Fas (CD95/Apo-1)–Mediated Damage to Ventricular Myocytes Induced by Cytotoxic T Lymphocytes From Perforin-Deficient Mice

Abstract

—Cytotoxic T lymphocytes (CTLs) that infiltrate the heart are important immune effectors implicated in heart transplant rejection, myocarditis, and other cardiomyopathies. To investigate the mechanism(s) underlying CTL damage to the myocardium through activation of the Fas receptor (Fas/CD95/Apo-1) by the Fas ligand, we explored the interaction between peritoneal exudate CTLs (PELs), derived from perforin gene–knockout (P−/−) mice, and murine ventricular myocytes. Fas expression on isolated ventricular myocytes was demonstrated immunohistochemically. Action potentials, [Ca 2+ ] i transients, and contractions of myocytes conjugated to P−/− PELs or treated with the apoptosis-inducing anti-Fas monoclonal antibody Jo2 were recorded. Action potential characteristics of nonconjugated myocytes and myocytes conjugated with P−/− PELs were, respectively, as follows: V m , −73.2±1.5 and −53.6±6.4 mV (mean±SEM); action potential amplitude, 117.9±3.9 and 74.3±21.2 mV; and action potential duration at 80% repolarization, 17±6 and 42±13 milliseconds (all P <.05). P−/− PELs also induced early and delayed afterdepolarizations as well as arrhythmogenic activity. Diastolic [Ca 2+ ] i increased during the cytocidal interaction with P−/− PELs, from a fluorescence ratio of 0.82±0.05 (n=7) to 1.98±0.09 (n=13) ( P <.05). All of the effects caused by P−/− PELs were reproduced by incubating the myocytes with Jo2. Heparin (50 μg/mL), an antagonist of inositol trisphosphate (IP 3 )–operated sarcoplasmic reticulum Ca 2+ channels, or U-73122 (2 μmol/L), a phospholipase C inhibitor, but not the inactive agonist U-73343, prevented Fas-mediated myocyte dysfunction. Additionally, intracellular application (through the patch pipette) of the active IP 3 analogue, inositol 1,4,5-trisphosphate, but not the inactive analogue, inositol 1,3,4-trisphosphate, caused electrophysiological changes resembling those resulting from P−/− PELs and Jo2, suggesting that CTL-induced Fas-based myocyte dysfunction is mediated by IP 3 . We conclude that a Fas-based perforin-independent mechanism of CTL action can account for the immunopathology seen in the allotransplanted heart, myocarditis, and dilated cardiomyopathy.

EGF and HGF levels are increased during active HBV infection and enhance survival signaling through extracellular matrix interactions in primary human hepatocytes

“…Thus, reduced sensitivity to CD95-mediated apoptosis signals can conceivably lead to escape of virusinfected cells from immune surveillance. [17][18][19][20][21][22] Here we have found elevated levels of HGF and EGF in HBVinfected individuals and show that these growth factors stimulate survival signaling in primary human hepatocytes. Our findings support the notion that survival programs induced by EGF/HGF signaling may contribute to an apoptosis resistant phenotype in hepatocytes in the infected liver, thus contributing to immune escape and persistence of the viral infection.…”

Electrical Remodeling of the Ventricular Myocardium in Myocarditis

“…In contrast, an in-vitro study has reported that the inflammatory cytokine or Fas /Fas ligand mediated apoptosis would change the ionic currents of myocyte. 27 Our present study is the first in-vivo report that documented the electrical remodeling in a model of CHF include by inflammatory process. The role of the inflammation in the ventricular electrical remodeling should be investigated in the future studies.…”

Emerging roles of inositol 1,4,5-trisphosphate signaling in cardiac myocytes

“…Rather than reinforcing their positive contribution to inotropy, the overwhelming majority of studies that have examined the consequence of activating IP 3 Rs in ventricular myocytes have concluded that the predominant effect is to stimulate arrhythmias [62,143]. Indeed, IP 3 R activity has been suggested to underlie ventricular arrhythmias resulting from hormonal stimulation [143], reperfusion [144,145], engagement of cytotoxic T-lymphocytes [146] and FAS receptor activation [147]. These data suggest that Ca 2+ flux through the relatively few IP 3 Rs in ventricular myocytes is perhaps more dangerous than beneficial, similar to the situation discussed above for atrial cells.…”