Secreted protein acidic and rich in cysteine is a matrix scavenger chaperone

Cloning, characterization, and spatio-temporal expression patterns of HdhSPARC and its responses to multiple stressors

SPARC is an extracellular Ca2+-binding, secreted glycoprotein that plays a dynamic role in the growth and development of organisms. This study aimed to describe the isolation, characterization, and expression analysis of HdhSPARC in Pacific abalone (Haliotis discus hannai) to infer its potential functional role. The isolated HdhSPARC was 1633 bp long, encoding a polypeptide of 284 amino acid residues. Structurally, the SPARC protein in abalone is comprised of three biological domains. However, the structure of this protein varied between vertebrates and invertebrates, as suggested by their distinct clustering patterns in phylogenetic analysis. In early development, HdhSPARC was variably expressed, and higher expression was found in veliger larvae. Moreover, HdhSPARC was highly expressed in juvenile abalone with rapid growth compared to their slower-growing counterparts. Among the testicular development stages, the growth stage exhibited higher HdhSPARC expression. HdhSPARC was also upregulated during muscle remodeling and shell biomineralization, as well as in response to different stressors such as heat shock, LPS, and H2O2 exposure. However, this gene was downregulated in Cd-exposed abalone. The present study first comprehensively characterized the HdhSPARC gene, and its spatio-temporal expressions were analyzed along with its responses to various stressors.

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.

Toward Single Cell Tattoos: Biotransfer Printing of Lithographic Gold Nanopatterns on Live Cells

Lithographic nanopatterning techniques such as photolithography, electron-beam lithography, and nanoimprint lithography (NIL) have revolutionized modern-day electronics and optics. Yet, their application for creating nanobio interfaces is limited by the cytotoxic and two-dimensional nature of conventional fabrication methods. Here, we present a biocompatible and cost-effective transfer process that leverages (a) NIL to define sub-300 nm gold (Au) nanopattern arrays, (b) amine functionalization of Au to transfer the NIL-arrays from a rigid substrate to a soft transfer layer, (c) alginate hydrogel as a flexible, degradable transfer layer, and (d) gelatin conjugation of the Au NIL-arrays to achieve conformal contact with live cells. We demonstrate biotransfer printing of the Au NIL-arrays on rat brains and live cells with high pattern fidelity and cell viability and observed differences in cell migration on the Au NIL-dot and NIL-wire printed hydrogels. We anticipate that this nanolithography-compatible biotransfer printing method could advance bionics, biosensing, and biohybrid tissue interfaces.

Toward single cell tattoos: Biotransfer printing of lithographic gold nanopatterns on live cells

Lithographic nanopatterning techniques like photolithography, electron-beam lithography, and nanoimprint lithography (NIL) have revolutionized modern-day electronics and optics. Yet, their application for creating nano-bio interfaces is limited by the cytotoxic and two-dimensional nature of conventional fabrication methods. Here, we present a biocompatible and cost-effective transfer process that leverages (a) NIL to define sub-300 nm gold (Au) nanopattern arrays, (b) amine functionalization of Au to transfer the NIL-arrays from a rigid substrate to a soft transfer layer, (c) alginate hydrogel as a flexible, degradable transfer layer, and (d) gelatin conjugation of the Au NIL-arrays to achieve conformal contact with live cells. We demonstrate biotransfer printing of the Au NIL-arrays on rat brains and live cells with high pattern fidelity and cell viability and observed differences in cell migration on the Au NIL-dot and NIL-wire printed hydrogels. We anticipate that this nanolithography-compatible biotransfer printing method could advance bionics, biosensing, and biohybrid tissue interfaces.

Cellular and Molecular Regulation of Exercise—A Neuronal Perspective

The beneficial effects of exercise on the proper functioning of the body have been firmly established. Multi-systemic metabolic regulation of exercise is the consequence of multitudinous changes that occur at the cellular level. The exercise responsome comprises all molecular entities including exerkines, miRNA species, growth factors, signaling proteins that are elevated and activated by physical exercise. Exerkines are secretory molecules released by organs such as skeletal muscle, adipose tissue, liver, and gut as a function of acute/chronic exercise. Exerkines such as FNDC5/irisin, Cathepsin B, Adiponectin, and IL-6 circulate through the bloodstream, cross the blood-brain barrier, and modulate the expression of important signaling molecules such as AMPK, SIRT1, PGC1α, BDNF, IGF-1, and VEGF which further contribute to improved energy metabolism, glucose homeostasis, insulin sensitivity, neurogenesis, synaptic plasticity, and overall well-being of the body and brain. These molecules are also responsible for neuroprotective adaptations that exercise confers on the brain and potentially ameliorate neurodegeneration. This review aims to detail important cellular and molecular species that directly or indirectly mediate exercise-induced benefits in the body, with an emphasis on the central nervous system.

