Natural aminoacyl tRNA synthetase fragment enhances cardiac function after myocardial infarction

Abstract

A naturally-occurring fragment of tyrosyl-tRNA synthetase (TyrRS) has been shown in higher eukaryotes to 'moonlight' as a pro-angiogenic cytokine in addition to its primary role in protein translation. Pro-angiogenic cytokines have previously been proposed to be promising therapeutic mechanisms for the treatment of myocardial infarction. Here, we show that systemic delivery of the natural fragment of TyRS, mini-TyrRS, improves heart function in mice after myocardial infarction. This improvement is associated with reduced formation of scar tissue, increased angiogenesis of cardiac capillaries, recruitment of c-kitpos cells and proliferation of myocardial fibroblasts. This work demonstrates that mini-TyrRS has beneficial effects on cardiac repair and regeneration and offers support for the notion that elucidation of the ever expanding repertoire of noncanonical functions of aminoacyl tRNA synthetases offers unique opportunities for development of novel therapeutics.

Figure 1. Mini-TyrRS treatment after coronary ligation improves myocardial function in vivo.

A. Representative images of M-Mode echocardiography for heart function of saline- and mini-TyrRS treated mice at 3d and 7d post MI. B–C. Left ventricle fractional shortening and ejection fraction after coronary artery ligation with or without mini-TyrRS treatment. Echocardiography results shown are mean ± SEM (n = 7–12 mice per group; P<0.03). Measurements were collected at the level of the papillary muscle in M-mode. D–E. End Diastolic volume and end systolic volume after coronary artery ligation with or without mini-TyrRS treatment. Results shown are mean ± SEM (n = 7–12 mice per group). Although results did not reach statistical significance (P<0.09), there is a trend towards significance for decreased end diastolic and end systolic volumes after mini-TyrRS treatment compared to saline controls.

Figure 2. Mini-TyrRS reduces levels of scar formation after infarction.

A. Representative H&E and Masson’s Trichrome stained sections 3d after coronary artery ligation and saline or mini-TyrRS treatment. B. Quantitation of scar tissue of hearts after coronary artery ligation; results are represented as fibrotic area/left ventricle area, mean ± SEM (n = 3 mice/group; 1 section taken from the middle of the LV was quantified/mouse, P<0.03). Bar is 50 um.

Figure 3. Mini-TyrRS treatment enhances vascularization after infarction.

A. Representative TRITC-lectin stained sections 3d after coronary artery ligation and saline or mini-TyrRS treatment. B. Quantitation of capillaries per cardiomyocyte; values shown are mean ± SEM (n = 3 mice/group; 9–11 images were quantified/mouse; *P<0.04). Bar is 20 um.

Figure 4. Mini-TyrRS promotes cell survival after coronary artery ligation.

A. Representative cleaved caspase-3 (CC3) stained sections 7d after coronary artery ligation and saline or mini-TyrRS treatment. B. Quantitation of CC3 positive cells/image; values shown are mean ± SEM (n = 3 mice/group; 10 images were quantified/mouse; *P<0.05). Bar is 100 um.

Figure 5. Mini-TyrRS treatment promotes cardiac fibroblast proliferation after infarction.

A. Representative sections of hearts 3d after coronary artery ligation and saline or mini-TyrRS treatment. Sections were immunostained for vimentin, PCNA and DAPI. B. Quantitation of vimentin- and PCNA- double positive cells in saline and mini-TyrRS treated hears; values represent fold change relative to saline group; values shown are mean ± SEM (n = 3 mice/group; 10 images were quantified/mouse; *P<0.05). Please note the increased number of vimentin-positive cells infiltrating hearts of mini-TyrRS-treated animals. Bar is 100 um.

Figure 6. Increased c-Kit^pos cells in mini-TyrRS-treated hearts after infarction.

A. Representative c-kit stained sections 3d after coronary artery ligation and saline or mini-TyrRS treatment. Arrows point to typical c-kit positive cells. B. Quantitation of c-kit positive cells/image; values shown are mean ± SEM (n = 3 mice/group; 15–16 images were quantified/mouse; *P<0.01). Bar is 100 um.