Instructor, Orthopaedic Surgery
Honors & Awards
PostDoctoral scholar award, Child Health Research Institute, Stanford (2015)
Although regeneration of human cartilage is inherently inefficient, age is an important risk factor for osteoarthritis. Recent reports have provided compelling evidence that juvenile chondrocytes (from donors below 13 years of age) are more efficient at generating articular cartilage as compared to adult chondrocytes. However, the molecular basis for such a superior regenerative capability is not understood. To identify the cell-intrinsic differences between juvenile and adult cartilage, we have systematically profiled global gene expression changes between a small cohort of human neonatal/juvenile and adult chondrocytes. No such study is available for human chondrocytes although young and old bovine and equine cartilage have been recently profiled. Our studies have identified and validated new factors enriched in juvenile chondrocytes as compared to adult chondrocytes including secreted extracellular matrix factors chordin-like 1 (CHRDL1) and microfibrillar-associated protein 4 (MFAP4). Network analyses identified cartilage development pathways, epithelial-mesenchymal transition, and innate immunity pathways to be overrepresented in juvenile-enriched genes. Finally, CHRDL1 was observed to aid the proliferation and survival of bone marrow-derived human mesenchymal stem cells (hMSC) while maintaining their stem cell potential. These studies, therefore, provide a mechanism for how young cartilage factors can potentially enhance stem cell function in cartilage repair.
View details for DOI 10.1089/ten.tea.2015.0366
View details for Web of Science ID 000374761600007
View details for PubMedID 26955889
Regulation of gene expression changes during chondrogenic differentiation by DNA methylation and demethylation is little understood. Methylated cytosines (5mC) are oxidized by the ten-eleven-translocation (TET) proteins to 5-hydroxymethylcytosines (5hmC), 5-formylcytosines (5fC) and 5-carboxylcytosines (5caC) eventually leading to a replacement by unmethylated cytosines (C) i.e. DNA demethylation. Additionally, 5hmC is stable and acts as an epigenetic mark by itself. Here, we report that global changes in 5hmC mark chondrogenic differentiation in vivo and in vitro. Tibia anlagen and growth plate analyses during limb development at mouse embryonic days E 11.5, 13.5 and 17.5 showed dynamic changes in 5hmC levels in the differentiating chondrocytes. A similar increase in 5hmC levels was observed in the ATDC5 chondroprogenitor cell line accompanied by increased expression of the TET proteins during in vitro differentiation. Loss of TET1 in ATDC5 decreased 5hmC levels and impaired differentiation, demonstrating a functional role for TET1-mediated 5hmC dynamics in chondrogenic differentiation. Global analyses of the 5hmC-enriched sequences during early and late chondrogenic differentiation identified 5hmC distribution to be enriched in the regulatory regions of genes preceding the transcription start site (TSS) as well as in the gene bodies. Stable gains in 5hmC were observed in specific subsets of genes including genes associated with cartilage development and in chondrogenic lineage-specific genes. 5hmC gains in regulatory promoter and enhancer regions as well as in gene bodies were strongly associated with activated but not repressed genes, indicating a potential regulatory role for DNA hydroxymethylation in chondrogenic gene expression. This article is protected by copyright. All rights reserved.
View details for DOI 10.1002/jbmr.2711
View details for Web of Science ID 000373596800006
View details for PubMedID 26363184
Regeneration of human cartilage is inherently inefficient; an abundant autologous source, such as human induced pluripotent stem cells (hiPSCs), is therefore attractive for engineering cartilage. We report a growth factor-based protocol for differentiating hiPSCs into articular-like chondrocytes (hiChondrocytes) within 2 weeks, with an overall efficiency >90%. The hiChondrocytes are stable and comparable to adult articular chondrocytes in global gene expression, extracellular matrix production, and ability to generate cartilage tissue in vitro and in immune-deficient mice. Molecular characterization identified an early SRY (sex-determining region Y) box (Sox)9(low) cluster of differentiation (CD)44(low)CD140(low) prechondrogenic population during hiPSC differentiation. In addition, 2 distinct Sox9-regulated gene networks were identified in the Sox9(low) and Sox9(high) populations providing novel molecular insights into chondrogenic fate commitment and differentiation. Our findings present a favorable method for generating hiPSC-derived articular-like chondrocytes. The hiChondrocytes are an attractive cell source for cartilage engineering because of their abundance, autologous nature, and potential to generate articular-like cartilage rather than fibrocartilage. In addition, hiChondrocytes can be excellent tools for modeling human musculoskeletal diseases in a dish and for rapid drug screening.-Lee, J., Taylor, S. E. B., Smeriglio, P., Lai, J., Maloney, W. J., Yang, F., Bhutani, N. Early induction of a prechondrogenic population allows efficient generation of stable chondrocytes from human induced pluripotent stem cells.
