Investigating the Presence of Connective Tissue Progenitor Cells within the Retrocalcaneal Bursa

Abstract

Category: Ankle; Basic Sciences/Biologics; Other Introduction/Purpose: The purpose of this study was to evaluate the presence of connective tissue progenitor cells within the retrocalcaneal bursa. The study evaluation included an assessment of the viability of connective tissue progenitor cells, their proliferative potential, and their ability to differentiate into osteoblasts, adipocytes, and chondrocytes. Methods: The retrocalcaneal bursa samples were excised from 10 patients (age: 51.5 +- 10.8 years) undergoing Achilles surgery in which the retrocalcaneal bursa is routinely excised. Bursal tissue was processed by digesting cells with collagenase and obtaining nucleated cell counts and cellular concentrations. The cells were cultured, and differentiated into osteoblasts, adipocytes, and chondrocytes. Analysis of bursal derived cells consisted of fluorescent activated cell sorting (FACS) analysis, cellular proliferation and viability assay, and analysis of differentiation into osteoblasts, adipocytes, and chondrocytes. The CTP differentiation was confirmed using histology staining to qualitatively express differentiation, and qPCR to quantify gene expression. Results: Cell migration at 3 weeks on average was found to be 3.84x107 nucleated cells/gram of tissue and nucleated cellular concentration on average was found to be 6.28x105 cells/mL of suspension. The proliferation data showed high levels of proliferation on average of 1.72 +-0.58. The FACS analysis showed a high percentage of positive surface markers for CTPs measuring greater than 96% (CD105, CD90, CD73) and measuring < 1.1% for negative surface markers (CD45 and CD31). Differentiation into osteoblasts, adipocytes, and chondrocytes were stained appropriately displaying differentiation. Conclusion: The retrocalcaneal bursa is a novel source of connective tissue progenitor cells. This is the first study to our knowledge analyzing the retrocalcaneal bursa as a novel source for CTPs, making it a potential augment to expedite the healing process of the Achilles tendon. Overall, it is unclear what the role of the CTPs within the bursa is, however, they may help to reduce the extensive healing time for the Achilles tendon thereby returning patients with Achilles tendon pathology back to functional status more promptly.