Decreased Insulin Sensitivity Of Pulmonary Artery Contributes To Hypoxic Pulmonary Hypertension And The Underlying Mechanisms

AIM: Hypoxic pulmonary hypertension (HPH) is more common in clinical patients withpulmonary hypertension. Epidemiology data shows that HPH has complex causes andconditions, and tends to merge multiple organ dysfunctions. Find new pathologicalmechanism to solve clinical problems is urgent. This study was aimed to determinewhether insulin sensitivity of rat pulmonary arterial endothelial cells (PAEC) wasdecreased under hypoxic in vivo and in vitro and the underlying mechanisms.METHODS: In vitro, there were21male SD rats randomly divided into three equalgroups: normal group and HPH group (exposed in hypobaric and hypoxia condition for4weeks) and HPH+PIO group (exposed in hypobaric and hypoxia condition for4weeks,but treated with pioglitazone in the second week,10mg/kg/d). Pulmonary arterial pressure(PAP) and insulin-induced vasodilatation effects of pulmonary artery rings were measured. The expression of TRB3, PPARγ, PI3-kinase p85, p-Akt, p-eNOS and p-ERK1/2inpulmonary artery was detected by western blot. In vivo, at first, primary rat PAEC werecultured respectively in normoxia (21%O2,37℃) and hypoxia (10%O2,37℃) incubators.Cultured after6h,24h,48h,96h, cells were collected to detect the expression of TRB3,PPARγ and insulin signaling proteins by Western blot, and culture supernatant was used todetect generation of nitric oxide (NO) and endonthelin1(ET-1). Then, PAEC were dividedinto normoxia group (21%O2,37℃, cultured without insulin), hypoxia group (10%O2,37℃, cultured with insulin), normoxia+insulin group and hypoixa+insulin group. All ofgroups detected the expression of TRB, PPARγ and insulin signaling proteins aftercultured48h. Finally, PAEC were transfected with Lentivirus to overexpress TRB3, andthen divided into normoxic+mock-vehicle group, normoxic+overexpress group,hypoxia+mock-vehicle group and hypoxia+overexpress group to observe changes of thesignal pathway of protein.RESULTS: Compared with those in normal group, mPAP significantly enhanced in HPHgroup, whereas insulin-induced vasodilatation was significantly attenuated (n=12, P<0.01).The above situation was partially reversed in HPH+PIO group. Compared with that innormoxic group, NO level significantly increased after6h, declined after24h in HPHgroup and further decreased with prolonged hypoxia. Such trends of NO changes wereconsistent with expressions of PI3K-p85, p-Akt, p-eNOS, but on-going decreasedp-ERK1/2expression was happened in prolonged hypoxia. In addition, expression ofTRB3was augmented, while PPARγ decreased. The expression of PPARγ and TRB3inPAEC cultivated whether with insulin or not had no significant changes under anoxic andaerobic environment, whereas the lever of p85, p-Akt, p-eNOS (n=7, P<0.05) in insulincultivated PAEC was increased contrary to p-ERK1/2(P<0.05). The overexpression ofTRB3in PAEC made PI3K, p-Akt, p-eNOS expression decreased significantly (P<0.05),and p-ERK1/2elevated. Then overexpression of TRB3was accompanied with PPARγdecrease, hypoxia can enhance the above phenomenon. CONCLUSION: We demonstrate firstly that pulmonary artery diastolic function inducedby insulin is reduced in HPH rats, due to TRB3upregulation and resultant PPARγdownregulation which decreases PI3K/Akt/eNOS signaling pathways and NO productionand increases ERK1/2and ET-1signaling. Administration of insulin sensitization agentpartly reduces PAP and enhances insulin-induced pulmonary arterial relaxation effects.These data suggest that vascular insulin resistance of pulmonary artery in HPH rats maypromote the formation and development of pulmonary hypertension.