Figure 2. Early administration of rNRG1 improves myocardial function and structure.

(A) Experimental design of mouse pre-clinical trials. (B–K) Mice underwent cryoinjury on day 1 of life (P1) and were treated with BSA or rNRG1 from day of birth (P0, early administration, B–D), or from P5 (late administration, E–G). (B,C) Prolonged improvement in myocardial function after early administration shown by echocardiography (B) and cMRI at 64 dpi (C). (E,F) Late administration of rNRG1 resulted in transient improvement of myocardial function measured by echocardiography (E) and cMRI at 64 dpi (F). (D,G) Indexed heart weights showed early rNRG1 administration reduced cardiac hypertrophy at 64 dpi. (H) Time-series of AFOG-stained section shows scar (blue) is formed within 10 dpi and still present at 64 dpi. Note transmural scars after cryoinjury in BSA and late rNRG1 treatment groups. (I,J) Quantification of scar size after AFOG-staining shows transient and significant scar reduction after early rNRG1 administration (I). (K) Early administration reduces the percent of transmural scars at 34 and 64 dpi. (L) Non-transmural injury site thickens in systole (64 dpi, early administration) (M) Relative thickening of non-transmural scars is similar to remote LV free wall myocardium. (N) Transmural and non-transmural scars were identified by AFOG sections (left panels). Black rectangles indicate photomicrographs shown in the middle panels. Non-transmural scars have cardiomyocytes connected by gap junctions visualized with Connexin 43 staining (64 dpi, early administration, middle and right panels). Yellow squares indicate zoomed areas (Right panels). Scale bars 1 mm (H), 500 μm (N, center panel), 50 μm (N, far right). dpi: days post injury; BSA: bovine serum albumin; SC: subcutaneous injection: P0: day of birth. Statistical significance was tested with t-test (C,F,M) and ANOVA Bonferroni's Multiple Comparison Test (B,D,E,G,I,J,K) * P < 0.05, ** P < 0.01, *** P < 0.001, **** P < 0.0001.