Noninvasive Assessment of Cardiac Abnormalities in Experimental Autoimmune Myocarditis by Magnetic Resonance Microscopy Imaging in the Mouse

Abstract

Myocarditis is an inflammation of the myocardium, but only ~10% of those affected show clinical manifestations of the disease. To study the immune events of myocardial injuries, various mouse models of myocarditis have been widely used. This study involved experimental autoimmune myocarditis (EAM) induced with cardiac myosin heavy chain (Myhc)-α 334–352 in A/J mice; the affected animals develop lymphocytic myocarditis but with no apparent clinical signs. In this model, the utility of magnetic resonance microscopy (MRM) as a non-invasive modality to determine the cardiac structural and functional changes in animals immunized with Myhc-α 334–352 is shown. EAM and healthy mice were imaged using a 9.4 T (400 MHz) 89 mm vertical core bore scanner equipped with a 4 cm millipede radio-frequency imaging probe and 100 G/cm triple axis gradients. Cardiac images were acquired from anesthetized animals using a gradient-echo-based cine pulse sequence, and the animals were monitored by respiration and pulse oximetry. The analysis revealed an increase in the thickness of the ventricular wall in EAM mice, with a corresponding decrease in the interior diameter of ventricles, when compared with healthy mice. The data suggest that morphological and functional changes in the inflamed hearts can be non-invasively monitored by MRM in live animals. In conclusion, MRM offers an advantage of assessing the progression and regression of myocardial injuries in diseases caused by infectious agents, as well as response to therapies.

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

“…31 Briefly, animals were anesthetized using 2% isoflurane and transferred onto animal holder, and the body temperature was monitored using a rectal thermometer. Respirometry and pulse oximetry were used to gate the respiratory and cardiac signals, respectively.…”

“…MRM imaging was performed using a wide-bore (89-mm) 9.4-T vertical-bore magnet (Varian, Inc., Walnut Creek, CA) equipped with triple axis gradients of 100 G/cm and a 4-cm radiofrequency imaging coil, as we have described previously. 31 Short axis slices of hearts were captured in eight time frames using an echo-based cine pulse sequence, and the images were analyzed using Segment software version 1.8 R1430 (Segment, Medviso, Sweden) to assess the structural (left ventricular wall thickness) and functional parameters [end diastolic volume, end systolic volume, stroke volume (SV), and ejection fraction (EF)].…”

“…31 Groups of mice were immunized with or without ANT 1 [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], and the animals were subjected for MRM imaging to measure end diastolic volume, end systolic volume, SV, EF, and left ventricular wall thickness. Expectedly, both SV and EF were significantly reduced in immunized animals on different days as compared to healthy group [day 30 to 35: SV, 11.33 AE 2.17 mL versus 25.67 AE 4.67 mL; EF, 30.17 AE 2.52% versus 65.67 AE 0.88% (P < 0.05); and day 46: SV, 9.00 AE 2.52 mL versus 29.00 AE 0.58 mL; EF, 24.00 AE 4.51% versus 60.00 AE 1.15% (P < 0.01)].…”

“…The presence of such a repertoire of cells has previously shown to be correlated with the lack of expression of autoantigens, like cardiac myosin and proteolipid protein in the thymus. 43,44 Splenocytes harvested from naïve mice were used to assess their reactivity to ANT 1 [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. Using RNase 43-56 as a control peptide, we noted that the splenocytes did not respond to ANT 1 21-40 (Supplemental Figure S2), suggesting the absence of preexisting endogenously derived repertoire of ANT-reactive T cells in the naïve animals.…”

“…One such model for cardiac autoimmunity is experimental autoimmune myocarditis (EAM), which involves induction of disease in susceptible rodent strains by immunizing animals with cardiac antigens or their peptide fragments. 23e25 In this study, we used the EAM model in A/J mice to demonstrate that ANT 1 possesses multiple immunodominant epitopes, and one of these, ANT 1 [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40], was found to induce myocarditis in the immunized animals. Furthermore, myocarditogenicity of ANT 1 [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] was associated with the generation of T cells capable of producing predominantly IL-17A, and the antigen-sensitized T cells can transfer the disease to naïve recipients, suggesting that ANT 1 can be a potential autoantigen in the heart autoimmunity.…”