| Myocardial ischemia/reperfusion injury(MI/RI)is characterized by the exacerbation of primary ischemic tissue dysfunction and structural damage following the restoration of blood supply to the myocardium after a certain period of interruption.Dexmedetomidine(DEX)is a highly selective α-adrenergic receptor agonist that is widely used in clinical practice.When combined with other anesthetic drugs,DEX can achieve better analgesia,sedation,and adverse stress control during coronary artery bypass surgery.While several studies have shown that DEX has a myocardial protective effect,the mechanism underlying this protective effect remains unclear.The present study aimed to clarify the effect of DEX on the secretion of fibroblast growth factor 21(FGF21)by brown adipose tissue(BAT)and explore the role and mechanism of promoting dialogue between BAT and heart to protect against myocardial ischemia reperfusion injury.The main results are as follows:(1)We established a mouse model of MIRI to verify the protective effect of DEX on MIRI and its ability to promote FGF21 release from BAT.Our results indicated that DEX significantly improved cardiac insufficiency related to myocardial ischemia and reperfusion,including the recovery of ventricular wall motion rhythm and the increase of left ventricular ejection fraction and shortening fraction.Furthermore,DEX preconditioning significantly reduced the serum level of myocardial injury marker CK-MB after myocardial ischemia and reperfusion.Additionally,after DEX pretreatment,the expression of FGF21 m RNA and protein in the interscapular brown adipose tissue(i BAT)significantly increased,along with a significant increase in the serum level of FGF21.In addition,the serum content of FGF21 in clinical patients was significantly increased after receiving DEX for 3h.(2)We determined the role of BAT in DEX-mediated cardiac protection by ablating i BAT or giving FGF21 neutralizing antibody before establishing the MIRI mouse model.The results showed that i BAT ablation blocked the protective effect of DEX on MI/R-related cardiac insufficiency,as characterized by decreased ventricular wall motion,decreased left ventricular ejection fraction and shortening fraction.Additionally,i BAT ablation increased CK-MB levels and markedly increased expression of apoptosis-related proteins Cleaved caspase3,Bax,and decreased expression of Bcl-2.Importantly,removal of i BAT significantly reduced the serum content of FGF21 in mice.The effect of FGF21 neutralizing antibody was similar to that of i BAT ablation,as it also significantly blocked the protective effect of DEX on MI/R-related cardiac insufficiency,characterized by decreased ventricular wall motion,decreased left ventricular ejection fraction and shortening fraction.Furthermore,pretreatment with FGF21 neutralizing antibody increased CK-MB levels,markedly increased expression of apoptosis-related proteins Cleaved caspase3,Bax,and decreased expression of Bcl-2.These results confirm that DEX plays a protective role in the heart during ischemia and reperfusion by promoting the secretion of FGF21 from brown adipose tissue.(3)In this study,we investigated the mechanism by which dexmedetomidine(DEX)promotes the release of fibroblast growth factor 21(FGF21)from brown adipose tissue(BAT).We established a model of myocardial ischemia-reperfusion injury(MIRI)in mice and used the HIB 1B brown adipocyte cell line to explore this mechanism.In animal experiments,we found that DEX significantly promoted the expression of phosphorylated AMP-activated protein kinase(p-AMPK)/AMPK and peroxisome proliferator-activated receptor gamma coactivator 1-alpha(PGC1α)in i BAT.We also found that pretreatment with the AMPK inhibitor compound C or the PGC1α inhibitor SR-18292 could significantly inhibit the transcription and expression of FGF21 in i BAT,as well as reduce the serum content of FGF21 in mice.Furthermore,we used the HIB 1B cell line to verify the effect of DEX on the AMPK/PGC1α pathway at the cellular level.Our results showed that pretreatment with different concentrations of DEX(0.1μM,1μM,10μM)could promote the expression of p-AMPK/AMPK and PGC1α in a concentration-dependent manner.Additionally,pretreatment with different concentrations of DEX could also promote the transcription of lipolysis genes such as uncoupling protein 1(UCP1),peroxisome proliferator-activated receptor alpha(PPARα),PR domain-containing 16(PRDM16),and cell death-inducing DFFA-like effector A(CIDEA)in a concentration-dependent manner.After treatment with compound C or SR-18292,the transcription and protein expression levels of FGF21 in HIB1 B were significantly inhibited,as were the transcription levels of lipolytic genes UCP1,PPARα,PRDM16,and CIDEA.Overall,our findings suggest that DEX promotes the release of FGF21 in i BAT and accelerates the lipolysis metabolism of brown adipocytes via activating the AMPK/PGC1α pathway.(4)To investigate the mechanism by which DEX mediates the release of FGF21 for myocardial protection,we used the conditioned medium from HIB 1B cells that were pretreated with DEX to interfere with the HL-1 cell line.We first established an in vitro model of cardiomyocyte hypoxia-reoxygenation injury using HL-1 cells and directly pretreated the cells with different concentrations of DEX(0.1μM、1μM、10μM).However,our results showed that direct pretreatment of HL-1 cells with DEX did not increase cell viability,reduce the activity of lactate dehydrogenase(LDH)in the medium,or reduce the apoptosis of cardiomyocytes.To verify the indirect myocardial protective effect of DEX,we chose to pretreat HIB 1B cells with 1μM DEX and extract conditioned medium for HL-1 cell culture.Our results showed that the conditioned medium without DEX pretreatment had a weak protective effect on cardiomyocytes,whereas the conditioned medium with DEX pretreatment significantly restored the activity of cardiomyocytes after hypoxia/reoxygenation,reduced the activity of LDH in the medium,and reduced the rate of cardiomyocyte apoptosis.Furthermore,the conditioned medium with DEX pretreatment significantly decreased the expression of apoptosis-related proteins cleaved caspase-3 and Bax in cardiomyocytes and significantly increased the expression of Bcl-2.In addition,co-culture of cardiac myocytes with CM-DEX significantly promoted the dissociation of Keap1/Nrf2 and the nuclear translocation of Nrf2 in cardiomyocytes,significantly activated the transcription of Nrf2 downstream antioxidant genes such as HO-1,NQO1,GCLM and GCLC,and reduced the ROS level in cardiomyocytes after hypoxia/reoxygenation.The above results showed that the FGF21 released by brown adipocytes mediated by DEX may alleviate the cardiomyocytes hypoxia/reoxygenation injury via activating the Keap1/Nrf2 pathway. |
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