Differential changes in transforming growth factor-beta isoform expression during postnatal cardiac growth

Transforming growth factor-beta (TGF-beta) is synthesised as an inactive precursor protein; this is cleaved to produce the mature peptide and a latency associated protein (LAP), which remains associated with the mature peptide until activation by LAP degradation. Isoform specific antibodies raised against the LAPs for TGF-beta 2 and -beta 3 were used to determine the myocardial levels of LAP (activatable TGF-beta) and full length precursor (inactive TGF-beta) forms during post-natal development in the rat. TGF-beta 2 was present predominantly as the precursor in 2 day old myocardium. There was an age-dependent shift from precursor protein to LAP between 2 and 28 days. A corresponding increase in the level of mature (activatable) TGF-beta 2 was found. TGF-beta 3 was detected in significant quantities only as LAP. However, a four-fold increase in the expression of TGF-beta 3 LAP was observed between 2 and 28 days. The substantial increases in activatable forms of TGF-beta 2 and -beta 3 that occur in myocardium during the first 28 days of life in the rat support a role for these proteins in post-natal cardiac development.