FKBP12.6Depletion In Cardiomyocytes Increases The Incidence And Severity Of Sepsis-induced Heart Dysfunction In Mice

[Objective]The presence of cardiovascular dysfunction in sepsis is associated with a significantly increased mortality compared with that in septic patients without myocardial impairment. Although a number of researches have shown that decreased contractility is a major factor that causes myocardial dysfunction in sepsis, the precise mechanism is still unclear. FK506binding protein12.6kDa (FKBP12.6), a protein which combines with the ryanodine Ca2+release channels (RyR2) on the sarcoplasmic reticulum stabilizes a closed state of RyR2in cardiac muscle and thereby control intracellular Ca2+release and myocardial contraction. Although many studies have clearly established abnormal contractility as the major factors which induce heart dysfunction in sepsis, the underlying mechanisms remain poorly understood. The aim of the present study was to test whether the deficiency of FKBP12.6in cardiomyocytes affects the propensity for heart dysfunction in a murine model of sepsis.[Methods]1、FKBP12.6-/-(KO) mice and wildtype (WT) littermates were used. They are randomly divided into four groups:WT operated group, KO operated group, and WT sham operated group, KO sham operated group. The first two groups were made septic by cecal ligation and puncture (CLP) followed by fluid resuscitation and the latter two received sham operation.2、18h after CLP, hearts from WT and FKBP12.6-/-mice were harvested for the next steps:①the changes of tissue morphology in hearts which were stained with hemataxylin-eosin (H&E) were observed under a light microscope.②The protein expression of RyR2was analyzed by Western blot.③Ca2+sparks in individual cells were measured using a confocal microscopy.3、Echocardiography was performed at baseline and at predefined time points after CLP. Stroke volume (SV), cardiac output (CO), fractional shortening (FS) and heart rate (HR) were measured.[Results]1、Histological analysis of H&E strained sections of heart showed the significantly increasing amount of red blood cells and vacuoles in cardiac tissue of KO septic mice compared with WT septic mouse.2、The protein expression of RyR2in myocardium:compared with WT operated mice, RyR2protein level elevated in KO operated group (p<0.05). 3、compared with KO mice without CLP, Ca2+spark frequency in individual cell increased in KO mice which are exposed to CLP (P<0.01). Ca2+kinetics were significantly altered in KO operated groups (the P value of amplification, Full width at half-maximum (FWHM) and time to peak (Ttp) is P<0.05, P<0.01and P<0.01respectively).4、Hemodynamic evaluation:after CLP, SV, CO, HR decreased in both WT and KO groups,[Conclusion]The results above demonstrate that, dissociation of FKBP12.6from the RyR2complex in cardiomyocytes does play a significant role in incidence and severity of sepsis-induced heart dysfunction. These data may, in part, explain the reason of this disease, and may bear important therapeutic implications.