Disease-Related TRPM3 Mutations Render the Channel Overactive via Different Mechanisms

Abstract

The Transient Receptor Potential Melastatin 3 (TRPM3) ion channelis a calcium permeable non-selective ion channel and it belongs to the Transient Receptor Potential (TRP) superfamily. TRPM3 has been identified as a thermosensitive nociceptor channel which can be activated by noxious heat. TRPM3 knockout mice show impairment in avoiding noxious heat and have defects in developing inflammatory heat hyperalgesia. TRPM3 can also be activated by chemical agonists such as pregnenolone sulfate (PregS), CIM0216 and clotrimazole.The presence of de novo substitutions of TRPM3 has been reported in human pediatric patients with intellectual disability and epilepsy recently. Either the Val 990 (992) Met or the Pro 1090 (1092) Gln was found in those patients, however the functional effects of those mutations were not reported. We find that both mutations make the channel overactive increasing basal activity, as well as increasing sensitivity to agonist and heat. The TRPM3-Val990Met mutant shows higher basal activity and it makes the channel more sensitive towards different agonists such as PregS and CIM0216 than the Pro1090Gln mutant. The Val to Mel substitution is located in the S4-S5 loop which could help to understand the increased sensitivity of mutated TRPM3 towards different agonists since the S4-S5 loop is the hot spots for ligand binding in many TRP channels. In contrast, the extracellular S6 segment mutation, Pro1090Gln, increases the sensitivity of TRPM3 towards heat activation to a larger extent than the Val990Met mutation. Both mutated TRPM3 channels can be inhibited by primidone, which is a clinically approved anti-epileptic drug, suggesting the potential treatment of this type of disease.