The results reported here are intriguing, suggesting that some aspects of the extracellular matrix structure in the brain are of great importance to neural plasticity loss of memory function with age, at least in mice. This is quite novel. Most work on neurodegeneration touches only lightly, if at all, on the structure and composition of the extracellular matrix. Researchers here used a gene therapy to adjust the proportion of different chondroitin sulphates in matrix structures in old mice, and the resulting restoration of memory function is quite impressive.
Recent evidence has emerged of the role of perineuronal nets (PNNs) in neuroplasticity - the ability of the brain to learn and adapt - and to make memories. PNNs are cartilage-like structures that mostly surround inhibitory neurons in the brain. Their main function is to control the level of plasticity in the brain. They appear at around five years old in humans, and turn off the period of enhanced plasticity during which the connections in the brain are optimised. Then, plasticity is partially turned off, making the brain more efficient but less plastic.
PNNs contain compounds known as chondroitin sulphates. Some of these, such as chondroitin 4-sulphate, inhibit the action of the networks, inhibiting neuroplasticity; others, such as chondroitin 6-sulphate, promote neuroplasticity. As we age, the balance of these compounds changes, and as levels of chondroitin 6-sulphate decrease, so our ability to learn and form new memories changes, leading to age-related memory decline.
Researchers investigated whether manipulating the chondroitin sulphate composition of the PNNs might restore neuroplasticity and alleviate age-related memory deficits. To do this, the team looked at 20-month old mice - considered very old - and using a suite of tests showed that the mice exhibited deficits in their memory compared to six-month old mice. The team treated the ageing mice using a 'viral vector', a virus capable of reconstituting the amount of 6-sulphate chondroitin sulphates to the PNNs and found that this completely restored memory in the older mice, to a level similar to that seen in the younger mice.