Phil G. Campbell

Cell Population Tracking and Lineage Construction with Spatiotemporal Context

Automated visual-tracking of cell populations in vitro using time-lapse phase contrast microscopy enables quantitative, systematic, and high-throughput measurements of cell behaviors. These measurements include the spatiotemporal quantification of cell migration, mitosis, apoptosis, and the reconstruction of cell lineages. The combination of low signal-to-noise ratio of phase contrast microscopy images, high and varying densities of the cell cultures, topological complexities of cell shapes, and wide range of cell behaviors poses many challenges to existing tracking techniques. This paper presents a fully automated multi-target tracking system that can efficiently cope with these challenges while simultaneously tracking and analyzing thousands of cells observed using time-lapse phase contrast microscopy. The system combines bottom-up and top-down image analysis by integrating multiple collaborative modules, which exploit a fast geometric active contour tracker in conjunction with adaptive interacting multiple models (IMM) motion filtering and spatiotemporal trajectory optimization. The system, which was tested using a variety of cell populations, achieved tracking accuracy in the range of 86.9-92.5%.

Microenvironments engineered by inkjet bioprinting spatially direct adult stem cells toward muscle- and bone-like subpopulations

In vivo, growth factors exist both as soluble and as solid‐phase molecules, immobilized to cell surfaces and within the extracellular matrix. We used this rationale to develop more biologically relevant approaches to study stem cell behaviors. We engineered stem cell microenvironments using inkjet bioprinting technology to create spatially defined patterns of immobilized growth factors. Using this approach, we engineered cell fate toward the osteogenic lineage in register to printed patterns of bone morphogenetic protein (BMP) 2 contained within a population of primary muscle‐derived stem cells (MDSCs) isolated from adult mice. This patterning approach was conducive to patterning the MDSCs into subpopulations of osteogenic or myogenic cells simultaneously on the same chip. When cells were cultured under myogenic conditions on BMP‐2 patterns, cells on pattern differentiated toward the osteogenic lineage, whereas cells off pattern differentiated toward the myogenic lineage. Time‐lapse microscopy was used to visualize the formation of multinucleated myotubes, and immunocytochemistry was used to demonstrate expression of myosin heavy chain (fast) in cells off BMP‐2 pattern. This work provides proof‐of‐concept for engineering spatially controlled multilineage differentiation of stem cells using patterns of immobilized growth factors. This approach may be useful for understanding cell behaviors to immobilized biological patterns and could have potential applications for regenerative medicine.

Phosphophoryn Regulates the Gene Expression and Differentiation of NIH3T3, MC3T3-E1, and Human Mesenchymal Stem Cells via the Integrin/MAPK Signaling Pathway

Extracellular matrix proteins (ECMs) serve as both a structural support for cells and a dynamic biochemical network that directs cellular activities. ECM proteins such as those of the SIBLING family (small integrin-binding ligand glycoprotein) could possess inherent growth factor activity. In this study, we demonstrate that exon 5 of dentin matrix protein 3 (phosphophoryn (PP)), a non-collagenous dentin ECM protein and SIBLING protein family member, up-regulates osteoblast marker genes in primary human adult mesenchymal stem cells (hMSCs), a mouse osteoblastic cell line (MC3T3-E1), and a mouse fibroblastic cell line (NIH3T3). Quantitative real-time PCR technology was used to quantify gene expression levels of bone markers such as Runx2, Osx (Osterix), bone/liver/kidney Alp (alkaline phosphatase), Ocn (osteocalcin), and Bsp (bone sialoprotein) in response to recombinant PP and stably transfected PP. PP up-regulated Runx2, Osx, and Ocn gene expression. PP increased OCN protein production in hMSCs and MC3T3-E1. ALP activity and calcium deposition was increased by PP in hMSC. Furthermore, an αvβ3 integrin-blocking antibody significantly inhibited recombinant PP-induced expression of Runx2 in hMSCs, suggesting that signaling by PP is mediated through the integrin pathway. PP was also shown to activate p38, ERK1/2, and JNK, three components of the MAPK pathway. These data demonstrate a novel signaling function for PP in cell differentiation beyond the hypothesized role of PP in biomineralization.

