A biological guide to glycosaminoglycans: current perspectives and pending questions.

Mammalian glycosaminoglycans (GAGs), except hyaluronan (HA), are sulfated polysaccharides that are covalently attached to core proteins to form proteoglycans (PGs). This article summarizes key biological findings for the most widespread GAGs, namely HA, chondroitin sulfate/dermatan sulfate (CS/DS), keratan sulfate (KS), and heparan sulfate (HS). It focuses on the major processes that remain to be deciphered to get a comprehensive view of the mechanisms mediating GAG biological functions. They include the regulation of GAG biosynthesis and postsynthetic modifications in heparin (HP) and HS, the composition, heterogeneity, and function of the tetrasaccharide linkage region and its role in disease, the functional characterization of the new PGs recently identified by glycoproteomics, the selectivity of interactions mediated by GAG chains, the display of GAG chains and PGs at the cell surface and their impact on the availability and activity of soluble ligands, and on their move through the glycocalyx layer to reach their receptors, the human GAG profile in health and disease, the roles of GAGs and particular PGs (syndecans, decorin, and biglycan) involved in cancer, inflammation, and fibrosis, the possible use of GAGs and PGs as disease biomarkers, and the design of inhibitors targeting GAG biosynthetic enzymes and GAG-protein interactions to develop novel therapeutic approaches.

BI-3231, an enzymatic inhibitor of HSD17B13, reduces lipotoxic effects induced by palmitic acid in murine and human hepatocytes.

17-ß-hydroxysteroid dehydrogenase 13 (HSD17B13), a lipid droplet-associated enzyme, is primarily expressed in the liver and plays an important role in lipid metabolism. Targeted inhibition of enzymatic function is a potential therapeutic strategy for treating steatotic liver disease (SLD). The present study is aimed at investigating the effects of the first selective HSD17B13 inhibitor, BI-3231, in a model of hepatocellular lipotoxicity using human cell lines and primary mouse hepatocytes in vitro. Lipotoxicity was induced with palmitic acid in HepG2 cells and freshly isolated mouse hepatocytes and the cells were coincubated with BI-3231 to assess the protective effects. Under lipotoxic stress, triglyceride (TG) accumulation was significantly decreased in the BI-3231-treated cells compared with that of the control untreated human and mouse hepatocytes. In addition, treatment with BI-3231 led to considerable improvement in hepatocyte proliferation, cell differentiation, and lipid homeostasis. Mechanistically, BI-3231 increased the mitochondrial respiratory function without affecting ß-oxidation. BI-3231 inhibited the lipotoxic effects of palmitic acid in hepatocytes, highlighting the potential of targeting HSD17B13 as a specific therapeutic approach in steatotic liver disease.NEW & NOTEWORTHY 17-ß-Hydroxysteroid dehydrogenase 13 (HSD17B13) is a lipid droplet protein primarily expressed in the liver hepatocytes. HSD17B13 is associated with the clinical outcome of chronic liver diseases and is therefore a target for the development of drugs. Here, we demonstrate the promising therapeutic effect of BI-3231 as a potent inhibitor of HSD17B13 based on its ability to inhibit triglyceride accumulation in lipid droplets (LDs), restore lipid metabolism and homeostasis, and increase mitochondrial activity in vitro.

Tissue factor binds to and inhibits interferon-α receptor 1 signaling.

Tissue factor (TF), which is a member of the cytokine receptor family, promotes coagulation and coagulation-dependent inflammation. TF also exerts protective effects through unknown mechanisms. Here, we showed that TF bound to interferon-α receptor 1 (IFNAR1) and antagonized its signaling, preventing spontaneous sterile inflammation and maintaining immune homeostasis. Structural modeling and direct binding studies revealed binding of the TF C-terminal fibronectin III domain to IFNAR1, which restricted the expression of interferon-stimulated genes (ISGs). Podocyte-specific loss of TF in mice (PodΔF3) resulted in sterile renal inflammation, characterized by JAK/STAT signaling, proinflammatory cytokine expression, disrupted immune homeostasis, and glomerulopathy. Inhibiting IFNAR1 signaling or loss of Ifnar1 expression in podocytes attenuated these effects in PodΔF3 mice. As a heteromer, TF and IFNAR1 were both inactive, while dissociation of the TF-IFNAR1 heteromer promoted TF activity and IFNAR1 signaling. These data suggest that the TF-IFNAR1 heteromer is a molecular switch that controls thrombo-inflammation.

Global impact of proteoglycan science on human diseases.

