MSC Transplantation Reduces Bone Loss via Epigenetic Regulation of Notch Signaling in Lupus

Mesenchymal stem cells from bone marrow, fat, and other tissues have been used in many clinical trials, experiments, and treatment regimens. While these cells are not magic bullets, they do have the ability to suppress unwanted inflammation, differentiate into bone, cartilage, tendon, smooth muscle, and fat, and can release a variety of healing molecules that help organs from hearts to kidneys heal themselves.

Mesenchymal stem cell transplantation (MSCT) is the main means by which mesenchymal stem cells are delivered to patients for therapeutic purposes. However, the precise mechanisms that underlie the success of these cells are not fully understood. In a paper by from the University Of Pennsylvania School Of Dental Medicine published in the journal Cell Metabolism, MSCT were able to re-establish the bone marrow function in MRL/lpr mice. The MRL/lpr mouse is a genetic model of a generalized autoimmune disease sharing many features and organ pathology with systemic lupus erythematosus (SLE). Such mice show bone loss and poor bone deposition, a condition known as “osteopenia.” Because mesenchymal stem cells are usually the cells in bone marrow that differentiate into osteoblasts (which make bone) a condition like osteopenia results from defective mesenchymal stem cell function.

In this paper, Shi and his coworkers and collaborators showed that the lack of the Fas protein in the mesenchymal stem cells from MRL/lpr mice prevents them from releasing a regulatory molecule called “miR-29b.” This regulatory molecule, mir-29b, is a small RNA molecule known as a microRNA. MicroRNAs regulate the expression of other genes, and the failure to release miR-29b increases the intracellular levels of miR-29b. This build-up in the levels of miR-29b causes the downregulation of an enzyme called “DNA methyltransferase 1” or Dnmt1. This is not surprising, since this is precisely what microRNAs do – they regulate genes. Dnmt1 attaches methyl groups (CH3 molecules) to the promoter or control regions of genes.

Decrease in the levels of Dnmt1 causes hypomethylation of the Notch1 promoter. When promoters are heavily methylated, genes are poorly expressed. When very methyl groups are attached to the promoters, then the gene has a greater chance of being highly expressed. Robust expression of the Notch1 genes activates Notch signaling. Increased Notch signaling leads to impaired bone production, since differentiation into bone-making cells requires mesenchymal stem cells to down-regulate Notch signaling.

When normal mesenchymal stem cells are transplanted into the bone marrow of MRL/lpr mice, they release small vesicles called exosomes that transfer the Fas protein to recipient MRL/lpr bone marrow mesenchymal stem cells. The presence of the Fas protein reduces intracellular levels of miR-29b, and this increases Dnmt1-mediated methylation of the Notch1 promoter. This decreases the expression of Notch1 and improves MRL/lpr BMMSC function.


These findings elucidate the means by which MSCT rescues MRL/lpr BMMSC function. Since MRL/lpr mice are a model system for lupus, it suggests that donor mesenchymal stem cell transplantation into lupus patients provides Fas protein to the defective, native mesenchymal stem cells, thereby regulating the miR-29b/Dnmt1/Notch epigenetic cascade that increases differentiation of mesenchymal stem cells into osteoblasts and bone deposition rates.

Delivery of a Missing Protein Heals Damaged Hearts in Animals

Stanford University School of Medicine scientists have enabled the regeneration of damaged heart tissue in animals by delivering a protein to it by means of a bioengineered collagen patch.

“This finding opens the door to a completely revolutionary treatment,” said Pilar Ruiz-Lozano, PhD, associate professor of pediatrics at Stanford. “There is currently no effective treatment to reverse the scarring in the heart after heart attacks.”

Ruiz-Lozano and her colleagues published their data online in the journal Nature.

During a heart attack, cardiac muscle cells or cardiomyocytes die from a lack of blood flow. Replacing dead cells is vital for the organ to fully recover, but, unfortunately, the adult mammalian heart does not possess a great deal of regenerative ability. Therefore, scar tissue forms instead of heart muscle, and since scar tissue does not contract, it compromises the ability of the heart to function properly.

Heart attacks kill millions of people every year, and the number of heart attacks is predicted to rise precipitously in the next few decades. The number of heart attacks might even triple by 2030. Approximately, 735,000 Americans suffer a heart attack each year, and even though many victims survive the initial injury, the resulting loss of cardiomyocytes can lead to heart failure and even death. “Consequently, most survivors face a long and progressive course of heart failure, with poor quality of life and very high medical costs,” Ruiz-Lozano said. Transplanting healthy muscle cells and stem cells into a damaged heart have been tried, but these trials have mixed results, typically, and have yet to produce consistent success in promoting healing of the heart.

Previous heart regeneration studies in zebrafish have shown that the outer layers of the heart, known as the epicardium, is one of the driving tissues for healing a damaged heart. Ruiz-Lozano said, “We wanted to know what in the epicardium stimulates the myocardium, the muscle of the heart, to regenerate.” Since adult mammalian hearts do not regenerate effectively, Ruiz-Lozano and her co-workers wanted to know whether epicardial substances might stimulate regeneration in mammalian hearts and restore function after a heart attack.

She and her colleagues focused on Fstl1, which is a protein secreted by the epicardium, and acts as a growth factor for cardiomyocytes. Not only did this protein kick-start the proliferation of cardiomyocytes in petri dishes, but Ruiz-Lozano and others found that it was missing from damaged epicardial tissue following heart attacks in humans.

Next, Ruiz-Lozano and her colleagues reintroduced Fstl1 back into the damaged epicardial tissue of mice and pigs that had suffered a heart attack. They embedded a bioengineered patch on to the damaged heart tissue that was imbued with Fstl1. Then they sutured the patch, loaded with Fstl1, to the damaged tissue. These patches were made of natural material known as collagen that had been structurally modified to mimic certain mechanical properties of the epicardium.

Because the patches are made of collagen, they contain no cells, which mean that recipients do not need immunosuppressive drugs to avoid rejection. With time, the collagen material is absorbed into the heart. The elasticity of the material resembles that of the fetal heart, and seems to be one of the keys to providing a hospitable environment for muscle regrowth. New blood vessels regenerated there as well.

Within two to four weeks of receiving the patch, heart muscle cells began to proliferate and the animals progressively recovered heart function. “Many were so sick prior to getting the patch that they would have been candidates for heart transplantation,” Ruiz-Lozano said. The hope is that a similar procedure could eventually be used in human heart-attack patients who suffer severe heart damage.

The work integrated the efforts of multiple labs around the world, including labs at the Sanford-Burnham-Prebys Medical Discovery Institute in San Diego, UC-San Diego, Boston University School of Medicine, Imperial College London and Shanghai Institutes for Biological Sciences.

Stanford has a patent on the patch, and Ruiz-Lozano is chief scientific officer at Epikabio Inc., which has an exclusive option to license this technology.