Osteogenic Stimulation of Human Adipose-Derived Mesenchymal Stem Cells Using a Fungal Metabolite That Suppresses the Polycomb Group Protein EZH2

Abstract

Strategies for musculoskeletal tissue regeneration apply adult mesenchymal stem/stromal cells (MSCs) that can be sourced from bone marrow‐ and lipo‐aspirates. Adipose tissue‐derived MSCs are more easily harvested in the large quantities required for skeletal tissue‐engineering approaches, but are generally considered to be less osteogenic than bone marrow MSCs. Therefore, we tested a new molecular strategy to improve their osteogenic lineage‐differentiation potential using the fungal metabolite cytochalasin D (CytoD). We show that CytoD, which may function by redistributing the intracellular location of β‐actin (ACTB), is a potent osteogenic stimulant as reflected by significant increases in alkaline phosphatase activity, extracellular matrix mineralization, and osteoblast‐related gene expression (e.g., RUNX2, ALPL, SPARC, and TGFB3). RNA sequencing analyses of MSCs revealed that acute CytoD treatment (24 hours) stimulates a broad program of osteogenic biomarkers and epigenetic regulators. CytoD decreases mRNA and protein levels of the Polycomb chromatin regulator Enhancer of Zeste Homolog 2 (EZH2), which controls heterochromatin formation by mediating trimethylation of histone 3 lysine 27 (H3K27me3). Reduced EZH2 expression decreases cellular H3K27me3 marks indicating a global reduction in heterochromatin. We conclude that CytoD is an effective osteogenic stimulant that mechanistically functions by blocking both cytoplasmic actin polymerization and gene‐suppressive epigenetic mechanisms required for the acquisition of the osteogenic phenotype in adipose tissue‐derived MSCs. This finding supports the use of CytoD in advancing the osteogenic potential of MSCs in skeletal regenerative strategies. Stem Cells Translational Medicine 2018;7:197–209

Epigenetic‐Based Mechanisms of Osteoblast Suppression in Multiple Myeloma Bone Disease

“…Further, in agreement with its role in MM‐induced suppression of OB differentiation, EZH2 is a well‐accepted negative regulator of osteogenesis . EZH2 plays a critical role during neural‐crest cell‐derived cartilage differentiation, osteogenic differentiation, and skeletal patterning during development (for review, see Dudakovic and van Wijnen). EZH2 is subjected to a variety of posttranscriptional (eg, miR‐101‐mediated) and posttranslational (eg, CDK1‐phosphorylation at Thr487) regulatory mechanisms that ensure its degradation and downregulation during osteogenic commitment of BMSCs (Fig.…”

β-Catenin Preserves the Stem State of Murine Bone Marrow Stromal Cells Through Activation of EZH2

“…To understand the role of the actin cytoskeleton on BMSC osteogenic differentiation, we previously disrupted the actin cytoskeleton with cytochalasin D. Previous reports suggested that failure to form cytoplasmic structure was associated with adipogenesis . However, in our cytochalasin D study we found that osteogenesis was strongly promoted in marrow‐derived as well as in adipose‐derived BMSCs . Interestingly, this was associated with a decrease in the polycomb repressive complex 2 (PRC2) member, enhancer of zeste homolog 2 (EZH2) .…”

Epigenetics as a New Frontier in Orthopedic Regenerative Medicine and Oncology

“…Thus, EZH2 inhibitors may have bone anabolic activity and anti‐bone resorptive activity. Furthermore, enhanced osteogenic differentiation of human MSCs using EZH2 inhibitors or molecular pathways drugs that indirectly impinge on EZH2 may have practical implications for bone tissue engineering.…”