In this comprehensive review, we will dissect the impact of research on proteoglycans focusing on recent developments involved in their synthesis, degradation, and interactions, while critically assessing their usefulness in various biological processes. The emerging roles of proteoglycans in global infections, specifically the SARS-CoV-2 pandemic, and their rising functions in regenerative medicine and biomaterial science have significantly affected our current view of proteoglycans and related compounds. The roles of proteoglycans in cancer biology and their potential use as a next-generation protein-based adjuvant therapy to combat cancer is also emerging as a constructive and potentially beneficial therapeutic strategy. We will discuss the role of proteoglycans in selected and emerging areas of proteoglycan science, such as neurodegenerative diseases, autophagy, angiogenesis, cancer, infections and their impact on mammalian diseases.

The iron chelator and OXPHOS inhibitor VLX600 induces mitophagy and an autophagy-dependent type of cell death in glioblastoma cells.

Induction of alternative, non-apoptotic cell death programs such as cell-lethal autophagy and mitophagy represent possible strategies to combat glioblastoma (GBM). Here we report that VLX600, a novel iron chelator and oxidative phosphorylation (OXPHOS) inhibitor, induces a caspase-independent type of cell death that is partially rescued in adherent U251 ATG5/7 (autophagy related 5/7) knockout (KO) GBM cells and NCH644 ATG5/7 knockdown (KD) glioma stem-like cells (GSCs), suggesting that VLX600 induces an autophagy-dependent cell death (ADCD) in GBM. This ADCD is accompanied by decreased oxygen consumption, increased expression/mitochondrial localization of BNIP3 (BCL2 interacting protein 3) and BNIP3L (BCL2 interacting protein 3 like), the induction of mitophagy as demonstrated by diminished levels of mitochondrial marker proteins [e.g., COX4I1 (cytochrome c oxidase subunit 4I1)] and the mitoKeima assay as well as increased histone H3 and H4 lysine tri-methylation. Furthermore, the extracellular addition of iron is able to significantly rescue VLX600-induced cell death and mitophagy, pointing out an important role of iron metabolism for GBM cell homeostasis. Interestingly, VLX600 is also able to completely eliminate NCH644 GSC tumors in an organotypic brain slice transplantation model. Our data support the therapeutic concept of ADCD induction in GBM and suggest that VLX600 may be an interesting novel drug candidate for the treatment of this tumor.NEW & NOTEWORTHY Induction of cell-lethal autophagy represents a possible strategy to combat glioblastoma (GBM). Here, we demonstrate that the novel iron chelator and OXPHOS inhibitor VLX600 exerts pronounced tumor cell-killing effects in adherently cultured GBM cells and glioblastoma stem-like cell (GSC) spheroid cultures that depend on the iron-chelating function of VLX600 and on autophagy activation, underscoring the context-dependent role of autophagy in therapy responses. VLX600 represents an interesting novel drug candidate for the treatment of this tumor.

Pathogenetic mechanisms and therapeutic approaches of acute-to-chronic liver failure.

Liver cirrhosis is the end stage of all chronic liver diseases and contributes significantly to overall mortality of 2% globally. The age-standardized mortality from liver cirrhosis in Europe is between 10 and 20% and can be explained by not only the development of liver cancer but also the acute deterioration in the patient's overall condition. The development of complications including accumulation of fluid in the abdomen (ascites), bleeding in the gastrointestinal tract (variceal bleeding), bacterial infections, or a decrease in brain function (hepatic encephalopathy) define an acute decompensation that requires therapy and often leads to acute-on-chronic liver failure (ACLF) by different precipitating events. However, due to its complexity and organ-spanning nature, the pathogenesis of ACLF is poorly understood, and the common underlying mechanisms leading to the development of organ dysfunction or failure in ACLF are still elusive. Apart from general intensive care interventions, there are no specific therapy options for ACLF. Liver transplantation is often not possible in these patients due to contraindications and a lack of prioritization. In this review, we describe the framework of the ACLF-I project consortium funded by the Hessian Ministry of Higher Education, Research and the Arts (HMWK) based on existing findings and will provide answers to these open questions.

Decoding the role of fatty acids and their metabolites in lung fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a progressive and life­threatening interstitial lung disease of familial or sporadic onset. The incidence and prevalence of IPF range from 0.09 to 1.3 and from 0.33 to 4.51 per 10 000 people, respectively. IPF has a poor prognosis, and death usually occurs within 2 to 5 years following the diagnosis due to secondary respiratory failure. Currently, there are 2 drugs available to treat IPF, pirfenidone and nintedanib. Both only slow the disease progression and, in addition, have unfavorable safety profiles. IPF bears the histology of usual interstitial pneumonia, which is characterized by bronchiolization of distal airspaces, honeycombing, fibroblastic foci, and abnormal epithelial hyperplasia. In the last years, alterations in metabolic pathways, in particular those associated with fatty acid (FA) metabolism have been linked with the pathogenesis of lung fibrosis. Changes in FA profiles have been reported in lung tissue, plasma, and bronchoalveolar lavage fluid of IPF patients, and have been found to correlate with the disease progression and outcome. In addition, they have been associated with the development of a profibrotic phenotype of epithelial cells, macrophages, and fibroblasts / myofibroblasts contributing to their (trans)differentiation and production of the disease­relevant mediators. Furthermore, strategies focusing on the correction of FA profiles in experimental models of lung fibrosis brought advances in understanding tissue scarring processes and contributed to the transition of new molecules into clinical development. This review highlights the role of FAs and their metabolites in IPF and provides evidence for therapeutic potential of lipidome manipulations in the treatment of this disease.

