Publication

Abstract : Cardiac fibroblasts (CFs) form the stromal skeleton of the adult heart. Stromal cells in bone marrow and adipose tissue exhibit stem cell like properties. However CFs are thought to be terminally differentiated cells, without any multipotent properties. In this report, we demonstrate that CFs are not terminally differentiated cells and possess mesenchymal stem cell like properties. Using genetically labeled CFs from FSP1 Cre: R26R tdTomato and Col1α2Cre ERT: R26R tdTomato mice, we demonstrate that CFs undergo tri-lineage differentiation into fat, bone and cartilage. Approximately 70% of labeled CFs (Col1 Tomato; 79.65 ± 1.3%, FSP1 Tomato; 73.74 ± 2.9%, mean±SEM) differentiate into fat within 7 days and about 30 to 45% cells (Col1 Tomato; 32.2 ± 1.8%, FSP1 Tomato; 44.4 ±1.6 %) differentiate into bone forming osteoblasts within 21 days of differentiation. In contrast, vascular smooth muscle cells from same animals do not undergo differentiation under identical conditions (n=3, p<0.05). CFs form cardiospheres similar to other multipotent stem cells. They also form single cell colony forming units and express markers of pluripotency such as Oct4, Nanog, and cMyC. CFs depleted of, Sca1 or ckit expressing cardiac progenitors and pericytes (PGDFRβ and alkaline phosphatase positive), exhibit similar efficiency of differentiation (71.5± 1.6 % FSP1+ve Sca1+ve and 67.3 ± 1.9% Sca1 -ve cells form fat , 53.13 ± 1.9% FSP1+ve Sca1 +ve and 44.76 ± 0.46% Sca1 -ve cells form bone, n=3, p<0.05). Expression of pluripotency markers, single cell colony forming ability and cardiosphere formation are also similar demonstrating that the stem cell like properties of CFs are not due to the presence of any known cardiac progenitors or pericytes. Finally, in a murine model of cardiac calcification, we demonstrate that CFs differentiate into osteoblast like cells expressing the osteogenic transcription factor, Runx2 and contribute to cardiac calcification. Our data reveals multipotent stem cell like characteristics of adult CFs and suggests that aberrant differentiation of CFs into osteogenic cells could contribute to pathologic cardiac calcification in vivo. Future studies will determine the molecular and epigenetic changes that underlie reprogramming or differentiation of CFs.