Fig 2: Genetic background, and not the absence of WARP, determines predisposition to cardiac rupture.(a) Improved survival in in-house bred Australian (AUS) WARP KO mice compared to commercial (com) European (EU) WT mice after an MI is shown by a Kaplan-Meier curve. (b & c) Histological analysis of LV sections of infarcted hearts (hematoxylin-eosin stained) revealed larger infarct sizes in in-house bred AUS WARP KO mice compared to EU WT com mice. (d) There was no difference in survival anymore when AUS WARP KO mice were backcrossed to the European C57Bl/6-J background and all mice were bred in-house. (e & f) Infarct sizes are the same after mice were backcrossed to the European C57Bl/6-J background. (g) Breeding/housing influences predisposition to cardiac rupture post-MI. WT mice bred in-house show improved survival after infarction when compared to commercial WT mice purchased from 2 different providers: Harlan and Charles River. (h&i) Despite the difference in survival, no difference in infarct size was seen between in-house bred and commercially purchased WT mice. n≥3; *p<0.05; **p<0.01; bars 1000 μm.

Fig 3: WARP expression pattern in the heart.(a) WARP mRNA levels were induced 3 and 7 days after MI. WARP mRNA levels peaked at 7 days after MI and then decreased again at 14 days. (b) Western blot analysis and (c) immunohistochemistry also showed an induction of WARP protein levels in the infarcted LV at 3, 7, and 14 days after MI. Because of different sample-loading, the blots of the 14 days MI were cut and pasted in the same order as the blots of the 3 and 7 days MI. Images of the original unadjusted blots are provided in S1 Fig (d and e) Confocal microscopy confirmed the co-localization of WARP with perlecan in the uninfarcted heart, showing a network of WARP and perlecan as a honeycomb-structure surrounding the cardiomyocytes. In the infarcted LV zones, the WARP-perlecan honeycomb-structure is reduced at 3 days after MI and completely absent at 7 and 14 days after MI and the interaction between WARP and perlecan is disrupted. (e) WARP did not localize on CD45 positive leukocytes or in alpha smooth muscle cells lining the vessels in the remote, border and infarcted zone of the heart 14 days after MI. n≥3; *p≤0.05; **p≤0.005; ***p≤0.001 versus sham, ##p≤0.005; ###p≤0.001 versus remote, bars 1000 μm for (c) and 100 μm for (d) and (e).