Background-Previous studies have shown that pericytes can differentiate into osteoblasts and form bone. This study investigated whether pericytes can also differentiate into chondrocytes and adipocytes. Methods and Results-Reverse transcription-polymerase chain reaction demonstrated that pericytes express mRNA for the chondrocyte markers Sox9, aggrecan, and type II collagen. Furthermore, when cultured at high density in the presence of a defined chondrogenic medium, pericytes formed well-defined pellets comprising cells embedded in an extracellular matrix rich in sulfated proteoglycans and type II collagen. In contrast, when endothelial cells were cultured under the same conditions, the pellets disintegrated after 48 hours. In the presence of adipogenic medium, pericytes but not endothelial cells expressed mRNA for peroxisome proliferator-activated receptor-␥2 (an adipocyte-specific transcription factor) and incorporated lipid droplets that stained with oil red O. To confirm that pericytes can differentiate along the chondrocytic and adipocytic lineages in vivo, these cells were inoculated into diffusion chambers and implanted into athymic mice for 56 days. Accordingly, mineralized cartilage, fibrocartilage, and a nonmineralized cartilaginous matrix with lacunae containing chondrocytes were observed within these chambers. Small clusters of cells that morphologically resembled adipocytes were also identified. Conclusions-These data demonstrate that pericytes are multipotent cells that may contribute to growth, wound healing, repair, and/or the development and progression of various pathological states.

Abstract-The aberrant differentiation of pericytes along the adipogenic, chondrogenic, and osteogenic lineages may contribute to the development and progression of several vascular diseases, including atherosclerosis and calcific vasculopathies. However, the mechanisms controlling pericyte differentiation and, in particular, adipogenic and chondrogenic differentiation are poorly defined. Wnt/␤-catenin signaling regulates cell differentiation during embryonic and postnatal development, and there is increasing evidence that it is involved in vascular pathology. Therefore, this study tested the hypothesis that Wnt/␤-catenin signaling regulates the chondrogenic and adipogenic differentiation of pericytes. We demonstrate that pericytes express several Wnt receptors, including LDL receptor-related proteins 5 and 6, and Frizzled 1 to 4 and 7, 8, and 10, and that Wnt/␤-catenin signaling is stimulated by both Wnt3a and LiCl. Furthermore, induction of Wnt/␤-catenin signaling by LiCl enhances chondrogenesis in pericyte pellet cultures in the presence of transforming growth factor-␤3, as demonstrated by increased Sox-9 expression and glycosaminoglycan accumulation into the matrix. In contrast, transduction of pericytes with a recombinant adenovirus encoding dominant-negative T-cell factor-4 (RAd/dnTCF), which blocks Wnt/␤-catenin signaling, inhibited chondrogenesis, leading to reduced Sox-9 and type II collagen expression and less glycosaminoglycan accumulation. Together, these data demonstrate that transforming growth factor-␤3 induces the chondrogenic differentiation of pericytes by inducing Wnt/␤-catenin signaling and T-cell factor-induced gene transcription. Induction of Wnt/␤-catenin signaling also attenuates adipogenic differentiation of pericytes in both pellet and monolayer cultures, as demonstrated by decreased staining with oil red O and reduced peroxisome proliferator-activated receptor ␥2 expression. This effect was negated by transduction of pericytes with RAd/dnTCF. Together, these results demonstrate that Wnt/␤-catenin signaling inhibits adipogenic and enhances chondrogenic differentiation of pericytes. (Circ Res. 2007;101:581-589.)Key Words: pericytes Ⅲ differentiation Ⅲ Wnt signaling Ⅲ chondrogenesis Ⅲ vascular disease T here is compelling evidence that cells with multilineage potential (pericytes, calcifying vascular cells, smooth muscle cells, and adventitial myofibroblasts) are present within the walls of blood vessels and that the aberrant differentiation of these cells contributes to the development and progression of several vascular pathologies. 1-9 For example, the acquisition of an adipogenic phenotype by some populations of vascular smooth muscle cells is thought to contribute both to the development of atherosclerotic lesions and to plaque instability. 9 On the other hand, the differentiation of vascular progenitor cells into chondrocytes and osteoblasts is thought to result in the deposition of cartilage and bone in the blood vessel wall. [1][2][3][4][5][6][7][8] This latter process, which has b...