Introduction:
Heart regeneration has been proposed as a treatment for heart failure. However, the challenge of detecting bona fide heart regeneration has complicated the validation of potential regenerative factors. We sought to develop a method for quantifying cardiomyogenesis in the mouse heart using multicolor lineage tracing.
Hypothesis:
We hypothesized that multicolor lineage tracing in combination with modeling of nearest neighbor distances could be used to quantify clonal expansion of cardiomyocytes (CMs) during growth and regeneration.
Methods:
Myh6- MerCreMer
;
R26R-Rainbow
bitransgenic mice underwent cryoinjury (CI) or sham injury on postnatal day 1 (P1). Tamoxifen was then administered such that limited numbers of CMs were randomly labeled with mCerulean, mOrange, or mCherry fluorophores. Hearts were collected at 21 days post CI. We analyzed a total of 81 sections, across 6 hearts (3 with sham injury and 3 with cryoinury). Images of entire cardiac sections were manually segmented to generate positional information for each labeled CM.
Results:
We used the nearest neighbor distributions of CMs carrying the same fluorophore and CMs carrying different fluorophores to develop a Bayesian model for estimating the probability that two CMs are clonally related. We found that, across a range of recombination efficiency, CMs carrying the same fluorophore within 30 μm are likely to be clonally related. By classifying CMs based on this distance threshold, we were able to confirm that clonally related CMs are smaller than non-clonally related CMs (165.20 ± 13.79 μm
2
vs 252.37 ± 20.51 μm
2
, p = 0.007, Welch t-test). We also confirmed that rates of cardiomyogenesis in cryoinjured and sham injured hearts are approximately the same (8.57 ± 2.69 % in cryoinjured hearts vs 9.45 ± 1.23 % in sham hearts, p=0.788).
Conclusions:
We have developed a robust and objective approach for quantifying cardiomyogenesis in the mouse heart. This method can be applied to studies of heart regeneration and can also be adapted to other tissues.