Distribution of the calcium-binding protein SPARC in tissues of embryonic and adult mice

Runx1+ vascular smooth muscle cells are essential for hematopoietic stem and progenitor cell development in vivo

Hematopoietic stem cells (HSCs) produce all essential cellular components of the blood. Stromal cell lines supporting HSCs follow a vascular smooth muscle cell (vSMC) differentiation pathway, suggesting that some hematopoiesis-supporting cells originate from vSMC precursors. These pericyte-like precursors were recently identified in the aorta-gonad-mesonephros (AGM) region; however, their role in the hematopoietic development in vivo remains unknown. Here, we identify a subpopulation of NG2+Runx1+ perivascular cells that display a sclerotome-derived vSMC transcriptomic profile. We show that deleting Runx1 in NG2+ cells impairs the hematopoietic development in vivo and causes transcriptional changes in pericytes/vSMCs, endothelial cells and hematopoietic cells in the murine AGM. Importantly, this deletion leads also to a significant reduction of HSC reconstitution potential in the bone marrow in vivo. This defect is developmental, as NG2+Runx1+ cells were not detected in the adult bone marrow, demonstrating the existence of a specialised pericyte population in the HSC-generating niche, unique to the embryo.

GP60 and SPARC as albumin receptors: key targeted sites for the delivery of antitumor drugs

Albumin is derived from human or animal blood, and its ability to bind to a large number of endogenous or exogenous biomolecules makes it an ideal drug carrier. As a result, albumin-based drug delivery systems are increasingly being studied. With these in mind, detailed studies of the transport mechanism of albumin-based drug carriers are particularly important. As albumin receptors, glycoprotein 60 (GP60) and secreted protein acidic and rich in cysteine (SPARC) play a crucial role in the delivery of albumin-based drug carriers. GP60 is expressed on vascular endothelial cells and enables albumin to cross the vascular endothelial cell layer, and SPARC is overexpressed in many types of tumor cells, while it is minimally expressed in normal tissue cells. Thus, this review supplements existing articles by detailing the research history and specific biological functions of GP60 or SPARC and research advances in the delivery of antitumor drugs using albumin as a carrier. Meanwhile, the deficiencies and future perspectives in the study of the interaction of albumin with GP60 and SPARC are also pointed out.

Effect of Sparc knockout on the extracellular matrix of mouse periodontal ligament cells

The periodontal ligament (PDL) is a critical component in maintaining tooth stability. It is composed of cells and an extracellular matrix (ECM), each with unique roles in tissue function and homeostasis. Secreted protein acidic and rich in cysteine (SPARC), a calcium-binding matricellular glycoprotein, plays a crucial role in regulating ECM assembly and turnover, alongside facilitating cellular-ECM interactions. In the present study, mass spectrometry-based proteomics was used to assess the impacts of Sparc-knockout (KO) on PDL-derived cells. Results demonstrated that Sparc-KO significantly reduces ECM production and alters its composition with increased levels of type I collagen. Despite this increase in Sparc-KO, type I collagen was not likely to be effectively integrated into the fibrils due to collagen cross-linking impairment. Furthermore, the pathway and process enrichment analyses suggested that SPARC plays a protective role against ECM degradation by antagonistically interacting with cell-surface collagen receptors. These findings provide detailed insights into the multifaceted role of SPARC in ECM organization, including its impact on ECM production, collagen regulation, and interactions with various cellular compartments. A better understanding of these complex mechanisms is crucial for comprehending the causes of periodontal disease and tissue regeneration, where precise control of ECM organization is necessary.

Increased blood meal size and feeding frequency compromise Aedes aegypti midgut integrity and enhance dengue virus dissemination

Aedes aegypti is a highly efficient vector for numerous pathogenic arboviruses including dengue virus (DENV), Zika virus, and yellow fever virus. This efficiency can in part be attributed to their frequent feeding behavior. We previously found that acquisition of a second, full, non-infectious blood meal could accelerate virus dissemination within the mosquito by temporarily compromising midgut basal lamina integrity; however, in the wild, mosquitoes are often interrupted during feeding and only acquire partial or minimal blood meals. To explore the impact of this feeding behavior further, we examined the effects of partial blood feeding on DENV dissemination rates and midgut basal lamina damage in Ae. aegypti. DENV-infected mosquitoes given a secondary partial blood meal had intermediate rates of dissemination and midgut basal lamina damage compared to single-fed and fully double-fed counterparts. Subsequently, we evaluated if basal lamina damage accumulated across feeding episodes. Interestingly, within 24 hours of feeding, damage was proportional to the number of blood meals imbibed; however, this additive effect returned to baseline levels by 96 hours. These data reveal that midgut basal lamina damage and rates of dissemination are proportional to feeding frequency and size, and further demonstrate the impact that mosquito feeding behavior has on vector competence and arbovirus epidemiology. This work has strong implications for our understanding of virus transmission in the field and will be useful when designing laboratory experiments and creating more accurate models of virus spread and maintenance.

The role of SPARC (secreted protein acidic and rich in cysteine) in the pathogenesis of obesity, type 2 diabetes, and non-alcoholic fatty liver disease

Secreted protein acidic and rich in cysteine (SPARC) is an extracellular matrix glycoprotein with pleiotropic functions, which is expressed in adipose, hepatic, muscular, and pancreatic tissue. Particularly, several studies demonstrated that SPARC is an important player in the context of obesity, diabetes, and fatty liver disease including advanced hepatic fibrosis and hepatocellular carcinoma. Evidence in murine and human samples indicates that SPARC is involved in adipogenesis, cellular metabolism, extracellular matrix modulation, glucose and lipid metabolism, among others. Furthermore, studies in SPARC knockout mouse model showed that SPARC contributes to adipose tissue formation, non-alcoholic fatty liver disease (NAFLD), and diabetes. Hence, SPARC may represent a novel and interesting target protein for future therapeutic interventions or a biomarker of disease progression. This review summarizes the role of SPARC in the pathophysiology of obesity, and extensively revised SPARC functions in physiological and pathological adipose tissue deposition, muscle metabolism, liver, and diabetes-related pathways.

Diosgenin restores memory function via SPARC-driven axonal growth from the hippocampus to the PFC in Alzheimer's disease model mice

Central nervous system axons have minimal capacity to regenerate in adult brains, hindering memory recovery in Alzheimer's disease (AD). Although recent studies have shown that damaged axons sprouted in adult and AD mouse brains, long-distance axonal re-innervation to their targets has not been achieved. We selectively visualized axon-growing neurons in the neural circuit for memory formation, from the hippocampus to the prefrontal cortex, and showed that damaged axons successfully extended to their native projecting area in mouse models of AD (5XFAD) by administration of an axonal regenerative agent, diosgenin. In vivo transcriptome analysis detected the expression profile of axon-growing neurons directly isolated from the hippocampus of 5XFAD mice. Secreted protein acidic and rich in cysteine (SPARC) was the most expressed gene in axon-growing neurons. Neuron-specific overexpression of SPARC via adeno-associated virus serotype 9 delivery in the hippocampus recovered memory deficits and axonal projection to the prefrontal cortex in 5XFAD mice. DREADDs (Designer receptors exclusively activated by designer drugs) analyses revealed that SPARC overexpression-induced axonal growth in the 5XFAD mouse brain directly contributes to memory recovery. Elevated levels of SPARC on axonal membranes interact with extracellular rail-like collagen type I to promote axonal remodeling along their original tracings in primary cultured hippocampal neurons. These findings suggest that SPARC-driven axonal growth in the brain may be a promising therapeutic strategy for AD and other neurodegenerative diseases.

Characterization and Expression Analysis of Regeneration-Associated Protein (Aj-Orpin) during Intestinal Regeneration in the Sea Cucumber Apostichopus japonicus

Apostichopus japonicus achieves intestinal regeneration in a short period after evisceration, and multiple genes are involved in this process. The transcriptome of A. japonicus was screened for regeneration-associated protein (Aj-Orpin), a gene that is specifically upregulated during intestinal regeneration. The expression and function of Aj-Orpin were identified and investigated in this study. The 5′ and 3′ RACE polymerase chain reaction (PCR) was used to clone the full-length cDNA of Aj-Orpin. The open reading frame codes for a 164 amino-acid protein with an EF-hand_7 domain and overlapping signal peptides and transmembrane regions. Moreover, Aj-Orpin mRNA and protein expression during intestinal regeneration was investigated using real-time quantitative PCR and Western blot. The expression pattern of Aj-Orpin in the regenerating intestine was investigated using immunohistochemistry. The results showed that Aj-Orpin is an exocrine protein with two EF-hand-like calcium-binding domains. Expression levels were higher in the regenerating intestine than in the normal intestine, but protein expression changes lagged behind mRNA expression changes. Aj-Orpin was found to play a role in the formation of blastema and lumen. It was primarily expressed in the serosal layer and submucosa, suggesting that it might be involved in proliferation. These observations lay the foundation for understanding the role of Orpin-like in echinoderm intestinal regeneration.