View details for DOI 10.1096/fj.14-269720
View details for Web of Science ID 000358796900027
View details for PubMedID 25911615
Regeneration of human cartilage is inherently inefficient. Current cell-based approaches for cartilage repair, including autologous chondrocytes, are limited by the paucity of cells, associated donor site morbidity, and generation of functionally inferior fibrocartilage rather than articular cartilage. Upon investigating the role of collagen VI (Col VI), a major component of the chondrocyte pericellular matrix (PCM), we observe that soluble Col VI stimulates chondrocyte proliferation. Interestingly, both adult and osteoarthritis chondrocytes respond to soluble Col VI in a similar manner. The proliferative effect is, however, strictly due to the soluble Col VI as no proliferation is observed upon exposure of chondrocytes to immobilized Col VI. Upon short Col VI treatment in 2D monolayer culture, chondrocytes maintain high expression of characteristic chondrocyte markers like Col2a1, agc, and Sox9 whereas the expression of the fibrocartilage marker Collagen I (Col I) and of the hypertrophy marker Collagen X (Col X) is minimal. Additionally, Col VI-expanded chondrocytes show a similar potential to untreated chondrocytes in engineering cartilage in 3D biomimetic hydrogel constructs. Our study has, therefore, identified soluble Col VI as a biologic that can be useful for the expansion and utilization of scarce sources of chondrocytes, potentially for autologous chondrocyte implantation. Additionally, our results underscore the importance of further investigating the changes in chondrocyte PCM with age and disease and the subsequent effects on chondrocyte growth and function.
View details for DOI 10.1089/ten.TEA.2014.0375
View details for PubMedID 25257043
Regeneration of human articular cartilage is inherently limited and extensive efforts have focused on engineering the cartilage tissue. Various cellular sources have been studied for cartilage tissue engineering including adult chondrocytes, as well as embryonic or adult stem cells. Juvenile chondrocytes (from donors below 13 years of age) have recently been reported to be a promising cell source for cartilage regeneration. Previous studies have compared the potential of adult and juvenile chondrocytes or adult and osteoarthritic (OA) chondrocytes. To comprehensively characterize the comparative potential of young, old and diseased chondrocytes, here we examined cartilage formation by juvenile, adult and OA chondrocytes in 3D biomimetic hydrogels composed of poly(ethylene glycol) and chondroitin sulfate. All three human articular chondrocytes were encapsulated in the 3D biomimetic hydrogels and cultured for 3 or 6 weeks to allow maturation and extracellular matrix formation. Outcomes were analyzed using quantitative gene expression, immunofluorescence staining, biochemical assays, and mechanical testing. After 3 and 6 weeks, juvenile chondrocytes showed a greater upregulation of chondrogenic gene expression than adult chondrocytes, while OA chondrocytes showed a downregulation. Aggrecan and type II collagen deposition and GAG accumulation were high for juvenile and adult chondrocytes but not for OA chondrocytes. Similar trend was observed in the compressive moduli of the cartilage constructs generated by the three different chondrocytes. In conclusion, the juvenile, adult and OA chondrocytes showed differential responses in the 3D biomimetic hydrogels. The 3D culture model described here may also provide a useful tool to further study the molecular differences among chondrocytes from different stages, which can help elucidate the mechanisms for age-related decline in the intrinsic capacity for cartilage repair.
View details for DOI 10.1089/ten.TEA.2014.0070
View details for PubMedID 25054343
Human articular cartilage is highly susceptible to damage and has limited self-repair and regeneration potential. Cell-based strategies to engineer cartilage tissue offer a promising solution to repair articular cartilage. To select the optimal cell source for tissue repair, it is important to develop an appropriate culture platform to systematically examine the biological and biomechanical differences in the tissue-engineered cartilage by different cell sources. Here we applied a three-dimensional (3D) biomimetic hydrogel culture platform to systematically examine cartilage regeneration potential of juvenile, adult, and osteoarthritic (OA) chondrocytes. The 3D biomimetic hydrogel consisted of synthetic component poly(ethylene glycol) and bioactive component chondroitin sulfate, which provides a physiologically relevant microenvironment for in vitro culture of chondrocytes. In addition, the scaffold may be potentially used for cell delivery for cartilage repair in vivo. Cartilage tissue engineered in the scaffold can be evaluated using quantitative gene expression, immunofluorescence staining, biochemical assays, and mechanical testing. Utilizing these outcomes, we were able to characterize the differential regenerative potential of chondrocytes of varying age, both at the gene expression level and in the biochemical and biomechanical properties of the engineered cartilage tissue. The 3D culture model could be applied to investigate the molecular and functional differences among chondrocytes and progenitor cells from different stages of normal or aberrant development.
