Nebulized platelet-derived extracellular vesicles attenuate chronic cigarette smoke-induced murine emphysema

Chronic obstructive pulmonary disease (COPD) is a prevalent lung disease usually resulting from cigarette smoking (CS). Cigarette smoking induces oxidative stress, which causes inflammation and alveolar epithelial cell apoptosis and represents a compelling therapeutic target for COPD. Purified human platelet-derived exosome product (PEP) is endowed with antioxidant enzymes and immunomodulatory molecules that mediate tissue repair. In this study, a murine model of CS-induced emphysema was used to determine whether nebulized PEP can influence the development of CS-induced emphysema through the mitigation of oxidative stress and inflammation in the lung. Nebulization of PEP effectively delivered the PEP vesicles into the alveolar region, with evidence of their uptake by type I and type II alveolar epithelial cells and macrophages. Lung function testing and morphometric assessment showed a significant attenuation of CS-induced emphysema in mice treated with nebulized PEP thrice weekly for 4 weeks. Whole lung immuno-oncology RNA sequencing analysis revealed that PEP suppressed several CS-induced cell injuries and inflammatory pathways. Validation of inflammatory cytokines and apoptotic protein expression on the lung tissue revealed that mice treated with PEP had significantly lower levels of S100A8/A9 expressing macrophages, higher levels of CD4+/FOXP3+ Treg cells, and reduced NF-κB activation, inflammatory cytokine production, and apoptotic proteins expression. Further validation using in vitro cell culture showed that pretreatment of alveolar epithelial cells with PEP significantly attenuated CS extract-induced apoptotic cell death. These data show that nebulization of exosomes like PEP can effectively deliver exosome cargo into the lung, mitigate CS-induced emphysema in mice, and suppress oxidative lung injury, inflammation, and apoptotic alveolar epithelial cell death.

MicroRNA-101a enhances trabecular bone accrual in male mice

High-throughput microRNA sequencing was performed during differentiation of MC3T3-E1 osteoblasts to develop working hypotheses for specific microRNAs that control osteogenesis. The expression data show that miR-101a, which targets the mRNAs for the epigenetic enzyme Ezh2 and many other proteins, is highly upregulated during osteoblast differentiation and robustly expressed in mouse calvaria. Transient elevation of miR-101a suppresses Ezh2 levels, reduces tri-methylation of lysine 27 in histone 3 (H3K27me3; a heterochromatic mark catalyzed by Ezh2), and accelerates mineralization of MC3T3-E1 osteoblasts. We also examined skeletal phenotypes of an inducible miR-101a transgene under direct control of doxycycline administration. Experimental controls and mir-101a over-expressing mice were exposed to doxycycline in utero and postnatally (up to 8 weeks of age) to maximize penetrance of skeletal phenotypes. Male mice that over-express miR-101a have increased total body weight and longer femora. MicroCT analysis indicate that these mice have increased trabecular bone volume fraction, trabecular number and trabecular thickness with reduced trabecular spacing as compared to controls. Histomorphometric analysis demonstrates a significant reduction in osteoid volume to bone volume and osteoid surface to bone surface. Remarkably, while female mice also exhibit a significant increase in bone length, no significant changes were noted by microCT (trabecular bone parameters) and histomorphometry (osteoid parameters). Hence, miR-101a upregulation during osteoblast maturation and the concomitant reduction in Ezh2 mediated H3K27me3 levels may contribute to the enhanced trabecular bone parameters in male mice. However, the sex-specific effect of miR-101a indicates that more intricate epigenetic mechanisms mediate physiological control of bone formation and homeostasis.

Efficacy and Tolerability of Topical Platelet Exosomes for Skin Rejuvenation: Six-Week Results

BACKGROUND

Exosomes are regenerative mediators for skin rejuvenation. In the context of aesthetic medicine, platelets are an ideal source for exosomal isolation given their role in skin healing. Human platelet extract (HPE) is an allogeneic exosome product derived from US-sourced, leukocyte-reduced apheresed platelets with consistent purity and potency.

OBJECTIVES

To better characterize the saftey and tolerability of novel human platelet extract (plated) Intensive Repair Serum, (Rion Aesthetics, Rochester, MN) and its maximal effects on skin rejuvenation at 6 weeks.

METHODS

This prospective, single-arm, non-randomized, longitudinal study investigated the safety and efficacy of human platelet extract. Structured sub-analysis evaluated multifactorial improvement in skin health following standardized skin care regimen to determine the maximal effect. Evaluation at baseline and 6-weeks included subject questionnaires and photodocumentation using VISIA-CR Generation 5 3D PRIMOS (Canfield Scientific Inc, Fairfield, NJ).

RESULTS

VISIA-CR imaging yielded quantifiable and statistically significant improvements in overall skin health (named "Skin Health Score" [SHS]), calculated by multiplying the luminosity and color evenness scores and dividing the result by wrinkle area x brown spot area x redness area). A greater score correlated to greater overall skin health and there was a statistically significant mean delta improvement 224.2 ± 112.8 (mean ± SD, p ≤ 0.0001) in SHS at 6-weeks compared to baseline. This correlated to reduction in redness, wrinkles, and melanin production across all cosmetic units (p = 0.005, p=0.0023, p ≤ 0.0001, respectively) and significant improvements in luminosity and color evenness (p ≤ 0.001).

CONCLUSIONS

A topically applied platelet-derived exosome product, human platelet extract, induced normalization to skin health at 4-6 weeks with improved various clinical measures of facial photodamage and cutaneous aging. It is safe, well-tolerated, and well-liked by subjects.

