Intra-myocardial delivery of mesenchymal stem cells ameliorates left ventricular and cardiomyocyte contractile dysfunction following myocardial infarction

Abstract

Although mesenchymal stem cells (MSCs) transplantation may improve the overall heart function, the heterogeneity of myocardial cells makes it difficult to determine the nature of cells benefited from transplantation. This study evaluated the effect of intra-myocardial MSC transplantation on myocardial function following MI. Enhanced green fluorescent protein (EGFP)-expressing donor MSCs from C57BL/6-Tg (UBC-GFP) 30Scha/J mice were transplanted into LV free wall in the region bordering an infarct in C57 recipient mice following ligation of left main coronary artery (MI+MSC group). Ten days after MI, LV function was assessed using echocardiography. Cardiomyocyte contractility and intracellular Ca(2+) transients were measured in cells from the area-at-risk surrounding the infarct scar. The EGFP donor cells were traced in the MSC recipient mice using fluorescence microscopy. TUNEL, H&E and Masson trichrome staining were used to assess apoptosis, angiogenesis and myocardial fibrosis, respectively. MI dilated LV as evidenced by increased end-diastolic and end-systolic diameters. MI significantly reduced fractional shortening, cardiomyocyte peak shortening, and maximal velocity of shortening and relengthening, all of which were attenuated or abrogated by MSC therapy. MI also reduced resting intracellular Ca(2+), intracellular Ca(2+) rise and decay rate, which were reconciled by MSC. MSC therapy attenuated MI-induced apoptosis and decreased angiogenesis but not myocardial fibrosis in the peri-infarct area. Taken together, our results demonstrated that MSC therapy significantly improved both LV and cardiomyocyte function possibly associated with its beneficial role in apoptosis and angiogenesis, indicating a key role for cardiomyocytes in stem cell tissue engineering.

Fig. 1

Echocardiographic evaluation of murine hearts following MI with or without MSC transplantation. A: Fraction shortening (%); B: Left ventricular end diastolic diameter (LVEDD); C: Left ventricular end systolic diameter (LVESD) Mean ± SEM, n = 5–7 mice per group, * p < 0.05 vs. C57 control (CONT) group; # p < 0.05 vs. MI group.

Fig. 2

Illustration of the EGFP-positive cells from frozen heart slices or isolated myocytes from the MI border zones 10 days after the MSCs transplantation. A, B: heart tissues; C, D: isolated cardiomyocytes.

Fig. 3

Effect of MI on cell shortening in cardiomyocytes from area at risk in the absence or presence of MSC transplantation. (A): resting cell length; (B): peak shortening (normalized to resting cell length); (C, D): maximal velocity of cell relengthening/shortening (± dL/dt); (E): time-to-peak shortening (TPS); and (F): time-to-90% relengthening (TR₉₀). Mean ± SEM, n = 140–148 myocytes per group, * p < 0.05 vs. C57 control (CONT) group; # p < 0.05 vs. MI group.

Fig. 4

Effect of MI on intracellular Ca²⁺ properties in cardiomyocytes from area at risk in the absence or presence of MSC transplantation. (A): Baseline intracellular Ca²⁺ fura-2 fluorescence intensity (FFI); (B): Electrically-stimulated increase in fura-2 fluorescence intensity (ΔFFI); (C): Single-exponential Ca²⁺ transient decay rate and (D): Bi-exponential Ca²⁺ transient decay rate. Mean ± SEM, n = 38–61 cells per group, * p < 0.05 vs. C57 control (CONT) group; # p < 0.05 vs. MI group.

Fig. 5

Change in peak shortening (PS) amplitude of cardiomyocytes from area at risk following MI in the absence or presence of MSC transplantation at different stimulus frequencies (0.1 – 5.0 Hz). PS at various stimulus frequencies was normalized to PS value obtained at 0.1 Hz from the same cell. Mean ± SEM, n = 22 cells per group, *p < 0.05 vs. control (CONT) group.

Fig. 6

Effect of MI on apoptosis using TUNEL staining in myocardium from area at risk in the absence or presence of MSC transplantation. All nuclei were stained with DAPI shown in blue in panel A (Control), D (MI) and G (MI+MSC); TUNEL(+) nuclei were visualized with fluorescein (green) in panel B (Control), E (MI) and H (MI+MSC); Panels C (Control), F (MI) and I (MI+MSC) displayed merged DAPI and TUNEL (+) nuclei staining. Mean ± SEM, n = 21 – 30 fields from 3 mice per group, * p < 0.05 vs. control (CONT); # p < 0.05 vs. MI group.

Fig. 7

H&E and Masson trichrome stained photomicrographs exhibiting angiogenesis and myocardial fibrosis, respectively, in myocardium from area at risk in the absence or presence of MSC transplantation. Panels A (Control), B (MI) and C (MI+MSC) display H&E staining indicative of vascular content; Panels D (Control), E (MI) and F (MI+MSC) display Masson trichrome staining exhibiting myocardial fibrosis. Panels G and H depict pooled data of vessel content (H&E staining) and myocardial fibrosis (Mason trichrome), respectively. Scale bar = 50 µm. Mean ± SEM, n = 10 – 15 fields from 3 mice per group, * p < 0.05 vs. control (CONT), # p < 0.05 vs. MI group.