Pericyte-like differentiation of human adipose-derived mesenchymal stem cells: An in vitro study

BACKGROUND: Adipose-derived mesenchymal stem cells (ASCs) are characterized by long-term self-renewal and a high proliferation rate. Under adequate conditions, they may differentiate into cells belonging to mesodermal, endodermal or ectodermal lineages. Pericytes support endothelial cells and play an important role in stabilizing the vessel wall at the microcirculation level. The loss of pericytes, as occurs in diabetic retinopathy, results in a breakdown of the blood-retina barrier (BRB) and infiltration of inflammatory cells. In this context, the use of pericyte-like differentiated ASCs may represent a valuable therapeutic strategy for restoring BRB damage. AIM: To test in vitro strategies to obtain pericyte-like differentiation of human ASCs (hASCs). METHODS: Different culture conditions were tested: hASCs cultured in a basal medium supplemented with transforming growth factor β1; and hASCs cultured in a specific pericyte medium (PM-hASCs). In a further sample, pericyte growth supplement was omitted from the PM. In addition, cultures of human retinal pericytes (hRPCs) were used for comparison. Pericyte-like differentiation of hASCs was tested by immunocytochemical staining and western blotting to evaluate the expression of α-smooth muscle actin (α-SMA) and neural/glial antigen 2 (NG2). Interactions between human retinal endothelial cells (hRECs) and different groups of hASCs were investigated in co-culture experiments. In these cases, the expression of typical junctional proteins such as vascular endothelial-Cadherin, zonula occludens-1 and Occludin were assessed in hRECs. In an in vitro model of the BRB, values of trans-endothelial electrical resistance were measured when hRECs were co-cultured with various groups of pretreated hASCs. The values observed were compared with co-cultures of hRECs and hRPCs as well as with cultures of hRECs alone. Three-dimensional co-cultures of hRECs and hRPCs or pericyte-like hASCs in Matrigel were designed to assess their reciprocal localization. RESULTS: After 3-6 d of culture, α-SMA and NG2 immunocytochemistry showed that the closest pericyte-like phenotype was observed when hASCs were cultured in Pericyte Medium (PM-hASCs). In particular, α-SMA immunoreactivity, already visible at the basal level in pericytes and ASCs, was strongly increased only when transforming growth factor was added to the culture medium. NG2 expression, almost undetectable in most conditions, was substantially increased only in PM-hASCs. Immunocytochemical results were confirmed by western blot analysis. The presence of pericyte growth supplement seems to increase NG2 expression rather than α-SMA, in agreement with its role in maintaining pericytes in the proliferative state. In co-culture experiments, immunoreactivity of vascular endothelial-Cadherin, zonula occludens-1 and Occludin was considerably increased in hRECs when hRPCs or PM-hASCs were also present. Supporting results were found by trans-endothelial electrical resistance measurements, gathered at 3 and 6 d of co-culture. The highest resistance values were obtained when hRECs were co-cultured with hRPCs or PM-hASCs. The pericyte-like phenotype of PM-hASCs was also confirmed in three-dimensional co-cultures in Matrigel, where PM-hASCs and hRPCs similarly localized around the tubular formations made by hRECs. CONCLUSION: PM-hASCs seem able to strengthen the intercellular junctions between hRECs, likely reinforcing the BRB; thus, hASC-based therapeutic approaches may be developed to restore the integrity of retinal microcirculation.