Brd4 is required for chondrocyte differentiation and endochondral ossification

Differentiation of multi-potent mesenchymal stromal cells (MSCs) is directed by the activities of lineage-specific transcription factors and co-factors. A subset of these proteins controls the accessibility of chromatin by recruiting histone acetyl transferases or deacetylases that regulate acetylation of the N-termini of H3 and H4 histone proteins. Bromodomain (BRD) proteins recognize these acetylation marks and recruit the RNA pol II containing transcriptional machinery. Our previous studies have shown that Brd4 is required for osteoblast differentiation in vitro. Here, we investigated the role of Brd4 on endochondral ossification in C57BL/6 mice and chondrogenic differentiation in cell culture models. Conditional loss of Brd4 in the mesenchyme (Brd4 cKO, Brd4^fl/fl: Prrx1-Cre) yields smaller mice that exhibit alteration in endochondral ossification. Importantly, abnormal growth plate morphology and delayed long bone formation is observed in juvenile Brd4 cKO mice. One week old Brd4 cKO mice have reduced proliferative and hypertrophic zones within the physis and exhibit a delay in the formation of the secondary ossification center. At the cellular level, Brd4 function is required for chondrogenic differentiation and maturation of both ATDC5 cells and immature mouse articular chondrocytes. Mechanistically, Brd4 loss suppresses Sox9 levels and reduces expression of Sox9 and Runx2 responsive endochondral genes (e.g., Col2a1, Acan, Mmp13 and Sp7/Osx). Collectively, our results indicate that Brd4 is a key epigenetic regulator required for normal chondrogenesis and endochondral ossification.

Brd4 Inactivation Increases Adenoviral Delivery of BMP2 for Paracrine Stimulation of Osteogenic Differentiation as a Gene Therapeutic Concept to Enhance Bone Healing

Bromodomain (BRD) proteins are histone code interpreters that recognize acetylated lysines and link the dynamic state of chromatin with the transcriptional machinery. Here, we demonstrate that ablation of the Brd4 gene in primary mouse bone marrow–derived mesenchymal stem cells via a conditional Brd4^fl/fl allele suppresses osteogenic lineage commitment. Remarkably, loss of Brd4 function also enhances expression of genes in engineered adenoviral vectors, including Cre recombinase and green fluorescent protein (GFP). Similarly, vector‐based expression of BMP2 mRNA and protein levels are enhanced upon Brd4 depletion in cells transduced with an adenoviral vector that expresses BMP2 (Ad‐BMP2). Importantly, Brd4 depletion in MC3T3‐E1 and human adipose‐derived mesenchymal stem cells (AMSCs) transduced with Ad‐BMP2 enhances osteogenic differentiation of naïve MC3T3‐E1 cells via paracrine mechanisms based on transwell and conditioned medium studies. Our studies indicate that Brd4 depletion enhances adenoviral transgene expression in mammalian cells, which can be leveraged as a therapeutic strategy to improve viral vector‐based gene therapies. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Multiple pharmacological inhibitors targeting the epigenetic suppressor enhancer of zeste homolog 2 (Ezh2) accelerate osteoblast differentiation

Skeletal development and bone formation are regulated by epigenetic mechanisms that either repress or enhance osteogenic commitment of mesenchymal stromal/stem cells and osteoblasts. The transcriptional suppressive trimethylation of histone 3 lysine 27 (H3K27me3) hinders differentiation of pre-committed osteoblasts. Osteoblast maturation can be stimulated by genetic loss of the H3K27 methyltransferase Ezh2 which can also be mimicked pharmacologically using the classical Ezh2 inhibitor GSK126. Identification of other Ezh2 inhibitors (iEzh2) that enhance osteogenic potential would increase chemical options for developing new bone stimulatory compounds. In this study, we examined a panel of iEzh2s and show that all eight inhibitors we tested are capable of accelerating osteoblast differentiation to different degrees at concentrations that are well below cytotoxic concentrations. Inhibition of Ezh2 is commensurate with loss of cellular H3K27me3 levels while forced expression of Ezh2 reverses the effect of Ezh2 suppression. Reduced Ezh2 function by siRNA depletion of Ezh2 mRNA and protein levels also stimulates osteoblastogenesis, consistent with the specificity of iEzh2 to target the active site of Ezh2. Diminished Ezh2 levels preempt the effects of iEzh2s on H3K27me3. GSK126, EPZ-6438 and siRNA depletion of Ezh2 each are effective in reducing H3K27me3 levels. However, EPZ-6438 is more potent than GSK126 in stimulating osteoblastogenesis, as reflected by increased extracellular matrix mineralization. Collectively, our data indicate that Ezh2 inhibitors properly target Ezh2 consistent with their biochemical affinities. The range of compounds capable of promoting osteogenesis presented in this study offers the opportunity to develop diverse bone anabolic strategies for distinct clinical scenarios, including spine fusion, non-union of bone and dental implant enhancement.

Emerging workforce readiness in regenerative healthcare

The biology of regenerative medicine has steadily matured, providing the foundation for randomized clinical trials and translation into validated applications. Today, the growing regenerative armamentarium is poised to impact disease management, yet a gap in training next-generation healthcare providers, equipped to adopt and deliver regenerative options, has been exposed. This special report highlights a multiyear experience in developing and deploying a comprehensive regenerative curriculum for medical trainees. For academicians and institutions invested in establishing a formalized regenerative medicine syllabus, the Regenerative Medicine and Surgery course provides a patient-focused prototype for next-generation learners, offering a dedicated educational experience that encompasses discovery, development and delivery of regenerative solutions. Built with the vision of an evolving regenerative care model, this transdisciplinary endeavor could serve as an adoptable education portal to advance the readiness of the emergent regenerative healthcare workforce globally.

