In a first of its kind, scientists from Duke University associated autism to one of the most well-studied pain molecules, TRPV1 (transient receptor potential ion channel subtype V1).
Published in the journal Neuron, the study pointed to a potential mechanism underlying pain insensitivity in autism.
"Not enough research has been done on the mechanisms driving sensory problems in autism, but it's important because sensory processing probably affects to some degree how the brain develops," said co-author Yong-hui Jiang.
In another study published earlier, Jiang and other collaborators described a mouse model of autism in which they deleted a prominent autism gene called SHANK3, which is mutated in 1 percent of people with the disorder.
These mice show several features of autism, including social deficits and excessive self-grooming.
That study did not examine pain.
But about 70 percent of individuals with autism or a related disorder called Phelan-McDermid syndrome that have mutations in SHANK3 are known to have sensory processing problems.
In the new study, Ji's group put SHANK3-deficient mice through a battery of sensory tests, finding that the animals had lower sensitivity than normal mice to heat and heat-related pain - akin to the soreness a person feels after sunburn.
It turns out that the SHANK3 protein is normally present not only in the brain, but also in a cluster of pain-sensing neurons called the dorsal root ganglion in mice.
The group also found SHANK3 in the same types of cells from human donors who did not have autism.
"This was a big surprise that SHANK3 is expressed in the peripheral nervous system, but before this study, no one had ever looked for it outside of the brain," Ji said.
The scientists found that TRPV1 and SHANK3 are actually present together in sensory neurons of the dorsal root ganglion, and that they interact.
In the mice missing SHANK3, TRPV1 never makes it to the cell surface, where it normally does its job.
Missing even half of normal level of SHANK3 drastically lowers TRPV1's ability to transmit pain signals, suggesting that SHANK3 is a crucial molecule for pain sensation.
SHANK3 is better known for its role in the brain. It is found in the tiny clefts called synapses where signals are passed from one neuron to the next.
Until now, it was believed to be present only in the receiving end of the synapse, called the postsynaptic terminal, where it acts as a scaffold to secure specific receptors that receive chemical messages.
The new study also shows that SHANK3 is expressed on the sending sides of the synapse, called presynaptic terminals.
The scientists hope to understand next what the protein might be doing there.
"That changes our understanding of how these two components (of the synapse) work together to contribute to autism-related behavior and will change how we develop effective treatments," Jiang said.
TRPV1 blockers are already the focus of intense research and development, but these compounds come with side effects.
The new study suggests a more specific way to block TRPV1 -- through its interaction with SHANK3 -- in order to avoid these side effects.
Disclaimer: No Business Standard Journalist was involved in creation of this content