Osx transcriptional regulation is mediated by additional pathways to BMP2/Smad signaling

Bone morphogenetic protein (BMP)‐2 induces Osterix (Osx) in mouse C2C12 cells and chondrocytes. Genetic studies place Osx downstream to the BMP‐2/Smad/Runx2 signaling pathway; however, limited information is available on the mediators of Osx expression in osteoblast lineage commitment. Several lines of research implicate the presence of Runx2‐independent ossification. Therefore, the purpose of this study was to identify possible mediators of Osx expression beyond the BMP‐2/Smad pathway. Using real‐time RT‐PCR, we showed upregulation of Osx in response to BMP‐2 in human mesenchymal stem cells (hMSC). Insulin‐like growth factor (IGF)‐I upregulated Osx, but not Runx2. Further, IGF‐I in combination with BMP‐2 was synergistic for Osx, suggesting a pathway beyond Smad signaling. MAPK was tested as a common mediator across BMP‐2 and IGF‐I signaling pathways. Inhibition of MAPK component ERK1/2 did not affect Runx2 gene expression, but inhibited Osx expression and matrix mineralization. BMP‐2‐mediated Osx expression was downregulated in response to p38 inhibition. We therefore conclude that during osteogenic lineage progression, in addition to the BMP‐2/Smad pathway, IGF‐I and MAPK signaling may mediate Osx.

Tissue engineering with the aid of inkjet printers

Tissue engineering holds the promise to create revolutionary new therapies for tissue and organ regeneration. This emerging field is extremely broad and eclectic in its various approaches. However, all strategies being developed are based on the therapeutic delivery of one or more of the following types of tissue building-blocks: cells; extracellular matrices or scaffolds; and hormones or other signaling molecules. So far, most work has used essentially homogenous combinations of these components, with subsequent self-organization to impart some level of tissue functionality occurring during in vitro culture or after transplantation. Emerging ‘bioprinting’ methodologies are being investigated to create tissue engineered constructs initially with more defined spatial organization, motivated by the hypothesis that biomimetic patterns can achieve improved therapeutic outcomes. Bioprinting based on inkjet and related printing technologies can be used to fabricate persistent biomimetic patterns that can be used both to study the underlying biology of tissue regeneration and potentially be translated into effective clinical therapies. However, recapitulating nature at even the most primitive levels such that printed cells, extracellular matrices and hormones become integrated into hierarchical, spatially organized three-dimensional tissue structures with appropriate functionality remains a significant challenge.

Bioprinting of growth factors onto aligned sub-micron fibrous scaffolds for simultaneous control of cell differentiation and alignment

The capability to spatially control stem cell orientation and differentiation simultaneously using a combination of geometric cues that mimic structural aspects of native extracellular matrix (ECM) and biochemical cues such as ECM-bound growth factors (GFs) is important for understanding the organization and function of musculoskeletal tissues. Herein, oriented sub-micron fibers, which are morphologically similar to musculoskeletal ECM, were spatially patterned with GFs using an inkjet-based bioprinter to create geometric and biochemical cues that direct musculoskeletal cell alignment and differentiation in vitro in registration with fiber orientation and printed patterns, respectively. Sub-micron polystyrene fibers (diameter ~ 655 nm) were fabricated using a Spinneret-based Tunable Engineered Parameters (STEP) technique and coated with serum or fibrin. The fibers were subsequently patterned with tendon-promoting fibroblast growth factor-2 (FGF-2) or bone-promoting bone morphogenetic protein-2 (BMP-2) prior to seeding with mouse C2C12 myoblasts or C3H10T1/2 mesenchymal fibroblasts. Unprinted regions of STEP fibers showed myocyte differentiation while printed FGF-2 and BMP-2 patterns promoted tenocyte and osteoblast fates, respectively, and inhibited myocyte differentiation. Additionally, cells aligned along the fiber length. Functionalizing oriented sub-micron fibers with printed GFs provides instructive cues to spatially control cell fate and alignment to mimic native tissue organization and may have applications in regenerative medicine.

Online Tracking of Migrating and Proliferating Cells Imaged with Phase-Contrast Microscopy

Automated visual-tracking of cell population in vitro using phase-contrast time-lapse microscopy is vital for the quantitative and systematic study of cell behaviors, including spatiotemporal quantification of migration, proliferation, and apoptosis. The low image quality, high and varying density of the cell culture, and the complexity of cell behaviors pose many challenges to existing tracking techniques. This paper presents a fully-automated multitarget tracking system that can simultaneously track hundreds of cells and efficiently cope with these challenges. The approach exploits a fast topology-constrained level-set method in conjunction with a stochastic motion filter, with a careful formulation that makes it suitable for real-time tracking during acquisition. Our methodology was applied to human tissue cell tracking in vitro under various imaging conditions and yielded a 88.4% tracking accuracy.

