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Astrocytes regulate synaptic connectivity in the CNS through secreted signals. Here we identified two astrocyte-secreted proteins, hevin and SPARC, as regulators of excitatory synaptogenesis in vitro and in vivo. Hevin induces the formation of synapses between cultured rat retinal ganglion cells. SPARC is not synaptogenic, but specifically antagonizes synaptogenic function of hevin. Hevin and SPARC are expressed by astrocytes in the superior colliculus, the synaptic target of retinal ganglion cells, concurrent with the excitatory synaptogenesis. Hevin-null mice had fewer excitatory synapses; conversely, SPARC-null mice had increased synaptic connections in the superior colliculus. Furthermore, we found that hevin is required for the structural maturation of the retinocollicular synapses. These results identify hevin as a positive and SPARC as a negative regulator of synapse formation and signify that, through regulation of relative levels of hevin and SPARC, astrocytes might control the formation, maturation, and plasticity of synapses in vivo.

Aged skeletal muscle is markedly affected by fatty muscle infiltration, and strategies to reduce the occurrence of intramuscular adipocytes are urgently needed. Here, we show that fibroblast growth factor-2 (FGF-2) not only stimulates muscle growth but also promotes intramuscular adipogenesis. Using multiple screening assays upstream and downstream of microRNA (miR)-29a signaling, we located the secreted protein and adipogenic inhibitor SPARC to an FGF-2 signaling pathway that is conserved between skeletal muscle cells from mice and humans and that is activated in skeletal muscle of aged mice and humans. FGF-2 induces the miR-29a/SPARC axis through transcriptional activation of FRA-1, which binds and activates an evolutionary conserved AP-1 site element proximal in the miR-29a promoter. Genetic deletions in muscle cells and adeno-associated virus–mediated overexpression of FGF-2 or SPARC in mouse skeletal muscle revealed that this axis regulates differentiation of fibro/adipogenic progenitors in vitro and intramuscular adipose tissue (IMAT) formation in vivo. Skeletal muscle from human donors aged >75 y versus <55 y showed activation of FGF-2–dependent signaling and increased IMAT. Thus, our data highlights a disparate role of FGF-2 in adult skeletal muscle and reveals a pathway to combat fat accumulation in aged human skeletal muscle.

Gastric adenocarcinoma (GAC), also known as stomach adenocarcinoma (STAD), is one of the most lethal malignancies in the world. It is vital to classify and detect the hub genes and key pathways participated in the initiation and progression of GAC. In this study, we collected and sequenced 15 pairs of GAC tumor tissues and the adjacent normal tissues. Differentially expressed genes (DEGs) were analyzed and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and Gene Ontology (GO) analysis were used to annotate the unique biological significance and important pathways of enriched DEGs. Moreover, we constructed the protein-protein interaction (PPI) network by Cytoscape and conducted KEGG enrichment analysis of the prime module. We further applied the TCGA database to start the survival analysis of these hub genes by Kaplan-Meier estimates. Finally, we obtained total 233 DEGs consisted of 64 up-regulated genes and 169 down-regulated genes. GO enrichment analysis found that DEGs most significantly enriched in single organism process, extracellular region, and extracellular region part. KEGG pathway enrichment analysis suggested that DEGs most significantly enriched in Protein digestion and absorption, Gastric acid secretion, and ECM-receptor interaction. Furthermore, the PPI network showed that the top 10 hub genes in GAC were IL8, COL1A1, MMP9, SST, COL1A2, TIMP1, FN1, SPARC, ALDH1A1, and SERPINE1 respectively. The prime gene interaction module in PPI network was enriched in protein digestion and absorption, ECM receptor interaction, the PI3K-Akt signaling pathway, and pathway in cancer. Survival analysis based on the TCGA database found that the expression of the FN1, SERPINE1, and SPARC significantly predicted poor prognosis of GAC. Collectively, we identified several hub genes and key pathways associated with GAC initiation and progression by analyzing the microarray data on DEGs, which provided a detailed molecular mechanism underlying GAC occurrence and progression.

SPARC is a matricellular protein, able to modulate cell/ECM interactions and influence cell responses to growth factors, and therefore is particularly attuned to contribute to physiological processes involving changes in ECM and cell mobilization. Indeed, the list of biological processes affected by SPARC includes wound healing, tumor progression, bone formation, fibrosis, and angiogenesis. The process of angiogenesis is complex and involves a number of cellular processes such as endothelial cell proliferation, migration, ECM degradation, and synthesis, as well as pericyte recruitment to stabilize nascent vessels. In this review, we will summarize current results that explore the function of SPARC in the regulation of angiogenic events with a particular emphasis on the modulation of growth factor activity by SPARC in the context of blood vessel formation. The primary function of SPARC in angiogenesis remains unclear, as SPARC activity in some circumstances promotes angiogenesis and in others is more consistent with an anti-angiogenic activity. Undoubtedly, the mercurial nature of SPARC belies a redundancy of functional proteins in angiogenesis as well as cell-type-specific activities that alter signal transduction events in response to unique cellular milieus. Nonetheless, the investigation of cellular mechanisms that define functional activities of SPARC continue to contribute novel and exciting paradigms to vascular biology.