Biological functions of chromobox (CBX) proteins in stem cell self-renewal, lineage-commitment, cancer and development

Epigenetic regulatory proteins support mammalian development, cancer, aging and tissue repair by controlling many cellular processes including stem cell self-renewal, lineage-commitment and senescence in both skeletal and non-skeletal tissues. We review here our knowledge of epigenetic regulatory protein complexes that support the formation of inaccessible heterochromatin and suppress expression of cell and tissue-type specific biomarkers during development. Maintenance and formation of heterochromatin critically depends on epigenetic regulators that recognize histone 3 lysine trimethylation at residues K9 and K27 (respectively, H3K9me3 and H3K27me3), which represent transcriptionally suppressive epigenetic marks. Three chromobox proteins (i.e., CBX1, CBX3 or CBX5) associated with the heterochromatin protein 1 (HP1) complex are methyl readers that interpret H3K9me3 marks which are mediated by H3K9 methyltransferases (i.e., SUV39H1 or SUV39H2). Other chromobox proteins (i.e., CBX2, CBX4, CBX6, CBX7 and CBX8) recognize H3K27me3, which is deposited by Polycomb Repressive Complex 2 (PRC2; a complex containing SUZ12, EED, RBAP46/48 and the methyl transferases EZH1 or EZH2). This second set of CBX proteins resides in PRC1, which has many subunits including other polycomb group factors (PCGF1, PCGF2, PCGF3, PCGF4, PCGF5, PCGF6), human polyhomeotic homologs (HPH1, HPH2, HPH3) and E3-ubiquitin ligases (RING1 or RING2). The latter enzymes catalyze the subsequent mono-ubiquitination of lysine 119 in H2A (H2AK119ub). We discuss biological, cellular and molecular functions of CBX proteins and their physiological and pathological activities in non-skeletal cells and tissues in anticipation of new discoveries on novel roles for CBX proteins in bone formation and skeletal development.

Molecular pathology of human knee arthrofibrosis defined by RNA sequencing

Arthrofibrosis is an abnormal histopathologic response, is debilitating for patients, and poses a substantial unsolved clinical challenge. This study characterizes molecular biomarkers and regulatory pathways associated with arthrofibrosis by comparing fibrotic and non-fibrotic human knee tissue. The fibrotic group encompasses 4 patients undergoing a revision total knee arthroplasty (TKA) for arthrofibrosis (RTKA-A) while the non-fibrotic group includes 4 patients undergoing primary TKA for osteoarthritis (PTKA) and 4 patients undergoing revision TKA for non-arthrofibrotic and non-infectious etiologies (RTKA-NA). RNA-sequencing of posterior capsule specimens revealed differences in gene expression between each patient group by hierarchical clustering, principal component analysis, and correlation analyses. Multiple differentially expressed genes (DEGs) were defined in RTKA-A versus PTKA patients (i.e., 2059 up-regulated and 1795 down-regulated genes) and RTKA-A versus RTKA-NA patients (i.e., 3255 up-regulated and 3683 down-regulated genes). Our findings define molecular and pathological markers of arthrofibrosis, as well as novel potential targets for risk profiling, early diagnosis and pharmacological treatment of patients.

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

During bone marrow stromal cell (BMSC) differentiation, both Wnt signaling and the development of a rigid cytoskeleton promote commitment to the osteoblastic over adipogenic lineage. β-catenin plays a critical role in the Wnt signaling pathway to facilitate downstream effects on gene expression. We show that β-catenin was additive with cytoskeletal signals to prevent adipogenesis, and β-catenin knockdown promoted adipogenesis even when the actin cytoskeleton was depolymerized. β-catenin also prevented osteoblast commitment in a cytoskeletal-independent manner, with β-catenin knockdown enhancing lineage commitment. Chromatin immunoprecipitation (ChIP)-sequencing demonstrated binding of β-catenin to the promoter of enhancer of zeste homolog 2 (EZH2), a key component of the polycomb repressive complex 2 (PRC2) complex that catalyzes histone methylation. Knockdown of β-catenin reduced EZH2 protein levels and decreased methylated histone 3 (H3K27me3) at osteogenic loci. Further, when EZH2 was inhibited, β-catenin's anti-differentiation effects were lost. These results indicate that regulating EZH2 activity is key to β-catenin's effects on BMSCs to preserve multipotentiality. © 2020 American Society for Bone and Mineral Research.

Inhibition of the epigenetic suppressor EZH2 primes osteogenic differentiation mediated by BMP2

Bone-stimulatory therapeutics include bone morphogenetic proteins (e.g. BMP2), parathyroid hormone, and antibody-based suppression of WNT antagonists. Inhibition of the epigenetic enzyme enhancer of zeste homolog 2 (EZH2) is both bone anabolic and osteoprotective. EZH2 inhibition stimulates key components of bone-stimulatory signaling pathways, including the BMP2 signaling cascade. Because of high costs and adverse effects associated with BMP2 use, here we investigated whether BMP2 dosing can be reduced by co-treatment with EZH2 inhibitors. Co-administration of BMP2 with the EZH2 inhibitor GSK126 enhanced differentiation of murine (MC3T3) osteoblasts, reflected by increased alkaline phosphatase activity, Alizarin Red staining, and expression of bone-related marker genes (e.g. Bglap and Phospho1). Strikingly, co-treatment with BMP2 (10 ng/ml) and GSK126 (5 μm) was synergistic and was as effective as 50 ng/ml BMP2 at inducing MC3T3 osteoblastogenesis. Similarly, the BMP2-GSK126 co-treatment stimulated osteogenic differentiation of human bone marrow-derived mesenchymal stem/stromal cells, reflected by induction of key osteogenic markers (e.g. Osterix/SP7 and IBSP). A combination of BMP2 (300 ng local) and GSK126 (5 μg local and 5 days of 50 mg/kg systemic) yielded more consistent bone healing than single treatments with either compound in a mouse calvarial critical-sized defect model according to results from μCT, histomorphometry, and surgical grading of qualitative X-rays. We conclude that EZH2 inhibition facilitates BMP2-mediated induction of osteogenic differentiation of progenitor cells and maturation of committed osteoblasts. We propose that epigenetic priming, coupled with bone anabolic agents, enhances osteogenesis and could be leveraged in therapeutic strategies to improve bone mass.