Vascular-derived SPARC and SerpinE1 regulate interneuron tangential migration and accelerate functional maturation of human stem cell-derived interneurons

Cortical interneurons establish inhibitory microcircuits throughout the neocortex and their dysfunction has been implicated in epilepsy and neuropsychiatric diseases. Developmentally, interneurons migrate from a distal progenitor domain in order to populate the neocortex - a process that occurs at a slower rate in humans than in mice. In this study, we sought to identify factors that regulate the rate of interneuron maturation across the two species. Using embryonic mouse development as a model system, we found that the process of initiating interneuron migration is regulated by blood vessels of the medial ganglionic eminence (MGE), an interneuron progenitor domain. We identified two endothelial cell-derived paracrine factors, SPARC and SerpinE1, that enhance interneuron migration in mouse MGE explants and organotypic cultures. Moreover, pre-treatment of human stem cell-derived interneurons (hSC-interneurons) with SPARC and SerpinE1 prior to transplantation into neonatal mouse cortex enhanced their migration and morphological elaboration in the host cortex. Further, SPARC and SerpinE1-treated hSC-interneurons also exhibited more mature electrophysiological characteristics compared to controls. Overall, our studies suggest a critical role for CNS vasculature in regulating interneuron developmental maturation in both mice and humans.

Exercise Training of Secreted Protein Acidic and Rich in Cysteine (Sparc) KO Mice Suggests That Exercise-Induced Muscle Phenotype Changes Are SPARC-Dependent

We previously identified secreted protein acidic and rich in cysteine (Sparc) as an exercise-induced gene in young and elderly individuals. Via this animal experiment, we aim to identify selected implications of SPARC mainly within the muscle in the contexts of exercise. Mice were divided into eight groups based on three variables (age, genotype and exercise): Old (O) or young (Y) × Sparc knock-out (KO) or wild-type (WT) × sedentary (Sed) or exercise (Ex). The exercised groups were trained for 12 weeks at the lactate threshold (LT) speed (including 4 weeks of adaptation period) and all mice were sacrificed afterwards. Body and selected tissues were weighed, and lactate levels in different conditions measured. Expression of skeletal muscle (SM) collagen type I alpha 1 chain (COL1A1) and mitochondrially encoded cytochrome c oxidase I (MT-CO1) in addition to SM strength (grip power) were also measured. Ageing increased the body and white adipose tissue (WAT) weights but decreased SM weight percentage (to body weight) and MT-CO1 expression (in WT). Exercise increased SM COL1A1 in WT mice and MT-CO1 expression, as well as weight percentage of the tibialis anterior muscle, and decreased WAT weight (trend). Compared to WT mice, Sparc KO mice had lower body, muscle and WAT weights, with a decrease in SM MT-CO1 and COL1A1 expression with no genotype effect on lactate levels in all our blood lactate measures. Sparc KO effects on body composition, adiposity and metabolic patterns are toward a reduced WAT and body weight, but with a negative metabolic and functional phenotype of SM. Whereas such negative effects on SM are worsened with ageing, they are relatively improved by exercise. Importantly, our data suggest that the exercise-induced changes in the SM phenotype, in terms of increased performance (metabolic, strength and development), including lactate-induced changes, are SPARC-dependent.

Secreted protein acidic and rich in cysteine (SPARC) knockout mice have greater outflow facility

Purpose

Secreted protein acidic and rich in cysteine (SPARC) is a matricellular protein that regulates intraocular pressure (IOP) by altering extracellular matrix (ECM) homeostasis within the trabecular meshwork (TM). We hypothesized that the lower IOP previously observed in SPARC -/- mice is due to a greater outflow facility.

Methods

Mouse outflow facility (C_live) was determined by multiple flow rate infusion, and episcleral venous pressure (P_e) was estimated by manometry. The animals were then euthanized, eliminating aqueous formation rate (F_in) and P_e. The C value was determined again (C_dead) while F_in was reduced to zero. Additional mice were euthanized for immunohistochemistry to analyze ECM components of the TM.

Results

The C_live and C_dead of SPARC -/- mice were 0.014 ± 0.002 μL/min/mmHg and 0.015 ± 0.002 μL/min/mmHg, respectively (p = 0.376, N/S). Compared to the C_live = 0.010 ± 0.002 μL/min/mmHg and C_dead = 0.011 ± 0.002 μL/min/mmHg in the WT mice (p = 0.548, N/S), the C_live and C_dead values for the SPARC -/- mice were higher. P_e values were estimated to be 8.0 ± 0.2 mmHg and 8.3 ± 0.7 mmHg in SPARC -/- and WT mice, respectively (p = 0.304, N/S). Uveoscleral outflow (F_u) was 0.019 ± 0.007 μL/min and 0.022 ± 0.006 μL/min for SPARC -/- and WT mice, respectively (p = 0.561, N/S). F_in was 0.114 ± 0.002 μL/min and 0.120 ± 0.016 μL/min for SPARC -/- and WT mice (p = 0.591, N/S). Immunohistochemistry demonstrated decreases of collagen types IV and VI, fibronectin, laminin, PAI-1, and tenascin-C within the TM of SPARC -/- mice (p < 0.05).

Conclusions

The lower IOP of SPARC -/- mice is due to greater aqueous humor outflow facility through the conventional pathway. Corresponding changes in several matricellular proteins and ECM structural components were noted in the TM of SPARC -/- mice.

The Tumor Microenvironment: Focus on Extracellular Matrix

The extracellular matrix (ECM) regulates the development and maintains tissue homeostasis. The ECM is composed of a complex network of molecules presenting distinct biochemical properties to regulate cell growth, survival, motility, and differentiation. Among their components, proteoglycans (PGs) are considered one of the main components of ECM. Its composition, biomechanics, and anisotropy are exquisitely tuned to reflect the physiological state of the tissue. The loss of ECM's homeostasis is seen as one of the hallmarks of cancer and, typically, defines transitional events in tumor progression and metastasis. In this chapter, we discuss the types of proteoglycans and their roles in cancer. It has been observed that the amount of some ECM components is increased, while others are decreased, depending on the type of tumor. However, both conditions corroborate with tumor progression and malignancy. Therefore, ECM components have an increasingly important role in carcinogenesis and this leads us to believe that their understanding may be a key in the discovery of new anti-tumor therapies. In this book, the main ECM components will be discussed in more detail in each chapter.

Investigating the role of super-enhancer RNAs underlying embryonic stem cell differentiation

BACKGROUND

Super-enhancer RNAs (seRNAs) are a kind of noncoding RNA transcribed from super-enhancer regions. The regulation mechanism and functional role of seRNAs are still unclear. Although super-enhancers play a critical role in the core transcriptional regulatory circuity of embryonic stem cell (ESC) differentiation, whether seRNAs have similar properties should be further investigated.

RESULTS

We analyzed cap analysis gene expression sequencing (CAGE-seq) datasets collected during the differentiation of embryonic stem cells (ESCs) to cardiomyocytes to identify the seRNAs. A non-negative matrix factorization algorithm was applied to decompose the seRNA profiles and reveal two hidden stages during the ESC differentiation. We further identified 95 and 78 seRNAs associated with early- and late-stage ESC differentiation, respectively. We found that the binding sites of master regulators of ESC differentiation, including NANOG, FOXA2, and MYC, were significantly observed in the loci of the stage-specific seRNAs. Based on the investigation of genes coexpressed with seRNA, these stage-specific seRNAs might be involved in cardiac-related functions such as myofibril assembly and heart development and act in trans to regulate the co-expressed genes.

CONCLUSIONS

In this study, we used a computational approach to demonstrate the possible role of seRNAs during ESC differentiation.

