Cardiomyocyte proliferation and progenitor cell recruitment underlie therapeutic regeneration after myocardial infarction in the adult mouse heart.
Bottom Line: After MI, new cardiomyocytes arise from both progenitors as well as pre-existing cardiomyocytes.Transplantation of CDCs upregulates host cardiomyocyte cycling and recruitment of endogenous progenitors, while boosting heart function and increasing viable myocardium.The observed phenomena cannot be explained by cardiomyocyte polyploidization, bi/multinucleation, cell fusion or DNA repair.
Affiliation: Cedars-Sinai Heart Institute, Los Angeles, CA, USA.Show MeSH
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Mentions: Flow cytometry of BrdU and Ki67 in FACS-sorted GFP+ cardiomyocytes revealed that the normal heart contains a small fraction of cycling endogenous cardiomyocytes (BrdU+: 0.08 ± 0.05% after the 1st week of BrdU pulsing, 0.4 ± 0.12% after 5 weeks of BrdU pulsing; Ki67+: 0.04 ± 0.03%). The low but measurable rate of basal cycling is consistent with some reports of cardiomyocyte turnover in the young adult heart (Bergmann et al, 2009; Soonpaa & Field, 1997), but not others (Kajstura et al 2010; Walsh et al, 2010). Tissue injury results in increased cardiomyocyte cycling, primarily during the first 3 weeks post-MI (BrdU+: 0.27 ± 0.09% after the 1st week of BrdU pulsing, 0.74 ± 0.05% after 5 weeks of BrdU pulsing; Ki67+: 0.14 ± 0.03%). Both the low rate of cardiomyocyte cycling under basal conditions, as well as the increase after injury, are notable. However, the most surprising finding is the amplification of cardiomyocyte cycling by cell therapy: the number of BrdU-incorporating preformed cardiomyocytes increases approximately threefold relative to MI (and approximately ninefold over basal levels) to 0.73 ± 0.11% after the 1st week of BrdU pulsing (2.09 ± 0.12% after 5 weeks of BrdU pulsing). Likewise, the Ki67+ percentage rises to 0.43 ± 0.09% 1 week after CDC administration (Fig 2A–D, Supporting Information Fig 2). The differences were greatest in the first 3 weeks post-injury. Immunocytochemistry of enzymatically dissociated cardiomyocytes (GFP+, αSA+) for BrdU, Ki67 and H3P (a marker of karyokinesis) confirmed these results (Fig 3).
Affiliation: Cedars-Sinai Heart Institute, Los Angeles, CA, USA.