Extracellular Matrix-mediated Signaling by Dentin Phosphophoryn Involves Activation of the Smad Pathway Independent of Bone Morphogenetic Protein

Cells have ingenious mechanisms for interpreting complex signals from their external microenvironment. Previously, we have shown that phosphophoryn (PP) regulates the expression of bone/dentin marker genes via the integrin/MAPK signaling pathway (Jadlowiec, J., Koch, H., Zhang, X., Campbell, P. G., Seyedain, M., and Sfeir, C. (2004) J. Biol. Chem. 279, 53323–53330). We hypothesize that other signaling pathways important for mineralized tissue morphogenesis such as the Smad pathway could be involved in PP signaling. We determined activation of the Smad pathway in human adult mesenchymal stem cells following treatment with recombinant PP (rPP). We observed that PP enhanced phosphorylation of Smad1 within 30 min and Smad1 translocation to the nucleus within 1 h. PP up-regulated the expression of Smad1 target genes, Smad6, Dlx5, and Runx2. The timing of PP activation of Smad1 implies this is a direct effect; however, we also investigated the possible involvement of bone morphogenetic proteins in PP stimulation of the Smad pathway. PP was shown to up-regulate Bmp-2 gene expression 12 h post-treatment with PP, which is much later than initial detection of Smad1 phosphorylation at 30 min. Furthermore, addition of Noggin did not block Smad1 phosphorylation by PP. We propose that PP could signal via the Smad pathway by either directly stimulating the phosphorylation of Smad1 via integrins or other mechanisms. These might include integrin/bone morphogenetic protein receptor interactions or involvement of PP with other growth factors leading to the modulation of intracellular signaling. It is noteworthy that a non-transforming growth factor-β family member activates the Smad pathway. The role of PP in regulating the Smad pathway raises very interesting questions regarding the role of PP during bone and tooth development.

The influence of polymer blend composition on the degradation of polymer/hydroxyapatite biomaterials

The in vitro degradation of biodegradable polymer/ceramic composites was assessed in two different environments under both static and pseudodynamic conditions. The blends, consisting of polycaprolactone, poly(lactic-co-glycolic acid), and hydroxyapatite, have potential use in bone tissue engineering applications, thus it is essential to establish a standardized method of characterizing the degradation of new biomaterials. In this study, the variation in polymer blend ratio was examined to observe a change in degradation rate. The porous blends were degraded in water and serum-containing media. A previous study examined in vitro degradation in serum-free buffer. Molecular weight loss, gravimetric weight loss, pH changes and morphological changes were evaluated. The changes in porosity were observed with scanning electron microscopy and quantitatively assessed using image analysis. There was a significant difference in molecular weight loss and gravimetric weight loss between the blends after 10 weeks in vitro. Blends containing the greatest amount of poly(lactic-co-glycolic acid) degraded most rapidly.

Role of RhoA-Specific Guanine Exchange Factors in Regulation of Endomitosis in Megakaryocytes

Polyploidization can precede the development of aneuploidy in cancer. Polyploidization in megakaryocytes (Mks), in contrast, is a highly controlled developmental process critical for efficient platelet production via unknown mechanisms. Using primary cells, we demonstrate that the guanine exchange factors GEF-H1 and ECT2, which are often overexpressed in cancer and are essential for RhoA activation during cytokinesis, must be downregulated for Mk polyploidization. The first (2N-4N) endomitotic cycle requires GEF-H1 downregulation, whereas subsequent cycles (>4N) require ECT2 downregulation. Exogenous expression of both GEF-H1 and ECT2 prevents endomitosis, resulting in proliferation of 2N Mks. Furthermore, we have shown that the mechanism by which polyploidization is prevented in Mks lacking Mkl1, which is mutated in megakaryocytic leukemia, is via elevated GEF-H1 expression; shRNA-mediated GEF-H1 knockdown alone rescues this ploidy defect. These mechanistic insights enhance our understanding of normal versus malignant megakaryocytopoiesis, as well as aberrant mitosis in aneuploid cancers.