Prechondrogenic ATDC5 Cell Attachment and Differentiation on Graphene Foam; Modulation by Surface Functionalization with Fibronectin

Graphene foam holds promise for tissue engineering applications. In this study, graphene foam was used as a three-dimension scaffold to evaluate cell attachment, cell morphology, and molecular markers of early differentiation. The aim of this study was to determine if cell attachment and elaboration of an extracellular matrix would be modulated by functionalization of graphene foam with fibronectin, an extracellular matrix protein that cells adhere well to, prior to the establishment of three-dimensional cell culture. The molecular dynamic simulation demonstrated that the fibronectin-graphene interaction was stabilized predominantly through interaction between the graphene and arginine side chains of the protein. Quasi-static and dynamic mechanical testing indicated that fibronectin functionalization of graphene altered the mechanical properties of graphene foam. The elastic strength of the scaffold increased due to fibronectin, but the viscoelastic mechanical behavior remained unchanged. An additive effect was observed in the mechanical stiffness when the graphene foam was both coated with fibronectin and cultured with cells for 28 days. Cytoskeletal organization assessed by fluorescence microscopy demonstrated a fibronectin-dependent reorganization of the actin cytoskeleton and an increase in actin stress fibers. Gene expression assessed by quantitative real-time polymerase chain reaction of 9 genes encoding cell attachment proteins (Cd44, Ctnna1, Ctnnb1, Itga3, Itga5, Itgav, Itgb1, Ncam1, Sgce), 16 genes encoding extracellular matrix proteins (Col1a1, Col2a1, Col3a1, Col5a1, Col6a1, Ecm1, Emilin1, Fn1, Hapln1, Lamb3, Postn, Sparc, Spp1, Thbs1, Thbs2, Tnc), and 9 genes encoding modulators of remodeling (Adamts1, Adamts2, Ctgf, Mmp14, Mmp2, Tgfbi, Timp1, Timp2, Timp3) indicated that graphene foam provided a microenvironment conducive to expression of genes that are important in early chondrogenesis. Functionalization of graphene foam with fibronectin modified the cellular response to graphene foam, demonstrated by decreases in relative gene expression levels. These findings illustrate the combinatorial factors of microscale materials properties and nanoscale molecular features to consider in the design of three-dimensional graphene scaffolds for tissue engineering applications.

Secreted protein acidic and rich in cysteine functions in colitis via IL17A regulation in mucosal CD4+ T cells

BACKGROUND AND AIM

Secreted protein acidic and rich in cysteine (SPARC) is a matricellular glycol that regulates cell proliferation, tissue repair, and tumorigenesis. Despite evidence linking SPARC to inflammation, the mechanisms are unclear. Accordingly, the role of SPARC in intestinal inflammation was investigated.

METHODS

Colitis was induced in wild-type (WT) and SPARC knockout (KO) mice using trinitrobenzene sulfonic acid (TNBS). Colons were assessed for damage; leukocyte infiltration; Tnf, Ifng, Il17a, and Il10 mRNA expression; and histology. Cytokine profiling of colonic lamina propria mononuclear cells (LPMCs) was performed by flow cytometry. Naïve CD4⁺ T cells were isolated from WT and SPARC KO mouse spleens, and the effect of SPARC on Th17 cell differentiation was examined. Recombination activating gene 1 knockout (RAG1 KO) mice reconstituted with T cells from either WT or SPARC KO mice were investigated.

RESULTS

Trinitrobenzene sulfonic acid exposure significantly reduced bodyweight and increased mucosal inflammation, leukocyte infiltration, and Il17a mRNA expression in WT relative to SPARC KO mice. The percentage of IL17A-producing CD4⁺ T cells among LPMCs from KO mice was lower than that in WT mice when both groups were exposed to TNBS. Th17 cell differentiation was suppressed in cells from SPARC KO mice. In the T cell transfer colitis model, RAG1 KO mice receiving T cells from WT mice were more severely affected than those reconstituted with cells from SPARC KO mice.

CONCLUSIONS

Secreted protein acidic and rich in cysteine accelerates colonic mucosal inflammation via modulation of IL17A-producing CD4⁺ T cells. SPARC is a potential therapeutic target for conditions involving intestinal inflammation.

Bispecific Antibody Binding To RANKL and Osteonectin with Enhanced Localization to the Bone

Therapeutics reducing bone turnover, such as denosumab (Dmab), an anti-RANKL antibody, can provide treatments for patients with bone destruction. However, some patients with osteoporosis or localized primary bone tumors and many patients with various types of bone-metastatic cancer display unsatisfactory responses to Dmab. For achieving greater efficiency of RANKL neutralization in the bone microenvironment by enhancing the distribution of Dmab to the bone, we reengineered Dmab by fusing with single-chain variable fragments of an antibody specific for osteonectin (On), which is abundantly expressed in osseous tissues. The bispecific antibody, Dmab-FvOn, showed a similar activity as Dmab in inhibiting RANKL as examined in an osteoclast differentiation assay. When administered to mice, Dmab-FvOn was found to localize in increased proportions at the endosteum of the bone where osteonectin is abundant. Our study suggests that by linking anti-RANKL with an osteonectin-targeting moiety, a greater proportion of the therapeutic effector can be distributed in the bone. Future studies are needed to investigate whether the bispecific antibody can achieve higher therapeutic efficacy and lower toxicity.

Formation of the inner ear during embryonic and larval development of the cichlid fish (Oreochromis mossambicus)

BACKGROUND

The vertebrate inner ear comprises mineralized elements, namely the otoliths (fishes) or the otoconia (mammals). These elements serve vestibular and auditory functions. The formation of otoconia and otoliths is described as a stepwise process, and in fish, it is generally divided into an aggregation of the otolith primordia from precursor particles and then a growth process that continues throughout life.

RESULTS

This study was undertaken to investigate the complex transition between these two steps. Therefore, we investigated the developmental profiles of several inner ear structural and calcium-binding proteins during the complete embryonic and larval development of the cichlid fish Oreochromis mossambicus in parallel with the morphology of inner ear and especially otoliths. We show that the formation of otoliths is a highly regulated temporal and spatial process which takes place throughout embryonic and larval development.

CONCLUSIONS

Based on our data we defined eight phases of otolith differentiation from the primordia to the mature otolith.

Heterozygous PTCH1 Mutations Impact the Bone Metabolism in Patients With Nevoid Basal Cell Carcinoma Syndrome Likely by Regulating SPARC Expression

Nevoid basal cell carcinoma syndrome (NBCCS) is an autosomal dominant disorder characterized by bone and skin abnormalities and a predisposition to various tumors. Keratocystic odontogenic tumors (KCOTs), which are common tumors of the jaw that cause extensive damage to the jawbone, are usually accompanied with NBCCS. Germline PTCH1 mutations in NBCCS tumorigenesis have been frequently studied; however, little is known regarding the pathogenesis of bone abnormalities in this disease. This study sought to investigate the mechanism underlying heterozygous PTCH1 mutation-mediated abnormal bone metabolism in patients with NBCCS. Stromal cells were isolated from the fibrous capsules of patients with NBCCS-associated or non-syndromic keratocystic odontogenic tumors and non-syndromic tumor stromal cells without PTCH1 mutations served as controls. Germline PTCH1 heterozygous mutations were confirmed in all NBCCS samples and differential protein expression was identified using tandem mass tag-labeled proteomics analysis. Our findings revealed that osteonectin/SPARC expression was significantly downregulated in syndromic stromal cells compared with non-syndromic stromal cells. SPARC expression was even lower in stromal cells carrying PTCH1 protein truncation mutations. PTCH1 siRNA transfection demonstrated that SPARC downregulation correlates with decreased PTCH1 expression. Furthermore, exogenous SPARC promoted osteogenic differentiation of syndromic stromal cells with enhanced development of calcium nodules. In addition, bone mineral density tests showed that patients with NBCCS exhibit weak bone mass compared with sex- and age-matched controls. This study indicates that germline PTCH1 heterozygous mutations play a major role in bone metabolism in patients with NBCCS, in particular in those with PTCH1 protein truncation mutations. SPARC may represent an important downstream modulator of PTCH1 mediation of bone metabolism. Thus, bone mineral density monitoring is critical for patients with NBCCS for prevention of osteoporosis. In addition, surgical procedures on syndromic-associated KCOTs should be performed with consideration of the weaker bone mass in such patients. © 2016 American Society for Bone and Mineral Research.

