Abstract 1160: The Anti-angiogenic Factor, Tenomodulin, Has A Pivotal Role In Maintaining Avascularity Of Chordae Tendineae Cordis
[Introduction] Cardiac valves and chordae tendineae cordis (CTC) are avascular tissues, although their avascularity is abrogated in several valvular heart diseases. We had recently reported that cardiac valves express chondromodulin-I (Chm-I), an angioinhibitory factor purified from cartilage, but it is not expressed in CTC. Instead, we found that tenomodulin (TEM), a Chm-I-related anti-angiogenic factor isolated from tendon, is expressed in CTC. This study investigated the molecular mechanisms underlying the avascularity of CTC.
[Methods and Results]
RT-PCR showed TEM was first expressed in the murine heart at embryonic day 14.5, and was constantly expressed in the adult. It was specifically expressed in CTC, but absent in the atrium, ventricle or cardiac valves. Western-blot analysis showed the same results.
Immunohistochemistry of the murine heart showed localization of TEM to CTC. Hematoxylin and eosin staining, elastica van Gieson staining and immunohistochemistry revealed that the expression of TEM in normal human CTC was restricted to the elastin-rich mid-layer, and was not found in the endothelial or core layer. No vessel formation was found in normal CTC.
Immunostaining of the CTC interstitial cells (CTC-ICs) obtained from the explant cultures of rabbit CTC showed TEM in the cytoplasm of CTC-ICs. RT-PCR confirmed that cultured CTC-ICs expressed TEM, which was inhibited by treatment with specific small interfering RNA (siRNA).
Capillary-like structures of human coronary artery endothelial cells (HCAECs) were less prominent following treatment with conditioned medium from CTC-ICs compared with mock or NIH3T3 cells. Quantitative analysis showed that CTC-ICs-CM inhibited the tube formation by 58.3% and that TEM-specific siRNA led to the recovery of tube formation capacity by 38.7%.
In a modified Boyden chamber, HCAECs cocultured with CTC-ICs lost their migratory capacity compared with NIH3T3 cells. Quantitative analysis showed that CTC-ICs decreased the number of migrated cells by 73.2%, and that siRNA specific to TEM recovered the migratory capacity by 36.6%.
[Conclusion] TEM is expressed in CTC specifically and inhibits angiogenesis. TEM plays a key role in maintaining CTC function.