The human heart beats on average 100,000 times a day, pumping 5 litres of blood to the extremities of the human body in order to provide the substances essential for survival. Human cells are known to be able to divide and repair tissues through cell replacement, a characteristic that we share with lizards, who are able to regenerate their tail after its detachment as a defense mechanism.
In order to pump blood continuously, the heart relies on specialised muscle cells called
cardiomyocytes. These cells, unlike other somatic (body) cells, become highly specialised
following birth and lose most of their ability to divide, making it thus challenging to replace heart muscle with new muscle cells during one’s lifetime. The average human heart maintains function by utilising existing enlarged cardiomyocytes which can be replaced at
very slow rates (around 1% per year). Permanent damage to these cells could result in a significant loss of heart function.
In a recent case study in Naples, Italy, a two-year-old boy suffering from a severe heart condition named cardiomyopathy required an urgent heart transplant. Cardiomyopathy refers
to the inability of the heart to pump blood. This meant his heart was unable to supply his
body cells with blood and so his body’s tissues were not supplied with the oxygen they require for survival. By miracle, a donor heart was available for him, but what failed to be communicated was the fact that this heart was stored in a transport container with dry ice. Dry ice causes freezing of the heart tissue and the formation of ice crystals which destroy the heart’s cells and cause the rupture of membranes. The oblivious doctors proceeded with the transplant, but later realised that the transplanted heart would never start beating independently due to severe cellular damage to the cardiomyocyte cells after it was frozen. This resulted in the young patient being put on life support for over two months, negatively impacting his other organs. In such conditions, the young patient was deemed unfit to undergo a second transplant.
This case study is a clear example of severe damage being irreversible when it comes to the heart, and how this not only affects the cardiovascular system but the entire body.
Scientists have been working on possible emerging technologies which could aid the heart
tissue in regeneration. Stem cell therapy has been studied as a possible treatment, where the injection of these in damaged heart tissue stimulates their division into new cardiac cells.
Apart from this, gene therapy has also been studied in its effectiveness when the reactivation of cell cycle genes in cardiomyocytes stimulates their division and regeneration.
Unlike humans, some animals, such as the zebrafish, have the ability to regenerate heart
tissue by re-activating the division of cardiomyocytes after damage. Scientists are using these species to study their specific genes that differ from human ones and that allow them to regenerate damaged heart tissue.
The heart lies at the centre of the human body – both literally and figuratively. While modern
medicine continues to make advances in the treatment of heart diseases, the heart’s limited
regenerative ability makes this extremely challenging. It’s important to consider regeneration
in other species and how this could be transferable to humans.