Retention of the Matricellular Protein SPARC in the Endoplasmic Reticulum of Chondrocytes from Patients with Pseudoachondroplasia

Pseudoachondroplasia (PSACH) is an autosomal dominant disease characterized by dwarfism, morphological irregularities of long bones and hips, and early-onset osteoarthritis. This disease has been attributed to mutations in a structural protein of the cartilage extracellular matrix (ECM), cartilage oligomeric matrix protein (COMP), which result in its selective retention in the chondrocyte rough endoplasmic reticulum (ER). Accumulation of excessive amounts of mutated COMP might reflect a defect in protein trafficking by PSACH chondrocytes. Here we identify the matricellular protein SPARC as a component of this trafficking deficit. SPARC was localized to the hypertrophic chondrocytes in the normal human tibial growth plate and in cultured control cartilage nodules. In contrast, concentrated intracellular depots of SPARC were identified in nodules cultured from three PSACH patients with mutations in COMP. The accumulated SPARC was coincident with COMP and with protein disulfide isomerase, a resident chaperone of the rough ER, whereas SPARC and COMP were not coincident in the ECM of control or PSACH nodules. SPARC-null mice develop severe osteopenia and degenerative intervertebral disc disease, and exhibit attenuation of collagenous ECM. The retention of SPARC in the ER of chondrocytes producing mutant COMP indicates a new intracellular function for SPARC in the trafficking/secretion of cartilage ECM.

Functional Analysis of the Matricellular Protein SPARC with Novel Monoclonal Antibodies

SPARC (osteonectin, BM-40) is a matricellular glycoprotein that is expressed in many embryogenic and adult tissues undergoing remodeling or repair. SPARC modulates cellular interaction with the extracellular matrix (ECM), inhibits cell adhesion and proliferation, and regulates growth factor activity. To explore further the function and activity of this protein in tissue homeostasis, we have developed several monoclonal antibodies (MAbs) that recognize distinct epitopes on SPARC. The MAbs bind to SPARC with high affinity and identify SPARC by ELISA, Western blotting, immunoprecipitation, immunocytochemistry, and/or immunohistochemistry. The MAbs were also characterized in functional assays for potential alteration of SPARC activity. SPARC binds to collagen I and laminin-1 through an epitope defined by MAb 293; this epitope is not involved in the binding of SPARC to collagen III. The other MAbs did not interfere with the binding of SPARC to collagen I or III or laminin-1. Inhibition of the anti-adhesive effect of SPARC on endothelial cells by MAb 236 was also observed. Functional analysis of SPARC in the presence of these novel MAbs now confirms that the activities ascribed to this matricellular protein can be assigned to discrete subdomains.

SPARC/osteonectin in mineralized tissue

Secreted protein acidic and rich in cysteine (SPARC/osteonectin/BM40) is one of the most abundant non-collagenous protein expressed in mineralized tissues. This review will focus on elucidating functional roles of SPARC in bone formation building upon results from non-mineralized cells and tissues, the phenotype of SPARC-null bones, and recent discoveries of human diseases with either dysregulated expression of SPARC or mutations in the gene encoding SPARC that give rise to bone pathologies. The capacity of SPARC to influence pathways involved in extracellular matrix assembly such as procollagen processing and collagen fibril formation as well as the capacity to influence osteoblast differentiation and osteoclast activity will be addressed. In addition, the potential for SPARC to regulate cross-linking of extracellular matrix proteins by members of the transglutaminase family of enzymes is explored. Elucidating defined biological functions of SPARC in terms of bone formation and turnover are critical. Further insight into specific cellular mechanisms involved in the formation and homeostasis of mineralized tissues will lead to a better understanding of disease progression.

Secreted Protein Acidic and Rich in Cysteine in Ocular Tissue

Secreted protein acidic and rich in cysteine (SPARC), also known as osteonectin or BM-40, is the prototypical matricellular protein. Matricellular proteins are nonstructural secreted proteins that provide an integration between cells and their surrounding extracellular matrix (ECM). Regulation of the ECM is important in maintaining the physiologic function of tissues. Elevated levels of SPARC have been identified in a variety of diseases involving pathologic tissue remodeling, such as hepatic fibrosis, systemic sclerosis, and certain carcinomas. Within the eye, SPARC has been identified in the trabecular meshwork, lens, and retina. Studies have begun to show the role of SPARC in these tissues and its possible role, specifically in primary open-angle glaucoma, cataracts, and proliferative vitreoretinopathy. SPARC may, therefore, be a therapeutic target in the treatment of certain ocular diseases. Further investigation into the mechanism of action of SPARC will be necessary in the development of SPARC-targeted therapy.

Molecular cloning and characterization of the matricellular protein Sparc/osteonectin in flatfish, Scophthalmus maximus, and its developmental stage-dependent transcriptional regulation during metamorphosis

SPARC/osteonectin is a multifunctional matricellular glycoprotein, which is expressed in embryonic and adult tissues that undergo active proliferation and dynamic morphogenesis. Recent studies indicate that Sparc expression appears early in development, although its function and regulation during development are largely unknown. In this report, we describe the isolation, characterization, post-embryonic developmental expression and environmental thermal regulation of sparc in turbot. The full-length turbot sparc cDNA contains 930 bp and encodes a protein of 310 amino acids, which shares 77, 75 and 80% identity with human, frog and zebrafish, respectively. Results of whole-mount in situ hybridization reveal a dynamic expression profile during post-embryonic turbot development. Sparc is expressed differentially in the cranioencephalic region; mainly in jaws, branchial arches, fin folds and rays of caudal, dorsal and anal fins. Furthermore, ontogenetic studies demonstrated that Sparc gene expression is dynamically regulated during post-embryonic turbot development, with high expression during stage-specific post-embryonic remodeling. Additionally, the effect of thermal environmental conditions on turbot development and on ontogenetic sparc expression was evaluated.

Novel role for matricellular proteins in the regulation of islet β cell survival: the effect of SPARC on survival, proliferation, and signaling

Understanding the mechanisms regulating islet growth and survival is critical for developing novel approaches to increasing or sustaining β cell mass in both type 1 and type 2 diabetes patients. Secreted protein acidic and rich in cysteine (SPARC) is a matricellular protein that is important for the regulation of cell growth and adhesion. Increased SPARC can be detected in the serum of type 2 diabetes patients. The aim of this study was to investigate the role of SPARC in the regulation of β cell growth and survival. We show using immunohistochemistry that SPARC is expressed by stromal cells within islets and can be detected in primary mouse islets by Western blot. SPARC is secreted at high levels by pancreatic stellate cells and is regulated by metabolic parameters in these cells, but SPARC expression was not detectable in β cells. In islets, SPARC expression is highest in young mice, and is also elevated in the islets of non-obese diabetic (NOD) mice compared with controls. Purified SPARC inhibits growth factor-induced signaling in both INS-1 β cells and primary mouse islets, and inhibits IGF-1-induced proliferation of INS-1 β cells. Similarly, exogenous SPARC prevents IGF-1-induced survival of primary mouse islet cells. This study identifies the stromal-derived matricellular protein SPARC as a novel regulator of islet survival and β cell growth.

Asbestos-associated mesothelial cell autoantibodies promote collagen deposition in vitro

Fibrosis, characterized by excessive collagen protein deposition, is a progressive disease that can fatally inhibit organ function. Prolonged exposure to pathogens or environmental toxicants such as asbestos can lead to chronic inflammatory responses associated with fibrosis. Significant exposure to amphibole asbestos has been reported in and around Libby, Montana due to local mining of asbestos-contaminated vermiculite. These exposures have been implicated in a unique disease etiology characterized predominantly by pleural disorders, including fibrosis. We recently reported the discovery of mesothelial cell autoantibodies (MCAAs) in the sera of Libby residents and demonstrated a positive and significant correlation with pleural disease; however, a mechanistic link was not determined. Here we demonstrate that MCAAs induce pleural mesothelial cells to produce a collagen matrix but do not affect production of the pro-inflammatory cytokine tumor growth factor-β. While autoantibodies commonly induce a pro-fibrotic state by inducing epithelial-mesenchymal transition (EMT) of target cells, we found no evidence supporting EMT in cells exposed to MCAA positive human sera. Although implicated in other models of pulmonary fibrosis, activity of the protein SPARC (secreted protein, acidic and rich in cysteine) did not affect MCAA-induced collagen deposition. However, matrix formation was dependent on matrix metalloproteinase (MMP) activity, and we noted increased expression of MMP-8 and -9 in supernatants of mesothelial cells incubated with MCAA positive sera compared to control. These data suggest a mechanism by which MCAA binding leads to increased collagen deposition through altering MMP expression and provides an important mechanistic link between MCAAs and asbestos-related, autoimmune-induced pleural fibrosis.