Clusterin, other extracellular chaperones, and eye disease

Proteostasis refers to all the processes that maintain the correct expression level, location, folding and turnover of proteins, essential to organismal survival. Both inside cells and in body fluids, molecular chaperones play key roles in maintaining proteostasis. In this article, we focus on clusterin, the first-recognized extracellular mammalian chaperone, and its role in diseases of the eye. Clusterin binds to and inhibits the aggregation of proteins that are misfolded due to mutations or stresses, clears these aggregating proteins from extracellular spaces, and facilitates their degradation. Clusterin exhibits three main homeostatic activities: proteostasis, cytoprotection, and anti-inflammation. The so-called "protein misfolding diseases" are caused by aggregation of misfolded proteins that accumulate pathologically as deposits in tissues; we discuss several such diseases that occur in the eye. Clusterin is typically found in these deposits, which is interpreted to mean that its capacity as a molecular chaperone to maintain proteostasis is overwhelmed in the disease state. Nevertheless, the role of clusterin in diseases involving such deposits needs to be better defined before therapeutic approaches can be entertained. A more straightforward case can be made for therapeutic use of clusterin based on its proteostatic role as a proteinase inhibitor, as well as its cytoprotective and anti-inflammatory properties. It is likely that clusterin works together in this way with other extracellular chaperones to protect the eye from disease, and we discuss several examples. We end this article by predicting future steps that may lead to development of clusterin as a biological drug.

The effect of amino acids on the bladder cycle: a concise review

The human bladder maintains a cycle of filling, storing, and micturating throughout an individual's lifespan. The cycle relies on the ability of the bladder to expand without increasing the intravesical pressure, which is only possible with the controlled relaxation of well-complaint muscles and the congruously organized construction of the bladder wall. A competent bladder outlet, which functions in a synchronous fashion with the bladder, is also necessary for this cycle to be completed successfully without deterioration. In this paper, we aimed to review the contemporary physiological findings on bladder physiology and examine the effects of amino acids on clinical conditions affecting the bladder, with special emphasis on the available therapeutic evidence and possible future roles of the amino acids in the treatment of the bladder-related disorders.

Secreted Protein Acidic and Rich in Cysteine as a Molecular Physiological and Pathological Biomarker

Secreted protein acidic and rich in cysteine (SPARC) is expressed in diverse tissues and plays roles in various biological functions and processes. Increased serum levels of SPARC or its gene overexpression have been reported following numerous physiological and pathological changes including injuries, exercise, regeneration, obesity, cancer, and inflammation. Such expression pattern interrelation between these biological changes and the SPARC expression/secretion points to it as a biomarker. This property could lead to a variety of potential applications ranging from mechanistic studies and animal model validation to the clinical and therapeutic evaluation of both disease prognosis and pharmacological agents.

Identifying Potential Candidate Hub Genes and Functionally Enriched Pathways in the Immune Responses to Quadrivalent Inactivated Influenza Vaccines in the Elderly Through Co-Expression Network Analysis

Insights into the potential candidate hub genes may facilitate the generation of safe and effective immunity against seasonal influenza as well as the development of personalized influenza vaccines for the elderly at high risk of influenza virus infection. This study aimed to identify the potential hub genes related to the immune induction process of the 2018/19 seasonal quadrivalent inactivated influenza vaccines (QIVs) in the elderly ≥60 years by using weighted gene co-expression network analysis (WGCNA). From 63 whole blood samples from16 elderly individuals, a total of 13,345 genes were obtained and divided into eight co-expression modules, with two modules being significantly correlated with vaccine-induced immune responses. After functional enrichment analysis, genes under GO terms of vaccine-associated immunity were used to construct the sub-network for identification and functional validation of hub genes. MCEMP1 and SPARC were confirmed as the hub genes with an obvious effect on QIVs-induced immunity. The MCEMP1 expression was shown to be negatively correlated with the QIVs-associated reactogenicity within 7 days after vaccination, which could be suppressed by the CXCL 8/IL-8 and exacerbated by the Granzyme-B cytotoxic mediator. Meanwhile, the SPARC expression was found to increase the immune responses to the QIVs and contribute to the persistence of protective humoral antibody titers. These two genes can be used to predict QIVs-induced adverse reaction, the intensity of immune responses, and the persistence of humoral antibody against influenza. This work has shed light on further research on the development of personalized QIVs with appropriate immune responses and long-lasting immunity against the forthcoming seasonal influenza.

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.

