Serglycin Is Involved in Adipose Tissue Inflammation in Obesity

SRGN amplifies microglia-mediated neuroinflammation and exacerbates ischemic brain injury

BACKGROUND

Microglia is the major contributor of post-stroke neuroinflammation cascade and the crucial cellular target for the treatment of ischemic stroke. Currently, the endogenous mechanism underlying microglial activation following ischemic stroke remains elusive. Serglycin (SRGN) is a proteoglycan expressed in immune cells. Up to now, the role of SRGN on microglial activation and ischemic stroke is largely unexplored.

METHODS

Srgn knockout (KO), Cd44-KO and wild-type (WT) mice were subjected to middle cerebral artery occlusion (MCAO) to mimic ischemic stroke. Exogenous SRGN supplementation was achieved by stereotactic injection of recombinant mouse SRGN (rSRGN). Cerebral infarction was measured by 2,3,5-triphenyltetrazolium chloride (TTC) staining. Neurological functions were evaluated by the modified neurological severity score (mNSS) and grip strength. Microglial activation was detected by Iba1 immunostaining, morphological analysis and cytokines' production. Neuronal death was examined by MAP2 immunostaining and FJB staining.

RESULTS

The expression of SRGN and its receptor CD44 was significantly elevated in the ischemic mouse brains, especially in microglia. In addition, lipopolysaccharide (LPS) induced SRGN upregulation in microglia in vitro. rSRGN worsened ischemic brain injury in mice and amplified post-stroke neuroinflammation, while gene knockout of Srgn exerted reverse impacts. rSRGN promoted microglial proinflammatory activation both in vivo and in vitro, whereas Srgn-deficiency alleviated microglia-mediated inflammatory response. Moreover, the genetic deletion of Cd44 partially rescued rSRGN-induced excessed neuroinflammation and ischemic brain injury in mice. Mechanistically, SRGN boosted the activation of NF-κB signal, and increased glycolysis in microglia.

CONCLUSION

SRGN acts as a novel therapeutic target in microglia-boosted proinflammatory response following ischemic stroke.

Investigation of serum endocan and serglycin levels in obstructive sleep apnea

BACKGROUND

Apnea-related hypoxia, hypercapnia, and blood pressure fluctuations cause production of various proinflammatory cytokines and trigger a vicious cycle that results in vascular endothelial damage and systemic inflammation in obstructive sleep apnea (OSA). Endothelial function is frequently impaired in OSA even in the absence of significant cardiac or vascular disorders.

AIMS

This study aimed to investigate the serum endocan and serglycin levels in OSA patients.

METHODS

This prospective study included 78 consecutive patients who admitted to the sleep laboratory of a tertiary referral center with the complaints of daytime sleepiness, witnessed sleep apnea, and/or snoring and who underwent all-night polysomnography (PSG). After PSG, the patients were divided into four groups in relation with their apnea-hypopnea indexes. The groups were compared for endocan and serglycin levels and their correlations with OSA severity. The correlations with demographic data and PSG findings were also investigated.

RESULTS

The OSA and the control groups had significantly different endocan and serglycin levels ([Formula: see text], for both). On univariate logistic regression analysis, it was found that serglycin and endocan levels and BMI were predictors of OSA. Multiple logistic regression analysis showed that endocan and serglycin levels were independent predictors for OSA ([Formula: see text] and [Formula: see text], respectively).

CONCLUSIONS

We have demonstrated that elevated endocan and serglycin levels are predictors for OSA. Furthermore, we have showed for the first time in literature that serglycin is correlated with OSA and is an independent predictor for OSA.

