Polyploidization of transplanted cardiac myocytes

Area of Science:

• Cardiology
• Developmental Biology
• Transplantation Biology

Background:

• Cardiac ventricular tissue from embryonic or neonatal rats can form viable, beating transplants when implanted under the kidney capsule of adult rats.
• These cardiac transplants were monitored for 40 days post-transplantation to assess their development and cellular characteristics.

Purpose of the Study:

• To investigate the cellular and nuclear changes in transplanted cardiac ventricular tissue over time.
• To compare the processes of cellular binucleation and nuclear polyploidization in cardiac transplants versus the in situ heart.
• To determine if cardiac myocyte growth is affected by transplantation and its relation to functional level.

Main Methods:

• Grafting of late embryonic or 1-day postnatal rat cardiac ventricular tissue beneath the kidney capsule of adult syngeneic hosts.
• Postoperative monitoring of transplants for up to 40 days.
• Analysis of cellular binucleation and nuclear polyploidization in transplant myocytes compared to myocytes in the intact heart.

Main Results:

• Transplanted cardiac tissue formed viable, beating structures.
• Cellular binucleation and nuclear polyploidization in transplants followed the same temporal schedule as in the native heart.
• A significantly lower percentage of non-diploid myocytes (30-60%) was observed in transplants compared to the intact heart (90%).
• Cardiac myocytes in transplants exhibited feeble growth after the polyploidization phase, unlike in the intact heart.

Conclusions:

• Transplantation preserves the normal timing of cellular binucleation and nuclear polyploidization in cardiac myocytes.
• A higher proportion of diploid myocytes is maintained in cardiac transplants compared to the in situ heart.
• Cardiac myocyte growth appears to be dependent on their level of function, which may be altered in the transplanted environment.