The comprehensive assessment of long-term effects of reducing intake of energy (CALERIE-II; NCT00427193) clinical trial established that caloric restriction (CR) in humans lowers inflammation. The identity and mechanism of endogenous CR-mimetics that can be deployed to control obesity-associated inflammation and diseases are not well understood. Our studies have found that 2 years of 14% sustained CR in humans inhibits the expression of the matricellular protein, secreted protein acidic and rich in cysteine (SPARC), in adipose tissue. In mice, adipose tissue remodeling caused by weight loss through CR and low-protein diet feeding decreased, while high-fat diet-induced (HFD-induced) obesity increased SPARC expression in adipose tissue. Inducible SPARC downregulation in adult mice mimicked CR's effects on lowering adiposity by regulating energy expenditure. Deletion of SPARC in adipocytes was sufficient to protect mice against HFD-induced adiposity, chronic inflammation, and metabolic dysfunction. Mechanistically, SPARC activates the NLRP3 inflammasome at the priming step and downregulation of SPARC lowers macrophage inflammation in adipose tissue, while excess SPARC activated macrophages via JNK signaling. Collectively, reduction of adipocyte-derived SPARC confers CR-like metabolic and antiinflammatory benefits in obesity by serving as an immunometabolic checkpoint of inflammation.

Background Colorectal cancer (CRC) is highly prevalent worldwide, with more patients experiencing colorectal cancer liver metastases (CRLM). This study aimed to identify key genes in CRLM through single-cell sequencing data reanalysis and experimental validation. Methods The study analyzed single-cell RNA-sequencing (scRNA-seq) data from the Gene Expression Omnibus (GEO) database. Gene ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) were used for gene functional enrichment analysis. The Cancer Genome Atlas (TCGA) data enabled bulk-RNA expression and survival prognosis analysis. Real-time polymerase chain reaction (qPCR) detected mRNA expression, whereas Western blot determined protein levels. Cell function experiments assessed SPARC’s impact on CRC cell behavior. Results Cluster analysis showed 23 classes among 17 CRLM samples, representing six cell types. A GO and KEGG analysis identified interleukin-1 beta (IL1B), CD2 molecule (CD2), and C-X-C motif chemokine ligand 8 (CXCL8) as significant prognostic factors in CRC. Secreted protein acidic and cysteine rich (SPARC) was one of the top differentially expressed genes (DEGs) in tissue stem cells, confirmed in primary and metastatic lesions. Metastatic lesions showed higher expression of SPARC and CRC stem cell marker leucine-rich repeat containing G protein-coupled receptor 5 (LGR5), which was significantly correlated positively with LGR5 expression. Knockdown of SPARC reduced CRC cell sphere- and colony-formation, invasion, and migration abilities. Overexpression of SPARC significantly increased the malignancy of CRC cells. Conclusions Several key genes were identified in the process of CRLM. In CRLM samples and those corresponding to CRC stem cells, SPARC was significantly upregulated. In the therapy of CRLM, SPARC might be a potential target.

Phenotypic plasticity represents the most relevant hallmark of the carcinoma cell as it bestows it with the capacity of transiently altering its morphological and functional features while en route to the metastatic site. However, the study of phenotypic plasticity is hindered by the rarity of these events within primary lesions and by the lack of experimental models. Here, we identified a subpopulation of phenotypic plastic colon cancer cells: EpCAM lo cells are motile, invasive, chemo-resistant, and highly metastatic. EpCAM lo bulk and single-cell RNAseq analysis indicated (1) enhanced Wnt/β-catenin signaling, (2) a broad spectrum of degrees of epithelial to mesenchymal transition (EMT) activation including hybrid E/M states (partial EMT) with highly plastic features, and (3) high correlation with the CMS4 subtype, accounting for colon cancer cases with poor prognosis and a pronounced stromal component. Of note, a signature of genes specifically expressed in EpCAM lo cancer cells is highly predictive of overall survival in tumors other than CMS4, thus highlighting the relevance of quasi-mesenchymal tumor cells across the spectrum of colon cancers. Enhanced Wnt and the downstream EMT activation represent key events in eliciting phenotypic plasticity along the invasive front of primary colon carcinomas. Distinct sets of epithelial and mesenchymal genes define transcriptional trajectories through which state transitions arise. pEMT cells, often earmarked by the extracellular matrix glycoprotein SPARC together with nuclear ZEB1 and β-catenin along the invasive front of primary colon carcinomas, are predicted to represent the origin of these (de)differentiation routes through biologically distinct cellular states and to underlie the phenotypic plasticity of colon cancer cells.