Mechanical strain-mediated reduction in RANKL expression is associated with RUNX2 and BRD2

Mechanical loading-related strains trigger bone formation by osteoblasts while suppressing resorption by osteoclasts, uncoupling the processes of formation and resorption. Osteocytes may orchestrate this process in part by secreting sclerostin (SOST), which inhibits osteoblasts, and expressing receptor activator of nuclear factor-κB ligand (RANKL/TNFSF11) which recruits osteoclasts. Both SOST and RANKL are targets of the master osteoblastic transcription factor RUNX2. Subjecting human osteoblastic Saos-2 cells to strain by four point bending down-regulates their expression of SOST and RANKL without altering RUNX2 expression. RUNX2 knockdown increases basal SOST expression, but does not alter SOST down-regulation following strain. Conversely, RUNX2 knockdown does not alter basal RANKL expression, but prevents its down-regulation by strain. Chromatin immunoprecipitation revealed RUNX2 occupies a region of the RANKL promoter containing a consensus RUNX2 binding site and its occupancy of this site decreases following strain. The expression of epigenetic acetyl and methyl writers and readers was quantified by RT-qPCR to investigate potential epigenetic bases for this change. Strain and RUNX2 knockdown both down-regulate expression of the bromodomain acetyl reader BRD2. BRD2 and RUNX2 co-immunoprecipitate, suggesting interaction within regulatory complexes, and BRD2 was confirmed to interact with the RUNX2 promoter. BRD2 also occupies the RANKL promoter and its occupancy was reduced following exposure to strain. Thus, RUNX2 may contribute to bone remodeling by suppressing basal SOST expression, while facilitating the acute strain-induced down-regulation of RANKL through a mechanosensitive epigenetic loop involving BRD2.

Knockdown of formin mDia2 alters lamin B1 levels and increases osteogenesis in stem cells

Nuclear actin plays a critical role in mediating mesenchymal stem cell (MSC) fate commitment. In marrow-derived MSCs, the principal diaphanous-related formin Diaph3 (mDia2) is present in the nucleus and regulates intranuclear actin polymerization, whereas Diaph1 (mDia1) is localized to the cytoplasm and controls cytoplasmic actin polymerization. We here show that mDia2 can be used as a tool to query actin-lamin nucleoskeletal structure. Silencing mDia2 affected the nucleoskeletal lamin scaffold, altering nuclear morphology without affecting cytoplasmic actin cytoskeleton, and promoted MSC differentiation. Attempting to target intranuclear actin polymerization by silencing mDia2 led to a profound loss in lamin B1 nuclear envelope structure and integrity, increased nuclear height, and reduced nuclear stiffness without compensatory changes in other actin nucleation factors. Loss of mDia2 with the associated loss in lamin B1 promoted Runx2 transcription and robust osteogenic differentiation and suppressed adipogenic differentiation. Hence, mDia2 is a potent tool to query intranuclear actin-lamin nucleoskeletal structure, and its presence serves to retain multipotent stromal cells in an undifferentiated state.

The epigenetic reader Brd4 is required for osteoblast differentiation

Transcription networks and epigenetic mechanisms including DNA methylation, histone modifications, and noncoding RNAs control lineage commitment of multipotent mesenchymal progenitor cells. Proteins that read, write, and erase histone tail modifications curate and interpret the highly intricate histone code. Epigenetic reader proteins that recognize and bind histone marks provide a crucial link between histone modifications and their downstream biological effects. Here, we investigate the role of bromodomain-containing (BRD) proteins, which recognize acetylated histones, during osteogenic differentiation. Using RNA-sequencing (RNA-seq) analysis, we screened for BRD proteins (n = 40) that are robustly expressed in MC3T3 osteoblasts. We focused functional follow-up studies on Brd2 and Brd4 which are highly expressed in MC3T3 preosteoblasts and represent "bromodomain and extra terminal domain" (BET) proteins that are sensitive to pharmacological agents (BET inhibitors). We show that small interfering RNA depletion of Brd4 has stronger inhibitory effects on osteoblast differentiation than Brd2 loss as measured by osteoblast-related gene expression, extracellular matrix deposition, and alkaline phosphatase activity. Similar effects on osteoblast differentiation are seen with the BET inhibitor +JQ1, and this effect is reversible upon its removal indicating that this small molecule has no lasting effects on the differentiation capacity of MC3T3 cells. Mechanistically, we find that Brd4 binds at known Runx2 binding sites in promoters of bone-related genes. Collectively, these findings suggest that Brd4 is recruited to osteoblast-specific genes and may cooperate with bone-related transcription factors to promote osteoblast lineage commitment and maturation.

Inhibition of COX-2 Pathway as a Potential Prophylaxis Against Arthrofibrogenesis in a Rabbit Model of Joint Contracture

Arthrofibrosis is a common complication following total knee arthroplasty caused by pathologic fibroblast activation and excessive collagen deposition around a synovial joint leading to debilitating loss of motion. Treatment options are limited because the pathologic mechanisms remain to be characterized. Dysregulation of the inflammatory cascade may lead to communication between myofibroblasts and immune cells triggering tissue metaplasia, and excessive collagen deposition described clinically as arthrofibrosis. We explored the novel use of celecoxib (selective cyclooxygenase-2 [COX-2] inhibitor) to disrupt the downstream effects of the post-traumatic inflammatory cascade and inhibit scar tissue formation in a validated rabbit model of arthrofibrosis combined with new parameters for quantifying the stiffness of the posterior capsule. Biomechanical and molecular analyses, of contracted rabbit knee posterior capsule tissue after COX-2 inhibition revealed increased maximal passive extension and down-regulation of collagen messenger RNA compared with controls. Histopathologic examination suggested a trend of decreased quantities of dense fibrous connective tissue with COX-2 inhibition. These data may suggest that inhibiting the inflammatory cascade could potentially reduce pathologic myofibroblast activation, thereby reducing scar tissue formation and increasing the range of motion in arthrofibrotic joints. Implementing a multi-modal pharmacologic approach may simultaneously target numerous cellular components contributing to the complex process of arthrofibrogenesis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2609-2620, 2019.

