Identifying the PDGFRβ Signaling Pathways That Mediate Opioid Tolerance
Stephanie Puig, Department of Psychiatry, Boston University
While opioids are the gold standard for the treatment of severe pain, with continued use, opioid safety is dramatically reduced because of CNS mediated side effects, such as dependence and addiction. As a result,
addiction and death due to opioid overdose have become a national emergency. Many aspects of this opioid crisis relate to the necessity of escalating doses as tolerance develops (gradual decrease in analgesic efficacy). Thus, novel strategies and therapeutic targets are needed to increase the safety of prolonged opioid use. An ongoing challenge with regard to opioid use is how to selectively prevent tolerance, dependence and reduce addiction liability without altering their pain-relieving effect. Recent studies have shown that activation of the mu-opioid receptor (MOR) by opioids induces phosphorylation of the platelet-derived growth factor receptor beta (PDGFRβ) in the spinal cord, which is mediated by spinal release of the platelet-derived growth factor type B (PDGF-B) ligand. Accordingly, inhibition of PDGFRβ signaling with imatinib, a PDGFRβ inhibitor, or with a selective PDGF-B ligand scavenger, prevents opioid tolerance. Notably, tolerance could develop in the absence of opioids through repeated activation of PDGFRβ by the PDGF-B ligand, thus suggesting that PDGFRβ signaling specifically mediates opioid tolerance. Although PDGFRβ inhibitors are FDA approved for treatment of malignancies and could be repurposed to treat chronic pain, they also target several other receptor tyrosine kinases (RTKs), which could lead to other highly undesirable side-effects. Therefore, it is necessary to find other targets, beyond PDGFRβ signaling, that could provide safer therapeutic treatments for tolerance. New targets for tolerance could be identified through the precise understanding of the signaling cascades downstream of PDGFRβ, and through identifying proteins that are regulated by these pathways.
In this project, we propose to use proteomics to begin to understand the signaling cascades activated downstream of PDGFRβ that mediate tolerance. PDGFRβ is an RTK that possesses multiple tyrosines (Y) that when phosphorylated recruit specific signaling pathways to mediate defined cellular functions. The PDGFRβ phosphorylated tyrosines (phospho-Ys) that are phosphorylated in the context of tolerance are unknown.
Phosphoproteomics experiments could help identify the specific PDGFRβ pY activated after opioid MOR activation and would indicate which signaling cascades are recruited by PDGFRβ to initiate tolerance. Proteomics of whole cell spinal lysates would also help identify proteins that are regulated in the context of tolerance by PDGFRβ signaling. Therefore, with this funding, we plan to: 1) use phosphoproteomics to precisely determine which PDGFRβ tyrosines are phosphorylated by chronically opioid activated MORs; and 2) use proteomics to discover proteins regulated by the tolerance inducing PDGFRβ signaling activated by chronic opioid treatments. Our laboratory will benefit from a proteomics approach, as this high throughput method will enable us to precisely identify PDGFRβ signaling cascades that mediate tolerance. These experiments will lay the foundation for future experiments and grant proposals that will focus on identifying targets that could help preserve long term opioid analgesic efficacy and prevent the occurrence of dependence and addiction.
addiction and death due to opioid overdose have become a national emergency. Many aspects of this opioid crisis relate to the necessity of escalating doses as tolerance develops (gradual decrease in analgesic efficacy). Thus, novel strategies and therapeutic targets are needed to increase the safety of prolonged opioid use. An ongoing challenge with regard to opioid use is how to selectively prevent tolerance, dependence and reduce addiction liability without altering their pain-relieving effect. Recent studies have shown that activation of the mu-opioid receptor (MOR) by opioids induces phosphorylation of the platelet-derived growth factor receptor beta (PDGFRβ) in the spinal cord, which is mediated by spinal release of the platelet-derived growth factor type B (PDGF-B) ligand. Accordingly, inhibition of PDGFRβ signaling with imatinib, a PDGFRβ inhibitor, or with a selective PDGF-B ligand scavenger, prevents opioid tolerance. Notably, tolerance could develop in the absence of opioids through repeated activation of PDGFRβ by the PDGF-B ligand, thus suggesting that PDGFRβ signaling specifically mediates opioid tolerance. Although PDGFRβ inhibitors are FDA approved for treatment of malignancies and could be repurposed to treat chronic pain, they also target several other receptor tyrosine kinases (RTKs), which could lead to other highly undesirable side-effects. Therefore, it is necessary to find other targets, beyond PDGFRβ signaling, that could provide safer therapeutic treatments for tolerance. New targets for tolerance could be identified through the precise understanding of the signaling cascades downstream of PDGFRβ, and through identifying proteins that are regulated by these pathways.
In this project, we propose to use proteomics to begin to understand the signaling cascades activated downstream of PDGFRβ that mediate tolerance. PDGFRβ is an RTK that possesses multiple tyrosines (Y) that when phosphorylated recruit specific signaling pathways to mediate defined cellular functions. The PDGFRβ phosphorylated tyrosines (phospho-Ys) that are phosphorylated in the context of tolerance are unknown.
Phosphoproteomics experiments could help identify the specific PDGFRβ pY activated after opioid MOR activation and would indicate which signaling cascades are recruited by PDGFRβ to initiate tolerance. Proteomics of whole cell spinal lysates would also help identify proteins that are regulated in the context of tolerance by PDGFRβ signaling. Therefore, with this funding, we plan to: 1) use phosphoproteomics to precisely determine which PDGFRβ tyrosines are phosphorylated by chronically opioid activated MORs; and 2) use proteomics to discover proteins regulated by the tolerance inducing PDGFRβ signaling activated by chronic opioid treatments. Our laboratory will benefit from a proteomics approach, as this high throughput method will enable us to precisely identify PDGFRβ signaling cascades that mediate tolerance. These experiments will lay the foundation for future experiments and grant proposals that will focus on identifying targets that could help preserve long term opioid analgesic efficacy and prevent the occurrence of dependence and addiction.