Expression of the proteoglycan SPOCK during mouse embryo development

Glycosaminoglycans, Instructive Biomolecules That Regulate Cellular Activity and Synaptic Neuronal Control of Specific Tissue Functional Properties

Glycosaminoglycans (GAGs) are a diverse family of ancient biomolecules that evolved over millennia as key components in the glycocalyx that surrounds all cells. GAGs have molecular recognition and cell instructive properties when attached to cell surface and extracellular matrix (ECM) proteoglycans (PGs), which act as effector molecules that regulate cellular behavior. The perception of mechanical cues which arise from perturbations in the ECM microenvironment allow the cell to undertake appropriate biosynthetic responses to maintain ECM composition and tissue function. ECM PGs substituted with GAGs provide structural support to weight-bearing tissues and an ability to withstand shear forces in some tissue contexts. This review outlines the structural complexity of GAGs and the diverse functional properties they convey to cellular and ECM PGs. PGs have important roles in cartilaginous weight-bearing tissues and fibrocartilages subject to tension and high shear forces and also have important roles in vascular and neural tissues. Specific PGs have roles in synaptic stabilization and convey specificity and plasticity in the regulation of neurophysiological responses in the CNS/PNS that control tissue function. A better understanding of GAG instructional roles over cellular behavior may be insightful for the development of GAG-based biotherapeutics designed to treat tissue dysfunction in disease processes and in novel tissue repair strategies following trauma. GAGs have a significant level of sophistication over the control of cellular behavior in many tissue contexts, which needs to be fully deciphered in order to achieve a useful therapeutic product. GAG biotherapeutics offers exciting opportunities in the modern glycomics arena.

Molecular profiling of the hippocampus of children with autism spectrum disorder

Several lines of evidence point to a key role of the hippocampus in Autism Spectrum Disorders (ASD). Altered hippocampal volume and deficits in memory for person and emotion related stimuli have been reported, along with enhanced ability for declarative memories. Mouse models have demonstrated a critical role of the hippocampus in social memory dysfunction, associated with ASD, together with decreased synaptic plasticity. Chondroitin sulfate proteoglycans (CSPGs), a family of extracellular matrix molecules, represent a potential key link between neurodevelopment, synaptic plasticity, and immune system signaling. There is a lack of information regarding the molecular pathology of the hippocampus in ASD. We conducted RNAseq profiling on postmortem human brain samples containing the hippocampus from male children with ASD (n = 7) and normal male children (3-14 yrs old), (n = 6) from the NIH NeuroBioBank. Gene expression profiling analysis implicated molecular pathways involved in extracellular matrix organization, neurodevelopment, synaptic regulation, and immune system signaling. qRT-PCR and Western blotting were used to confirm several of the top markers identified. The CSPG protein BCAN was examined with multiplex immunofluorescence to analyze cell-type specific expression of BCAN and astrocyte morphology. We observed decreased expression of synaptic proteins PSD95 (p < 0.02) and SYN1 (p < 0.02), increased expression of the extracellular matrix (ECM) protease MMP9 (p < 0.03), and decreased expression of MEF2C (p < 0.03). We also observed increased BCAN expression with astrocytes in children with ASD, together with altered astrocyte morphology. Our results point to alterations in immune system signaling, glia cell differentiation, and synaptic signaling in the hippocampus of children with ASD, together with alterations in extracellular matrix molecules. Furthermore, our results demonstrate altered expression of genes implicated in genetic studies of ASD including SYN1 and MEF2C.

The secreted neuronal signal Spock1 promotes blood-brain barrier development

The blood-brain barrier (BBB) is a unique set of properties of the brain vasculature which severely restrict its permeability to proteins and small molecules. Classic chick-quail chimera studies have shown that these properties are not intrinsic to the brain vasculature but rather are induced by surrounding neural tissue. Here, we identify Spock1 as a candidate neuronal signal for regulating BBB permeability in zebrafish and mice. Mosaic genetic analysis shows that neuronally expressed Spock1 is cell non-autonomously required for a functional BBB. Leakage in spock1 mutants is associated with altered extracellular matrix (ECM), increased endothelial transcytosis, and altered pericyte-endothelial interactions. Furthermore, a single dose of recombinant SPOCK1 partially restores BBB function in spock1 mutants by quenching gelatinase activity and restoring vascular expression of BBB genes including mcamb. These analyses support a model in which neuronally secreted Spock1 initiates BBB properties by altering the ECM, thereby regulating pericyte-endothelial interactions and downstream vascular gene expression.