Bariatric Surgery and Gut-Brain-Axis Driven Alterations in Cognition and Inflammation

Obesity is associated with systemic inflammation, comorbidities like diabetes, cardiovascular disease and several cancers, cognitive decline and structural and functional brain changes. To treat, or potentially prevent these related comorbidities, individuals with obesity must achieve long-term sustainable weight loss. Often life style interventions, such as dieting and increased physical activity are not successful in achieving long-term weight loss. Meanwhile bariatric surgery has emerged as a safe and effective procedure to treat obesity. Bariatric surgery causes changes in physiological processes, but it is still not fully understood which exact mechanisms are involved. The successful weight loss after bariatric surgery might depend on changes in various energy regulating hormones, such as ghrelin, glucagon-like peptide-1 and peptide YY. Moreover, changes in microbiota composition and white adipose tissue functionality might play a role. Here, we review the effect of obesity on neuroendocrine effects, microbiota composition and adipose tissue and how these may affect inflammation, brain structure and cognition. Finally, we will discuss how these obesity-related changes may improve after bariatric surgery.

CRISPR/Cas9-mediated deletion of adipocyte genes associated with NAFLD alters adipocyte lipid handling and reduces steatosis in hepatocytes in vitro

Obesity is a major risk factor for the development of nonalcoholic fatty liver disease (NAFLD), and the subcutaneous white adipose tissue (scWAT) is the primary lipid storage depot and regulates lipid fluxes to other organs. Our previous work identified genes upregulated in scWAT of patients with NAFLD: SOCS3, DUSP1, and SIK1. Herein, we knocked down (KD) their expression in human adipose-derived mesenchymal stem cells (hADMSCs) using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology and characterized their phenotype. We found that SOCS3, DUSP1, and SIK1 expression in hADMSC-derived adipocytes was not critical for adipogenesis. However, the metabolic characterization of the cells suggested that the genes played important roles in lipid metabolism. Reduction of SIK1 expression significantly increased both de novo lipogenesis (DNL) and palmitate-induced lipogenesis (PIL). Editing out SOCS3 reduced DNL while increasing isoproterenol-induced lipolysis and insulin-induced palmitate accumulation. Conversely, DUSP1 reduced PIL and DNL. Moreover, RNA-sequencing analysis of edited cells showed that these genes not only altered lipid metabolism but also other biological pathways related to inflammatory processes, in the case of DUSP1, extracellular matrix remodeling for SOCS3, or cellular transport for SIK1. Finally, to evaluate a possible adipocyte-hepatocyte axis, human hepatoma HepG2 cells were cocultured with edited hADMSCs-derived adipocytes in the presence of [3H]-palmitate. All HepG2 cells cultured with DUSP1-, SIK1-, or SOCS3-KD adipocytes decreased [3H]-palmitate accumulation compared with control adipocytes. These results support our hypotheses that SOCS3, DUSP1, and SIK1 regulate multiple aspects of adipocyte function, which may play a role in the progression of obesity-associated comorbidities, such as NAFLD.NEW & NOTEWORTHY Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology successfully edited genomic DNA of human adipose-derived mesenchymal stem cells (hADMSC). SOCS3, SIK1, and DUSP1 regulate adipocyte lipid handling. Silencing SOCS3, SIK1, and DUSP1 expression in hADMSC-derived adipocytes reduces hepatocyte lipid storage in vitro.

Decellularised spinal cord matrix manipulates glial niche into repairing phase via serglycin-mediated signalling pathway

Astrocytes are the most abundant and widespread glial cells in the central nervous system. The heterogeneity of astrocytes plays an essential role in spinal cord injury (SCI) repair. Decellularised spinal cord matrix (DSCM) is advantageous for repairing SCI, but little is known regarding the exact mechanisms and niche alterations. Here, we investigated the DSCM regulatory mechanism of glial niche in the neuro-glial-vascular unit using single-cell RNA sequencing. Our single cell sequencing, molecular and biochemical experiments validated that DSCM facilitated the differentiation of neural progenitor cells through increasing the number of immature astrocytes. Upregulation of mesenchyme-related genes, which maintained astrocyte immaturity, causing insensitivity to inflammatory stimuli. Subsequently, we identified serglycin (SRGN) as a functional component of DSCM, which involves inducing CD44-AKT signalling to trigger human spinal cord-derived primary astrocytes (hspASCs) proliferation and upregulation of genes related to epithelial-mesenchymal transition, thus impeding astrocyte maturation. Finally, we verified that SRGN-COLI and DSCM had similar functions in the human primary cell co-culture system to mimic the glia niche. In conclusion, our work revealed that DSCM reverted astrocyte maturation and altered the glia niche into the repairing phase through the SRGN-mediated signalling pathway.