The Human Epidermal Basement Membrane: A Shaped and Cell Instructive Platform That Aging Slowly Alters

One of the most important functions of skin is to act as a protective barrier. To fulfill this role, the structural integrity of the skin depends on the dermal-epidermal junction-a complex network of extracellular matrix macromolecules that connect the outer epidermal layer to the underlying dermis. This junction provides both a structural support to keratinocytes and a specific niche that mediates signals influencing their behavior. It displays a distinctive microarchitecture characterized by an undulating pattern, strengthening dermal-epidermal connectivity and crosstalk. The optimal stiffness arising from the overall molecular organization, together with characteristic anchoring complexes, keeps the dermis and epidermis layers extremely well connected and capable of proper epidermal renewal and regeneration. Due to intrinsic and extrinsic factors, a large number of structural and biological changes accompany skin aging. These changes progressively weaken the dermal-epidermal junction substructure and affect its functions, contributing to the gradual decline in overall skin physiology. Most changes involve reduced turnover or altered enzymatic or non-enzymatic post-translational modifications, compromising the mechanical properties of matrix components and cells. This review combines recent and older data on organization of the dermal-epidermal junction, its mechanical properties and role in mechanotransduction, its involvement in regeneration, and its fate during the aging process.

Secreted Chaperones in Neurodegeneration

Protein homeostasis, or proteostasis, is a combination of cellular processes that govern protein quality control, namely, protein translation, folding, processing, and degradation. Disruptions in these processes can lead to protein misfolding and aggregation. Proteostatic disruption can lead to cellular changes such as endoplasmic reticulum or oxidative stress; organelle dysfunction; and, if continued, to cell death. A majority of neurodegenerative diseases involve the pathologic aggregation of proteins that subverts normal neuronal function. While prior reviews of neuronal proteostasis in neurodegenerative processes have focused on cytoplasmic chaperones, there is increasing evidence that chaperones secreted both by neurons and other brain cells in the extracellular - including transsynaptic - space play important roles in neuronal proteostasis. In this review, we will introduce various secreted chaperones involved in neurodegeneration. We begin with clusterin and discuss its identification in various protein aggregates, and the use of increased cerebrospinal fluid (CSF) clusterin as a potential biomarker and as a potential therapeutic. Our next secreted chaperone is progranulin; polymorphisms in this gene represent a known genetic risk factor for frontotemporal lobar degeneration, and progranulin overexpression has been found to be effective in reducing Alzheimer's- and Parkinson's-like neurodegenerative phenotypes in mouse models. We move on to BRICHOS domain-containing proteins, a family of proteins containing highly potent anti-amyloidogenic activity; we summarize studies describing the biochemical mechanisms by which recombinant BRICHOS protein might serve as a therapeutic agent. The next section of the review is devoted to the secreted chaperones 7B2 and proSAAS, small neuronal proteins which are packaged together with neuropeptides and released during synaptic activity. Since proteins can be secreted by both classical secretory and non-classical mechanisms, we also review the small heat shock proteins (sHsps) that can be secreted from the cytoplasm to the extracellular environment and provide evidence for their involvement in extracellular proteostasis and neuroprotection. Our goal in this review focusing on extracellular chaperones in neurodegenerative disease is to summarize the most recent literature relating to neurodegeneration for each secreted chaperone; to identify any common mechanisms; and to point out areas of similarity as well as differences between the secreted chaperones identified to date.

Efficacy and safety of nanoparticle albumin-bound paclitaxel as neoadjuvant chemotherapy in HER2-negative breast cancer

CONTEXT

Nanoparticle albumin-bound paclitaxel (Nab-PTX) is a form of paclitaxel bound to albumin nanoparticles and is used widely in a neoadjuvant setting for patients with breast cancer.

AIMS

We conducted a retrospective study to compare the efficacy and safety of Nab-PTX to PTX as neoadjuvant chemotherapy for patients with operable HER2-negative breast cancer.

SETTINGS AND DESIGN

In total, 50 patients were enrolled. Nab-PTX was administered in the study group, and PTX was administered in the control group.

SUBJECTS AND METHODS

The clinical response and safety profile were recorded. The expression of secreted protein acidic rich in cysteine (SPARC) in tumor tissue was examined.

STATISTICAL ANALYSIS

The efficacy and safety analyses were computed using SPSS statistical software. Multiple logistic regression analysis was performed to evaluate the exploratory variables (age, stage, estrogen receptor, partial response, and SPARC expression) for the pathological complete response (pCR), and Fisher's exact test was performed to evaluate the relationship between SPARC and pCR.

RESULTS

Both groups of patients achieved a good clinical response. The pCR rate for the Nab-PTX regimen was significantly higher than that for the PTX regimen. The most common adverse events were neutropenia, peripheral sensory neuropathy, arthralgia, and myalgia. In 68% of cases in the Nab-PTX group, high SPARC expression was observed.

CONCLUSIONS

As neoadjuvant therapy, the Nab-PTX regimen has advantages over conventional taxane regimen in patients with HER2-negative breast cancer. With this regimen, a high pCR rate was achieved with a good safety profile.

