Syndecan-1 and -4 influence Wnt signaling and cell migration in human breast cancers.

Heparan sulfate proteoglycans (HSPGs) participate in numerous normal and pathophysiological cellular functions. HSPGs are crucial components of the extracellular matrix (ECM) binding signalling molecules such as fibroblast growth factors (FGF) and Wnts to mediate various cellular processes including cell proliferation, migration, and cancer invasion. The syndecans (SDCs1-4) are a major family of four HSPGs, implicated in the development of breast carcinomas. This study examined syndecan-1 (SDC1) and syndecan-4 (SDC4; SDC1/4) in breast cancer (BC) in vitro cell models and their role in tumorigenesis. Gene expression of HSPG core proteins, biosynthesis and modification enzymes along with Wnt/FGF morphogen pathway components were examined following inhibition of SDC1 and SDC4 via small interfering RNA (siRNA), and enhancement of HSPGs via addition of heparin and FGF. siRNAs knockdowns (KDs) were performed in the MCF-7 (lowly invasive and poorly metastatic) and the MDA-MB-231 (highly invasive and metastatic) human BC cell lines. Significantly decreased gene expression of SDC1 and SDC4 was observed in both cell lines following KD. Additionally, via gene expression analysis, downregulation of SDC1/4 decreased the biosynthesis of heparan sulfate modification enzymes and reduced expression of Wnt signalling molecules. Following the enhancement/inhibition of HSPGs via heparin/siRNA treatment, heparin increased the migratory characteristics of MCF-7 cells while KD of SDC1 increased cell migration in both MCF-7 and MDA-MB-231 cells when compared to scramble negative control conditions. Our findings suggest that a niche-specific function exists for SDC1/4 in the BC microenvironment, mediating Wnt signalling cascades and potentially regulating migration of BC cells.

Three-Dimensional Human Neural Stem Cell Models to Mimic Heparan Sulfate Proteoglycans and the Neural Niche.

Heparan sulfate proteoglycans (HSPGs) are a diverse family of polysaccharides, consisting of a core protein with glycosaminoglycan (GAG) side chains attached. The heterogeneous GAG side-chain carbohydrates consist of repeating disaccharides, with each side chain possessing a specific sulfation pattern. It is the variable sulfation pattern that allows HSPGs to interact with numerous ligands including growth factors, cytokines, chemokines, morphogens, extracellular matrix (ECM) glycoproteins, collagens, enzymes, and lipases. HSPGs are classified according to their localization within an individual cell, and include the membrane bound syndecans (SDCs) and glypicans (GPCs), with perlecan, agrin, and type-XVIII collagen secreted into the ECM. The stem cell niche is defined as the environment that circumscribes stem cells when they are in their naïve state, and includes the ECM, which provides a complex contribution to various biological processes during development and throughout life. These contributions include facilitating cell adhesion, proliferation, migration, differentiation, specification, and cell survival. In contrast, HSPGs play an anticoagulant role in thrombosis through being present on the luminal surface of cells, while also playing roles in the stimulation and inhibition of angiogenesis, highlighting their varied and systemic roles in cellular control. To fully understand the complexities of cell-cell and cell-matrix interactions, three-dimensional (3D) models such as hydrogels offer researchers exciting opportunities, such as controllable 3D in vitro environments, that more readily mimic the in vivo/in situ microenvironment. This review examines our current knowledge of HSPGs in the stem cell niche, human stem cell models, and their role in the development of 3D models that mimic the in vivo neural ECM.

Syndecan-1 Facilitates the Human Mesenchymal Stem Cell Osteo-Adipogenic Balance.

Bone marrow-derived human mesenchymal stems cells (hMSCs) are precursors to adipocyte and osteoblast lineage cells. Dysregulation of the osteo-adipogenic balance has been implicated in pathological conditions involving bone loss. Heparan sulfate proteoglycans (HSPGs) such as cell membrane-bound syndecans (SDCs) and glypicans (GPCs) mediate hMSC lineage differentiation and with syndecan-1 (SDC-1) reported in both adipogenesis and osteogenesis, these macromolecules are potential regulators of the osteo-adipogenic balance. Here, we disrupted the HSPG profile in primary hMSC cultures via temporal knockdown (KD) of SDC-1 using RNA interference (RNAi) in undifferentiated, osteogenic and adipogenic differentiated hMSCs. SDC-1 KD cultures were examined for osteogenic and adipogenic lineage markers along with changes in HSPG profile and common signalling pathways implicated in hMSC lineage fate. Undifferentiated hMSC SDC-1 KD cultures exhibited a pro-adipogenic phenotype with subsequent osteogenic differentiation demonstrating enhanced maturation of osteoblasts. In cultures where SDC-1 KD was performed following initiation of differentiation, increased adipogenic gene and protein marker expression along with increased Oil Red O staining identified enhanced adipogenesis, with impaired osteogenesis also observed in these cultures. These findings implicate SDC-1 as a facilitator of the hMSC osteo-adipogenic balance during early induction of lineage differentiation.

HSPGs glypican-1 and glypican-4 are human neuronal proteins characteristic of different neural phenotypes.

Generating neurons from human stem cells has potential for brain damage therapy and neurogenesis modeling, but current efficacy is limited by culture heterogeneity and the lack of markers. We have previously reported the heparan sulfate proteoglycans (HSPGs) glypican-1 (GPC1) and -4 (GPC4) as the markers of lineage-specific human neural stem cells (hNSCs) and mediators of hNSC lineage potential. Here, we further examined phenotypical characteristics and GPC1 and GPC4 during neural differentiation of hNSCs in the presence of two neurogenic growth factors reported to bind to heparan sulfate: brain-derived neurotrophic factor (BDNF) and platelet-derived growth factor-B (PDGF-B). In hNSC neural cultures, GPC1 and GPC4 were expressed along neurites and cell bodies in long-term (40-60 days) neural differentiation cultures demonstrating the areas of differential localization-suggesting potentially different functions. Neural differentiation cultures in the presence of BDNF or PDGF-B generated phenotypically different neural cells with BDNF treatment associated with higher GPC4 versus GPC1 expression, increased heterogeneity, and differential neuron subtype marker expression to PDGF-B cultures. PDGF-B cultures exhibited higher levels of spontaneous activity and reduced heterogeneity over long-term culture associated with decreased GPC4. Untreated neural cultures were highly variable, supporting the use of neuroregulatory growth factors for guided differentiation. Targeted siRNA downregulation of GPC1/4 reduced neural differentiation markers and altered response to exogenous BDNF and PDGF-B. This work confirms GPC1 and GPC4 as regulators of human neural differentiation and supports their use as novel markers of neural cell characterization.