Painful conditions are a huge medical burden with an estimated prevalence of 32% per year and an economic burden over $600 billion accounting for treatment and lost productivity costs. While opioids can provide analgesic relief for some patients, their increasing use in medicine led to an epidemic of its own, with an ever-increasing mortality rate due to overdose, highlighting the need for novel, non-opioid analgesics. Recently, research to meet this need has been fueled by the study of mutations leading to painlessness (Congenital Insensitivity to Pain (CIP)). As part of this effort, I have focused on a newly identified variant of CIP caused by a series of loss-of- function mutations in the chromatin-modifying factor, PRDM12. Patients with Prdm12 mutations are unable to detect painful (nociceptive) stimuli, without defects in other sensory modalities (touch, vibration, proprioception, and itch). Furthermore, Prdm12 has been proposed to play a role in nociceptor development, consistent with the finding that humans with PRDM12-associated CIP lack small diameter nociceptors responsible for transmitting pain sensation. To better understand how Prdm12 loss-of-function leads to CIP, I developed a mouse model of Prdm12-associated CIP to test the hypothesis that PRDM12 expression is required for the development and maintenance of nociceptive sensory neurons.
In Aim 1, I will use this model to analyze the developmental and behavioral defects that result from Prdm12 loss-of-function mice compared to controls. I will start by looking for differences in neurogenesis, cell type specification, or cell death in dorsal root ganglia of Prdm12 loss-of-function mice. I will then compare these developmental changes with behavioral studies investigating nociceptive sensation of these mice to understand how loss of particular subsets of sensory neurons leads to defects in specific modalities of nociception. Finally, I will use mRNA-seq to begin to investigate the mechanism of action of PRDM12 at various stages of development.
In Aim 2, I will test whether PRDM12 is involved in the maintenance of nociceptive sensory neurons. I will do this by using a tamoxifen-inducible model to knockout Prdm12 at late embryonic to adulthood stages, and examining the DRG composition, pain behavior phenotype, and transcriptional changes in these mice. Additionally, I will use cultured DRG neurons from these mice to assess changes in neuronal populations and excitability using electrophysiology. Overall, the project will provide new insight into the developmental role of Prdm12 and our understanding of pain sensation, while also serving to open potentially new areas of analgesic discovery that could benefit both acute and chronic pain conditions.
Painful conditions are a leading cause of morbidity all over the world, and have very limited treatment options that are both safe and effective. Recent study of painless conditions resulting from genetic mutations in humans, including those of the transcription factor PRDM12, has helped to uncover the sensory processing mechanisms of pain, and may well fuel the development of a new wave of non-opioid analgesics. This proposal seeks to use a newly generated mouse model of PRDM12-associated congenital insensitivity to pain to study nociceptor development and function and determine whether PRDM12 or its downstream effectors may represent good candidate targets for analgesic discovery.
