Derivation of functional smooth muscle cells from multipotent human hair follicle mesenchymal stem cells

Engineering fibrin-binding TGF-β1 for sustained signaling and contractile function of MSC based vascular constructs

We present a strategy to conjugate TGF-β1 into fibrin hydrogels to mimic the in vivo presentation of the growth factor in a 3D context. To this end, we engineered fusion proteins between TGF-β1 and a bi-functional peptide composed of a Factor XIII domain and a plasmin cleavage site. In another version the protease cleavage site was omitted to examine whether the growth factor that could not be released from the scaffold by cells had different effects on tissue constructs. The optimal insertion site which yielded correctly processed, functional protein was found between the latency associated peptide and mature TGF-β1 domains. In solution the fusion proteins exhibited similar biological activity as native TGF-β1 as evidenced by inhibition of cell proliferation and promoter activity assays. Immunoprecipitation experiments demonstrated that the fusion TGF-β1 protein bound to fibrinogen in a Factor XIII dependent manner and could be released from the peptide by the action of plasmin. In contrast to bolus delivery, immobilized TGF-β1 induced sustained signaling in fibrin-embedded cells for several days as evidenced by Smad2 phosphorylation. Prolonged pathway activation correlated with enhanced contractile function of vascular constructs prepared from hair follicle mesenchymal stem cells or bone marrow derived smooth muscle cells. Our results suggest that fibrin-immobilized TGF-β1 may be used to enhance the local microenvironment and improve the function of engineered tissues in vitro and potentially also after implantation in vivo where growth factor delivery faces overwhelming challenges.

Clonal multipotency and effect of long-term in vitro expansion on differentiation potential of human hair follicle derived mesenchymal stem cells

Hair follicle harbors a rich stem cell pool with mesenchymal lineage differentiation potential. Although previous studies with rodent cells demonstrated that hair follicle sheath and papilla cells possess multi-lineage differentiation potential, human hair follicle derived mesenchymal stem cells (hHF-MSCs) have not been characterized in detail in terms of their multipotency. In addition, it is not clear whether these cells are true stem cells that can differentiate along multiple lineages or whether they represent a collection of progenitor cells with restricted differentiation potential. Here we report that hHF-MSCs are highly proliferative cells that can be maintained in culture for ~45 population doublings before they start to show signs of cellular senescence. Under appropriate culture conditions, hHF-MSCs differentiated along the myogenic, osteogenic, adipogenic and chondrogenic lineages, as demonstrated by kinetic gene expression profiling and functional assays. Interestingly, the differentiation potential decreased with time in culture in a lineage-specific manner. Specifically, myogenesis and chondrogenesis showed a moderate decrease over time; osteogenesis was maximum at intermediate passages and adipogenesis was highly sensitive to long-term culture and was diminished at late passages. Finally, hHF-MSCs were clonally multipotent as the majority of hHF-MSCs clones (73%) demonstrated bi- or tri-lineage differentiation potential. These results suggest that hHF-MSCs may present as an alternative source of easily accessible, autologous stem cells for tissue engineering and regenerative medicine.

Hair follicle-derived smooth muscle cells and small intestinal submucosa for engineering mechanically robust and vasoreactive vascular media

Our laboratory recently reported a new source of smooth muscle cells (SMCs) derived from hair follicle (HF) mesenchymal stem cells. HF-SMCs demonstrated high proliferation and clonogenic potential as well as contractile function. In this study, we aimed at engineering the vascular media using HF-SMCs and a natural biomaterial, namely small intestinal submucosa (SIS). Engineering functional vascular constructs required application of mechanical force, resulting in actin reorganization and cellular alignment. In turn, cell alignment was necessary for development of receptor- and nonreceptor-mediated contractility as soon as 24 h after cell seeding. Within 2 weeks in culture, the cells migrated into SIS and secreted collagen and elastin, the two major extracellular matrix components of the vessel wall. At 2 weeks, vascular reactivity increased significantly up to three- to fivefold and mechanical properties were similar to those of native ovine arteries. Taken together, our data demonstrate that the combination of HF-SMCs with SIS resulted in mechanically strong, biologically functional vascular media with potential for arterial implantation.

Lentiviral microarrays for real-time monitoring of gene expression dynamics

We developed scalable live-cell microarrays to measure gene expression dynamics in real time and in a high-throughput manner. To this end, we generated dual-promoter lentiviral vectors harboring a transcriptional regulatory element encoding for green fluorescence protein to monitor cell activation in response to exogenous stimuli and a constitutive promoter driving red fluorescence protein for internal signal normalization. Lentivirus preparations were immobilized in a microarray format and after transduction on the array surface target cells were treated with cytokines and interrogated in real time using automated fluorescence microscopy, providing rich dynamic information over a period of several days. Data normalization by red fluorescence intensity eliminated errors due to spot-to-spot variability in transduction efficiency or changes in cell proliferation upon cytokine treatment. These results suggest that the lentivirus microarray can monitor gene expression in real-time and high-throughput manner thereby providing a useful tool for quantitative measurements of gene expression dynamics.