Therapy-refractory disease is one of the main contributors of treatment failure in cancer. In colorectal cancer (CRC), SPARC can function as a sensitizer to conventional chemotherapy by enhancing apoptosis by interfering with the activity of Bcl-2. Here, we examine a novel mechanism by which SPARC further potentiates apoptosis via its modulation of the unfolded protein response (UPR). Using mass spectrometry to identify SPARC-associated proteins, GRP78 was identified as a protein partner for SPARC in CRC. In vitro studies conducted to assess the signaling events resulting from this interaction, included induction of ER stress with tunicamycin, 5-fluorouracil (5-FU), and irinotecan (CPT-11). We found that the interaction between GRP78 and SPARC increased during exposure to 5-FU, CPT-11, and tunicamycin, resulting in an attenuation of GRP78’s inhibition of apoptosis. In addition, we also show that SPARC can sensitize CRC cells to PERK/eIF2α and IRE1α/XBP-1 UPR signaling by interfering with ER stress following binding to GRP78, which leads to ER stress-associated cell death in CRC cells. In line with these findings, a lower expression of GRP78 relative to SPARC in CRC is associated with a lower IC 50 for 5-FU in either sensitive or therapy-refractory CRC cells. Interestingly, this observation correlates with tissue microarray analysis of 143 human CRC, where low GRP78 to SPARC expression level was prognostic of higher survival rate ( P  = 0.01) in individuals with CRC. This study demonstrates that modulation of UPR signaling by SPARC promotes ER stress-associated death and potentiates apoptosis. This may be an effective strategy that can be combined with current treatment options to improve therapeutic efficacy in CRC.

Gastric cancer (GC) is one of the most lethal malignancies worldwide. Despite extensive efforts to develop novel therapeutic targets, effective drugs for GC remain limited. Recent studies have indicated that Lipocalin (LCN)2 abnormalities significantly impact GC progression; however, its regulatory network remains unclear. Our study investigates the functional role and regulatory mechanism of action of LCN2 in GC progression. We observed a positive correlation between LCN2 expression, lower GC grade, and better prognosis in patients with GC. LCN2 overexpression suppressed GC proliferation and metastasis both in vitro and in vivo. Transcriptome sequencing identified secreted protein acidic and rich in cysteine (SPARC) as a pivotal downstream target of LCN2. Mechanistically, c-Jun acted as a transcription factor inducing SPARC expression, and LCN2 downregulated SPARC by inhibiting the JNK/c-Jun pathway. Moreover, LCN2 bound to its receptor, 24p3R, via autocrine signaling, which directly inhibited JNK phosphorylation and then inhibited the JNK/c-Jun pathway. Finally, analysis of clinical data demonstrated that SPARC expression correlated negatively with lower GC grade and better prognosis, and that LCN2 expression correlated negatively with p-JNK, c-Jun, and SPARC expression in GC. These findings suggest that the LCN2/24p3R/JNK/c-Jun/SPARC axis is crucial in the malignant progression of GC, offering novel prognostic markers and therapeutic targets.

The secretion of the SPARC protein by adipose tissue has been associated with obesity, insulin resistance and diabetes-related complications. Kos and Wilding discuss the effects of SPARC in the extracellular matrix and its role in subcutaneous adipose tissue fibrosis. They further discuss the effects of leptin, inflammation and hypoxia in the development of SPARC-mediated fibrosis and the possible contributions of this process to the pathology of obesity and obesity-related metabolic complications. SPARC (secreted protein acidic and rich in cysteine, also known as osteonectin or BM-40) is a widely expressed profibrotic protein with pleiotropic roles, which have been studied in a variety of conditions. Notably, SPARC is linked to human obesity; SPARC derived from adipose tissue is associated with insulin resistance and secretion of SPARC by adipose tissue is increased by insulin and the adipokine leptin. Furthermore, SPARC is associated with diabetes complications such as diabetic retinopathy and nephropathy, conditions that are ameliorated in the Sparc -knockout mouse model. As a regulator of the extracellular matrix, SPARC also contributes to adipose-tissue fibrosis. Evidence suggests that adipose tissue becomes increasingly fibrotic in obesity. Fibrosis of subcutaneous adipose tissue may restrict accumulation of triglycerides in this type of tissue. These triglycerides are, therefore, diverted and deposited as ectopic lipids in other tissues such as the liver or as intramyocellular lipids in skeletal muscle, which predisposes to insulin resistance. Hence, SPARC may represent a novel and important link between obesity and diabetes mellitus. This Review is focused on whether SPARC could be a key player in the pathology of obesity and its related metabolic complications. Key Points An increase in the levels of SPARC is found in animals and human individuals with obesity and insulin resistance Raised SPARC concentrations are associated with the development of diabetes-associated complications SPARC is involved in strengthening bone but raised concentrations of the protein are associated with increased cardiovascular risk Associations between SPARC and cancer have been postulated, but the exact role of this protein in tumorigenesis is unclear SPARC antagonism may help in the prevention of obesity-related complications