Matricellular proteins in the trabecular meshwork: review and update

Abstract Primary open-angle glaucoma (POAG) is a leading cause of blindness worldwide, and intraocular pressure (IOP) is an important modifiable risk factor. IOP is a function of aqueous humor production and aqueous humor outflow, and it is thought that prolonged IOP elevation leads to optic nerve damage over time. Within the trabecular meshwork (TM), the eye's primary drainage system for aqueous humor, matricellular proteins generally allow cells to modulate their attachments with and alter the characteristics of their surrounding extracellular matrix (ECM). It is now well established that ECM turnover in the TM affects outflow facility, and matricellular proteins are emerging as significant players in IOP regulation. The formalized study of matricellular proteins in TM has gained increased attention. Secreted protein acidic and rich in cysteine (SPARC), myocilin, connective tissue growth factor (CTGF), and thrombospondin-1 and -2 (TSP-1 and -2) have been localized to the TM, and a growing body of evidence suggests that these matricellular proteins play an important role in IOP regulation and possibly the pathophysiology of POAG. As evidence continues to emerge, these proteins are now seen as potential therapeutic targets. Further study is warranted to assess their utility in treating glaucoma in humans.

Using proteomics to uncover extracellular matrix interactions during cardiac remodeling

The left ventricle (LV) responds to a myocardial infarction with an orchestrated sequence of events that result in fundamental changes to both the structure and function of the myocardium. This collection of responses is termed as LV remodeling. Myocardial ischemia resulting in necrosis is the initiating event that culminates in the formation of an extracellular matrix (ECM) rich infarct scar that replaces necrotic myocytes. While the cardiomyocyte is the major cell type that responds to ischemia, infiltrating leukocytes and cardiac fibroblasts coordinate the subsequent wound healing response. The matrix metalloproteinase family of enzymes regulates the inflammatory and ECM responses that modulate scar formation. Matridomics is the proteomic evaluation focused on ECM, while degradomics is the proteomic evaluation of proteases as well as their inhibitors and substrates. This review will summarize the use of proteomics to better understand matrix metalloproteinase roles in post myocardial infarction LV remodeling.

Uncemented primary total hip arthroplasty, presentation of pain, and expression of osteonectin

Osteonectin (ON) is an important matrix glycoprotein highly expressed in bone. In several in vitro and animal model studies, ON was used as indicator of the state of osseointegration of implanted devices. There are, however, no studies on ON expression in the synovial fluid of patients with total hip joint replacement (THJR). The purpose of our study was to determine the ON concentration in synovial fluid from three groups of patients: primary uncemented THJR with hip pain ("pain" group; n = 15) and without pain ("no-pain" group; n = 12), and patients with osteoarthitis scheduled to receive a primary THJR (control group; n = 5). For the prosthesized groups, the statistical nature of the correlation between ON concentration and patient age, in situ life of the THJR, presence of periprosthetic osteolysis, and presence of debris in the synovial fluid was individually investigated. ON concentration was determined using enzyme-linked immunosorbent assay, the presence of periprosthetic osteolysis was established using X-radiography and Engh's criteria, and the presence of debris was determined using digestion and EDX spectroscopy. ON concentration was significantly lower in the "pain" group compared with the "no-pain" one (median values 19.0 and 53.2 ng/mL, respectively). ON concentration in the control group (median value: 16.9 ng/mL) was comparable with that reported in the literature. In the prosthesized groups, ON concentration was not correlated with patient age, in situ life of the prosthesis, presence of periprosthetic osteolysis, or presence of debris in the synovial fluid. Our results suggest that cases of unexplained pain in THJR patients could be treated by paying special attention to the osseointegration status of the implant by using ON concentration as an early indicator of this status.

Progress in understanding role of SPARC protein in gastric cancer

SPARC is a cysteine-rich secretory protein that is highly conservative and shares >70% amino acid sequence homology across all kinds of living organisms. The single-copy gene encoding the SPARC protein is located on human chromosome 5q31.3-q32, consists of 10 exons, and has a full length of 25 900 bp. SPARC protein is mainly expressed in tissue repair-related fibroblasts and endothelial cells, and high expression of SPARC protein has been noted in some aggressive malignant tumors. The incidence and mortality of gastric cancer are high in China, and the high mortality is closely related with tumor invasion and metastasis. SPARC protein is abnormally expressed in gastric carcinoma, and there is still controversy over the role of SPARC in gastric carcinoma. In this paper we review recent progress in understanding the role of SPARC protein in gastric cancer.

Hippocampal SPARC regulates depression-related behavior

SPARC (secreted protein acidic and rich in cysteine) is a matricellular protein highly expressed during development, reorganization and tissue repair. In the central nervous system, glial cells express SPARC during development and in neurogenic regions of the adult brain. Astrocytes control the glutamate receptor levels in the developing hippocampus through SPARC secretion. To further characterize the role of SPARC in the brain, we analyzed the hippocampal-dependent adult behavior of SPARC KO mice. We found that SPARC KO mice show increased levels of anxiety-related behaviors and reduced levels of depression-related behaviors. The antidepressant-like phenotype could be rescued by adenoviral vector-mediated expression of SPARC in the adult hippocampus, but anxiety-related behavior persisted in these mice. To identify the cellular mechanisms underlying these behavioral alterations, we analyzed neuronal activity and neurogenesis in the dentate gyrus (DG). SPARC KO mice have increased levels of neuronal activity, evidenced as more neurons that express c-Fos after a footshock. SPARC also affects cell proliferation in the subgranular zone of the DG, although it does not affect maturation and survival of new neurons. SPARC expression in the adult DG does not revert the proliferation phenotype in KO mice, but our results suggest a role of SPARC in limiting the survival of new neurons in the DG. This work suggests that SPARC could affect anxiety-related behavior by modulating neuronal activity, and that depression-related behavior is dependent upon the adult expression of SPARC, which affects adult brain function by mechanisms that need to be elucidated.

Matricellular proteins in cardiac adaptation and disease

The term matricellular proteins describes a family of structurally unrelated extracellular macromolecules that, unlike structural matrix proteins, do not play a primary role in tissue architecture, but are induced following injury and modulate cell-cell and cell-matrix interactions. When released to the matrix, matricellular proteins associate with growth factors, cytokines, and other bioactive effectors and bind to cell surface receptors transducing signaling cascades. Matricellular proteins are upregulated in the injured and remodeling heart and play an important role in regulation of inflammatory, reparative, fibrotic and angiogenic pathways. Thrombospondin (TSP)-1, -2, and -4 as well as tenascin-C and -X secreted protein acidic and rich in cysteine (SPARC), osteopontin, periostin, and members of the CCN family (including CCN1 and CCN2/connective tissue growth factor) are involved in a variety of cardiac pathophysiological conditions, including myocardial infarction, cardiac hypertrophy and fibrosis, aging-associated myocardial remodeling, myocarditis, diabetic cardiomyopathy, and valvular disease. This review discusses the properties and characteristics of the matricellular proteins and presents our current knowledge on their role in cardiac adaptation and disease. Understanding the role of matricellular proteins in myocardial pathophysiology and identification of the functional domains responsible for their actions may lead to design of peptides with therapeutic potential for patients with heart disease.

Comparative transcriptome analyses indicate molecular homology of zebrafish swimbladder and mammalian lung

The fish swimbladder is a unique organ in vertebrate evolution and it functions for regulating buoyancy in most teleost species. It has long been postulated as a homolog of the tetrapod lung, but the molecular evidence is scarce. In order to understand the molecular function of swimbladder as well as its relationship with lungs in tetrapods, transcriptomic analyses of zebrafish swimbladder were carried out by RNA-seq. Gene ontology classification showed that genes in cytoskeleton and endoplasmic reticulum were enriched in the swimbladder. Further analyses depicted gene sets and pathways closely related to cytoskeleton constitution and regulation, cell adhesion, and extracellular matrix. Several prominent transcription factor genes in the swimbladder including hoxc4a, hoxc6a, hoxc8a and foxf1 were identified and their expressions in developing swimbladder during embryogenesis were confirmed. By comparison of enriched transcripts in the swimbladder with those in human and mouse lungs, we established the resemblance of transcriptome of the zebrafish swimbladder and mammalian lungs. Based on the transcriptomic data of zebrafish swimbladder, the predominant functions of swimbladder are in its epithelial and muscular tissues. Our comparative analyses also provide molecular evidence of the relatedness of the fish swimbladder and mammalian lung.