View details for DOI 10.3791/53085
View details for PubMedID 26484414
In skeletal muscle, the resting chloride conductance (gCl), due to the ClC-1 chloride channel, controls the sarcolemma electrical stability. Indeed, loss-of-function mutations in ClC-1 gene are responsible of myotonia congenita. The ClC-1 channel can be phosphorylated and inactivated by protein kinases C (PKC), but the relative contribution of each PKC isoforms is unknown. Here, we investigated on the role of PKCθ in the regulation of ClC-1 channel expression and activity in fast- and slow-twitch muscles of mouse models lacking PKCθ. Electrophysiological studies showed an increase of gCl in the PKCθ-null mice with respect to wild type. Muscle excitability was reduced accordingly. However, the expression of the ClC-1 channel, evaluated by qRT-PCR, was not modified in PKCθ-null muscles suggesting that PKCθ affects the ClC-1 activity. Pharmacological studies demonstrated that although PKCθ appreciably modulates gCl, other isoforms are still active and concur to this role. The modification of gCl in PKCθ-null muscles has caused adaptation of the expression of phenotype-specific genes, such as calcineurin and myocyte enhancer factor-2, supporting the role of PKCθ also in the settings of muscle phenotype. Importantly, the lack of PKCθ has prevented the aging-related reduction of gCl, suggesting that its modulation may represent a new strategy to contrast the aging process.
View details for DOI 10.1007/s00424-014-1495-1
View details for PubMedID 24643479
A variety of markers are invaluable for identifying and purifying stem/progenitor cells. Here we report the generation of a murine reporter line driven by Pw1 that reveals cycling and quiescent progenitor/stem cells in all adult tissues thus far examined, including the intestine, blood, testis, central nervous system, bone, skeletal muscle, and skin. Neurospheres generated from the adult PW1-reporter mouse show near 100% reporter-gene expression following a single passage. Furthermore, epidermal stem cells can be purified solely on the basis of reporter-gene expression. These cells are clonogenic, repopulate the epidermal stem-cell niches, and give rise to new hair follicles. Finally, we demonstrate that only PW1 reporter-expressing epidermal cells give rise to follicles that are capable of self-renewal following injury. Our data demonstrate that PW1 serves as an invaluable marker for competent self-renewing stem cells in a wide array of adult tissues, and the PW1-reporter mouse serves as a tool for rapid stem cell isolation and characterization.
View details for DOI 10.1073/pnas.1103873108
View details for Web of Science ID 000292635200039
View details for PubMedID 21709251
Fusion of mononucleated myoblasts to form multinucleated myofibers is an essential phase of skeletal myogenesis, which occurs during muscle development as well as during postnatal life for muscle growth, turnover, and regeneration. Many cell adhesion proteins, including integrins, have been shown to be important for myoblast fusion in vertebrates, and recently focal adhesion kinase (FAK), has been proposed as a key mediator of myoblast fusion. Here we focused on the possible role of PKC, the PKC isoform predominantly expressed in skeletal muscle, in myoblast fusion. We found that the expression of PKC is strongly up-regulated following freeze injury-induced muscle regeneration, as well as during in vitro differentiation of satellite cells (SCs; the muscle stem cells). Using both PKC knockout and muscle-specific PKC dominant-negative mutant mouse models, we observed delayed body and muscle fiber growth during the first weeks of postnatal life, when compared with wild-type (WT) mice. We also found that myofiber formation, during muscle regeneration after freeze injury, was markedly impaired in PKC mutant mice, as compared with WT. This phenotype was associated with reduced expression of the myogenic differentiation program executor, myogenin, but not with that of the SC marker Pax7. Indeed in vitro differentiation of primary muscle-derived SCs from PKC mutants resulted in the formation of thinner myotubes with reduced numbers of myonuclei and reduced fusion rate, when compared with WT cells. These effects were associated to reduced expression of the profusion genes caveolin-3 and β1D integrin and to reduced activation/phosphorylation of their up-stream regulator FAK. Indeed the exogenous expression of a constitutively active mutant form of PKC in muscle cells induced FAK phosphorylation. Moreover pharmacologically mediated full inhibition of FAK activity led to similar fusion defects in both WT and PKC-null myoblasts. We thus propose that PKC signaling regulates myoblast fusion by regulating, at least in part, FAK activity, essential for profusion gene expression.
View details for DOI 10.1091/mbc.E10-10-0821
View details for Web of Science ID 000289558600025
View details for PubMedID 21346196