Mesenchymal condensation-dependent accumulation of collagen VI stabilizes organ-specific cell fates during embryonic tooth formation.

BACKGROUND: Mechanical compression of cells during mesenchymal condensation triggers cells to undergo odontogenic differentiation during tooth organ formation in the embryo. However, the mechanism by which cell compaction is stabilized over time to ensure correct organ-specific cell fate switching remains unknown. RESULTS: Here, we show that mesenchymal cell compaction induces accumulation of collagen VI in the extracellular matrix (ECM), which physically stabilizes compressed mesenchymal cell shapes and ensures efficient organ-specific cell fate switching during tooth organ development. Mechanical induction of collagen VI deposition is mediated by signaling through the actin-p38MAPK-SP1 pathway, and the ECM scaffold is stabilized by lysyl oxidase in the condensing mesenchyme. Moreover, perturbation of synthesis or cross-linking of collagen VI alters the size of the condensation in vivo. CONCLUSIONS: These findings suggest that the odontogenic differentiation process that is induced by cell compaction during mesenchymal condensation is stabilized and sustained through mechanically regulated production of collagen VI within the mesenchymal ECM.

Circulating CD34(+) progenitor cell frequency is associated with clinical and genetic factors.

Circulating blood CD34(+) cells consist of hematopoietic stem/progenitor cells, angiogenic cells, and endothelial cells. In addition to their clinical use in hematopoietic stem cell transplantation, CD34(+) cells may also promote therapeutic neovascularization. Therefore, understanding the factors that influence circulating CD34(+) cell frequency has wide implications for vascular biology in addition to stem cell transplantation. In the present study, we examined the clinical and genetic characteristics associated with circulating CD34(+) cell frequency in a large, community-based sample of 1786 Framingham Heart Study participants.Among subjects without cardiovascular disease (n = 1595), CD34(+) frequency was inversely related to older age, female sex, and smoking. CD34(+) frequency was positively related to weight, serum total cholesterol, and statin therapy. Clinical covariates accounted for 6.3% of CD34(+) variability. CD34(+) frequency was highly heritable (h(2) = 54%; P < .0001). Genome-wide association analysis of CD34(+) frequency identified suggestive associations at several loci, including OR4C12 (chromosome 11; P = 6.7 × 10(-7)) and ENO1 and RERE (chromosome 1; P = 8.8 × 10(-7)). CD34(+) cell frequency is reduced in older subjects and is influenced by environmental factors including smoking and statin use. CD34(+) frequency is highly heritable. The results of the present study have implications for therapies that use CD34(+) cell populations and support efforts to better understand the genetic mechanisms that underlie CD34(+) frequency.

Association of colony-forming units with coronary artery and abdominal aortic calcification.

BACKGROUND: Certain bone marrow-derived cell populations, called endothelial progenitor cells, have been reported to possess angiogenic activity. Experimental data suggest that depletion of these angiogenic cell populations may promote atherogenesis, but limited data are available on their relation to subclinical atherosclerotic cardiovascular disease in humans. METHODS AND RESULTS: We studied 889 participants of the Framingham Heart Study who were free of clinically apparent cardiovascular disease (mean age, 65 years; 55% women). Participants underwent endothelial progenitor cell phenotyping with an early-outgrowth colony-forming unit assay and cell surface markers. Participants also underwent noncontrast multidetector computed tomography to assess the presence of subclinical atherosclerosis, as reflected by the burden of coronary artery calcification and abdominal aortic calcification. Across decreasing tertiles of colony-forming units, there was a progressive increase in median coronary artery calcification and abdominal aortic calcification scores. In multivariable analyses adjusting for traditional cardiovascular risk factors, each 1-SD increase in colony-forming units was associated with a ≈16% decrease in coronary artery calcification (P=0.02) and 17% decrease in abdominal aortic calcification (P=0.03). In contrast, neither CD34(+)/KDR(+) nor CD34(+) variation was associated with significant differences in coronary or aortic calcification. CONCLUSIONS: In this large, community-based sample of men and women, lower colony-forming unit number was associated with a higher burden of subclinical atherosclerosis in the coronary arteries and aorta. Decreased angiogenic potential could contribute to the development of atherosclerosis in humans.

Mechanical induction of dentin-like differentiation by adult mouse bone marrow stromal cells using compressive scaffolds.

