Identification of an Epitope from Adenine Nucleotide Translocator 1 That Induces Inflammation in Heart in A/J Mice

Abstract

Heart failure, a leading cause of death in humans, can emanate from myocarditis. Although most individuals with myocarditis recover spontaneously, some develop chronic dilated cardiomyopathy. Myocarditis may result from both infectious and noninfectious causes, including autoimmune responses to cardiac antigens. In support of this notion, intracellular cardiac antigens, like cardiac myosin heavy chain-a, cardiac troponin-I, and adenine nucleotide translocator 1 (ANT 1 ), have been identified as autoantigens in cardiac autoimmunity. Herein, we demonstrate that ANT 1 can induce autoimmune myocarditis in A/J mice by generating autoreactive T cells. We show that ANT 1 encompasses multiple immunodominant epitopes (namely, ANT 1 21-40, ANT 1 31-50, ANT 1 171-190, and ANT 1 181-200). Although all four peptides induce comparable T-cell responses, only ANT 1 21-40 was found to be a major myocarditogenic epitope in immunized animals. The myocarditis-inducing ability of ANT 1 21-40 was associated with the generation of T cells producing predominantly IL-17A, and the antigen-sensitized T cells could transfer the disease to naïve recipients. These data indicate that cardiac mitochondrial proteins can be target autoantigens in myocarditis, supporting the notion that the antigens released as a result of primary damage may contribute to the persistence of chronic inflammation through autoimmunity. Myocarditis can occur as a result of exposure to various infectious and noninfectious insults, but does not generally lead to a fatal outcome (ie, most affected individuals can recover spontaneously). However, a proportion of those affected can develop dilated cardiomyopathy (DCM). Estimates indicate that approximately half of DCM patients undergo heart transplantation because of a lack of alternative therapeutic options.1e3 Furthermore, several clinical studies suggest that DCM patients can have autoantibodies to several cardiac antigens, including adenine nucleotide translocator (ANT).4e6 Because DCM can arise as a sequel to myocarditis, it has been postulated that autoimmune response may be an underlying mechanism in its pathogenesis. 7ANT exists in multiple isoforms, all four of which are expressed in humans (ANT 1 , ANT 2 , ANT 3 , and ANT 4 ), but only three in mice (ANT 1 , ANT 2 , and ANT 4 ). ANT 1 is expressed in muscle tissues (heart and skeletal) and the brain, ANT 2 can be expressed in liver, kidney, and heart, and ANT 4 expression is restricted to the testes in mice.

Branched chain α‐ketoacid dehydrogenase kinase 111–130, a T cell epitope that induces both autoimmune myocarditis and hepatitis in A/J mice

“…6). While these results agree with the expected cytokine pattern as seen in other EAM models such as cardiac myosin, cTnI, and ANT 1 [2,26,27,29,30], we also found elevated levels of the antiinflammatory cytokine IL-10. However, IL-10 at a $200fold decreased level than that of IFN-g alone suggests that eventhough both pro-and anti-inflammatory cytokine responses occur with BCKD k , the balance is shifted in favor of the pro-inflammatory state.…”

“…Since BCKD k is also expressed in non-cardiac tissues such as liver, lungs, kidneys, skeletal muscles, and brain, we determined whether BCKD k peptides could induce inflammation in multiple organs. Livers obtained from naive mice showed the presence of scattered inflammatory cell foci (1.80 AE 0.58), and, as expected, their numbers were significantly increased in those derived from the CFA/PT group (21.89 AE 2.75;p < 0.005) as we and others have previously described [2,20]. By using the CFA/PT group as a baseline, we compared the inflammatory cell foci detected in animals immunized with BCKD k peptides, leading us to note that the livers from only the BCKD k 111-130-immunized group showed a significant increase in the number of foci with leukocytes scattered all through the parenchyma (69.59 AE 8.98; p < 0.005), as compared to naive or CFA/PT groups ( Table 2).…”

“…The lesions were also noted in the periportal (centroacinar) areas as noted in the mouse model of autoimmune hepatitis [28]. It should be noted, however, that animals receiving CFA/PT can show elevations in the inflammatory foci in the liver resulting from non-specific effects of the adjuvant, as we and others have reported previously [2,20]. Nonetheless, the finding that the number of liver foci were increased only in animals immunized with BCKD k 111-130 but not the other eight peptides and also an irrelevant antigen (RNase 43-56) ( Table 2) suggests that BCKD k 111-130 also can be an autoantigen in the mediation of autoimmune hepatitis.…”

“…It is unexpected that mitochondria which are sub-cellular organelles can give rise to proteins capable of generating an autoimmune response. However, other mitochondrial proteins have been documented to play a role in autoimmune pathology including the E2 subunit of pyruvate dehydrogenase, which has been shown to act as a target antigen in the mediation of primary biliary cirrhosis [32,33] and ANT 1 21-40 that we have previously shown to induce myocarditis in a manner similar to BCKD k peptides [2]. Our studies raise questions that how the mitochondrial proteins could be presented specifically to autoreactive CD4 T cells to induce disease in heart and liver.…”

“…Mechanistically, autoimmune responses against cardiac antigens are believed to mediate the development of DCM, as sera from DCM patients have been shown to contain autoantibodies for cardiac antigens, such as cardiac myosin, and cardiac troponin-I (cTnI) [3][4][5][6][7]. Recently, we demonstrated that the mitochondrial inner membrane protein, adenine nucleotide translocator 1 (ANT 1 ) can be a target autoantigen in the pathogenesis of DCM by identifying ANT 1 [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] as the disease-inducing epitope in A/J mice [2]. In this report, we describe the potential relevance of the mitochondrial matrix branched chain a-ketoacid dehydrogenase (BCKD) complex proteins to myocarditis and hepatitis.…”