Changes in coexpression of pericytes and endogenous cardiac progenitor cells from heart development to disease state

Focussing on the potential role of cardiovascular cell therapy, we investigated the spatial relationship between pericytes (cells with cardiac repair capabilities that ensheath blood vessels) and endogenous cardiac progenitors within stem cells' niches. We explored possible changes in their co-localisation in developing human hearts from foetal to adult stage and following ischaemia.

Foetal and adult human heart specimens, obtained under ethical consent (University of Edinburgh ethics committee), were used for immunohistochemistry, cell isolation, culture and differentiation. Multi-lineage differentiation in culture, by single and double staining was completed for CD 146+ foetal pericytes and c-kit+ cells. Endothelial markers (CD31) gene expression was quantified by qPCR.

c-kit+ cells frequency and coexpression with pericytes decrease with heart development, already evident by gestation week 19th. Pericytes and c-kit+ cells express the early cardiac transcription factors Nkx2.5 and Islet 1. Only c-kit+ cells express the stemness marker SSEA3 (24%), known to progressively decrease with cell differentiation. Endothelial differentiation assessment shows that cardiac pericytes and c-kit+ cells do not form CD31+ networks. This finding correlates with absence of staining for CD31 marker in both cultured cells' types. The cardiac marker α-actin was present in both cell populations. In healthy adult heart, pericyte markers CD146 localise within the vasculature. Following ischaemia this pericyte marker becomes also evident outside the vasculature.In healthy adult atrium, c-kit expression is low and coexpression with other markers inconspicuous. Ischaemia leads to increased c-kit expression, particularly in blood vessels <50um diameter. Furthermore, following ischaemia c-kit, endothelium and pericyte markers co-localise within the same atrial cells. Blood vessels >50microm diameter showed mostly only staining for endothelial (vWF) and pericyte (CD146) markers, with no co-expression of c-kit marker identified. Staining patterns within the ischaemic regions of the right and left atrial appendages revealed low levels of colocalisation between vWF and CD146. Acute ischaemia of the left ventricle affected the detection of cardiac stem cells markers in the area of injury, due to myocardium disruption.

Foetal heart pericytes and c-kit+ cells express early cardiac transcription factors and show trans-differentiation potential, which decreases in healthy adult hearts. The preservation and activity of cardiac stem cells niches within the atrium vasculature appears re-activated in post-ischaemic hearts. Better understanding of cardiac c-kit+ and pericyte cells during-human embryonic development and during ischaemia may identify alternative novel therapeutic strategy against coronary artery disease.