Heart regeneration after apex resection in rats: morphologic and molecular characterization

Author(s)

Camila Zogbi Nogueira

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina (FM/SBD)
• Defense date: 2016-08-24

Examining board members

Jose Eduardo Krieger; Elia Tamaso Espin Garcia Caldini; Rui Curi; Martin Conrad Harmsen

• Advisor: Jose Eduardo Krieger

Abstract

The replacement of cardiomyocytes in postnatal life has proven to be one of the biggest challenges in regenerative medicine. The concept that cardiomyocytes proliferate actively during development but cease completely right after birth has been recently questioned when first evidences showed the existence of endogenous mechanisms of cardiac regeneration in one-day-old mice. We sought to evaluate this phenomenon in one-day-old rats (P1) and to assess the impact of the early regenerative process on long-term tissue perfusion and overall cardiac function in response to stress. We confirmed the successful apical resection surgery through magnetic resonance imaging (MRI) and that P1 heart was associated with evidence of cardiomyocytes neoformation as indicated by Troponin I and Connexin 43 expression at 21 days postresection, while in seven-day-old rats (P7) mainly scar tissue replacement ensued. Interestingly, there was an apparent lack of uniform alignment of newly formed cells in P1, and cardiac tissue hypoperfusion has been detected for both groups at 21 postresection and at 60 days through SPECT scanning. Direct basal cardiac function at 60 days, was preserved in all groups, whereas under hemodynamic stress the degree of change on LVDEP, Stroke Volume and Stroke Work indicated diminished overall cardiac function in P7. Furthermore, the End-Diastolic Pressure-Volume relationship and increased interstitial collagen deposition in P7 is consistent with increased chamber stiffness. Collectively, we showed that regenerative potential with slight collagen deposition is restricted to P1 rats. Then we sought to evaluate the molecular mechanisms that regulate this phenomenon through explorative tools. Although it has been previously described that the immune system is not fully mature at birth, total RNA sequenced from sham-operated, P1 and P7 heart rats showed that surgery is sufficient to activate inflammatory pathways, and considering pro (M1) and anti-inflammatory (M2) macrophages subpopulations, we suggested that invaded macrophages in resected P1 hearts are different from the traditional pro-fibrotic M2-like adult cells. Conditioned M1 and M2 medium elevated cardiomyocytes proliferative rate under basal conditions, but only M2 produced the same effect in cardiomyocytes under hypoxia and prevented myofibroblasts-induced differentiation through ?SMA intensity expression. Membrane array for cytokines showed 15 common cytokines for both M1 and M2 conditioned medium, but only 4, as IL-4, IL-1?, IL-6 and Fractalkine, were M2 exclusive and possible candidates to the regenerative potential. Additional experiments are needed to further explore these cytokines and to maybe develop new therapeutic strategies (AU)

• FAPESP's process: 12/10107-4 - Heart regeneration in neonatal rats submitted to apex resection and identification of regulatory pathways of this process.
• Grantee: Camila Zogbi Nogueira Perez
• Support Opportunities: Scholarships in Brazil - Doctorate