Downregulation of Sparc-like protein 1 during cisplatin-induced inhibition of myogenic differentiation of C2C12 myoblasts

Patients with cancer often experience muscle atrophy, which worsens their prognosis. Decreased muscle regenerative capacity plays an important role in the complex processes involved in muscle atrophy. Administration of cisplatin, a cancer chemotherapeutic agent, has been implicated as a cause of muscle atrophy. In this study, we examined whether cisplatin affects the differentiation of myoblasts into myotubes. We treated C2C12 myoblasts with a differentiation medium containing cisplatin and its vehicle during for 8 days and observed the changes in the expression of myosin heavy chain (MyHC) and myogenin in the myoblasts. Cisplatin was injected in mice for 4 consecutive days; on Day 5, the mice quadriceps muscles were sampled and examined. The expression of MyHCs increased and that of myogenin decreased after cisplatin treatment. The secretion of acidic cysteine-rich proteins (e.g., Sparc proteins) reportedly promotes C2C12 myoblast differentiation. Therefore, we investigated the Sparc family gene expression during myogenesis in C2C12 myoblasts after cisplatin treatment. Of all the genes investigated, Sparc-like protein 1 (Sparcl1) expression was significantly suppressed by cisplatin on Days 4-8. Simultaneous treatment with recombinant mouse Sparcl1 almost inhibited the cisplatin-induced suppression of total MyHC and myogenin protein levels. Moreover, Sparcl1 expression decreased in the skeletal muscles of mice, leading to cisplatin-induced muscle atrophy. Our results suggest that cisplatin-induced myogenesis suppression causes muscle atrophy and inhibits the expression of Sparcl1, which promotes C2C12 cell differentiation during myogenesis.

SPOCK1 with unexpected function. The start of a new career

SPOCK1, 2 and 3 are considered as matricellular proteoglycans without structural role. Their functions are only partly elucidated. SPOCK1 was detected in the brain as a member of the neural synapses, then in the neuromuscular junctions. It plays a role in the regulation of blood-brain barrier. Its best characterized activity was its oncogenic potential discovered in 2012. Its deleterious effect on tumor progression was detected on 36 different types of tumors by the end of 2020. However, its mode of actions is still not completely understood. Furthermore, even less was discovered about its physiological function. The fact that it was found to localize in the mitochondria and interfered with the lipid metabolism indicated, that the full discovery of SPOCK1 still waiting for us.

SPOCK1 Involvement in Epithelial-to-Mesenchymal Transition: A New Target in Cancer Therapy?

Background

Cancer metastasis is the main obstacle to increasing the lifespan of cancer patients. Epithelial-to-mesenchymal transition (EMT) plays a significant role in oncogenic processes, including tumor invasion, intravasation, and micrometastasis formation, and is especially critical for cancer invasion and metastasis. The extracellular matrix (ECM) plays a crucial role in the occurrence of EMT corresponding to the change in adhesion between cells and matrices.

Conclusion

SPOCK1 is a critical regulator of the ECM and mediates EMT in cancer cells. This suggests an important role for SPOCK1 in tumorigenesis, migration and invasion. SPOCK1 is a critical regulator of some processes involved in cancer progression, including cancer cell proliferation, apoptosis and migration. Herein, the functions of SPOCK1 in cancer progression are expounded, revealing the association between SPOCK1 and EMT in cancer metastasis. SPOCK1 is a positive downstream regulator of transforming growth factor-β, and SPOCK1-mediated EMT regulates invasion and metastasis through the Wnt/β-catenin pathway and PI3K/Akt signaling pathway. It is of significance that SPOCK1 may be an attractive prognostic biomarker and therapeutic target in cancer treatment.