Sustained perfusion of revascularized bioengineered livers heterotopically transplanted into immunosuppressed pigs

Implanted bioengineered livers have not exceeded three days of continuous perfusion. Here, we show that decellularized whole porcine livers revascularized with human umbilical endothelial cells and implanted heterotopically into immunosuppressed pigs whose spleen has been removed can sustain perfusion for up to 15 days. We identified peak glucose consumption rate as a main predictor of the patency of the revascularized bioengineered livers (rBELs). On heterotopic implantation of the rBELs into pigs in the absence of anticoagulation therapy led to sustained perfusion for 3 days, followed by significant immune responses directed against the human endothelial cells. A 10-day steroid-based immunosuppression protocol and a splenectomy at time of rBEL implantation reduced the immune responses and resulted in continuous perfusion of the rBELs for over two weeks. We also show that the human endothelial cells in the perfused rBELs colonize the liver sinusoids and express sinusoidal endothelial markers similar to those in normal liver tissue. Revascularized liver scaffolds that can maintain blood perfusion at physiological pressures might eventually help overcome the chronic shortage of transplantable human livers.

Hypothermia and nutrient deprivation alter viability of human adipose-derived mesenchymal stem cells

PURPOSE

Adipose-derived mesenchymal stem cells (MSCs) are attractive biological agents in regenerative medicine. To optimize cell therapies, it is necessary to determine the most effective delivery method for MSCs. Therefore, we evaluated the biological properties of MSCs after exposure to various temperatures to define optimal storage conditions prior to therapeutic delivery of MSCs.

DESIGN

Prospective observational study.

METHODS AND MATERIALS

Adherent and non-adherent MSCs were incubated at multiple temperatures (i.e., 4, 23 and 37 °C) in Lactated Ringers (LR) solution lacking essential cell growth ingredients, or in culture media which is optimized for cell growth. Cells were assessed either after the temperature changes (4 h) or after recovery (24 h). Metabolic activity of MSCs, cell number and expression of representative mRNA biomarkers were evaluated to assess the biological effects of temperature. We monitored changes in mRNAs expression related to cytoprotective- or stress-related responses (e.g., FOS, JUN, ATF1, ATF4, EGR1, EGR2, MYC), proliferation (e.g., HIST2H4, CCNB2), and extracellular matrix production (ECM; e.g., COL3A1, COL1A1) by quantitative real time reverse-transcriptase polymerase chain reaction (RT-qPCR) analysis.

RESULTS

Our study demonstrates that storing MSCs in Lactated Ringers (LR) solution for 4 h decreases cell number and metabolic activity. The number of viable MSCs decreased significantly when cultured at physiological temperature (37 °C) and severe hypothermia (4 °C), while cells grown at ambient temperature (23 °C) exhibited the least detrimental effects. There were no appreciable biological differences in mRNA markers for proliferation or ECM deposition at any of the temperatures. However, biomarkers related to cytoprotective- or stress-responses were selectively elevated depending on temperature or media type (i.e., LR versus standard media).

CONCLUSION

The biological impact of nutrient-free media and temperature changes after 4 h exposure persists after a 24 h recovery period. Hence, storage temperature and media conditions should be optimized to improve effective dosing of MSCs.

Loss of histone methyltransferase Ezh2 stimulates an osteogenic transcriptional program in chondrocytes but does not affect cartilage development

Ezh2 is a histone methyltransferase that suppresses osteoblast maturation and skeletal development. We evaluated the role of Ezh2 in chondrocyte lineage differentiation and endochondral ossification. Ezh2 was genetically inactivated in the mesenchymal, osteoblastic, and chondrocytic lineages in mice using the Prrx1-Cre, Osx1-Cre, and Col2a1-Cre drivers, respectively. WT and conditional knockout mice were phenotypically assessed by gross morphology, histology, and micro-CT imaging. Ezh2-deficient chondrocytes in micromass culture models were evaluated using RNA-Seq, histologic evaluation, and Western blotting. Aged mice with Ezh2 deficiency were also evaluated for premature development of osteoarthritis using radiographic analysis. Ezh2 deficiency in murine chondrocytes reduced bone density at 4 weeks of age but caused no other gross developmental effects. Knockdown of Ezh2 in chondrocyte micromass cultures resulted in a global reduction in trimethylation of histone 3 lysine 27 (H3K27me3) and altered differentiation in vitro RNA-Seq analysis revealed enrichment of an osteogenic gene expression profile in Ezh2-deficient chondrocytes. Joint development proceeded normally in the absence of Ezh2 in chondrocytes without inducing excessive hypertrophy or premature osteoarthritis in vivo In summary, loss of Ezh2 reduced H3K27me3 levels, increased the expression of osteogenic genes in chondrocytes, and resulted in a transient post-natal bone phenotype. Remarkably, Ezh2 activity is dispensable for normal chondrocyte maturation and endochondral ossification in vivo, even though it appears to have a critical role during early stages of mesenchymal lineage commitment.

Validation of Osteogenic Properties of Cytochalasin D by High-Resolution RNA-Sequencing in Mesenchymal Stem Cells Derived from Bone Marrow and Adipose Tissues

Differentiation of mesenchymal stromal/stem cells (MSCs) involves a series of molecular signals and gene transcription events required for attaining cell lineage commitment. Modulation of the actin cytoskeleton using cytochalasin D (CytoD) drives osteogenesis at early timepoints in bone marrow-derived MSCs and also initiates a robust osteogenic differentiation program in adipose tissue-derived MSCs. To understand the molecular basis for these pronounced effects on osteogenic differentiation, we investigated global changes in gene expression in CytoD-treated murine and human MSCs by high-resolution RNA-sequencing (RNA-seq) analysis. A three-way bioinformatic comparison between human adipose tissue-derived MSCs (hAMSCs), human bone marrow-derived MSCs (hBMSCs), and mouse bone marrow-derived MSCs (mBMSCs) revealed significant upregulation of genes linked to extracellular matrix organization, cell adhesion and bone metabolism. As anticipated, the activation of these differentiation-related genes is accompanied by a downregulation of nuclear and cell cycle-related genes presumably reflecting cytostatic effects of CytoD. We also identified eight novel CytoD activated genes-VGLL4, ARHGAP24, KLHL24, RCBTB2, BDH2, SCARF2, ACAD10, HEPH-which are commonly upregulated across the two species and tissue sources of our MSC samples. We selected the Hippo pathway-related VGLL4 gene, which encodes the transcriptional co-factor Vestigial-like 4, for further study because this pathway is linked to osteogenesis. VGLL4 small interfering RNA depletion reduces mineralization of hAMSCs during CytoD-induced osteogenic differentiation. Together, our RNA-seq analyses suggest that while the stimulatory effects of CytoD on osteogenesis are pleiotropic and depend on the biological state of the cell type, a small group of genes including VGLL4 may contribute to MSC commitment toward the bone lineage.

