Human and Equine Tenocytes Localize Tenomodulin to Chromatin during Mitosis

Norman W, Kim J, Qi J, Banes AN, Banes AJ. 14th Annual Conference of the North Carolina Tissue Engineering and Regenerative Medicine Society, Raleigh, NC, September 10, 2012.

Tenomodulin is an accepted tenocyte biomarker that is co-expressed with scleraxis and Mohawk during tendon development. Tnmd is also expressed differentially in human flexor carpi radialis and biceps tendons from surgery. It is thought to be involved in anti-angiogenesis but results in a KO mouse model found only a reduction in cell proliferation in tendons. We hypothesized that Tnmd might have a role in regulation of cell division and found Tnmd localization in mitotic tenocytes. Flexor carpi radialis (FCR) or biceps tendon (BT) cells were isolated from surgical specimens. Equine superficial digital flexor tendon cells were isolated form tendons at necropsy. Cells were tested for Tnmd expression and were found to express Tnmd differentially. Cells were plated on cover slips and paused in prometaphase with 50 nM nocodazole for 16h, then released in serum-containing medium to restart the cells. Cells were assessed in prometaphase, metaphase, anaphase and telophase for Tnmd localization and DNA by DAPI stain. Tenocytes in mitosis showed robust stain for Tnmd around the chromatin and distinct co-localization with chromosomes in metaphase, anaphase and telophase. Human tenocytes from control (FCR) and pathologic (BT) tenocytes likely express different ratios of Tnmd isoforms due to the different metabolic states and rates of cell proliferation. Tnmd clearly has a role in mitotic cells as it co-localizes with chromatin and with lamin B in a peri-chromosomal locale. Given that equine tenocytes do not make I2 but do show chromatin binding, Tnmd I1 and I3 are likely binding chromatin and regulate cell proliferation.