A Genome-Wide Association Study Identifies Genetic Variants Associated with Mathematics Ability

Mathematics ability is a complex cognitive trait with polygenic heritability. Genome-wide association study (GWAS) has been an effective approach to investigate genetic components underlying mathematic ability. Although previous studies reported several candidate genetic variants, none of them exceeded genome-wide significant threshold in general populations. Herein, we performed GWAS in Chinese elementary school students to identify potential genetic variants associated with mathematics ability. The discovery stage included 494 and 504 individuals from two independent cohorts respectively. The replication stage included another cohort of 599 individuals. In total, 28 of 81 candidate SNPs that met validation criteria were further replicated. Combined meta-analysis of three cohorts identified four SNPs (rs1012694, rs11743006, rs17778739 and rs17777541) of SPOCK1 gene showing association with mathematics ability (minimum p value 5.67 × 10⁻¹⁰, maximum β −2.43). The SPOCK1 gene is located on chromosome 5q31.2 and encodes a highly conserved glycoprotein testican-1 which was associated with tumor progression and prognosis as well as neurogenesis. This is the first study to report genome-wide significant association of individual SNPs with mathematics ability in general populations. Our preliminary results further supported the role of SPOCK1 during neurodevelopment. The genetic complexities underlying mathematics ability might contribute to explain the basis of human cognition and intelligence at genetic level.

Altered expression pattern of testican-1 mRNA after brain injury

Testican, a chondroitin/heparan sulfate proteoglycan, is primarily expressed in neurons of the adult and embryonic mouse brain, suggesting its role in normal and/or proliferation and differentiation processes of neurons. However, the role of testican in injured brain remains unclear. In the present study we investigated testican-1 mRNA expression pattern after cryo-injury of the brain. In situ hybridization histochemistry revealed that testican-1 mRNA is induced in the region surrounding the necrotic tissue. Time course study of testican-1 mRNA showed the highest level of signal intensity at 7 days after the injury. To determine which cell types express testican-1 mRNA, we performed in situ hybridization histochemistry combined with immunohistochemistry of several cell markers. Testican-1 mRNA signals were detected in the proximal reactive astrocytes, whereas the distribution pattern of testican-1 mRNA positive cells was different from those of mature oligodendrocytes and activated microglia. In addition, signals for testican-1 mRNA overlapped with those of FGF-2 mRNA, showing that these molecules are coexpressed in reactive astrocytes. These results suggest a possibility that testican-1 plays a permissive role for regenerating axons in reactive astrocytes after injury.

Expression profiling of clonal lymphocyte cell cultures from Rett syndrome patients

Background

More than 85% of Rett syndrome (RTT) patients have heterozygous mutations in the X-linked MECP2 gene which encodes methyl-CpG-binding protein 2, a transcriptional repressor that binds methylated CpG sites. Because MECP2 is subject to X chromosome inactivation (XCI), girls with RTT express either the wild type or mutant MECP2 in each of their cells. To test the hypothesis that MECP2 mutations result in genome-wide transcriptional deregulation and identify its target genes in a system that circumvents the functional mosaicism resulting from XCI, we performed gene expression profiling of pure populations of untransformed T-lymphocytes that express either a mutant or a wild-type allele.

Methods

Single T lymphocytes from a patient with a c.473C>T (p.T158M) mutation and one with a c.1308-1309delTC mutation were subcloned and subjected to short term culture. Gene expression profiles of wild-type and mutant clones were compared by oligonucleotide expression microarray analysis.

Results

Expression profiling yielded 44 upregulated genes and 77 downregulated genes. We compared this gene list with expression profiles of independent microarray experiments in cells and tissues of RTT patients and mouse models with Mecp2 mutations. These comparisons identified a candidate MeCP2 target gene, SPOCK1, downregulated in two independent microarray experiments, but its expression was not altered by quantitative RT-PCR analysis on brain tissues from a RTT mouse model.

Conclusion

Initial expression profiling from T-cell clones of RTT patients identified a list of potential MeCP2 target genes. Further detailed analysis and comparison to independent microarray experiments did not confirm significantly altered expression of most candidate genes. These results are consistent with other reported data.

Testican-1 is dispensable for mouse development

Testicans are proteoglycans belonging to the BM-40/SPARC/osteonectin family of extracellular calcium-binding proteins. Testican-1 is strongly expressed in the brain and has been reported to modulate neuronal attachment and matrix metalloproteinase activation. Characterization of the mouse testican-1 gene (Ticn1), consisting of 12 exons out of which exon 3 is alternatively spliced, allowed the construction of a gene targeting construct. Mice deficient in testican-1 showed no obvious morphological or behavioral abnormalities, were fertile, and had normal life spans. Despite the fact that neither of the testican-1 homologues expressed in the brain, testican-2, testican-3 and SC1/hevin, showed an increased expression in Ticn1 null mice, these results, together with those from other gene targetings, indicate extensive functional redundancy among brain proteoglycans.