Increased Rate of Retinal Pigment Epithelial Cell Migration and Pro-Angiogenic Potential Ensuing From Reduced Cystatin C Expression

Purpose

Variant B precursor cysteine protease inhibitor cystatin C, a known recessive risk factor for developing exudative age-related macular degeneration (AMD), presents altered intracellular trafficking and reduced secretion from retinal pigment epithelial (RPE) cells. Because cystatin C inhibits multiple extracellular matrix (ECM)-degrading cathepsins, this study evaluated the role of this mutation in inducing ECM-related functional changes in RPE cellular behavior.

Methods

Induced pluripotent stem cells gene-edited bi-allelically by CRISPR/Cas9 to express the AMD-linked cystatin C variant were differentiated to RPE cells and assayed for their ability to degrade fluorescently labeled ECM proteins. Cellular migration and adhesion on multiple ECM proteins, differences in transepithelial resistance and polarized protein secretion were tested. Vessel formation induced by gene edited cells-conditioned media was quantified using primary human dermal microvascular epithelial cells.

Results

Variant B cystatin C-expressing induced pluripotent stem cells-derived RPE cells displayed a significantly higher rate of laminin and fibronectin degradation 3 days after seeding on fluorescently labeled ECM (P < 0.05). Migration on matrigel, collagen IV and fibronectin was significantly faster for edited cells compared with wild-type (WT) cells. Both edited and WT cells displayed polarized secretion of cystatin C, but transepithelial resistance was lower in gene-edited cells after 6 weeks culture, with significantly lower expression of tight junction protein claudin-3. Media conditioned by gene-edited cells stimulated formation of significantly longer microvascular tubes (P < 0.05) compared with WT-conditioned media.

Conclusions

Reduced levels of cystatin C lead to changes in the RPE ability to degrade, adhere, and migrate supporting increased invasiveness and angiogenesis relevant for AMD pathology.

Secreted protein acidic and rich in cysteine (SPARC) improves glucose tolerance via AMP-activated protein kinase activation

During exercise, skeletal muscles release cytokines, peptides, and metabolites that exert autocrine, paracrine, or endocrine effects on glucose homeostasis. In this study, we investigated the effects of secreted protein acidic and rich in cysteine (SPARC), an exercise-responsive myokine, on glucose metabolism in human and mouse skeletal muscle. SPARC-knockout mice showed impaired systemic metabolism and reduced phosphorylation of AMPK and protein kinase B in skeletal muscle. Treatment of SPARC-knockout mice with recombinant SPARC improved glucose tolerance and concomitantly activated AMPK in skeletal muscle. These effects were dependent on AMPK-γ3 because SPARC treatment enhanced skeletal muscle glucose uptake in wild-type mice but not in AMPK-γ3-knockout mice. SPARC strongly interacted with the voltage-dependent calcium channel, and inhibition of calcium-dependent signaling prevented SPARC-induced AMPK phosphorylation in human and mouse myotubes. Finally, chronic SPARC treatment improved systemic glucose tolerance and AMPK signaling in skeletal muscle of high-fat diet-induced obese mice, highlighting the efficacy of SPARC treatment in the management of metabolic diseases. Thus, our findings suggest that SPARC treatment mimics the effects of exercise on glucose tolerance by enhancing AMPK-dependent glucose uptake in skeletal muscle.-Aoi, W., Hirano, N., Lassiter, D. G., Björnholm, M., Chibalin, A. V., Sakuma, K., Tanimura, Y., Mizushima, K., Takagi, T., Naito, Y., Zierath, J. R., Krook, A. Secreted protein acidic and rich in cysteine (SPARC) improves glucose tolerance via AMP-activated protein kinase activation.

Secreted protein acidic and rich in cysteine (SPARC) induces lipotoxicity in neuroblastoma by regulating transport of albumin complexed with fatty acids

SPARC is a matrix protein that mediates interactions between cells and the microenvironment. In cancer, SPARC may either promote or inhibit tumor growth depending upon the tumor type. In neuroblastoma, SPARC is expressed in the stromal Schwannian cells and functions as a tumor suppressor. Here, we developed a novel in vivo model of stroma-rich neuroblastoma using non-tumorigenic SHEP cells with modulated levels of SPARC, mixed with tumorigenic KCNR cells. Tumors with stroma-derived SPARC displayed suppressed growth, inhibited angiogenesis and increased lipid accumulation. Based on the described chaperone function of SPARC, we hypothesized that SPARC binds albumin complexed with fatty acids and transports them to tumors. We show that SPARC binds albumin with Kd=18.9±2.3 uM, and enhances endothelial cell internalization and transendothelial transport of albumin in vitro. We also demonstrate that lipids induce toxicity in neuroblastoma cells and show that lipotoxicity is increased when cells are cultured in hypoxic conditions. Studies investigating the therapeutic potential of SPARC are warranted.

