Researchers at Houston’s Rice University and Texas Children’s Hospital have found that stem cells drawn from amniotic fluid show promise for tissue engineering, but it is important to determine what they can and cannot do. A new Rice/TCH study led by bioengineer Jeff Jacot has observed that amniotic stem cells can communicate with mature heart cells and form electrical couplings with each other similar to those found in heart tissue, but these electrical connections alone don’t result in the amniotic cells to become cardiac cells.
Jacot, who has a joint appointment as assistant professor of bioengineering at Rice, director of the Pediatric Cardiac Bioengineering Laboratory, the Congenital Heart Surgery Service at Texas Children’s, and is an adjunct assistant professor at Baylor College of Medicine, is at the forefront of ongoing research into techniques for repairing hearts of infants born with congenital defects. Prof. Jacot’s lab is involved with designing scaffold patches that can be implanted into newborn infant hearts, and if the patches could be successfully seeded with stem cells from the mother of the child’s own amniotic fluid, the hoped-for outcome would be repair and growth of healthy tissue that would not be rejected by the child’s immune system.
(Credit: Jeff Fitlow/Rice University)
However, to achieve that objective, researchers must figure out how signals that are passed from cell to cell might guide stem cells to differentiate into heart tissue. In a OnlineOpen paper published this week in the Journal of Cellular and Molecular Medicine, Prof. Jacot and his team describe how amniotic fluid stem cells that are cultured with but physically separated from rat heart cells (to keep them from fusing) don’t differentiate into heart cells. However, the stem and heart cells do communicate through channels in the thin membrane that allow ions and small molecules to pass.
The paper, entitled “Formation of functional gap junctions in amniotic fluid-derived stem cells induced by transmembrane co-culture with neonatal rat cardiomyocytes” (DOI: 10.1111/jcmm.12056) is co-authored by Jeffrey G. Jacot with graduate student Jennifer Petsche Connell and junior Emily Augustini of Rice University’s Department of Bioengineering; and maternal-fetal specialists Kenneth Moise Jr. and Anthony Johnson of Rice’s Department of Bioengineering and the Baylor College of Medicine Department of Obstetrics and Gynecology.
In the paper’s Abstract, the research team explains how their study investigated whether or not culture of amniotic fluid-derived stem cells (AFSC) on the opposite side of a Transwell membrane from neonatal rat ventricular myocytes (NRVM), allowing for contact and communication without confounding factors such as cell fusion, could direct cardiac differentiation and enhance gap junction formation. Results were compared to shared media (Transwell), conditioned media and monoculture media controls, and that their results suggest that direct transmembrane co-culture does not induce cardiomyocyte differentiation of AFSC, although though calsequestrin expression is increased. However, direct transmembrane co-culture does enhance connexin-43-mediated gap junction communication between AFSC.
In the Introduction to their full report they expand that cardiac potential of AFSC has been reported upon direct co-culture with neonatal rat ventricular myocytes (NRVM), resulting in expression of cardiac markers such as sarcomere proteins, although the effect decreases when cells are separated in a Transwell system or grown in NRVM-conditioned media, and that research in other progenitor cell types has found that apparent cardiac differentiation in co-culture conditions is the result of cell fusion as opposed to cell differentiation, and that this possibility has not been eliminated in AFSC studies.
The transfer of dye from one amniotic fluid stem cell to another demonstrated functional gap junction communication in amniotic cells exposed to heart cells. (Credit: Jacot Lab/Rice University)
Amniotic fluid-derived stem cells cultured in a direct transmembrane co-culture with NRVM had significantly higher dye diffusion distance than all other groups for direct transmembrane, shared media, conditioned media and maintenance media control respectively. In addition, the dye diffused through an increased number of cells in the direct transmembrane co-culture compared with the other experimental group’s cells for direct transmembrane, shared media, conditioned media and maintenance media control respectively. These increased measures of dye diffusion indicate an increased level of intercellular gap junction formation and communication in the direct transmembrane co-cultures.
Prof. Jacot says In a Rice University release that: “People have suggested that if amniotic fluid cells are in an environment where they’re near heart cells, something happens that causes differentiation of the amniotic fluid cells into cardiac tissue, Jacot said. We found that isn’t the case.” He adds that researchers have seen other types of stem cells take on the characteristics of cardiac cells, and determined that it was because the cells had fused together resulting in a single cell with proteins from both the stem cells and the heart cells.
He explains that the researchers wanted to see if amniotic cells could take on the characteristics of heart cells if they weren’t allowed to fuse, noting: “We showed there’s no evidence of actual cardiac differentiation, although there were some changes in protein expression (among the stem cells), he said. But the stem cells become electrically coupled to each other, like cardiac cells do with each other. That was the main finding: We do get very good electrical coupling, which we call functional gap junction connections. Electrical ions or really small molecules that are in one cell can diffuse directly into a cell next to it. Its like they put holes in their membranes when they’re up against each other. Knowing what signals are passed is of great value as researchers figure out how to prompt stem cells to differentiate into the desired tissue.”
Prof. Jacot says other labs are studying how injecting amniotic fluid stem cells directly into hearts can help recovery after a heart attack, and notes that this is being done with bone marrow-derived stem cells in the U.S., including at two of the biggest groups in Houston, the Methodist Hospital and the Texas Heart Institute. “They seem to find what we call paracrine signaling effects, where the stem cells draw in more blood vessel-forming cells,” he says. “There’s some discussion as to whether they stabilize the cells, but don’t seem to actually make new heart tissue. Prof. Jacot suggests that there are probably many ways to get amniotic fluid stem cells to differentiate into viable tissue for medical uses, and the new results are just a small step toward the goal of finding the best way, and that while what he and his colleagues have observed is a little removed from any kind of translational therapeutic aspect, “we feel what we’ve observed will help us understand amniotic fluid stem cells in this environment.”
This research was supported by Texas Children’s Hospital, a grant from the Virginia and L.E. Simmons Family Foundation (JGJ), a National Science Foundation Graduate Fellowship (grant no. 0940902 to JPC), a National Science Foundation CAREER Award (JGJ), and a grant from the American Heart Association (JGJ). JPC and EA, performed the research and analysed the data, JPC and JGJ designed the research study and wrote the paper, KJM and AJ provided the primary amniotic fluid and clinical expertise.
The full Journal of Cellular and Molecular Medicine paper “Formation of functional gap junctions in amniotic fluid-derived stem cells induced by transmembrane co-culture with neonatal rat cardiomyocytes,” can be viewed or downloaded (PDF) at: