Determinants of multi-scale patterning in growth plate cartilage

ABSTRACT Functional architectures of complex adaptive systems emerge by dynamic control over properties of individual components. During skeletal development, growth plate cartilage matches bone geometries to body plan requisites by spatiotemporally regulating chondrocyte actions. Bone growth potential is managed by the proximodistal patterning of chondrocyte populations into differentiation zones, while growth vectors are specified by the unique columnar arrangement of clonal groups. Chondrocyte organization at both tissue and cell levels is influenced by a cartilage-wide communication network that relies on zone-specific release and interpretation of paracrine signals. Despite genetic characterization of signaling interactions necessary for cartilage maturation, the regulatory mechanisms that couple positional information with polarized chondrocyte activities to coordinate skeletal morphogenesis remain poorly understood. Building on previous kinematic descriptions of column formation, the work contained in this dissertation suggests cytoskeletal regulation mediates crosstalk between long-range signaling and local cell behavior. Rearranging daughter chondrocytes specifically recruit actomyosin contractility to cortical surfaces, indicating a primary role for the actin cytoskeleton as the engine powering column formation kinetics. Disrupted chondrocyte contractility patterns are observed after genetic perturbation of planar cell polarity signaling, and after inhibiting integrin extracellular matrix binding, implicating actomyosin as a sensor able to integrate global with local signaling cues. To gain greater analytical control towards dissecting the mechanochemical patterning systems underlying cartilage architecture, an alginate hydrogel-based model of growth plate was developed. Daughter chondrocytes encapsulated in alginate beads deposit extracellular matrix in anisotropic and hierarchical configurations that resemble myosin localization in vivo, hinting cytoskeletal forces may sculpt the solid-state environment. Single-cell transcriptomic analysis of chondrocytes stimulated with recombinant ligands demonstrates the functionality of the IHH/PTHrP circuit in alginate beads, and points towards a novel role for PTHrP signaling gradients in transcriptional regulation of cytoskeletal and ECM proteins. Basal bead cultures tend towards resting/proliferative phenotypes driven by endogenous PTHrP expression, but activating IHH signaling induces position-dependent gene expression, consistent with a model of zone formation where concentration gradients generate spatial cues. Together, the work suggests that in addition to regulating chondrocyte differentiation, the tissue-wide signaling network in cartilage can influence cell-matrix interactions that may be important for cell behavior, and presents a novel culture model that can be used for future studies investigating how chondrocytes discern positional information to shape the growing tissue

Use of a three-dimensional in vitro alginate hydrogel culture model to direct zonal formation of growth plate cartilage

Growth plate cartilage is found at the ends of long bones, and is responsible for the growth of the bones as a person is developing. The architecture of this growth plate is very specific and contributes to proper function to allow for bone growth. Although there are many factors known to be involved in the formation of the growth plate and its proper regulation, the exact mechanisms involved in these processes are not fully understood. So far, previous attempts to recapitulate a functioning growth plate in vitro have been unsuccessful. In this study, a new method to study the growth plate and the mechanisms involved in its formation was developed using an in vitro cell culture system made of alginate hydrogel scaffolds. Chondrocytes isolated from neonatal mouse growth plates were encapsulated within hydrogel beads and cultured. Please click Additional Files below to see the full abstract

A Tunable, Three-Dimensional \u3ci\u3eIn Vitro\u3c/i\u3e Culture Model of Growth Plate Cartilage Using Alginate Hydrogel Scaffolds

Defining the final size and geometry of engineered tissues through precise control of the scalar and vector components of tissue growth is a necessary benchmark for regenerative medicine, but it has proved to be a significant challenge for tissue engineers. The growth plate cartilage that promotes elongation of the long bones is a good model system for studying morphogenetic mechanisms because cartilage is composed of a single cell type, the chondrocyte; chondrocytes are readily maintained in culture; and growth trajectory is predominately in a single vector. In this cartilage, growth is generated via a differentiation program that is spatially and temporally regulated by an interconnected network composed of long- and short-range signaling mechanisms that together result in the formation of functionally distinct cellular zones. To facilitate investigation of the mechanisms underlying anisotropic growth, we developed an in vitro model of the growth plate cartilage by using neonatal mouse growth plate chondrocytes encapsulated in alginate hydrogel beads. In bead cultures, encapsulated chondrocytes showed high viability, cartilage matrix deposition, low levels of chondrocyte hypertrophy, and a progressive increase in cell proliferation over 7 days in culture. Exogenous factors were used to test functionality of the parathyroid-related protein–Indian hedgehog (PTHrP-IHH) signaling interaction, which is a crucial feedback loop for regulation of growth. Consistent with in vivo observations, exogenous PTHrP stimulated cell proliferation and inhibited hypertrophy, whereas IHH signaling stimulated chondrocyte hypertrophy. Importantly, the treatment of alginate bead cultures with IHH or thyroxine resulted in formation of a discrete domain of hypertrophic cells that mimics tissue architecture of native growth plate cartilage. Together, these studies are the first demonstration of a tunable in vitro system to model the signaling network interactions that are required to induce zonal architecture in growth plate chondrocytes, which could also potentially be used to grow cartilage cultures of specific geometries to meet personalized patient needs

Prediction of neo-adjuvant chemotherapy response in bladder cancer: the impact of clinical parameters and routine biomarkers

PurposeTo investigate the role of clinical parameters and immunohistochemical (IHC) biomarkers in their feasibility to predict the effect of neo-adjuvant chemotherapy (NAC) in patients with muscle-invasive urothelial bladder cancer (MIBC).Materials and methodsThe first 76 consecutive patients with MIBC treated with NAC and radical cystectomy in two University hospitals in Finland between 2008 and 2013 were chosen for this study. After excluding patients with non-urothelial cancer, less than two cycles of chemotherapy, no tissue material for IHC analysis or non-muscle-invasive bladder cancer in re-review, 59 patients were included in the final analysis. A tissue microarray block was constructed from the transurethral resection samples and IHC stainings of Ki-67, p53, Her-2 and EGFR were made. The correlations between histological features in transurethral resection samples and immune-histochemical stainings were calculated. The associations of clinicopathological parameters and IHC stainings with NAC response were evaluated. Factors affecting survival were estimated.ResultsThe complete response rate after NAC was 44%. A higher number of chemotherapy cycles was associated with better response to neo-adjuvant chemotherapy. No response to neo-adjuvant chemotherapy and female gender was associated with decreased cancer-specific survival. The IHC stainings used failed to show an association with neo-adjuvant chemotherapy response and overall or cancer specific survival.ConclusionsPatients who do not respond to neo-adjuvant chemotherapy do significantly worse than responders. This study could not find clinical tools to distinguish responders from non-responders. Further studies preferably with larger cohorts addressing this issue are warranted to improve the selection of patients for neo-adjuvant chemotherapy.</p

Oriented clonal cell dynamics enables accurate growth and shaping of vertebrate cartilage.

Cartilaginous structures are at the core of embryo growth and shaping before the bone forms. Here we report a novel principle of vertebrate cartilage growth that is based on introducing transversally-oriented clones into pre-existing cartilage. This mechanism of growth uncouples the lateral expansion of curved cartilaginous sheets from the control of cartilage thickness, a process which might be the evolutionary mechanism underlying adaptations of facial shape. In rod-shaped cartilage structures (Meckel, ribs and skeletal elements in developing limbs), the transverse integration of clonal columns determines the well-defined diameter and resulting rod-like morphology. We were able to alter cartilage shape by experimentally manipulating clonal geometries. Using in silico modeling, we discovered that anisotropic proliferation might explain cartilage bending and groove formation at the macro-scale

A Tunable, Three-Dimensional in vitro Culture Model of Growth Plate Cartilage Using Alginate Hydrogel Scaffolds

