Molecular mechanism of NAT1.7-modulated negative regulation of SCN9A expression

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Pain is a major clinical problem and affects more people than diabetes, heart disease and cancer combined. At any one time about 20% of the population is in chronic pain and in approximately 6% the pain is severe, resulting in serious personal and economic consequences. Pain is a cofactor in many medical conditions yet pain medicines are often only partially effective, and the problem is increasing with an aging population. A major reason for the poor progress in the development of new analgesics is our incomplete understanding of pain as a disease due to its complex nature. By understanding the cellular and molecular processes that control the sensation of pain, effective targeted therapies can be developed to alleviate suffering. One way of doing so is analysing genetic conditions in which patients have altered levels of pain sensitivity, in particular the cases where pain sensitivity and perception are diminished. Identifying human genes which are responsible for such a phenotype and their functional products, allows us to pinpoint the key players in the chain of molecular events providing for pain sensation. In this way, SCN9A has been identified as one of the key pain genes. The gene codes for a protein called Nav1.7, a sodium transmembrane channel which is regulated by the membrane's charge. In doing so the protein transmits pain signalling from the dorsal root ganglia neurons where it is expressed predominantly, towards the brain. Loss of this gene and/or mutations deactivating the protein cause loss of pain sensation, and thus SCN9A is an important target for the pharmaceutical industry with several selective drug blockers of its activity currently in development. A different strategy targeting Nav1.7 therapeutically is by focusing on the SCN9A gene itself and exploit any natural mechanism that downregulates the gene expression and therefore potentially reduce pain sensitivity. We have recently discovered and characterised a new regulatory gene located next to SCN9A that encodes a natural antisense transcript that is conserved in humans and mice (NAT1.7). Essentially NAT1.7 is coded by the second complementary strand of DNA that is directly opposite to the main SCN9A gene, with the two genes partially overlapping.In recently published results we demonstrated that the expression levels of these two genes show a clear discordant pattern, that is tissues expressing high levels of SCN9A transcript have low levels of NAT1.7 (such as DRG) and tissues with high levels of NAT1.7 have low or no expression of SCN9A (such as spinal cord and brain). Moreover, when we generated cells with high levels of NAT1.7 it led to a significant reduction in Nav1.7 expression levels, and importantly its activity, pointing out that NAT1.7 is a negative regulator of SCN9A. We now propose an experimental plan aimed to elucidate the molecular mechanism(s) by which NAT1.7 acts as a negative regulator of SCN9A. In order to uncover this mechanism we aim to answer three main questions: how, where and when does NAT1.7 downregulate SCN9A expression? Through the detailed analysis of NAT1.7 function at the molecular and mouse behavioural levels in a newly developed mouse model, this proposal aims to provide a comprehensive understanding of the NAT1.7 role in the regulatory control of SCN9A expression. We will also pay attention to any other genes being modulated by NAT1.7, as it will give us important information on any potential side effects arising if NAT1.7 is used as an analgesic agent. In addition, by manipulating elevated NAT1.7 levels we aim to determine the translational potential of this novel gene for treating pain. We believe that understanding of the mechanism by which NAT1.7 downregulates SCN9A and assessment of its analgesic potential in our mouse behavioural models will form a solid platform for further research into the translational potential of this conserved gene and the development of novel therapies targeting pain conditions.