Project Summary/Abstract Loss of vascular tone is characteristic for cardiovascular collapse during hemorrhagic shock and fluid resuscitation (HS/R). Dysfunction and desensitization of α1-adrenergic receptors (ARs) is considered the hallmark in the development of vasodilatory shock. The mechanisms responsible for α1-AR dysfunction are unknown. The chemokines (C-C motif) chemokine ligand 2 (CCL2), CCL3, CCL5 and CCL22 have been identified as key drivers of the initial inflammatory response to HS/R, and as early biomarkers that segregate surviving and non-surviving trauma patients. The pathophysiological and molecular mechanisms underlying these important clinical correlations, however, remain to be determined. We discovered that the chemokine receptors (CRs) (C-C motif) chemokine receptor 1 (CCR1), CCR2 and CCR4, which are receptors for CCL2, CCL3, CCL5 and CCL22, form heteromeric complexes with α1-AR in the tunica media of resistance arteries. We provide preliminary evidence that activation of CCR2 antagonizes α1-AR mediated constriction of isolated resistance arteries and cross-recruits b-arrestin to α1-AR, a molecular signaling event that initiates removal of α1-AR from the plasma membrane. This leads to our main hypothesis that chemokine release during early phases of HS/R impairs vascular tone and blood pressure regulation through activation of their CRs, which interact with and regulate α1-AR in vascular smooth muscle cells (VSMCs). This implies that pharmacological targeting of the CRs that interact with α1-AR will provide new therapeutic options to stabilize vascular tone and hemodynamics, prevent cardiovascular collapse and improve resuscitation after HS. To test this hypothesis, we propose three specific aims: 1) To determine how the CR heteromerization partners of α1-AR regulate vascular function ex vivo. We will utilize pressure myography with isolated resistance arteries as a test platform to define the roles of the identified CR heteromerization partners in the regulation of intrinsic vascular function and vasopressor responsiveness. 2) To test how pharmacological targeting of the CR heteromerization partners of α1-AR modulates cardiovascular function in vivo. We will determine how blockade and activation of CR heteromerization partners affect normal cardiovascular function, vasopressor responsiveness and cardiovascular function during HS/R. 3) To determine the molecular mechanisms by which the CR heteromerization partners of α1-AR regulate α1-AR function. We will determine the mechanisms of cross-talk between the identified CRs and α1-AR, and elucidate the pathways by which the CR heteromerization partners of α1-AR modulate α1-AR-induced signaling and VSMC contraction. New knowledge gained from this proposal will advance our understanding of the regulation of vascular function and identify new molecular targets that could be used to improve blood pressure control during HS/R, and in hemodynamically instable critically ill patients i...