Defining the final size and geometry of engineered tissues through precise control of the scalar and vector components of tissue growth is a necessary benchmark for regenerative medicine, but it has proved to be a significant challenge for tissue engineers. The growth plate cartilage that promotes elongation of the long bones is a good model system for studying morphogenetic mechanisms because cartilage is composed of a single cell type, the chondrocyte; chondrocytes are readily maintained in culture; and growth trajectory is predominately in a single vector. In this cartilage, growth is generated via a differentiation program that is spatially and temporally regulated by an interconnected network composed of long- and short-range signaling mechanisms that together result in the formation of functionally distinct cellular zones. To facilitate investigation of the mechanisms underlying anisotropic growth, we developed an in vitro model of the growth plate cartilage by using neonatal mouse growth plate chondrocytes encapsulated in alginate hydrogel beads. In bead cultures, encapsulated chondrocytes showed high viability, cartilage matrix deposition, low levels of chondrocyte hypertrophy, and a progressive increase in cell proliferation over 7 days in culture. Exogenous factors were used to test functionality of the parathyroid-related protein–Indian hedgehog (PTHrP-IHH) signaling interaction, which is a crucial feedback loop for regulation of growth. Consistent with in vivo observations, exogenous PTHrP stimulated cell proliferation and inhibited hypertrophy, whereas IHH signaling stimulated chondrocyte hypertrophy. Importantly, the treatment of alginate bead cultures with IHH or thyroxine resulted in formation of a discrete domain of hypertrophic cells that mimics tissue architecture of native growth plate cartilage. Together, these studies are the first demonstration of a tunable in vitro system to model the signaling network interactions that are required to induce zonal architecture in growth plate chondrocytes, which could also potentially be used to grow cartilage cultures of specific geometries to meet personalized patient needs. Includes Supplementary materials

A Tunable, Three-Dimensional \u3ci\u3eIn Vitro\u3c/i\u3e Culture Model of Growth Plate Cartilage Using Alginate Hydrogel Scaffolds

Defining the final size and geometry of engineered tissues through precise control of the scalar and vector components of tissue growth is a necessary benchmark for regenerative medicine, but it has proved to be a significant challenge for tissue engineers. The growth plate cartilage that promotes elongation of the long bones is a good model system for studying morphogenetic mechanisms because cartilage is composed of a single cell type, the chondrocyte; chondrocytes are readily maintained in culture; and growth trajectory is predominately in a single vector. In this cartilage, growth is generated via a differentiation program that is spatially and temporally regulated by an interconnected network composed of long- and short-range signaling mechanisms that together result in the formation of functionally distinct cellular zones. To facilitate investigation of the mechanisms underlying anisotropic growth, we developed an in vitro model of the growth plate cartilage by using neonatal mouse growth plate chondrocytes encapsulated in alginate hydrogel beads. In bead cultures, encapsulated chondrocytes showed high viability, cartilage matrix deposition, low levels of chondrocyte hypertrophy, and a progressive increase in cell proliferation over 7 days in culture. Exogenous factors were used to test functionality of the parathyroid-related protein–Indian hedgehog (PTHrP-IHH) signaling interaction, which is a crucial feedback loop for regulation of growth. Consistent with in vivo observations, exogenous PTHrP stimulated cell proliferation and inhibited hypertrophy, whereas IHH signaling stimulated chondrocyte hypertrophy. Importantly, the treatment of alginate bead cultures with IHH or thyroxine resulted in formation of a discrete domain of hypertrophic cells that mimics tissue architecture of native growth plate cartilage. Together, these studies are the first demonstration of a tunable in vitro system to model the signaling network interactions that are required to induce zonal architecture in growth plate chondrocytes, which could also potentially be used to grow cartilage cultures of specific geometries to meet personalized patient needs

A branching model of lineage differentiation underpinning the neurogenic potential of enteric glia

Abstract Glial cells have been proposed as a source of neural progenitors, but the mechanisms underpinning the neurogenic potential of adult glia are not known. Using single cell transcriptomic profiling, we show that enteric glial cells represent a cell state attained by autonomic neural crest cells as they transition along a linear differentiation trajectory that allows them to retain neurogenic potential while acquiring mature glial functions. Key neurogenic loci in early enteric nervous system progenitors remain in open chromatin configuration in mature enteric glia, thus facilitating neuronal differentiation under appropriate conditions. Molecular profiling and gene targeting of enteric glial cells in a cell culture model of enteric neurogenesis and a gut injury model demonstrate that neuronal differentiation of glia is driven by transcriptional programs employed in vivo by early progenitors. Our work provides mechanistic insight into the regulatory landscape underpinning the development of intestinal neural circuits and generates a platform for advancing glial cells as therapeutic agents for the treatment of neural deficits