Inactivation of SPARC enhances high-fat diet-induced obesity in mice

Secreted protein, acidic and rich in cysteine (SPARC), a matricellular protein, modulates extracellular matrix assembly and turnover in many physiological processes. SPARC-null mice exhibit an increased accumulation of adipose tissue. To distinguish between the functions of SPARC in adipogenesis during development and adulthood, we studied wild-type (WT) and SPARC-null mice maintained on a normal (low-fat) or high-fat (HF) diet. On an HF diet, SPARC-null mice exhibited significantly greater weight gain, in comparison to their WT counterparts, and had an enhanced cortical bone area that was likely due to increased mechanical loading. Diet-induced obesity (DIO) was also associated with an increase in vertebral trabecular bone in WT mice, but a significant change in this parameter was not observed in SPARC-null animals. We show that SPARC inhibits mitotic clonal expansion of preadipocytes at an early stage of adipogenesis. Moreover, there were substantially diminished levels of type I collagen in SPARC-null adipose tissue, as well as a reduction in the number of cross-linked, mature collagen fibers. In the absence of SPARC, mice show enhanced DIO. In adult animals, SPARC functions in the production and remodeling of adipose tissue, as well as in the regulation of preadipocyte differentiation.

Transcriptome analysis of the desert locust central nervous system: production and annotation of a Schistocerca gregaria EST database

BACKGROUND

The desert locust (Schistocerca gregaria) displays a fascinating type of phenotypic plasticity, designated as 'phase polyphenism'. Depending on environmental conditions, one genome can be translated into two highly divergent phenotypes, termed the solitarious and gregarious (swarming) phase. Although many of the underlying molecular events remain elusive, the central nervous system (CNS) is expected to play a crucial role in the phase transition process. Locusts have also proven to be interesting model organisms in a physiological and neurobiological research context. However, molecular studies in locusts are hampered by the fact that genome/transcriptome sequence information available for this branch of insects is still limited.

METHODOLOGY

We have generated 34,672 raw expressed sequence tags (EST) from the CNS of desert locusts in both phases. These ESTs were assembled in 12,709 unique transcript sequences and nearly 4,000 sequences were functionally annotated. Moreover, the obtained S. gregaria EST information is highly complementary to the existing orthopteran transcriptomic data. Since many novel transcripts encode neuronal signaling and signal transduction components, this paper includes an overview of these sequences. Furthermore, several transcripts being differentially represented in solitarious and gregarious locusts were retrieved from this EST database. The findings highlight the involvement of the CNS in the phase transition process and indicate that this novel annotated database may also add to the emerging knowledge of concomitant neuronal signaling and neuroplasticity events.

CONCLUSIONS

In summary, we met the need for novel sequence data from desert locust CNS. To our knowledge, we hereby also present the first insect EST database that is derived from the complete CNS. The obtained S. gregaria EST data constitute an important new source of information that will be instrumental in further unraveling the molecular principles of phase polyphenism, in further establishing locusts as valuable research model organisms and in molecular evolutionary and comparative entomology.

Knockdown of SPARC leads to decreased cell-cell adhesion and lens cataracts during post-gastrula development in Xenopus laevis

SPARC is a multifunctional matricellular glycoprotein with complex, transient tissue distribution during embryonic development. In Xenopus laevis embryos, zygotic activation of SPARC is first detected during late gastrulation, undergoing rapid changes in its spatiotemporal distribution throughout organogenesis. Injections of anti-sense Xenopus SPARC morpholinos (XSMOs) into 2- and 4-cell embryos led to a dose-dependent dissociation of embryos during neurula and tailbud stages of development. Animal cap explants derived from XSMO-injected embryos also dissociated, resulting in the formation of amorphous ciliated microspheres. At low doses of XSMOs, lens cataracts were formed, phenocopying that observed in Sparc-null mice. At XSMOs concentrations that did not result in a loss of axial tissue integrity, adhesion between myotomes at intersomitic borders was compromised with a reduction in SPARC concentration. The combined data suggest a critical requirement for SPARC during post-gastrula development in Xenopus embryos and that SPARC, directly or indirectly, promotes cell-cell adhesion in vivo.

TP53INP1 decreases pancreatic cancer cell migration by regulating SPARC expression

Tumor protein 53 induced nuclear protein 1 (TP53INP1) is a p53 target gene that induces cell growth arrest and apoptosis by modulating p53 transcriptional activity. TP53INP1 interacts physically with p53 and is a major player in the p53-driven oxidative stress response. Previously, we demonstrated that TP53INP1 is downregulated in an early stage of pancreatic cancerogenesis and when restored is able to suppress pancreatic tumor development. TP53INP1 downregulation in pancreas is associated with an oncogenic microRNA miR-155. In the present work, we studied the effects of TP53INP1 on cell migration. We found that TP53INP1 inactivation correlates with increased cell migration both in vivo and in vitro. The impact of TP53INP1 expression on cell migration was studied in different cellular contexts: mouse embryonic fibroblast and different pancreatic cancer cell lines. Its expression decreases cell migration by the transcriptional downregulation of secreted protein acidic and rich in cysteine (SPARC). SPARC is a matrix cellular protein, which governs diverse cellular functions and has a pivotal role in regulating cell-matrix interactions, cellular proliferation and migration. SPARC was also showed to be upregulated in normal pancreas and in pancreatic intraepithelial neoplasia lesions in a pancreatic adenocarcinoma mouse model only in the TP53INP1-deficient animals. This novel TP53INP1 activity on the regulation of SPARC expression could explain in part its tumor suppressor function in pancreatic adenocarcinoma by modulating cellular spreading during the metastatic process.

Immunohistochemical expression of SPARC is correlated with recurrence, survival and malignant potential in meningiomas

Meningioma is a common neoplasm that constitutes almost 30% of all primary central nervous system tumors and is associated with inconsistent clinical outcomes. The extracellular matrix proteins play a crucial role in meningioma cell biology and are important in tumor cell invasion and in progression to malignancy. SPARC (secreted protein, acidic and rich in cysteine) (osteonectin) is a matricellular glycoprotein that regulates cell function by interacting with different extracellular matrix proteins. The aim of this study was to evaluate the expression of SPARC with proliferation index, p53 reactivity in WHO grade 1 (benign), grade 2 (atypical) and grade 3 (anaplastic) meningiomas and correlate with clinical features of the patients, including location of the tumor, recurrence of the tumor and survival of patients. We studied 111 meningiomas, 69 being benign, 34 being atypical and eight being anaplastic meningiomas of various histological types. Using immunohistochemical analysis, we evaluated the expression of SPARC, Ki-67 (MIB-1) and p53 in meningiomas. Immunohistochemical scores of SPARC were determined as the sum of frequency (0-3) and intensity (0-3) of immunolabeling of the tumor cells. A high immunohistochemical score (4-6) for SPARC was more frequent in atypical and in anaplastic meningiomas than in benign meningiomas (p < 0.01). MIB-1 proliferation index showed significant association between tumor grades in meningiomas (p < 0.01). At the end of a follow-up period of 47.53 +/- 25.04 months, 30 tumors recurred. A high SPARC expression was significantly associated with tumor recurrence (p = 0.02). The immunoreactivity of p53 protein and MIB-1 score were significantly higher in recurrent meningiomas than in non-recurrent meningiomas. The cumulative survival of patients with high SPARC expression was significantly lower than patients with low SPARC expression. The high SPARC expression scores were predominantly identified in meningothelial, fibrous and chordoid meningiomas; low SPARC expression scores were mostly spotted in secretory and psammomatous meningiomas. Evaluating SPARC expression might help assessing recurrence risk and survival estimation in meningiomas.

miR-29 suppression of osteonectin in osteoblasts: regulation during differentiation and by canonical Wnt signaling

The matricellular protein osteonectin, secreted protein acidic and rich in cysteine (SPARC, BM-40), is the most abundant non-collagenous matrix protein in bone. Matricellular proteins play a fundamental role in the skeleton as regulators of bone remodeling. In the skeleton, osteonectin is essential for the maintenance of bone mass and for balancing bone formation and resorption in response to parathyroid hormone (PTH). It promotes osteoblast differentiation and cell survival. Mechanisms regulating the expression of osteonectin in the skeleton and in other tissues remain poorly understood. We found that the proximal region of the mouse osteonectin 3' untranslated region (UTR) contains a well-conserved, dominant regulatory motif that interacts with microRNAs (miRs)-29a and -29c. Transfection of osteoblastic cells with miR-29a inhibitors increased osteonectin protein levels, whereas transfection of miR-29a precursor RNA decreased osteonectin. miR-29a and -29c were increased during osteoblastic differentiation in vitro. The up-regulation of these miRNAs correlated with decreased osteonectin protein during the matrix maturation and mineralization phases of late differentiation. In contrast, osteonectin transcript levels remained relatively constant during this process, implying repression of translation. Treatment of osteoblasts with LiCl induced miR-29a and -29c expression and decreased osteonectin synthesis. When cells were treated with Dickkopf-1 (Dkk-1), miR-29a and -29c expression was repressed. These data suggest that canonical Wnt signaling, which is increased during osteoblastic differentiation, induces expression of miR-29. Osteonectin and miR-29 are co-expressed in extra-skeletal tissues, and the post-transcriptional mechanisms regulating osteonectin in osteoblasts are likely to be active in other cell systems.