Proteoglycans in brain development

Proteoglycans, as part of the extracellular or cell-surface milieu of most tissues and organ systems, play important roles in morphogenesis by modulating cell-matrix or cell-cell interactions, cell adhesiveness, or by binding and presenting growth and differentiation factors. Chondroitin sulfate proteoglycans which constitute the major population of proteoglycans in the central nervous system may influence formation of neuronal nuclei, establishment of boundaries for axonal growth and act as modulators of neuronal outgrowth during brain development, as well as during regeneration after injury. There is a paucity of information on the role of chondroitin sulfate proteoglycans in central nervous system organogenesis. In the chick embryo, aggrecan has a regionally specific and developmentally regulated expression profile during brain development. By Northern and Western blot analysis, aggrecan expression is first detected in chick brain on embryonic day 7 (E7), increases from E7 to E13, declines markedly after E16, and is not evident in hatchling brains. The time course and pattern of aggrecan expression observed in ventricular zone cells suggested that it might play a role in gliogenesis. We have analyzed the role of aggrecan during brain development using a aggrecan-deficient model, nanomelia. In nanomelic chicks, expression and levels of neurocan and brevican is not affected, indicating a non-redundant role for these members of the aggrecan gene family. Our analysis of the aggrecan-deficient model found a severely altered phenotype which affects cell behavior in a neuronal culture paradigm and expression of astrocytic markers in vivo . Taken together our results suggest a function for aggrecan in the specification of a sub-set of glia precursors that might give rise to astrocytes in vivo.

Mouse Testican-2

Mouse testican-2 was cloned, sequenced, and shown to be a proteoglycan with a multidomain structure closely similar to that of the human ortholog, previously described as a calcium binding extracellular matrix molecule of the BM-40/SPARC/osteonectin family (Vannahme, C., Schübel, S., Herud, M., Gösling, S., Hülsmann, H., Paulsson, M., Hartmann, U., and Maurer, P. (1999). J. Neurochem. 73, 12-20). Recombinant mouse testican-2 was used to prepare specific antibodies that allowed the detection of testican-2 in various brain structures but also in lung, testis, and in several endocrine glands. Although the testican-2 expressed in EBNA-293 cells carried both heparan sulfate and chondroitin/dermatan sulfate glycosaminoglycan chains, the tissue form always contained only heparan sulfate. Both tissue-derived and recombinant testican-2 carried N-linked glycans. Tissue-derived forms of testican-2 were detected as proteoglycans of varying size, whereas a portion of the molecules produced by EBNA-293 cells were core proteins, lacking glycosaminoglycans. Both the proteoglycan and core protein forms of testican-2 inhibited neurite extension from cultured primary cerebellar neurons and may play regulatory roles in the development of the central nervous system.

Testican-1: A Differentially Expressed Proteoglycan with Protease Inhibiting Activities

Testican-1 is a highly conserved, multidomain proteoglycan that is most prominently expressed in the thalamus of the brain, and is upregulated in activated astroglial cells of the cerebrum. Several functions of this gene product have now been demonstrated in vitro including membrane-type matrix metalloproteinase inhibition, cathepsin L inhibition, and low-affinity calcium binding. The purified gene product has been shown to inhibit cell attachment and neurite extensions in culture. Functions of testican in vivo have yet to be demonstrated in knockout mice or other models. Testican has been shown to carry substantial amounts of chondroitin sulfate as well as other oligosaccharides, but the biological significance of these embellishments is not yet known.

