrocytosis. The wandering white cells in the brain known as microglia did a better job of gobbling up protein aggregates and clearing them from the brain, and the markers of inflammation were significantly reduced. I asked the investigator if there were plans to try to move this to clinical trials, and she said that she was unable to do so because of a lack of funding. Maybe someone will collaborate with this dear lady to make it so?

In another poster, the overexpression of an enzyme called heparanase in the brain decreased the burden of protein aggregates in the brains of mice with Alzheimer’s disease. I was not able to get into the details of this poster because of time.

In another poster, a very energetic young man told me about his very interesting work with a Parkinson’s disease model in rodents. If mice are administered a drug called MPTP (short for 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), the dopamine-using neurons in the brain will specifically take up this drug in high concentrations and it will kill them. Therefore, this drug is an excellent model system to study Parkinson’s disease in mice.

Prokineticin-2 is a gene that is expressed in high quantities in the surviving dopamine-using neurons that came from the brains of Parkinson’s disease patients after their deaths. When Prokineticin-2 was overexpressed in cultured dopaminergic neurons, they unregulated a protein called Bcl-2. Bcl-2 is one of the group of proteins can protect cells from dying. Therefore, Prokineticin-2 is a prosurvival protein.

Next, this chap switched from a culture system to a “in a living animal” system or an in vivo system. By using genetically engineered viruses that overexpressed Prokineticin-2 in the brains of mice, he discovered that this viruses did not adversely affect the mice and he did in fact achieve high levels of Prokineticin-2 in the brains of mice with this recombinant viruses. The overexpression did not affect the mice in the least. When he did the same experiment with MPTP-treated mice – oh, just to be clear, he overexpressed Prokineticin-2 first and then administered the MPTP because it takes about 30 days for the viruses to properly upregulate Prokineticin-2 – he saw decreased inflammation in the brain, and increase in Bcl-2 and Pink1 expression in the brain (both of these genes are pro-survival genes), and the behavioral problems of the mice never emerged with the severity of the MPTP mice. When he examined TH – an enzyme that makes the neurotransmitter dopamine, he saw that levels of this enzyme were up too. This means that the dopamine-using neurons were surviving. Is this cool stuff or what?

That’s enough for now. More later.

Mesenchymal Stem Cells Improve Movement and Decrease Neurodegeneration in Ataxic Mice


Friedrich’s ataxia (FA) results from insufficient concentrations of a protein called Frataxin.  Frataxin serves as an iron metabolism protein that puts iron into proteins that need it.  Because several proteins that play crucial roles in energy metabolism in cells use iron, Frataxin is a very busy molecule and without sufficient quantities of Frataxin, energy metabolism decreases and metabolically active cells, such as nerves and muscles, weaken and die.

Frataxin crystal structure.
Frataxin crystal structure.

In patients with FA, the dorsal root ganglia, which lie just in front of the spinal cord, are the first to die off and degenerate.  Can stem cell treatments provide relief from the ravages of FA?

DRG

To test this possibility, Salvador Martinez and his colleagues from the University Miguel Hernández in Alicante, Spain examined two mouse populations, both of which harbored loss-of-function mutations in the Frataxin (FXN) gene.  Mice from both groups were injected with bone marrow-derived mesenchymal stem cells isolated from either wild-type or YG8 mice.  YG8 mice a genetically manipulated so that they suffer from a mouse form of FA that shows several similarities to human FA.  The mesenchymal stem cells injections were “intrathecal” injections, which means that they were directly injected into the nervous system.

As a result of the stem cell injections,  both groups of mice showed improved motor skills compared to nontreated mice.  The dorsal root ganglia also showed increased frataxin expression in the treated groups, and less cell death.

Why did the stem cell-injected mice fare better?  Further investigations revealed that the injected mesenchymal stem cells expressed the following growth factors:  NT3, NT4, and BDNF.  All of these growth factors can bind to specific receptors embedded in the membranes of those sensory neurons located within the dorsal root ganglia and buck up their survival, thus preventing them from dying.  The stem cell-treated mice also had increased levels of “antioxidant enzymes.”. These are enzymes found in our own cells that dispose of dangerous molecules.  Enzymes such as catalase, superoxide dismutase and so on are examples of antioxidant enzymes.  The stem cell-treated mice had higher levels of catalase and GPX-1 in their dorsal root ganglia, which is significant because YG8 mice show decreased levels of these antioxidant enzymes.

Interestingly, the results were not significantly different if the injected stem cells were isolated from wild-type or YG8 mice. In both cases injected mesenchymal stem cells ameliorated the condition of the FA mice.

In conclusion, transplantation of bone marrow mesenchymal stem cells, either the patient’s own stem cells or donated stem cells, is a feasible therapeutic procedure that might delay the onset of cell death in the dorsal root ganglia of patients with Friedreich’s ataxia.