Enhancer of zeste homolog 2 (Ezh2) controls bone formation and cell cycle progression during osteogenesis in mice

Epigenetic mechanisms control skeletal development and osteoblast differentiation. Pharmacological inhibition of the histone 3 Lys-27 (H3K27) methyltransferase enhancer of zeste homolog 2 (EZH2) in WT mice enhances osteogenesis and stimulates bone formation. However, conditional genetic loss of Ezh2 early in the mesenchymal lineage (i.e. through excision via Prrx1 promoter-driven Cre) causes skeletal abnormalities due to patterning defects. Here, we addressed the key question of whether Ezh2 controls osteoblastogenesis at later developmental stages beyond patterning. We show that Ezh2 loss in committed pre-osteoblasts by Cre expression via the osterix/Sp7 promoter yields phenotypically normal mice. These Ezh2 conditional knock-out mice (Ezh2 cKO) have normal skull bones, clavicles, and long bones but exhibit increased bone marrow adiposity and reduced male body weight. Remarkably, in vivo Ezh2 loss results in a low trabecular bone phenotype in young mice as measured by micro-computed tomography and histomorphometry. Thus, Ezh2 affects bone formation stage-dependently. We further show that Ezh2 loss in bone marrow-derived mesenchymal cells suppresses osteogenic differentiation and impedes cell cycle progression as reflected by decreased metabolic activity, reduced cell numbers, and changes in cell cycle distribution and in expression of cell cycle markers. RNA-Seq analysis of Ezh2 cKO calvaria revealed that the cyclin-dependent kinase inhibitor Cdkn2a is the most prominent cell cycle target of Ezh2 Hence, genetic loss of Ezh2 in mouse pre-osteoblasts inhibits osteogenesis in part by inducing cell cycle changes. Our results suggest that Ezh2 serves a bifunctional role during bone formation by suppressing osteogenic lineage commitment while simultaneously facilitating proliferative expansion of osteoprogenitor cells.

Molecular characterization of physis tissue by RNA sequencing

The physis is a well-established and anatomically distinct cartilaginous structure that is crucial for normal long-bone development and growth. Abnormalities in physis function are linked to growth plate disorders and other pediatric musculoskeletal diseases. Understanding the molecular pathways operative in the physis may permit development of regenerative therapies to complement surgically-based procedures that are the current standard of care for growth plate disorders. Here, we performed next generation RNA sequencing on mRNA isolated from human physis and other skeletal tissues (e.g., articular cartilage and bone; n = 7 for each tissue). We observed statistically significant enrichment of gene sets in the physis when compared to the other musculoskeletal tissues. Further analysis of these upregulated genes identified physis-specific networks of extracellular matrix proteins including collagens (COL2A1, COL6A1, COL9A1, COL14A1, COL16A1) and matrilins (MATN1, MATN2, MATN3), and signaling proteins in the WNT pathway (WNT10B, FZD1, FZD10, DKK2) or the FGF pathway (FGF10, FGFR4). Our results provide further insight into the gene expression networks that contribute to the physis' unique structural composition and regulatory signaling networks. Physis-specific expression profiles may guide ongoing initiatives in tissue engineering and cell-based therapies for treatment of growth plate disorders and growth modulation therapies. Furthermore, our findings provide new leads for therapeutic drug discovery that would permit future intervention through pharmacological rather than surgical strategies.

Histone H4 Methyltransferase Suv420h2 Maintains Fidelity of Osteoblast Differentiation

Osteogenic lineage commitment and progression is controlled by multiple signaling pathways (e.g., WNT, BMP, FGF) that converge on bone-related transcription factors. Access of osteogenic transcription factors to chromatin is controlled by epigenetic regulators that generate post-translational modifications of histones ("histone code"), as well as read, edit and/or erase these modifications. Our understanding of the biological role of epigenetic regulators in osteoblast differentiation remains limited. Therefore, we performed next-generation RNA sequencing (RNA-seq) and established which chromatin-related proteins are robustly expressed in mouse bone tissues (e.g., fracture callus, calvarial bone). These studies also revealed that cells with increased osteogenic potential have higher levels of the H4K20 methyl transferase Suv420h2 compared to other methyl transferases (e.g., Suv39h1, Suv39h2, Suv420h1, Ezh1, Ezh2). We find that all six epigenetic regulators are transiently expressed at different stages of osteoblast differentiation in culture, with maximal mRNAs levels of Suv39h1 and Suv39h2 (at day 3) preceding maximal expression of Suv420h1 and Suv420h2 (at day 7) and developmental stages that reflect, respectively, early and later collagen matrix deposition. Loss of function analysis of Suv420h2 by siRNA depletion shows loss of H4K20 methylation and decreased expression of bone biomarkers (e.g., alkaline phosphatase/Alpl) and osteogenic transcription factors (e.g., Sp7/Osterix). Furthermore, Suv420h2 is required for matrix mineralization during osteoblast differentiation. We conclude that Suv420h2 controls the H4K20 methylome of osteoblasts and is critical for normal progression of osteoblastogenesis. J. Cell. Biochem. 118: 1262-1272, 2017. © 2016 Wiley Periodicals, Inc.

