Expression of Tropomyosin 2 Gene Isoforms in Human Cardiac Tissue

Previous studies have shown that although the transcript levels of TPM1α and TPM1k are expressed in human hearts in comparable levels, the level of TPM1α protein is ~90%. The proteins of TPM1κ and TPM2α are about 5% of the total sarcomeric TM. The TPM2 gene is known to generate three alternatively spliced isoforms, which are designated as TPM2α, TPM2β, and TPM2γ. The expression level of TPM2β and TPM2γ in human hearts is unknown. Using a series of primers pairs and probes for RNA PCR, we found that both TPM2α and β but not γ were expressed in fetal and adult heart tissue, with about the same amounts of each isoform in fetal hearts and more β than α in adult hearts. Four new isoforms of TPM2 RNA were identified (TPM2δ - η). Most of these were present in very small amounts in both the fetal and adult hearts with the exception of TPM2ξ, which was present at about 40% of the level of TPM2α in adult heart tissue. Western blot analyses using a series of anti-tropomyosin antibodies indicate that TPM2 protein is present in both fetal and adult hearts at about the same levels as TPM1κ and much less than TPM1α. We are unsure about the expression of TPM2δ, TPM2ζ, and TPM2η proteins in fetal and adult human hearts. The exact function of these new TPM2 isoforms in heart and their role(s) in cardiac disease remain to be elucidated.