160
Burridge and colleagues found that L-ascorbic acid 2-phosphate and recombinant
human albumin, along with transient exposure to CHIR99021 (a glycogen synthase
kinase 3 inhibitor) and IWR-1 (an inhibitor of Wnt/β-catenin signaling), are sufficient to induce cardiac differentiation in 11 hiPSC lines [12].
Dozens of factors have been identified as promoting angiogenesis, enacting their
effects via a variety of mechanisms. Among the most relevant and researched, in the
context of vascularized cardiac tissues, are vascular endothelial growth factor (VEGF),
platelet-derived growth factor subunit B (PDGF-B), and angiopoietin-1 (Ang-1). In
tri-culture experiments combining hESC-derived cardiomyocytes with endothelial
cells and fibroblasts, Caspi et al. showed that the tri-cultures developed much more
significant vasculature and also showed increased expression of VEGF, PDGF-B, and
Ang-1 [13]. The importance of these factors was further confirmed when Hao and
colleagues reported increased vascular development, in the infarcted myocardium of
mice, in response to hydrogel-delivered VEGF-A and PDGF-BB [41]. In addition to
traditionally recognized proangiogenic factors, some hormones and cytokines with
unrelated primary functions have been shown to improve vasculature in engineered
cardiac tissues; specifically, insulin-like growth factor 1 (IGF-1) and stromal cellderived factor 1 (SDF-1) in combination with VEGF increased the vascular development in an engineered cardiac patch [24]. This effect was at least partially mediated
by SDF-1’s ability to attract CD34-positive hematopoietic progenitor cells.
The functional mechanisms of cytokines and hormones are often complex and
influenced by the method of delivery. Alberti and colleagues concluded that these
effects can drastically alter stem cell fate, by showing that immobilizing leukemia
inhibitory factor in a gelatin matrix significantly improved its ability to maintain
pluripotency in hESCs [1]. Similarly striking effects were observed in studies of
biochemical control of vascularization. Early experiments revealed that heparinmediated binding of VEGF to a collagen matrix promoted endothelial cell proliferation [110] and that immobilizing VEGF promoted penetration of endothelial cells
into collagen matrices [104]. Chiu and Radisic subsequently demonstrated that
endothelial cells formed significantly more vasculature on scaffolds with covalently
immobilized VEGF and Ang-1 than scaffolds treated with soluble factor [16]. In
that experiment the authors utilized 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (sulfo-NHS) to covalently bind VEGF and Ang-1 to the collagen substrate. Factor immobilization using
sulfonated alginate matrices has proven a very effective tool for promoting vasculature in complex tissue environments with many cell types, including cardiac tissue.
FGF presented in this manner produced twice the blood vessel density as soluble
FGF, when implanted subcutaneously in mice, and matrix-bound hepatocyte growth
factor (HGF) similarly increased vascular density by nearly twofold, over all controls in mouse hind limb ischemia model [33, 99]. Despite these advances, the utility of presenting pro-cardiac molecules in this manner has not been rigorously
evaluated. For the most part, experiments using multiple cell types have administered these molecules either before they are used in the patch or by including them
as soluble factors in the media.
J. Morrissette-McAlmon et al.
Burridge and colleagues found that L-ascorbic acid 2-phosphate and recombinant
human albumin, along with transient exposure to CHIR99021 (a glycogen synthase
kinase 3 inhibitor) and IWR-1 (an inhibitor of Wnt/β-catenin signaling), are sufficient to induce cardiac differentiation in 11 hiPSC lines [12].
Dozens of factors have been identified as promoting angiogenesis, enacting their
effects via a variety of mechanisms. Among the most relevant and researched, in the
context of vascularized cardiac tissues, are vascular endothelial growth factor (VEGF),
platelet-derived growth factor subunit B (PDGF-B), and angiopoietin-1 (Ang-1). In
tri-culture experiments combining hESC-derived cardiomyocytes with endothelial
cells and fibroblasts, Caspi et al. showed that the tri-cultures developed much more
significant vasculature and also showed increased expression of VEGF, PDGF-B, and
Ang-1 [13]. The importance of these factors was further confirmed when Hao and
colleagues reported increased vascular development, in the infarcted myocardium of
mice, in response to hydrogel-delivered VEGF-A and PDGF-BB [41]. In addition to
traditionally recognized proangiogenic factors, some hormones and cytokines with
unrelated primary functions have been shown to improve vasculature in engineered
cardiac tissues; specifically, insulin-like growth factor 1 (IGF-1) and stromal cellderived factor 1 (SDF-1) in combination with VEGF increased the vascular development in an engineered cardiac patch [24]. This effect was at least partially mediated
by SDF-1’s ability to attract CD34-positive hematopoietic progenitor cells.
The functional mechanisms of cytokines and hormones are often complex and
influenced by the method of delivery. Alberti and colleagues concluded that these
effects can drastically alter stem cell fate, by showing that immobilizing leukemia
inhibitory factor in a gelatin matrix significantly improved its ability to maintain
pluripotency in hESCs [1]. Similarly striking effects were observed in studies of
biochemical control of vascularization. Early experiments revealed that heparinmediated binding of VEGF to a collagen matrix promoted endothelial cell proliferation [110] and that immobilizing VEGF promoted penetration of endothelial cells
into collagen matrices [104]. Chiu and Radisic subsequently demonstrated that
endothelial cells formed significantly more vasculature on scaffolds with covalently
immobilized VEGF and Ang-1 than scaffolds treated with soluble factor [16]. In
that experiment the authors utilized 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (sulfo-NHS) to covalently bind VEGF and Ang-1 to the collagen substrate. Factor immobilization using
sulfonated alginate matrices has proven a very effective tool for promoting vasculature in complex tissue environments with many cell types, including cardiac tissue.
FGF presented in this manner produced twice the blood vessel density as soluble
FGF, when implanted subcutaneously in mice, and matrix-bound hepatocyte growth
factor (HGF) similarly increased vascular density by nearly twofold, over all controls in mouse hind limb ischemia model [33, 99]. Despite these advances, the utility of presenting pro-cardiac molecules in this manner has not been rigorously
evaluated. For the most part, experiments using multiple cell types have administered these molecules either before they are used in the patch or by including them
as soluble factors in the media.
J. Morrissette-McAlmon et al.