Findings from a recent study conducted by researchers in the Department of Neurosciences suggest that a grape-rich diet can improve functional recovery following stroke by strengthening the network of cells that protect axons found in white matter, as well as conserving axonal energy production. A grape powder diet has previously been shown to protect gray matter against ischemic injury, but until now, its effect on white matter—the part of the brain most damaged by stroke—has been largely unknown.
When blood supply to the brain is cut off, as happens during an ischemic stroke, cells do not get enough oxygen and glucose to power basic cellular processes, including metabolism, or energy production. As a result, neurons lose function and ultimately die.
It is damage to neurons in the brain's subcortical white matter that is at the root of the neurological dysfunction that commonly accompanies stroke. White matter, unlike gray matter, is primarily made up of myelinated axons—the part of the neuron responsible for communicating with and transmitting signals to neighboring cells. This explains why stroke patients often experience paralysis, memory loss and speech and language problems, among other symptoms that result from poor communication between the central and peripheral nervous systems.
Armed with the knowledge that a grape powder diet confers benefits to other parts of the brain, the team led by Selva Baltan, MD, PhD, and Sylvain Brunet, PhD, tested a 5% and 10% grape powder diet in mice. After simulating ischemic injury, they measured the functional and structural effects in the optic nerves, which are composed exclusively of white matter.
Compared to a normal diet, the grape powder diet was shown to increase both the size and number of various types of glial cells—cells that create the protective myelin that surround and support axons. The grape powder diets at 5% and 10% were found to confer these benefits equally. Additionally, mice on the grape powder diet had longer and thicker mitochondria than the control group. The mitochondria were less fragmented and remained motile longer following oxygen and glucose deprivation. These are all indicators of metabolic function and energy production.
Currently, the team is taking this work a step further to understand how exactly the grape powder confers these benefits. They believe the grape-enhanced diet may promote the growth of beneficial bacteria in the gut, called microbiota. Microbiota play an important role in keeping the body healthy, including defending against pathogens and protecting the immune system. Specifically, certain bacterial species are known to produce short-chain fatty acids, which can enter the bloodstream from the gut and eventually circulate to the brain. These short-chain fatty acids may preserve mitochondria during ischemia, allowing them to maintain energy production despite the loss of oxygen and glucose. This work is being conducted by medical student researcher Ryan Zhang.
This early-stage work suggests for the first time that a grape-enhanced diet can protect axon function and white matter integrity by modifying networks of axonal support cells and improving metabolism in axons. Dr. Baltan hopes that additional research will confirm these results in human tissues and possibly progress to human clinical trials. The project was presented by undergraduate student researcher Danielle Scerbo at this past summer's Student Research Day.
(This study was supported by an award to Selva Baltan & Sylvain Brunet by California Grape Commission.)