Tooth formation during embryogenesis is controlled through a complex interplay between mechanical and chemical cues. We have previously shown that physical cell compaction of dental mesenchyme cells during mesenchymal condensation is responsible for triggering odontogenic differentiation during embryogenesis, and that expression of Collagen VI stabilizes this induction. In addition, we have shown that synthetic polymer scaffolds that artificially induce cell compaction can induce embryonic mandible mesenchymal cells to initiate tooth differentiation both in vitro and in vivo. As embryonic cells would be difficult to use for regenerative medicine applications, here we explored whether compressive scaffolds coated with Collagen VI can be used to induce adult bone marrow stromal cells (BMSCs) to undergo an odontogenic lineage switch. These studies revealed that when mouse BMSCs are compressed using these scaffolds they increase expression of critical markers of tooth differentiation in vitro, including the key transcription factors Pax9 and Msx1. Implantation under the kidney capsule of contracting scaffolds bearing these cells in mice also resulted in local mineralization, calcification and production of dentin-like tissue. These findings show that these chemically-primed compressive scaffolds can be used to induce adult BMSCs to undergo a lineage switch and begin to form dentin-like tissue, thus raising the possibility of using adult BMSCs for future tooth regeneration applications.

Developmentally-inspired shrink-wrap polymers for mechanical induction of tissue differentiation.

A biologically inspired thermoresponsive polymer has been developed that mechanically induces tooth differentiation in vitro and in vivo by promoting mesenchymal cell compaction as seen in each pore of the scaffold. This normally occurs during the physiological mesenchymal condensation response that triggers tooth formation in the embryo.

A combinatorial cell-laden gel microarray for inducing osteogenic differentiation of human mesenchymal stem cells.

Development of three dimensional (3D) microenvironments that direct stem cell differentiation into functional cell types remains a major challenge in the field of regenerative medicine. Here, we describe a new platform to address this challenge by utilizing a robotic microarray spotter for testing stem cell fates inside various miniaturized cell-laden gels in a systematic manner. To demonstrate the feasibility of our platform, we evaluated the osteogenic differentiation of human mesenchymal stem cells (hMSCs) within combinatorial 3D niches. We were able to identify specific combinations, that enhanced the expression of osteogenic markers. Notably, these 'hit' combinations directed hMSCs to form mineralized tissue when conditions were translated to 3D macroscale hydrogels, indicating that the miniaturization of the experimental system did not alter stem cell fate. Overall, our findings confirmed that the 3D cell-laden gel microarray can be used for screening of different conditions in a rapid, cost-effective, and multiplexed manner for a broad range of tissue engineering applications.

Genetic and clinical correlates of early-outgrowth colony-forming units.

BACKGROUND: Several bone marrow-derived cell populations may have angiogenic activity, including cells termed endothelial progenitor cells. Decreased numbers of circulating angiogenic cell populations have been associated with increased cardiovascular risk. However, few data exist from large, unselected samples, and the genetic determinants of these traits are unclear. METHODS AND RESULTS: We examined the clinical and genetic correlates of early-outgrowth colony-forming units (CFUs) in 1799 participants of the Framingham Heart Study (mean age, 66 years; 54% women). Among individuals without cardiovascular disease (n = 1612), CFU number was inversely related to advanced age (P = 0.004), female sex (P = 0.04), and triglycerides (P = 0.008) and positively related to hormone replacement (P = 0.008) and statin therapy (P = 0.027) in stepwise multivariable analyses. Overall, CFU number was inversely related to the Framingham risk score (P = 0.01) but not with prevalent cardiovascular disease. In genome-wide association analyses in the entire sample, polymorphisms were associated with CFUs at the MOSC1 locus (P = 3.3 × 10(-7)) and at the SLC22A3-LPAL2-LPA locus (P = 4.9 × 10(-7)), a previously replicated susceptibility locus for myocardial infarction. Furthermore, alleles at the SLC22A3-LPAL2-LPA locus that were associated with decreased CFUs were also related to increased risk of myocardial infarction (P = 1.1 × 10(-4)). CONCLUSIONS: In a community-based sample, early-outgrowth CFUs are inversely associated with select cardiovascular risk factors. Furthermore, genetic variants at the SLC22A3-LPAL2-LPA locus are associated with both decreased CFUs and an increased risk of myocardial infarction. These findings are consistent with the hypothesis that decreased circulating angiogenic cell populations promote susceptibility to myocardial infarction.