Profiling of human epigenetic regulators using a semi-automated real-time qPCR platform validated by next generation sequencing

Epigenetic mechanisms control phenotypic commitment of mesenchymal stromal/stem cells (MSCs) into osteogenic, chondrogenic or adipogenic lineages. To investigate enzymes and chromatin binding proteins controlling the epigenome, we developed a hybrid expression screening strategy that combines semi-automated real-time qPCR (RT-qPCR), next generation RNA sequencing (RNA-seq), and a novel data management application (FileMerge). This strategy was used to interrogate expression of a large cohort (n>300) of human epigenetic regulators (EpiRegs) that generate, interpret and/or edit the histone code. We find that EpiRegs with similar enzymatic functions are variably expressed and specific isoforms dominate over others in human MSCs. This principle is exemplified by analysis of key histone acetyl transferases (HATs) and deacetylases (HDACs), H3 lysine methyltransferases (e.g., EHMTs) and demethylases (KDMs), as well as bromodomain (BRDs) and chromobox (CBX) proteins. Our results show gender-specific expression of H3 lysine 9 [H3K9] demethylases (e.g., KDM5D and UTY) as expected and upregulation of distinct EpiRegs (n>30) during osteogenic differentiation of MSCs (e.g., HDAC5 and HDAC7). The functional significance of HDACs in osteogenic lineage commitment of MSCs was functionally validated using panobinostat (LBH-589). This pan-deacetylase inhibitor suppresses osteoblastic differentiation as evidenced by reductions in bone-specific mRNA markers (e.g., ALPL), alkaline phosphatase activity and calcium deposition (i.e., Alizarin Red staining). Thus, our RT-qPCR platform identifies candidate EpiRegs by expression screening, predicts biological outcomes of their corresponding inhibitors, and enables manipulation of the human epigenome using molecular or pharmacological approaches to control stem cell differentiation.

Safety Studies for Use of Adipose Tissue-Derived Mesenchymal Stromal/Stem Cells in a Rabbit Model for Osteoarthritis to Support a Phase I Clinical Trial

Adipose‐derived mesenchymal stem cells (AMSCs) offer potential as a therapeutic option for clinical applications in musculoskeletal regenerative medicine because of their immunomodulatory functions and capacity for trilineage differentiation. In preparation for a phase I clinical trial using AMSCs to treat patients with osteoarthritis, we carried out preclinical studies to assess the safety of human AMSCs within the intra‐articular joint space. Culture‐expanded human AMSCs grown in human platelet‐lysate were delivered via intra‐articular injections into normal healthy rabbit knees and knees at risk for the development of osteoarthritis after bilateral medial anterior hemimeniscectomy. Treatment outcomes and safety were evaluated by assessing the general health, function, and behavior of the animals. Joint tissues were analyzed by x‐ray, magnetic resonance imaging, and histopathology. Intra‐articular AMSC therapy was well tolerated in this study. We did not observe adverse systemic reactions, nor did we find evidence of damage to intra‐articular joint tissues. Thus, the data generated in this study show a favorable safety profile for AMSCs within the joint space in support of a phase I clinical trial evaluating the clinical utility of AMSCs to treat osteoarthritis. Stem Cells Translational Medicine2017;6:910–922

Enhancer of Zeste Homolog 2 Inhibition Stimulates Bone Formation and Mitigates Bone Loss Caused by Ovariectomy in Skeletally Mature Mice

Perturbations in skeletal development and bone degeneration may result in reduced bone mass and quality, leading to greater fracture risk. Bone loss is mitigated by bone protective therapies, but there is a clinical need for new bone-anabolic agents. Previous work has demonstrated that Ezh2 (enhancer of zeste homolog 2), a histone 3 lysine 27 (H3K27) methyltransferase, suppressed differentiation of osteogenic progenitors. Here, we investigated whether inhibition of Ezh2 can be leveraged for bone stimulatory applications. Pharmacologic inhibition and siRNA knockdown of Ezh2 enhanced osteogenic commitment of MC3T3 preosteoblasts. Next generation RNA sequencing of mRNAs and real time quantitative PCR profiling established that Ezh2 inactivation promotes expression of bone-related gene regulators and extracellular matrix proteins. Mechanistically, enhanced gene expression was linked to decreased H3K27 trimethylation (H3K27me3) near transcriptional start sites in genome-wide sequencing of chromatin immunoprecipitations assays. Administration of an Ezh2 inhibitor modestly increases bone density parameters of adult mice. Furthermore, Ezh2 inhibition also alleviated bone loss in an estrogen-deficient mammalian model for osteoporosis. Ezh2 inhibition enhanced expression of Wnt10b and Pth1r and increased the BMP-dependent phosphorylation of Smad1/5. Thus, these data suggest that inhibition of Ezh2 promotes paracrine signaling in osteoblasts and has bone-anabolic and osteoprotective potential in adults.

Identification and validation of multiple cell surface markers of clinical-grade adipose-derived mesenchymal stromal cells as novel release criteria for good manufacturing practice-compliant production

Background

Clinical translation of mesenchymal stromal cells (MSCs) necessitates basic characterization of the cell product since variability in biological source and processing of MSCs may impact therapeutic outcomes. Although expression of classical cell surface markers (e.g., CD90, CD73, CD105, and CD44) is used to define MSCs, identification of functionally relevant cell surface markers would provide more robust release criteria and options for quality control. In addition, cell surface expression may distinguish between MSCs from different sources, including bone marrow-derived MSCs and clinical-grade adipose-derived MSCs (AMSCs) grown in human platelet lysate (hPL).

Methods

In this work we utilized quantitative PCR, flow cytometry, and RNA-sequencing to characterize AMSCs grown in hPL and validated non-classical markers in 15 clinical-grade donors.

Results

We characterized the surface marker transcriptome of AMSCs, validated the expression of classical markers, and identified nine non-classical markers (i.e., CD36, CD163, CD271, CD200, CD273, CD274, CD146, CD248, and CD140B) that may potentially discriminate AMSCs from other cell types. More importantly, these markers exhibit variability in cell surface expression among different cell isolates from a diverse cohort of donors, including freshly prepared, previously frozen, or proliferative state AMSCs and may be informative when manufacturing cells.

Conclusions

Our study establishes that clinical-grade AMSCs expanded in hPL represent a homogeneous cell culture population according to classical markers,. Additionally, we validated new biomarkers for further AMSC characterization that may provide novel information guiding the development of new release criteria.