SPARC accelerates disease progression in experimental crescentic glomerulonephritis

Podocytopenia characterizes many forms of glomerular disease, preceding the development of glomerulosclerosis. While detachment of viable podocytes from the underlying glomerular basement membrane is an important mechanism of podocyte loss, the underlying factors involved remain unclear. Secreted protein acidic and rich in cysteine (SPARC), a matricellular protein with counteradhesive properties, is normally expressed at low levels by the podocyte but is markedly increased following podocyte injury. Accordingly, we elucidate the role of SPARC in mediating experimental crescentic glomerulonephritis by inducing passive nephrotoxic nephritis in SPARC(+/+) and SPARC(-/-) mice. By days 4, 7, and 21 following disease induction, podocyte number is better preserved, glomerulosclerosis is ameliorated, and proteinuria is reduced in SPARC(-/-) mice as compared with SPARC(+/+) littermates. Moreover, the preserved podocyte number in SPARC(-/-) mice correlates with reduced urinary levels of both nephrin and podocin. To establish a causal role for SPARC in mediating detachment, cultured SPARC(+/+) and SPARC(-/-) podocytes were subjected to mechanical strain as well as trypsin digestion, and detachment assays were performed. While podocytes lacking SPARC were more resistant to stretch-induced detachment, stable re-expression of SPARC restored detachment rates to levels comparable with SPARC(+/+) podocytes. Taken together, this study proves that SPARC plays a causal role in mediating podocyte detachment and accelerating glomerulosclerosis in experimental crescentic glomerulonephritis.

Matricellular proteins in the trabecular meshwork

The trabecular meshwork is one of the primary tissues of interest in the normal regulation and dysregulation of intraocular pressure (IOP) that is a causative risk factor for primary open-angle glaucoma. Matricellular proteins generally function to allow cells to modulate their attachments with and alter the characteristics of their surrounding extracellular matrix (ECM). In non-ocular tissues, matricellular proteins generally increase fibrosis. Since ECM turnover is very important to the outflow facility, matricellular proteins may have a significant role in the regulation of IOP. The formalized study of matricellular proteins in trabecular meshwork is in its infancy. SPARC, thrombospondins-1 and -2, and tenascins-C and -X, and osteopontin have been localized to varying areas within the trabecular meshwork. Preliminary evidence indicates that SPARC and thrombospondin-1 play a role in the regulation of IOP and possibly the pathophysiology of glaucoma. These data show promise that matricellular proteins are involved in IOP dysregulation and are potential therapeutic targets. Further study is needed to clarify these roles.

SPARC is expressed by macroglia and microglia in the developing and mature nervous system

SPARC (secreted protein, acidic and rich in cysteine) is a matricellular protein that is highly expressed during development, tissue remodeling, and repair. SPARC produced by olfactory ensheathing cells (OECs) can promote axon sprouting in vitro and in vivo. Here, we show that in the developing nervous system of the mouse, SPARC is expressed by radial glia, blood vessels, and other pial-derived structures during embryogenesis and postnatal development. The rostral migratory stream contains SPARC that becomes progressively restricted to the SVZ in adulthood. In the adult CNS, SPARC is enriched in specialized radial glial derivatives (Müller and Bergmann glia), microglia, and brainstem astrocytes. The peripheral glia, Schwann cells, and OECs express SPARC throughout development and in maturity, although it appears to be down-regulated with maturation. These data suggest that SPARC may be expressed by glia in a spatiotemporal manner consistent with a role in cell migration, neurogenesis, synaptic plasticity, and angiogenesis.

Secreted protein acidic and rich in cysteine (SPARC) in human skeletal muscle

Secreted protein acidic and rich in cysteine (SPARC)/osteonectin is expressed in different tissues during remodeling and repair, suggesting a function in regeneration. Several gene expression studies indicated that SPARC was expressed in response to muscle damage. Studies on myoblasts further indicated a function of SPARC in skeletal muscle. We therefore found it of interest to study SPARC expression in human skeletal muscle during development and in biopsies from Duchenne and Becker muscular dystrophy and congenital muscular dystrophy, congenital myopathy, inclusion body myositis, and polymyositis patients to analyze SPARC expression in a selected range of inherited and idiopathic muscle wasting diseases. SPARC-positive cells were observed both in fetal and neonatal muscle, and in addition, fetal myofibers were observed to express SPARC at the age of 15-16 weeks. SPARC protein was detected in the majority of analyzed muscle biopsies (23 of 24), mainly in mononuclear cells of which few were pax7 positive. Myotubes and regenerating myofibers also expressed SPARC. The expression-degree seemed to reflect the severity of the lesion. In accordance with these in vivo findings, primary human-derived satellite cells were found to express SPARC both during proliferation and differentiation in vitro. In conclusion, this study shows SPARC expression both during muscle development and in regenerating muscle. The expression is detected both in satellite cells/myoblasts and in myotubes and muscle fibers, indicating a role for SPARC in the skeletal muscle compartment.

Haemocyte-derived SPARC is required for collagen-IV-dependent stability of basal laminae in Drosophila embryos

SPARC is an evolutionarily conserved collagen-binding extracellular matrix (ECM) glycoprotein whose morphogenetic contribution(s) to embryonic development remain elusive despite decades of research. We have therefore used Drosophila genetics to gain insight into the role of SPARC during embryogenesis. In Drosophila embryos, high levels of SPARC and other basal lamina components (such as network-forming collagen IV, laminin and perlecan) are synthesized and secreted by haemocytes, and assembled into basal laminae. A SPARC mutant was generated by P-element mutagenesis that is embryonic lethal because of multiple developmental defects. Whereas no differences in collagen IV immunostaining were observed in haemocytes between wild-type and SPARC-mutant embryos, collagen IV was not visible in basal laminae of SPARC-mutant embryos. In addition, the laminin network of SPARC-mutant embryos appeared fragmented and discontinuous by late embryogenesis. Transgenic expression of SPARC protein by haemocytes in SPARC-mutant embryos restored collagen IV and laminin continuity in basal laminae. However, transgenic expression of SPARC by neural cells failed to rescue collagen IV in basal laminae, indicating that the presence of collagen IV deposition requires SPARC expression by haemocytes. Our previous finding that haemocyte-derived SPARC protein levels are reduced in collagen-IV-mutant embryos and the observation that collagen-IV-mutant embryos showed a striking phenotypic similarity to SPARC-mutant embryos suggests a mutual dependence between these major basal laminae components during embryogenesis. Patterning defects and impaired condensation of the ventral nerve cord also resulted from the loss SPARC expression prior to haemocyte migration. Hence, SPARC is required for basal lamina maturation and condensation of the ventral nerve cord during Drosophila embryogenesis.

Tumor associated stromal cells play a critical role on the outcome of the oncolytic efficacy of conditionally replicative adenoviruses

The clinical efficacy of conditionally replicative oncolytic adenoviruses (CRAd) is still limited by the inefficient infection of the tumor mass. Since tumor growth is essentially the result of a continuous cross-talk between malignant and tumor-associated stromal cells, targeting both cell compartments may profoundly influence viral efficacy. Therefore, we developed SPARC promoter-based CRAds since the SPARC gene is expressed both in malignant cells and in tumor-associated stromal cells. These CRAds, expressing or not the Herpes Simplex thymidine kinase gene (Ad-F512 and Ad(I)-F512-TK, respectively) exerted a lytic effect on a panel of human melanoma cells expressing SPARC; but they were completely attenuated in normal cells of different origins, including fresh melanocytes, regardless of whether cells expressed or not SPARC. Interestingly, both CRAds displayed cytotoxic activity on SPARC positive-transformed human microendothelial HMEC-1 cells and WI-38 fetal fibroblasts. Both CRAds were therapeutically effective on SPARC positive-human melanoma tumors growing in nude mice but exhibited restricted efficacy in the presence of co-administered HMEC-1 or WI-38 cells. Conversely, co-administration of HMEC-1 cells enhanced the oncolytic efficacy of Ad(I)-F512-TK on SPARC-negative MIA PaCa-2 pancreatic cancer cells in vivo. Moreover, conditioned media produced by stromal cells pre-infected with the CRAds enhanced the in vitro viral oncolytic activity on pancreatic cancer cells, but not on melanoma cells. The whole data indicate that stromal cells might play an important role on the outcome of the oncolytic efficacy of conditionally replicative adenoviruses.

