Mechanistic Characterization of the E102Q Mutation in the Sigma 1 Receptor

Abstract

weeks old pre-hypertensive SHRs and Wistar rats. Two PKA biosensors expressing cytoplasmic and the outer mitochondrial membrane (OMM) targeted AKAR4 were transferred to cultured sympathetic neurons. Fluorescence resonance energy transfer technique was used to measure dynamic changes of PKA concentration. No significant difference in Forskolin-evoked PKA activity was observed in the cytosol or at the OMM between SHR and Wistar neurons. However, direct PKA activation using Sp-8-Br-cAMP led to significantly higher PKA activity being detected at the OMM in SHR. In the presence of Bay60-7550 (a PDE2A specific inhibitor), greater Forskolin-evoked PKA activity was also observed in SHR neurons at the OMM. Evidence presented in this study demonstrates that there is impairment of PKA signalling at the OMM in sympathetic neurons of the SHR. This might be caused by over-activity of PDE2A. Our findings suggest that impaired cAMP-PKA signalling at the OMM may have important functional consequences linked to enhanced sympathetic neurotransmission. PDE2A may be a valuable therapeutic target for dysautonomia associated in the treatment of hypertension. Inflammation underlies many acute and chronic pain conditions. Excitation of peripheral afferents innervating the inflamed tissue is a primary event in generation of the inflammatory pain. Such excitation is produced by 'inflammatory mediators' -reactive compounds released by the damaged tissue and the immune cells at the inflammation site. Many of these inflammatory mediators (e.g. bradykinin, histamine, prostaglandins, ATP etc.) are ligands of G protein coupled receptors (GPCR) which activate phospholipase C (PLC) and induce release of Ca 2þ from the endoplasmic reticulum (ER). Ca 2þ signals induced by these receptors in sensory neurons produce excitation and trigger pain. A crucial mechanism maintaining the ER Ca 2þ store refill and the GPCR-mediated Ca 2þ signaling, is the calcium release-activated channel (CRAC). Here we characterized the expression of CRAC components within the rat dorsal root ganglion (DRG) neurons and explored the role of CRAC channel complex in the inflammatory GPCR signaling in DRG. STIM1/2 and Orai1/3 were expressed within DRG neurons of different sensory modalities with STIM1 and Orai1 being the predominant subunits. STIM1 and Orai1 formed clusters upon ER store depletion, as demonstrated by the proximity ligation assay (PLA). STIM2 was preferentially expressed in large-diameter (presumed mechanosensory) neurons. Store-operated Ca 2þ entry (SOCE) in DRG neurons was sensitive to CRAC inhibitors YM58483 and Synta66. CRAC channel complex assembly relies on the close proximity of the plasma membrane and endoplasmic reticulum. We show that junctional proteins junctophilin-3 and junctophilin-4 are expressed in DRG. Knocking-down JPH4 disrupted the Orai1-STIM1 clustering and inhibited SOCE. Moreover, JPH4 knockdown impaired the ability of DRG neurons to generate multiple Ca 2þ transients in response to inflammatory mediators (bradykinin and ATP). Taken togethe...