Collagen IV trafficking: The inside-out and beyond story

Collagen IV networks endow basement membranes (BMs) with remarkable tensile strength and function as morphoregulatory substrata for diverse tissue-specific developmental events. A complex repertoire of intracellular and extracellular molecular interactions are required for collagen IV secretion and supramolecular assembly into BMs. These include intracellular chaperones such as Heat shock protein 47 (Hsp47) and the chaperone-binding trafficking protein Transport and Golgi organization protein 1 (Tango1). Mutations in these proteins lead to compromised collagen IV protomer stability and secretion, leading to defective BM assembly and function. In addition to intracellular chaperones, a role for extracellular chaperones orchestrating the transport, supramolecular assembly, and architecture of collagen IV in BM is emerging. We present evidence derived from evolutionarily distant model organisms that supports an extracellular collagen IV chaperone-like activity for the matricellular protein SPARC (Secreted Protein, Acidic, Rich in Cysteine). Loss of SPARC disrupts BM homeostasis and compromises tissue biomechanics and physiological function. Thus, the combined contributions of intracellular and extracellular collagen IV-associated chaperones and chaperone-like proteins are critical to ensure proper secretion and stereotypic assembly of collagen IV networks in BMs.

Preoperative neoadjuvant chemotherapy using nanoparticle albumin-bound paclitaxel followed by epirubicin and cyclophosphamide for operable breast cancer: a multicenter phase II trial

Background

Recently, the use of taxane-based regimens before anthracycline-based regimens has been shown to achieve high pathological complete response (pCR) rates in patients with breast cancer. Nanoparticle albumin-bound paclitaxel (nab-PTX) has been reported as highly effective and less toxic compared with Cremophor-based Taxol. This phase II clinical trial evaluated the safety and efficacy of preoperative neoadjuvant chemotherapy (NAC) with nab-PTX followed by an epirubicin plus cyclophosphamide (EC)-based regimen for operable breast cancer.

Patients and methods

From June 2012 to January 2014, four cycles of every-3-week (q3w) nab-PTX [plus q3w trastuzumab in cases of human epidermal growth factor 2 (HER2) positivity] followed by four cycles of q3w EC were administered to patients with operable breast cancer (stage IC–IIIA). The primary endpoint was the pCR rate (ypT0/TisypN0).

Results

A total of 55 patients were enrolled, 54 of whom received at least one nab-PTX dose. All patients underwent radical surgery after chemotherapy. The overall pCR rate was 22.2% (p = 0.006). The pCR rates for patients with the luminal B, luminal/HER2, HER2-rich, and triple-negative breast cancer subtypes were 10.5, 29.4, 60, and 15.4%, respectively. Stepwise logistic regression analysis revealed only HER2 as a significant factor for pCR (odds ratio 5.603; p = 0.024). The expression of secreted protein acidic and rich in cysteine showed no association with pCR. The clinical response rate was 70.4% (38/54), and the safety profile was tolerable.

Conclusion

Preoperative NAC with nab-PTX followed by EC is effective and safe for operable breast cancer.

Thrombospondin expression in myofibers stabilizes muscle membranes

Skeletal muscle is highly sensitive to mutations in genes that participate in membrane stability and cellular attachment, which often leads to muscular dystrophy. Here we show that Thrombospondin-4 (Thbs4) regulates skeletal muscle integrity and its susceptibility to muscular dystrophy through organization of membrane attachment complexes. Loss of the Thbs4 gene causes spontaneous dystrophic changes with aging and accelerates disease in 2 mouse models of muscular dystrophy, while overexpression of mouse Thbs4 is protective and mitigates dystrophic disease. In the myofiber, Thbs4 selectively enhances vesicular trafficking of dystrophin-glycoprotein and integrin attachment complexes to stabilize the sarcolemma. In agreement, muscle-specific overexpression of Drosophila Tsp or mouse Thbs4 rescues a Drosophila model of muscular dystrophy with augmented membrane residence of βPS integrin. This functional conservation emphasizes the fundamental importance of Thbs' as regulators of cellular attachment and membrane stability and identifies Thbs4 as a potential therapeutic target for muscular dystrophy.

SPARC Promotes Cell Invasion In Vivo by Decreasing Type IV Collagen Levels in the Basement Membrane

Overexpression of SPARC, a collagen-binding glycoprotein, is strongly associated with tumor invasion through extracellular matrix in many aggressive cancers. SPARC regulates numerous cellular processes including integrin-mediated cell adhesion, cell signaling pathways, and extracellular matrix assembly; however, the mechanism by which SPARC promotes cell invasion in vivo remains unclear. A main obstacle in understanding SPARC function has been the difficulty of visualizing and experimentally examining the dynamic interactions between invasive cells, extracellular matrix and SPARC in native tissue environments. Using the model of anchor cell invasion through the basement membrane (BM) extracellular matrix in Caenorhabditis elegans, we find that SPARC overexpression is highly pro-invasive and rescues BM transmigration in mutants with defects in diverse aspects of invasion, including cell polarity, invadopodia formation, and matrix metalloproteinase expression. By examining BM assembly, we find that overexpression of SPARC specifically decreases levels of BM type IV collagen, a crucial structural BM component. Reduction of type IV collagen mimicked SPARC overexpression and was sufficient to promote invasion. Tissue-specific overexpression and photobleaching experiments revealed that SPARC acts extracellularly to inhibit collagen incorporation into BM. By reducing endogenous SPARC, we also found that SPARC functions normally to traffic collagen from its site of synthesis to tissues that do not express collagen. We propose that a surplus of SPARC disrupts extracellular collagen trafficking and reduces BM collagen incorporation, thus weakening the BM barrier and dramatically enhancing its ability to be breached by invasive cells.

Periostin promotes secretion of fibronectin from the endoplasmic reticulum

Extracellular matrix (ECM) proteins are synthesized in the endoplasmic reticulum (ER), transported to the extracellular milieu through the secretory pathway, and assembled into an extracellular architecture. A previous study of ours showed that periostin, a secretory protein, interacts with fibronectin and is involved in ECM remodeling. Here we show that periostin played a role in fibronectin secretion from the ER. Co-immunoprecipitation and in situ proximity ligation assays revealed an interaction between periostin and fibronectin in the ER. Although accumulation of fibronectin was detected in the ER of fibroblastic C3H10T1/2 cells, forced expression of periostin in those cells decreased the accumulation of fibronectin in the ER, suggesting that periostin promoted the secretion of fibronectin. A substitution mutant of tryptophan at the position 65 to alanine in the EMI domain of periostin, which caused periostin to lose its ability to interact with fibronectin, did not decrease the accumulation. Furthermore, targeted disruption of periostin in mice caused the non-fibrillar and ectopic deposition of fibronectin in the periodontal ligament. Thus, these results demonstrate a subcellular role of periostin in promotion of fibronectin secretion from the ER.

Dynamic regulation of basement membrane protein levels promotes egg chamber elongation in Drosophila

Basement membranes (BMs) are sheet-like extracellular matrices that provide essential support to epithelial tissues. Recent evidence suggests that regulated changes in BM architecture can direct tissue morphogenesis, but the mechanisms by which cells remodel BMs are largely unknown. The Drosophila egg chamber is an organ-like structure that transforms from a spherical to an ellipsoidal shape as it matures. This elongation coincides with a stage-specific increase in Type IV Collagen (Col IV) levels in the BM surrounding the egg chamber; however, the mechanisms and morphogenetic relevance of this remodeling event have not been established. Here, we identify the Collagen-binding protein SPARC as a negative regulator of egg chamber elongation, and show that SPARC down-regulation is necessary for the increase in Col IV levels to occur. We find that SPARC interacts with Col IV prior to secretion and propose that, through this interaction, SPARC blocks the incorporation of newly synthesized Col IV into the BM. We additionally observe a decrease in Perlecan levels during elongation, and show that Perlecan is a negative regulator of this process. These data provide mechanistic insight into SPARC's conserved role in matrix dynamics and demonstrate that regulated changes in BM composition influence organ morphogenesis.

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.

Mechano-regulation of collagen biosynthesis in periodontal ligament

Periodontal ligament (PDL) plays critical roles in the development and maintenance of periodontium such as tooth eruption and dissipation of masticatory force. The mechanical properties of PDL are mainly derived from fibrillar type I collagen, the most abundant extracellular component. The biosynthesis of type I collagen is a long, complex process including a number of intra- and extracellular post-translational modifications. The final modification step is the formation of covalent intra- and intermolecular cross-links that provide collagen fibrils with stability and connectivity. It is now clear that collagen post-translational modifications are regulated by groups of specific enzymes and associated molecules in a tissue-specific manner; and these modifications appear to change in response to mechanical force. This review focuses on the effect of mechanical loading on collagen biosynthesis and fibrillogenesis in PDL with emphasis on the post-translational modifications of collagens, which is an important molecular aspect to understand in the field of prosthetic dentistry.

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.

Revisiting the matricellular concept

The concept of a matricellular protein was first proposed by Paul Bornstein in the mid-1990s to account for the non-lethal phenotypes of mice with inactivated genes encoding thrombospondin-1, tenascin-C, or SPARC. It was also recognized that these extracellular matrix proteins were primarily counter or de-adhesive. This review reappraises the matricellular concept after nearly two decades of continuous investigation. The expanded matricellular family as well as the diverse and often unexpected functions, cellular location, and interacting partners/receptors of matricellular proteins are considered. Development of therapeutic strategies that target matricellular proteins are discussed in the context of pathology and regenerative medicine.

