Microgravity has a profound effect on cardiovascular function, however, little is known about the impact of microgravity on progenitors that reside within the heart. We investigated the effect of simulated microgravity exposure on progenitors isolated from the neonatal and adult human heart by quantifying changes in functional parameters, gene expression and protein levels after 6-7 days of 2D clinorotation. Utilization of neonatal and adult cardiovascular progenitors in ground-based studies has provided novel insight into how microgravity may affect cells differently depending on age.Simulated microgravity exposure did not impact AKT or ERK phosphorylation levels and did not influence cell migration, but elevated transcripts for paracrine factors were identified in neonatal and adult cardiovascular progenitors. Age-dependent responses surfaced when comparing the impact of microgravity on differentiation. Endothelial cell tube formation was unchanged or increased in progenitors from adults whereas neonatal cardiovascular progenitors showed a decline in tube formation (p<0.05). Von Willebrand Factor, an endothelial differentiation marker, and MLC2v and Troponin T, markers for cardiomyogenic differentiation, were elevated in expression in adult progenitors after simulated microgravity. DNA repair genes and telomerase reverse transcriptase which are highly expressed in early stem cells were increased in expression in neonatal but not adult cardiac progenitors after growth under simulated microgravity conditions. Neonatal cardiac progenitors demonstrated higher levels of MESP1, OCT4, and brachyury, markers for early stem cells. MicroRNA profiling was used to further investigate the impact of simulated microgravity on cardiovascular progenitors. Fifteen microRNAs were significantly altered in expression, including microRNAs-99a and 100 (which play a critical role in cell dedifferentiation). These microRNAs were unchanged in adult cardiac progenitors.The effect of exposure to simulated microgravity in cardiovascular progenitors is age-dependent. Adult cardiac progenitors showed elevated expression of markers for endothelial and cardiomyogenic differentiation whereas neonatal progenitors acquired characteristics of dedifferentiating cells.

Although clinical benefit can be achieved after cardiac transplantation of adult c-kit+ or cardiosphere-derived cells for myocardial repair, these stem cells lack the regenerative capacity unique to neonatal cardiovascular stem cells. Unraveling the molecular basis for this age-related discrepancy in function could potentially transform cardiovascular stem cell transplantation. In this report, clonal populations of human neonatal and adult cardiovascular progenitor cells were isolated and characterized, revealing the existence of a novel subpopulation of endogenous cardiovascular stem cells that persist throughout life and co-express both c-kit and isl1. Epigenetic profiling identified 41 microRNAs whose expression was significantly altered with age in phenotypically-matched clones. These differences were correlated with reduced proliferation and a limited capacity to invade in response to growth factor stimulation, despite high levels of growth factor receptor on progenitors isolated from adults. Further understanding of these differences may provide novel therapeutic targets to enhance cardiovascular regenerative capacity.

The sacroiliac joint is a major weight-bearing joint interposed between the hip and the spine. Its vulnerability to injury and disease-related processes can lead to painful, irreversible changes of the sacroiliac joint, requiring surgical arthrodesis. Many surgical methods have been described for ablation of the sacroiliac joint, yet controversies surround reliable healing, imaging and confirmation of effective joint ablation. This article provides a historical review of sacroiliac joint arthrodesis techniques presented in the literature. The data are presented in three sections: overview of diagnostic methods, surgical and perioperative methods, and outcomes. A critique of each method is presented chronologically, and reasons for lack of progress or failure explored. A new method of surgical arthrodesis by calibrated distraction and grafting interposition of the joint/recess is presented.

Background: Laboratory large animal models are important for establishing the efficacy of stem cell therapies that may be translated into clinical use. The similarity of ovine and human cardiovascular systems provides an opportunity to use the sheep as a large animal model in which to optimize cell-based treatments for the heart. Recent clinical trials in humans using endogenous cardiovascular progenitor cells report significant improvement in cardiac function following stem cell-based therapy. To date, however, endogenous cardiovascular progenitor cells have not been isolated from the sheep heart.Methods: Cardiovascular cells expressing SSEA-4, CD105 and c-kit were isolated by flow cytometry and cloned from the right atrium of neonatal sheep. The expression of GATA-4, c-kit, and Isl1 was identified by PCR in the cloned cells. Immunohistochemical staining was used to compare the number of SSEA-4 positive cells in the right auricle, right atrium, left ventricle and the apex of the heart of fetal, neonatal and adult sheep. The number of SSEA4+cells was also compared in fetal, pregnant and non-pregnant adult sheep. Results:Four distinct cardiac progenitor cell sub-populations were identified in sheep, including CD105+SSEA-4+c-kit+Isl1+GATA-4+cells, CD105+SSEA-4+c-kit+Isl1+GATA-4-cells, CD105+SSEA-4-c-kit-Isl1+GATA-4-cells, and CD105+SSEA-4-c-kit+Isl1+GATA-4-cells. Immunohistochemical staining for SSEA-4 showed that labeled cells were most abundant in the right atrium of fetal hearts where niches of progenitor cells could be identified. Conclusion:We determined the phenotype and distribution of cardiac progenitor cells in the sheep heart. The availability of cloned endogenous cardiac progenitor cells from sheep will provide a valuable resource for optimizing the conditions for cardiac repair in the ovine model.

Aims: Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) or mesenchymal stem cells (MSCs) facilitate post-infarct recovery, but the potential benefit of combination therapy using MSCs and hESC-CMs has not been examined. Our objective was to define the gene expression changes in donor and host-derived cells that are induced in vivo after co-transplantation of cardiomyocytes with and without mesenchymal stem cells expressing the prosurvival gene heme oxygenase 1. Methods and results: Human MSCs were engineered to over-express heme oxygenase-1 (HO-1) following lentiviral vector-mediated transduction. Athymic nude rats were subjected to myocardial infarction and received hESC-CMs alone, hESC-CMs plus human MSCs, hESC-CMs plus MSCs overexpressing HO-1, or saline. Real time PCR identified gene expression changes. Cardiac function was assessed by angiography. Co-transplantation of unmodified MSCs plus hESC-CMs elevated CXCR4, HGF, and IGF expression over levels induced by injection of hESC-derived cardiomyocytes alone. In animals co-transplanted with MSC over-expressing HO-1, the expression of these genes was further elevated. Gene expression levels of VEGF, TGF-β, CCL2, SMAD7, STAT3 and cardiomyocyte transcription factors were highest in the HO-1 MSC plus hESC-CM group at 30 days. Human CD31+, CD34+, isl-1+, NXK2.5 and c-kit+ transcripts were elevated. Rodent genes encoding NKX2.5, troponin T and CD31 were elevated and cell cycle genes were induced. Ejection fraction improved by six to seven percent. Conclusions: Co-administration of HO-1 MSCs plus hESC-CMs increased expression of pro-survival and angiogenesis-promoting genes in human cells and transcripts of cardiac and endothelial cell markers in rodent cells, consistent with activation of tissue repair in both transplanted hESC-CMs and the host heart.