Obesity Is Associated with Distorted Proteoglycan Expression in Adipose Tissue

Proteoglycans are central components of the extracellular matrix (ECM) and binding partners for inflammatory chemokines. Morphological differences in the ECM and increased inflammation are prominent features of the white adipose tissues in patients with obesity. The impact of obesity and weight loss on the expression of specific proteoglycans in adipose tissue is not well known. This study aimed to investigate the relationship between adiposity and proteoglycan expression. We analyzed transcriptomic data from two human bariatric surgery cohorts. In addition, RT-qPCR was performed on adipose tissues from female and male mice fed a high-fat diet. Both visceral and subcutaneous adipose tissue depots were analyzed. Adipose mRNA expression of specific proteoglycans, proteoglycan biosynthetic enzymes, proteoglycan partner molecules, and other ECM-related proteins were altered in both human cohorts. We consistently observed more profound alterations in gene expression of ECM targets in the visceral adipose tissues after surgery (among others VCAN (p = 0.000309), OGN (p = 0.000976), GPC4 (p = 0.00525), COL1A1 (p = 0.00221)). Further, gene analyses in mice revealed sex differences in these two tissue compartments in obese mice. We suggest that adipose tissue repair is still in progress long after surgery, which may reflect challenges in remodeling increased adipose tissues. This study can provide the basis for more mechanistic studies on the role of proteoglycans in adipose tissues in obesity.

Screening of Biomarkers in Liver Tissue after Bariatric Surgery Based on WGCNA and SVM-RFE Algorithms

As the most common chronic liver disease around the world, nonalcoholic fatty liver disease (NAFLD) has a close connection with obesity, diabetes, and metabolic syndrome. Bariatric surgery (BS) is considered to be the most effective treatment for NAFLD. However, the regulatory mechanism of hepatic lipid metabolism after BS remains poorly elucidated. By analyzing two transcriptome datasets regarding liver tissues after BS, namely, GSE83452 and GSE106737, we acquired 110 differentially expressed genes (DEGs). By further analysis of DEGs in terms of the weighted gene coexpression network analysis (WGCNA) and support vector machine-recursive feature elimination (SVM-RFE) algorithms, we identified four crucial genes participating in the regulation of hepatic lipid metabolism: SRGN, THEMIS2, SGK1, and FPR3. In addition, the results of gene set enrichment analysis (GSEA) showed that BS can activate immune-related regulatory pathways and change immune cell infiltration levels. Finally, through cellular level studies, we found that the silencing of SRGN affects the expression of SREBP-1, SIRT1, and FAS during adipogenesis in the liver and the formation of lipid droplets in the liver. In summary, the immune system in the liver is activated after BS, and SRGN participates in the regulation of hepatic lipid metabolism.

Serglycin Is Involved in TGF-β Induced Epithelial-Mesenchymal Transition and Is Highly Expressed by Immune Cells in Breast Cancer Tissue

Serglycin is a proteoglycan highly expressed by immune cells, in which its functions are linked to storage, secretion, transport, and protection of chemokines, proteases, histamine, growth factors, and other bioactive molecules. In recent years, it has been demonstrated that serglycin is also expressed by several other cell types, such as endothelial cells, muscle cells, and multiple types of cancer cells. Here, we show that serglycin expression is upregulated in transforming growth factor beta (TGF-β) induced epithelial-mesenchymal transition (EMT). Functional studies provide evidence that serglycin plays an important role in the regulation of the transition between the epithelial and mesenchymal phenotypes, and it is a significant EMT marker gene. We further find that serglycin is more expressed by breast cancer cell lines with a mesenchymal phenotype as well as the basal-like subtype of breast cancers. By examining immune staining and single cell sequencing data of breast cancer tissue, we show that serglycin is highly expressed by infiltrating immune cells in breast tumor tissue.