Sparc (Osteonectin) functions in morphogenesis of the pharyngeal skeleton and inner ear

Sparc (Osteonectin), a matricellular glycoprotein expressed by many differentiated cells, is a major non-collagenous constituent of vertebrate bones. Recent studies indicate that Sparc expression appears early in development, although its function and regulation during embryogenesis are largely unknown. We cloned zebrafish sparc and investigated its role during development, using a mo rpholino antisense oligonucleotide-based knockdown approach. Consistent with its strong expression in the otic vesicle and developing pharyngeal cartilages, knockdown of Sparc function resulted in specific inner ear and cartilage defects that are highlighted by changes in gene expression, morphology and behavior. We rescued the knockdown phenotypes by co-injecting sparc mRNA, providing evidence that the knockdown phenotype is due specifically to impairment of Sparc function. A comparison of the phenotypes of Sparc knockdown and known zebrafish mutants with similar defects places Sparc downstream of sox9 in the genetic network that regulates development of the pharyngeal skeleton and inner ear of vertebrates.

SPARC from olfactory ensheathing cells stimulates Schwann cells to promote neurite outgrowth and enhances spinal cord repair

Olfactory ensheathing cells (OECs) transplanted into the lesioned CNS can stimulate reportedly different degrees of regeneration, remyelination, and functional recovery, but little is known about the mechanisms OECs may use to stimulate endogenous repair. Here, we used a functional proteomic approach, isotope-coded affinity tagging and mass spectrometry, to identify active components of the OEC secreteome that differentially stimulate outgrowth. SPARC (secreted protein acidic rich in cysteine) (osteonectin) was identified as an OEC-derived matricellular protein that can indirectly enhance the ability of Schwann cells to stimulate dorsal root ganglion outgrowth in vitro. SPARC stimulates Schwann cell-mediated outgrowth by cooperative signal with laminin-1 and transforming growth factor beta. Furthermore, when SPARC-null OECs were transplanted into lesioned rat spinal cord, the absence of OEC-secreted SPARC results in an attenuation of outgrowth of specific subsets of sensory and supraspinal axons and changes the pattern of macrophage infiltration in response to the transplanted cells. These data provide the first evidence for a role for SPARC in modulating different aspects of CNS repair and indicate that SPARC can change the activation state of endogenous Schwann cells, resulting in the promotion of outgrowth in vitro, and in vivo.

Splenic and immune alterations of the Sparc-null mouse accompany a lack of immune response

Sparc-null mice have been used as models to assess tumor-host immune cell interactions. However, it is not known if they have a competent immune system. In this study, the immune systems of Sparc wild-type and null mice were compared. Mice were assessed for differences in total body weight, spleen weight and spleen-to-body weight ratios. Spleens were compared with respect to morphology, and Sparc, Ki-67, MOMA-1 and IgM expression. Immune cells in blood, bone marrow and spleen were assessed by blood smears, automated blood panel, and flow cytometry. Additionally, the ability of Sparc-null mice to respond to immune challenge was evaluated using a footpad model. The morphological and immunohistochemical results indicated that Sparc-null spleens had more white pulp, hyperproliferative B cells in the germinal centers, and decreased marginal zones. Sparc-null spleens lacked normal Sparc expression in red and white pulp, marginal zones, endothelial and sinusoidal cells. By flow analysis, B cells were decreased and T cells were increased in the bone marrow. Finally, Sparc-null mice were unable to mount an immune response following footpad lipopolysaccharide challenge. These data confirm that Sparc-null mice have an impaired immune system.

Trafficking of osteonectin by retinal pigment epithelial cells: Evidence for basolateral secretion

Osteonectin is a glycoprotein that modulates several aspects of cellular behaviour including proliferation and adhesion. The retinal pigment epithelium forms a continuous monolayer of polarised cells immediately bellow the neuroretina, and is integral to the homeostasis of photoreceptor cells. While osteonectin is expressed by normal retinal pigment epithelium in situ, its expression is significantly increased in retinal pigment epithelial cells associated with several common retinal diseases. This pattern of expression implies an important role for osteonectin in the biology of retinal pigment epithelial cells. However, the trafficking, processing, and eventual fate of osteonectin in these cells is not clear at present. Although the theoretical report of a leader sequence within the osteonectin open reading frame and its extracellular presence in some tissues indirectly support secretion of the protein, there is no direct experimental demonstration of the secretion route to date. As a first step towards understanding the role of osteonectin in retinal pigment epithelium, we studied the intracellular distribution and trafficking of the protein in living cells. Here, we present experimental evidence that a precursor osteonectin fusion protein is targeted to the endoplasmic reticulum/Golgi pathway, with a likely basal secretion in retinal pigment epithelial cells. In addition, we show that the precursor osteonectin protein having the leader sequence masked fails to undergo secretion leading to cell death, a phenotype which may be of relevance not only for retinal pathology, but also for other diseases such as the bone disorder known as pseudoachondroplasia that is associated with a lack of osteonectin secretion.

Differential zonal expression and adrenocorticotropin regulation of secreted protein acidic and rich in cysteine (SPARC), a matricellular protein, in the midgestation human fetal adrenal gland: implications for adrenal development

CONTEXT

Matricellular proteins are a group of secreted, multifunctional extracellular matrix glycoproteins that includes thrombospondins (TSPs), tenascin-C, and secreted protein acidic and rich in cysteine (SPARC). They may be implicated in the dynamic developmental processes of the human fetal adrenal (HFA) in which the outer, definitive zone (DZ) cells are postulated to proliferate, migrate centripetally, differentiate, and populate the inner, steroidogenic fetal zone (FZ).

OBJECTIVE

The objective of the study was to identify a matricellular molecule that likely plays a major role in HFA development.

DESIGN

Studies involved RNA, cryosections, and cell cultures from 14- to 23-wk HFAs and human adult adrenal RNA.

MAIN OUTCOME MEASURES

Measures included transcripts encoding matricellular proteins, using real-time quantitative RT-PCR; SPARC localization by immunostaining; and ACTH regulation of SPARC expression and secretion by quantitative RT-PCR and Western blot.

RESULTS

SPARC HFA mRNA was 100-, 700-, and 300-fold higher than TSP-1, TSP-2, and tenascin-C mRNA, respectively. HFA SPARC mRNA was 3-fold higher than adult adrenals (P < 0.005), comparable with levels in adult brain (positive control), whereas mRNAs encoding TSP-1 and TSP-2 were lower in fetal than adult adrenals. SPARC immunoreactivity was detected exclusively in the FZ, not DZ. ACTH, a key regulator of HFA growth and function, increased SPARC mRNA (by 1.7-fold at 1 nm, 48 h, P < 0.05) in isolated FZ cells but not DZ cells. ACTH up-regulation of SPARC protein was also detected in FZ cell lysates and culture medium.

CONCLUSIONS

Results suggest a possible role for SPARC in development of functional and/or structural zonation of the HFA.

Age-related changes in cochlear gene expression in normal and shaker 2 mice

The vertebrate cochlea is a complex organ optimized for sound transduction. Auditory hair cells, with their precisely arranged stereocilia bundles, transduce sound waves to electrical signals that are transmitted to the brain. Mutations in the unconventional myosin XV cause deafness in both human DFNB3 families and in shaker 2 (sh2) mice as a result of defects in stereocilia. In these mutant mice, hair cells have relatively normal spatial organization of stereocilia bundles but lack the graded, stair-step organization. We used sh2 mice as an experimental model to investigate the molecular consequences of the sh2 mutation in the Myo15 gene. Gene expression profiling with Affymetrix GeneChips in deaf homozygous (sh2/sh2) mice at 3 weeks and 3 months of age, and in age-matched, normal-hearing heterozygotes (+/sh2) identified only a few genes whose expression was affected by genotype, but a large number with age-associated changes in expression in both normal mice and sh2/sh2 homozygotes. Microarray data analyzed using Robust Multiarray Average identified Aim1, Dbi, and Tm4sf3 as genes with increased expression in sh2/sh2 homozygotes. These increases were confirmed by quantitative reverse transcription-polymerase chain reaction. Genes exhibiting altered expression with age encoded collagens and proteins involved in collagen maturation, extracellular matrix, and bone mineralization. These results identified potential cellular pathways associated with myosin XV defects, and age-associated molecular events that are likely to be involved in maturation of the cochlea and auditory function.