AMP-activated protein kinase regulates intraocular pressure, extracellular matrix, and cytoskeleton in trabecular meshwork

PURPOSE

In this study, we investigate how adenosine monophosphate-activated protein kinase (AMPK) affects extracellular matrix (ECM) and cellular tone in the trabecular meshwork (TM), and examine how deletion of its catalytic α2 subunit affects IOP and aqueous humor clearance in mice.

METHODS

Human TM tissue was examined for expression of AMPKα1 and AMPKα2, genomically distinct isoforms of the AMPK catalytic subunit. Primary cultured human TM cells were treated for 24 hours with the AMPK activator 5-amino-1-β-Dffff-ribofuranosyl-imidazole-4-carboxamide (AICAR), under basal or TGF-β2 stimulatory conditions. Conditioned media (CM) was probed for secreted protein acidic and rich in cysteine (SPARC), thrombospondin-1 (TSP-1), and ECM proteins, and cells were stained for F-actin. Cells underwent adenoviral infection with a dominant negative AMPKα subunit (ad.DN.AMPKα) and were similarly analyzed. Intraocular pressure, central corneal thickness (CCT), and aqueous clearance were measured in AMPKα2-null and wild-type (WT) mice.

RESULTS

Both AMPKα1 and AMPKα2 are expressed in TM. AICAR activated AMPKα and suppressed the expression of various ECM proteins under basal and TGF-β2 stimulatory conditions. AICAR decreased F-actin staining and increased the phospho-total RhoA ratio (Ser188). Transforming growth factor-β2 transiently dephosphorylated AMPKα. Infection with ad.DN.AMPKα upregulated various ECM proteins, decreased the phospho-total RhoA ratio, and increased F-actin staining. AMPKα2-null mice exhibited 6% higher IOP and decreased aqueous clearance compared with WT mice, without significant differences in CCT or angle morphology.

CONCLUSIONS

Collectively, our data identify AMPK as a critical regulator of ECM homeostasis and cytoskeletal arrangement in the TM. Mice that are AMPKα2-null exhibit higher IOPs and decreased aqueous clearance than their WT counterparts.

Nab-paclitaxel for metastatic pancreatic cancer: clinical outcomes and potential mechanisms of action

For almost 15 years there has been stagnation in the systemic treatment of patients with pancreatic ductal adenocarcinoma (PDAC). Recently, several developments seem to indicate clinically relevant improvements in the treatment of patients with metastatic disease. One of these developments is the introduction of nanoparticle albumin-bound paclitaxel (nab-paclitaxel) into the firstline treatment of metastatic disease. In this review, underlying preclinical and clinical data are discussed, with a special focus on mechanisms of action, the potential interaction with albumin and calcium-binding matricellular glycoproteins, such as the secreted protein acidic and rich in cysteine (SPARC), as well as the clinical outcome associated with the use of nab-paclitaxel.

Integrated analysis of global mRNA and protein expression data in HEK293 cells overexpressing PRL-1

BACKGROUND

The protein tyrosine phosphatase PRL-1 represents a putative oncogene with wide-ranging cellular effects. Overexpression of PRL-1 can promote cell proliferation, survival, migration, invasion, and metastasis, but the underlying mechanisms by which it influences these processes remain poorly understood.

METHODOLOGY

To increase our comprehension of PRL-1 mediated signaling events, we employed transcriptional profiling (DNA microarray) and proteomics (mass spectrometry) to perform a thorough characterization of the global molecular changes in gene expression that occur in response to stable PRL-1 overexpression in a relevant model system (HEK293).

PRINCIPAL FINDINGS

Overexpression of PRL-1 led to several significant changes in the mRNA and protein expression profiles of HEK293 cells. The differentially expressed gene set was highly enriched in genes involved in cytoskeletal remodeling, integrin-mediated cell-matrix adhesion, and RNA recognition and splicing. In particular, members of the Rho signaling pathway and molecules that converge on this pathway were heavily influenced by PRL-1 overexpression, supporting observations from previous studies that link PRL-1 to the Rho GTPase signaling network. In addition, several genes not previously associated with PRL-1 were found to be significantly altered by its expression. Most notable among these were Filamin A, RhoGDIα, SPARC, hnRNPH2, and PRDX2.

CONCLUSIONS AND SIGNIFICANCE

This systems-level approach sheds new light on the molecular networks underlying PRL-1 action and presents several novel directions for future, hypothesis-based studies.

