Lisa J. Harris

Differentiation of Adult Stem Cells into Smooth Muscle for Vascular Tissue Engineering

BACKGROUND Herein we evaluate the potential of adipose-derived stem cells (ASC) to differentiate into smooth muscle cells (SMC) and their potential for use in a tissue-engineered vascular graft. MATERIALS AND METHODS We isolated ASC (CD13+29+90+) from the peri-umbilical adipose tissue of patients undergoing vascular surgery, and cultured them in media containing angiotensin II (AngII), sphingosylphosphorylcholine (SPC), or transforming growth factor-beta 1 (TGFβ1) for up to 3 weeks. SMC differentiation was assessed by (1) expression of early (calponin, caldesmon) and late (myosin heavy chain, MHC) SMC markers by RT-PCR, qPCR and Western blot, and (2) contraction upon plating on collagen gel. Differentiated ASCs were seeded onto a vascular graft (decellularized saphenous vein) within a bioreactor, and cell attachment was determined using confocal microscopy. RESULTS Prior to differentiation, ASC expressed low levels of all three molecular markers. After culture in each differentiating medium, the extent of up-regulation of calponin, caldesmon, and MHC was variable across all cell lines. After seeding onto collagen gel, ASCs differentiated in SPC and TGFβ1 exhibit contractile properties, similar to smooth muscle cell controls. Differentiated stem cells adhered and proliferated on the vascular graft. CONCLUSION These data suggest that human adipose-derived stem cells (1) exhibit variable expression of SMC molecular markers after differentiation, (2) exhibit a contractile phenotype after differentiation with SPC and TGFβ1, and (3) proliferate on a vascular graft scaffold. Thus, ASCs are potentially useful in the construction of autologous arteries.

The Role of Hypoxia in Stem Cell Differentiation and Therapeutics

Stem cells differentiate into a variety of cell lines, making them attractive for tissue engineering and regenerative medicine. Specific microenvironmental cues regulate self-renewal and differentiation capabilities. Oxygen is an important component of the cellular microenvironment, serving as both metabolic substrate and signaling molecule. Oxygen has been shown to have a variety of effects on embryonic and adult stem cells. This review examines the role of hypoxia in regulating stem cell biology, specifically focusing on growth, maintenance of pluripotency, differentiation, and production of growth factors. Particular attention is paid to hypoxia and stem cells in relation to therapeutic angiogenesis. We conclude that further study is needed to optimize the use of hypoxia as a stimulus for various stem cell functions, including its potential role in therapeutic angiogenesis.

Availability of adipose-derived stem cells in patients undergoing vascular surgical procedures

BACKGROUND Most research evaluating adipose-derived stem cells (ASC) uses tissue obtained from young, healthy patients undergoing plastic surgical procedures. Given the propensity of other adult stem cell lines to diminish with increasing patient age and co-morbidities, we assess the availability of ASC in elderly patients undergoing vascular surgical procedures, and evaluate their acquisition of endothelial cell (EC) traits to define their potential use in vascular tissue engineering. METHODS AND METHODS Adipose tissue obtained by liposuction from patients undergoing vascular procedures (n = 50) was digested with collagenase and centrifuged to remove mature adipocytes. The resultant number of cells, defined as the stromal-vascular (SV) pellet, was quantified. Following a 7-d culture period and negative selection for CD31 and CD45, the resultant number of ASC was quantified. After culture in differentiating media (EMG-2), ASCs were tested for the acquisition of endothelial-specific traits (expression of CD31, realignment in shear, cord formation on Matrigel). RESULTS The SV pellet contained 2.87 ± 0.34 × 10(5) cells/g fat, and the resultant number of ASCs obtained was 1.41 ± 0.18 × 10(5) cells/g fat. Flow cytometry revealed a homogeneous ASC population (>98% positive for CD13, 29, 90). Advanced age or co-morbidity (obesity, diabetes, renal or peripheral vascular disease) did not significantly alter yield of ASC. After culture in differentiating media (EMG-2), ASCs acquired each of the endothelial-specific traits. CONCLUSION ASC isolation appears independent of age and co-morbidities, and ASCs harvested from patients with vascular disease retain their ability to differentiate into endothelial-like cells. Adipose tissue, therefore, is a practical source of autologous, adult stem cells for vascular tissue engineering.