Pericytes protect rats and mice from sepsis-induced injuries by maintaining vascular reactivity and barrier function:implication of miRNAs and microvesicles

Background Vascular hyporeactivity and leakage are key pathophysiologic features that produce multi-organ damage upon sepsis.We hypothesized that pericytes,a group of pluripotent cells that maintain vascular integrity and tension,are protective against sepsis via regulating vascular reactivity and permeability.Methods We conducted a series of in vivo experiments using wild-type(WT),platelet-derived growth factor receptor-β(PDGFR-β)-Cre+mT/mG transgenic mice and Tie2-Cre+Cx43^(flox/flox)mice to examine the relative contribution of pericytes in sepsis,either induced by cecal ligation and puncture(CLP)or lipopolysaccharide(LPS)challenge.In a separate set of experiments with Sprague-Dawley(SD)rats,pericytes were depleted using CP-673451,a selective PDGFR-βinhibitor,at a dosage of 40 mg/(kg·d)for 7 consecutive days.Cultured pericytes,vascular endothelial cells(VECs)and vascular smooth muscle cells(VSMCs)were used for mechanistic investigations.The effects of pericytes and pericyte-derived microvesicles(PCMVs)and candidate miRNAs on vascular reactivity and barrier function were also examined.Results CLP and LPS induced severe injury/loss of pericytes,vascular hyporeactivity and leakage(P<0.05).Transplantation with exogenous pericytes protected vascular reactivity and barrier function via microvessel colonization(P<0.05).Cx43 knockout in either pericytes or VECs reduced pericyte colonization in microvessels(P<0.05).Additionally,PCMVs transferred miR-145 and miR-132 to VSMCs and VECs,respectively,exerting a protective effect on vascular reactivity and barrier function after sepsis(P<0.05).miR-145 primarily improved the contractile response of VSMCs by activating the sphingosine kinase 2(Sphk2)/sphingosine-1-phosphate receptor(S1PR)1/phosphorylation of myosin light chain 20 pathway,whereas miR-132 effectively improved the barrier function of VECs by activating the Sphk2/S1PR2/zonula occludens-1 and vascular endothelial-cadherin pathways.Conclusions Pericytes are protective against sepsis through regulating vascular reactivity and barrier function.Possible mechanisms include both direct colonization of microvasculature and secretion of PCMVs.

Beneficial effect of arginine vasopressin on hemorrhagic shock through improving the vascular reactivity

The vascular reactivity and calcium sensitivity were decreased following hemorrhagic shock.Arginine vasopressin(AVP)was beneficial to endotoxic,infec-tious/septic and hemorrhagic shock.Our previous studies found that Rho kinase played an important role in the occurrence of calcium desensitization following shock.It was reported that AVP was with stimulation effect of Rho kinase.So we hypothesized that AVP might have bene-ficial effect on shock via activation of Rho kinase to regu-late the calcium sensitivity and vascular reactivity.Hemorrhagic shock(40 mmHg for 2 h)Wistar rats in vivo were adopted to observe the effects of small dose of AVP on hemodynamics,24-h survival rate,the pressor effect of norepinephrine(NE)and the contractility of superior mesenteric artery(SMA).Isolated SMAs from hemorrha-gic shock rats were adopted to observe the effects of AVP on vascular reactivity and calcium sensitivity and its rela-tionship to Rho kinase with an isolated organ perfusion system.The results show that AVP at the concentration of 0.1 U/kg and 0.4 U/kg significantly improved the hemo-dynamic parameters and the 24-h survival rate of hemor-rhagic shock rats.Meanwhile,these dosages of AVP significantly increased the pressor effect of NE and the contractile response of SMA to NE.Y-27632(3 mg/kg),a Rho kinase specific inhibitor,abolished the beneficial effects of AVP.In vitro,the calcium sensitivity and vas-cular reactivity of SMA to calcium and NE were signifi-cantly decreased following hemorrhagic shock.AVP at the concentration of 0.5 nmol/L and 5 nmol/L signifi-cantly increased the calcium sensitivity and vascular react-ivity.These effects of AVP were abolished by Y-27632(10 mmol/L).Taken together,the results suggest that AVP at 0.1 U/kg and 0.4 U/kg is beneficial to hemorrha-gic shock by improving the vascular reactivity,which involves activation of Rho kinase.

Vascular contractile response and signal transduction in endothelium-denuded aorta from cirrhotic rats

AIM: The mechanism of decreased vascular reactivity to vasoconstrictors in portal hypertension is still unclear. In addition to nitric oxide, defects in post-receptor signal transduction pathway have been suggested to play a role.However, substantial evidences observed equivocal changes of vascular reactivity following different agonists that challenged the hypothesis of the post-receptor defect. The current study was to evaluate the vascular reactivity to different agonists and the inositol trisphosphate (IP3)changes in signal transduction cascade from cirrhotic rats with portal hypertension.METHODS: The endothelial denuded aortic rings from cirrhotic and sham-operated rats were obtained for ex vivo tension study and measurement of the corresponding [3H] IP3 formation following different receptor and nonreceptor-mediated agonists' stimulation. Additionally,iNOS protein expression was measured in thoracic aorta.The contractile response curves to phenylephrine were performed in endothelial denuded aortic rings with and without preincubation with a specific iNOS inhibitor (L-N (6)-(1-iminoethyl)-lysine, L-NIL).RESULTS: In endothelial denuded aortic rings of cirrhotic rats, the vascular responses were reduced with phenylephrine and arginine vasopressin (AVP) stimulation but were normal with U-46619, NaF/AlCl3, and phorbol esterdibutyrate (PdBU) stimulation. Compared to the corresponding control groups, the degree of the increment of [3H] IP3 formation from basal level was also decreased with phenylephrine and AVP stimulation, but was normal with U-46619 and NaF/AlCl3 stimulation. The preincubation with L-NIL did not modify the hyporesponsiveness to phenylephrine. Additionally, the iNOS protein expression in thoracic aorta was not different in cirrhotic and shamoperated rats.CONCLUSION: Without the influence of nitric oxide, vascular hyporeactivity to vasoconstrictors persisted in cirrhotic rats with portal hypertension. However, the decreased vascular reactivity is an agonist-specific phenomenon. In addition,G-protein and phospholipase C pathway associated with the IP3 productions may be intact in cirrhotic rats with portal hypertension.