Testican-1 inhibits attachment of Neuro-2a cells

Testican-1 is a highly conserved, multidomain, chondroitin sulfate proteoglycan that is most abundantly transcribed in the brain by neurons. This testican messenger RNA is not detected in normal quiescent astrocytes, but is up regulated when these cells are activated in response to injury such as cerebral stroke. Other chondroitin sulfate proteoglycans found in glial scars, including neurocan, have been shown to inhibit neural cell attachment and neurite extensions and may thus impede axonal regeneration. Here we report the expression and purification of a proteoglycan form of recombinant testican and its effects on neuron-derived cells in culture. We demonstrate that testican inhibits attachment of Neuro-2a cells and their ability to form neurite extensions. Both testican proteoglycan and the core glycoprotein that has been depleted of chondroitin sulfate inhibit cell attachment. Pre-treatment of the culture substratum with testican inhibits Neuro-2a attachment, but pre-treatment of the cells with testican does not inhibit their attachment. Testican, therefore, blocks attachment sites on cultureware and may also block attachment sites in the extracellular matrix of the brain.

Characterization of SMOC-1, a novel modular calcium-binding protein in basement membranes

We have isolated the novel gene SMOC-1 that encodes a secreted modular protein containing an EF-hand calcium-binding domain homologous to that in BM-40. It further consists of two thyroglobulin-like domains, a follistatin-like domain and a novel domain. Recombinant expression in human cells showed that SMOC-1 is a glycoprotein with a calcium-dependent conformation. Results from Northern blots, reverse transcriptase-PCR, and immunoblots revealed a widespread expression in many tissues. Immunofluorescence studies with an antiserum directed against recombinant human SMOC-1 demonstrated a basement membrane localization of the protein and additionally its presence in other extracellular matrices. Immunogold electron microscopy confirmed the localization of SMOC-1 within basement membranes in kidney and skeletal muscle as well as its expression in the zona pellucida surrounding the oocyte.

Spatiotemporal distribution of heparan sulfate epitopes during myogenesis and synaptogenesis: a study in developing mouse intercostal muscle

Formation of a basal lamina (BL) ensheathing developing skeletal muscle cells is one of the earliest events in mammalian skeletal muscle myogenesis. BL-resident heparan sulfate proteoglycans have been implicated in various processes during myogenesis, including synaptic differentiation. However, attention has focused on the proteoglycan protein core, ignoring the glycosaminoglycan moiety mainly because of a lack of appropriate tools. Recently, we selected a panel of anti-heparan sulfate antibodies applied here to study the spatiotemporal distribution of specific heparan sulfate (HS) epitopes during myogenesis. In mouse intercostal muscle at embryonic day (E14), formation of acetylcholine receptor clusters at synaptic sites coincides with HS deposition. Although some HS epitopes show a general appearance throughout the BL, one epitope preferably clusters at synaptic sites but does so only from E16 onward. During elongation and maturation of primary myotubes, a process preceding secondary myotube development, significant changes in the HS epitope constitution of both synaptic and extrasynaptic BL were observed. As a whole, the data presented here strengthen previous observations on developmental regulation by BL components, and add to the putative roles of specific HS epitopes in myogenesis and synaptogenesis.

Proteoglycans in the nervous system--the quest for functional roles in vivo

Large numbers of different proteoglycans are expressed in tightly regulated spatio-temporal patterns by both the nerve cells (neurons) and the supporting glial cells of the nervous system. Several of these proteoglycans have been shown by studies in vitro to affect the migration of neural precursor cells, the elongation and pathfinding of neurites and the formation and stabilization of synapses. Such processes are important for the accurate wiring of the nervous system, and so it has been postulated that proteoglycans play an essential role during neural development. However, with few exceptions, the phenotypes of null mutations in mice and some human genetic diseases have provided little support for this view. Here we will review recent data from both in vitro and in vivo studies analyzing the function of proteoglycans in the nervous system in order to provide possible explanations for their apparent lack of function.

Regulated expression of the proteoglycan SPOCK in the neuromuscular system

SPOCK is prevalent in developing synaptic fields of the central nervous system (Charbonnier et al., 2000. Mech. Dev. 90, 317-321). The expression of SPOCK during neuromuscular junction (NMJ) formation was compared to agrin and acetylcholine receptor (AChR) distribution. SPOCK is detected within the myogenic masses during the early steps of embryonic development, and distributed in the cytoplasm of myotubes before coclustering with AChRs. In the adult, SPOCK is present in axons and is highly expressed by Schwann cells. SPOCK altered expression pattern after nerve lesioning, or cholinergic transmission blockade, strongly indicate that its cellular distribution at the NMJ depends on innervation.