Tumour-stroma interactions in pancreatic ductal adenocarcinoma: rationale and current evidence for new therapeutic strategies

Most patients with pancreatic cancer present with advanced/metastatic disease and have a dismal prognosis. Despite the proven albeit modest benefits of gemcitabine demonstrated over a decade ago, subsequent advances have been slow, suggesting it may be time to take a different approach. It is thought that some key characteristics of pancreatic cancer, such as the desmoplasia, restricted vasculature and hypoxic environment, may prevent the delivery of chemotherapy to the tumour thereby explaining the limited benefits observed to-date. Moreover, there is evidence to suggest that the stroma is not only a mechanical barrier but also constitutes a dynamic compartment of pancreatic tumours that is critically involved in tumour formation, progression and metastasis. Thus, targeting the stroma and the tumour represents a promising therapeutic strategy. Currently, several stroma-targeting agents are entering clinical development. Among these, nab-paclitaxel appears promising since it combines cytotoxic therapy with targeted delivery via its proposed ability to bind SPARC on tumour and stromal cells. Preclinical data indicate that co-treatment with nab-paclitaxel and gemcitabine results in stromal depletion, increased tumour vascularization and intratumoural gemcitabine concentration, and increased tumour regression compared with either agent alone. Phase I/II study data also suggest that a high level of antitumor activity can be achieved with this combination in pancreatic cancer. This was recently confirmed in a Phase III study which showed that nab-paclitaxel plus gemcitabine significantly improved overall survival (HR 0.72) and progression-free survival (HR 0.69) versus gemcitabine alone for the first-line treatment of patients with metastatic pancreatic cancer.

Overexpression of SPARC in human trabecular meshwork increases intraocular pressure and alters extracellular matrix

PURPOSE

Intraocular pressure (IOP) regulation is largely unknown. SPARC-null mice demonstrate a lower IOP resulting from increased outflow. SPARC is a matricellular protein often associated with fibrosis. We hypothesized that SPARC overexpression would alter IOP by affecting extracellular matrix (ECM) synthesis and/or turnover in the trabecular meshwork (TM).

METHODS

An adenoviral vector containing human SPARC was used to increase SPARC expression in human TM endothelial cells and perfused human anterior segments using multiplicities of infection (MOIs) 25 or 50. Total RNA from TM was used for quantitative PCR, while protein from cell lysates and conditioned media were used for immunoblot analyses and zymography. After completion of perfusion, the anterior segments were fixed, sectioned, and examined by light and confocal microscopy.

RESULTS

SPARC overexpression increased the IOP of perfused human anterior segments. Fibronectin and collagens IV and I protein levels were elevated in both TM cell cultures and within the juxtacanalicular (JCT) region of perfused anterior segments. Collagen VI and laminin protein levels were increased in TM cell cultures but not in perfused anterior segments. The protein levels of pro-MMP-9 decreased while the kinetic inhibitors of metalloproteinases, TIMP-1 and PAI-1 protein levels, increased at MOI 25. At MOI 50, the protein levels of pro-MMP-1, -3, and -9 also decreased while PAI-1 and TIMP-1 and -3 increased. Only MMP-9 activity was decreased on zymography. mRNA levels of the collagens, fibronectin, and laminin were not affected by SPARC overexpression.

CONCLUSIONS

SPARC overexpression increases IOP in perfused cadaveric human anterior segments resulting from a qualitative change the JCT ECM. Selective decrease of MMP-9 activity is likely part of the mechanism. SPARC is a regulatory node for IOP.

The expression, regulation and function of secreted protein, acidic, cysteine-rich in the follicle–luteal transition

The role of the tissue remodelling protein, secreted protein, acidic, cysteine-rich (SPARC), in key processes (e.g. cell reorganisation and angiogenesis) that occur during the follicle–luteal transition is unknown. Hence, we investigated the regulation of SPARC in luteinsing follicular cells and potential roles of SPARC peptide 2.3 in a physiologically relevant luteal angiogenesis culture system. SPARC protein was detected mainly in the theca layer of bovine pre-ovulatory follicles, but its expression was considerably greater in the corpus haemorrhagicum. Similarly, SPARC protein (western blotting) was up-regulated in luteinising granulosa but not in theca cells during a 6-day culture period. Potential regulatory candidates were investigated in luteinising granulosa cells: LH did not affect SPARC (P>0.05); transforming growth factor (TGF) B1 (P<0.001) dose dependently induced the precocious expression of SPARC and increased final levels: this effect was blocked (P<0.001) by SB505124 (TGFB receptor 1 inhibitor). Additionally, fibronectin, which is deposited during luteal development, increased SPARC (P<0.01). In luteal cells, fibroblast growth factor 2 decreased SPARC (P<0.001) during the first 5 days of culture, while vascular endothelial growth factor A increased its expression (P<0.001). Functionally, KGHK peptide, a SPARC proteolytic fragment, stimulated the formation of endothelial cell networks in a luteal cell culture system (P<0.05) and increased progesterone production (P<0.05). Collectively, these findings indicate that SPARC is intricately regulated by pro-angiogenic and other growth factors together with components of the extracellular matrix during the follicle–luteal transition. Thus, it is possible that SPARC plays an important modulatory role in regulating angiogenesis and progesterone production during luteal development.