Clinical trials

Use of Autologous Bone Marrow Aspirate Concentrate in Painful Knee Osteoarthritis (BMAC): Clinicaltrials.gov NCT01931007. Registered August 26, 2013.

MSC for Occlusive Disease of the Kidney: Clinicaltrials.gov NCT01840540. Registered April 23, 2013.

Mesenchymal Stem Cell Therapy in Multiple System Atrophy: Clinicaltrials.gov NCT02315027. Registered October 31, 2014.

Efficacy and Safety of Adult Human Mesenchymal Stem Cells to Treat Steroid Refractory Acute Graft Versus Host Disease. Clinicaltrials.gov NCT00366145. Registered August 17, 2006.

A Dose-escalation Safety Trial for Intrathecal Autologous Mesenchymal Stem Cell Therapy in Amyotrophic Lateral Sclerosis. Clinicaltrials.gov NCT01609283. Registered May 18, 2012.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0370-8) contains supplementary material, which is available to authorized users.

Osteogenic potential of human adipose-tissue-derived mesenchymal stromal cells cultured on 3D-printed porous structured titanium

Integration of porous metal prosthetics, which restore form and function of irreversibly damaged joints, into remaining healthy bone is critical for implant success. We investigated the biological properties of adipose-tissue-derived mesenchymal stromal/stem cells (AMSCs) and addressed their potential to alter the in vitro microenvironment of implants. We employed human AMSCs as a practical source for musculoskeletal applications because these cells can be obtained in large quantities, are multipotent, and have trophic paracrine functions. AMSCs were cultured on surgical-grade porous titanium disks as a model for orthopedic implants. We monitored cell/substrate attachment, cell proliferation, multipotency, and differentiation phenotypes of AMSCs upon osteogenic induction. High-resolution scanning electron microscopy and histology revealed that AMSCs adhere to the porous metallic surface. Compared to standard tissue culture plastic, AMSCs grown in the porous titanium microenvironment showed differences in temporal expression for genes involved in cell cycle progression (CCNB2, HIST2H4), extracellular matrix production (COL1A1, COL3A1), mesenchymal lineage identity (ACTA2, CD248, CD44), osteoblastic transcription factors (DLX3, DLX5, ID3), and epigenetic regulators (EZH1, EZH2). We conclude that metal orthopedic implants can be effectively seeded with clinical-grade stem/stromal cells to create a pre-conditioned implant.

RNA sequencing reveals a depletion of collagen targeting microRNAs in Dupuytren's disease

Background

Dupuytren’s disease is an inherited disorder in which patients develop fibrotic contractures of the hand. Current treatment strategies include surgical excision or enzymatic digestion of fibrotic tissue. MicroRNAs, which are key posttranscriptional regulators of genes expression, have been shown to play an important regulatory role in disorders of fibrosis. Therefore in this investigation, we apply high throughput next generation RNA sequencing strategies to characterize microRNA expression in diseased and healthy palmar fascia to elucidate molecular mechanisms responsible for pathogenic fibrosis.

Methods

We applied high throughput RNA sequencing techniques to quantify the expression of all known human microRNAs in Dupuytren’s and control palmar fascia. MicroRNAs that were differentially expressed between diseased and healthy tissue samples were used for computational target prediction using the bioinformatics tool ComiR. Molecular pathways that were predicted to be differentially expressed based on computational analysis were validated by performing RT-qPCR on RNA extracted from diseased and non-diseased palmar fascia biopsies.

Results

A comparison of microRNAs expressed in Dupuytren’s fascia and control fascia identified 74 microRNAs with a 2-fold enrichment in Dupuytren’s tissue, and 32 microRNAs with enrichment in control fascia. Computational target prediction for differentially expressed microRNAs indicated preferential targeting of collagens and extracellular matrix related proteins in control palmar fascia. RT-qPCR confirmed the decreased expression of microRNA targeted collagens in control palmar fascia tissues.

Discussion

Control palmar fascia show decreased expression of mRNAs encoding collagens that are preferentially targeted by microRNAs enriched in non-diseased fascia. Thus alterations in microRNA regulatory networks may play an important role in driving the pathogenic fibrosis seen in Dupuytren’s disease via direct regulatory effects on extracellular matrix protein synthesis.

Conclusion

Dupuytren’s fascia and healthy palmar fascia can be distinguished by unique microRNA profiles, which are predicted to preferentially target collagens and other extracellular matrix proteins.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-015-0135-8) contains supplementary material, which is available to authorized users.

Epigenetic Control of Skeletal Development by the Histone Methyltransferase Ezh2

Epigenetic control of gene expression is critical for normal fetal development. However, chromatin-related mechanisms that activate bone-specific programs during osteogenesis have remained underexplored. Therefore, we investigated the expression profiles of a large cohort of epigenetic regulators (>300) during osteogenic differentiation of human mesenchymal cells derived from the stromal vascular fraction of adipose tissue (AMSCs). Molecular analyses establish that the polycomb group protein EZH2 (enhancer of zeste homolog 2) is down-regulated during osteoblastic differentiation of AMSCs. Chemical inhibitor and siRNA knockdown studies show that EZH2, a histone methyltransferase that catalyzes trimethylation of histone 3 lysine 27 (H3K27me3), suppresses osteogenic differentiation. Blocking EZH2 activity promotes osteoblast differentiation and suppresses adipogenic differentiation of AMSCs. High throughput RNA sequence (mRNASeq) analysis reveals that EZH2 inhibition stimulates cell cycle inhibitory proteins and enhances the production of extracellular matrix proteins. Conditional genetic loss of Ezh2 in uncommitted mesenchymal cells (Prrx1-Cre) results in multiple defects in skeletal patterning and bone formation, including shortened forelimbs, craniosynostosis, and clinodactyly. Histological analysis and mRNASeq profiling suggest that these effects are attributable to growth plate abnormalities and premature cranial suture closure because of precocious maturation of osteoblasts. We conclude that the epigenetic activity of EZH2 is required for skeletal patterning and development, but EZH2 expression declines during terminal osteoblast differentiation and matrix production.