Associate Professor Cooper Medical School of Rowan University Camden, New Jersey, United States
Abstract Body : Introduction: Infarcted myocardium follows a well-established sequence of reparative events resolving with scar formation. Several populations of resident and circulating cells as well as a range of signaling and regulatory molecules are implicated in this process, some of which are still not fully elucidated. Recently, much research has been done to develop therapies capable of modifying scar formation in hopes of minimizing adverse cardiac remodeling. In this regard, the recognition of myocardial CD34-positive (+) stromal cells/telocytes (SC/TCs) as a novel resident cell type, there is a need to further investigate their role in myocardial repair. This study aims to determine a spatial distribution of the resident CD34+ SC/TCs during the proliferative (granulation tissue) phase of post-MI scar development. Methods: A large transmural MI was induced in 12-month-old male Sprague-Dawley rats (n = 15) under ketamine and xylazine anesthesia by permanent ligation of the left anterior descending coronary artery. Sham-operated rats (n = 9) served as an age-matched control. To recognize the proliferating cells, the post-MI rats were infused with BrdU (12.5 mg/kg/day) via intraperitoneal osmotic minipumps for 72 hours beginning on day 0, 4, or 11 after surgery. Subsequently, the rats were euthanized on day 3, 7 and 14 after MI, their hearts were excised and processed to paraffin for histology and immunostaining with an array of antibodies and GS-IB4 lectin. Resident CD34+ SC/TCs were distinguished based on their positive reaction with an anti-CD34 antibody and cell morphology. Results: We found that on the third day after MI the CD34+ SC/TCs were present in interstitial spaces between cardiac myocytes (CMs) on both edges of the infarcted region, within the adventitia of residual coronary vessels, and surrounding surviving CMs in subepicardial and subendocardial regions. In contrast, CD34+ SC/TCs were not detectable within the necrotic tissue. On the seventh day after MI, many of the CD34+ SC/TCs within all above-mentioned regions appeared enlarged and were labeled with BrdU, indicating their increased proliferative activity. Furthermore, numerous clusters of CD34+ SC/TCs became visible inside the developing granulation tissue, particularly, in the space between acellular laminin-stained basement membrane of the resorbed CMs, suggesting that these cells had actively migrated from the periphery towards regions which were cleared of necrotic debris. On the fourteenth day after MI, the population of CD34+ SC/TCs appeared to be distributed through all areas of the scar, except the regions with residual necrotic tissue and the aggregates of alpha smooth muscle actin-positive myofibroblasts in the granulation tissue and in the fibroelastic thickening of subepicardial and subendocardial regions. Most interesting, the aggregates of flattened CD34+ SC/TCs cells were seen at the edges of the scar covering the surface of survived longitudinally oriented CMs which were imbedded in the deposits of the fibrillar collagen. Conclusion and Significance: Our findings, for the first time, demonstrate that the population of resident CD34+ SC/TCs has followed a unique and dynamic pattern of distribution within the ischemic region of the heart during the healing process, suggesting their involvement in post-MI scar formation. Accordingly, we presume that these cells should be considered as a potential target for scar modifying therapies. Supported by Camden Health Research Initiative