The emerging role of extracellular vesicles as communicators between adipose tissue and pathologic lungs with a special focus on asthma.

Extracellular vesicles (EVs) gain increasing attention due to their (patho-)physiological role in intercellular signaling, specifically in the communication between distant organs. Recent studies highlight a connection between the adipose tissue (AT) and the lung via (immuno-)modulatory EVs in disorders such as obesity-associated asthma and lung cancer-associated cachexia. Although lung cancer-derived EVs induce lipolysis and myotube atrophy in vivo, pathogenic effects were also reported in the opposite direction with the involvement of AT-derived EVs in cancer-promoting responses and potentially in asthma development. In contrast, the majority of studies on AT-derived EVs demonstrate their protective influence on the asthmatic lung. Beneficial effects, such as induction of anti-inflammatory pathways in vitro and in ovalbumin (OVA)-induced asthma mouse models, were particularly conveyed by EVs enriched from AT-derived mesenchymal stem/stromal cells (AT-MSCs), which therefore pose an interesting subject in possible future therapeutic applications. Likewise, AT-MSC-derived EVs exerted beneficial effects in several other pulmonary abnormalities, such as different types of lung injury or pathological changes related to chronic obstructive pulmonary disease. These contradictory findings highlight the need for extensive research to widen the understanding of the role of EVs in the development of diseases and interconnectivity between organs.

Biglycan regulates bone development and regeneration.

Endochondral bone development and regeneration relies on activation and proliferation of periosteum derived-cells (PDCs). Biglycan (Bgn), a small proteoglycan found in extracellular matrix, is known to be expressed in bone and cartilage, however little is known about its influence during bone development. Here we link biglycan with osteoblast maturation starting during embryonic development that later affects bone integrity and strength. Biglycan gene deletion reduced the inflammatory response after fracture, leading to impaired periosteal expansion and callus formation. Using a novel 3D scaffold with PDCs, we found that biglycan could be important for the cartilage phase preceding bone formation. The absence of biglycan led to accelerated bone development with high levels of osteopontin, which appeared to be detrimental to the structural integrity of the bone. Collectively, our study identifies biglycan as an influencing factor in PDCs activation during bone development and bone regeneration after fracture.

Evaluation of the In Vitro and In Vivo Effects of Biglycan in Innate Immunity.

Biglycan, a small leucine-rich proteoglycan (SLRP), is a crucial component of the extracellular matrix (ECM) associated with the maintenance of tissue homeostasis. In response to tissue damage, the ECM-derived soluble form of biglycan acts as a danger signal by triggering an inflammatory response via the toll-like receptor (TLR)2/TLR4 in macrophages and dendritic cells. The impact and signaling mechanism of biglycan in innate immunity is better understood with the use of specific and reliable research tools and investigation techniques. Accordingly, our lab has established explicit and detailed experimental protocols to examine the in vitro and in vivo effects of biglycan in cellular immune responses. To evaluate the in vitro effects of biglycan on macrophage activation, a comprehensive protocol that makes use of murine peritoneal macrophages has been described. Further, to study the in vivo effects of biglycan, a method that uses a pLIVE vector to generate transgenic mice transiently overexpressing human biglycan is detailed. A step-by-step protocol for analyzing the effects of soluble biglycan overexpression in transgenic mice is explained under the following sections: (1) construction of pLIVE-hBGN plasmid, (2) intravenous delivery of transgenic vector, (3) identification of hBGN transgene in hepatocytes (4) detection of transgenic biglycan protein in the plasma of transgenic mice, and (5) evaluation of the presence and pro-inflammatory effects of transgenic biglycan in extrahepatic mouse tissues.

Diverse functions of apolipoprotein A-I in lung fibrosis.

Apolipoprotein A-I (apoA-I) mediates reverse cholesterol transport (RCT) out of cells. In addition to its important role in the RTC, apoA-I also possesses anti-inflammatory and antioxidative functions including the ability to activate inflammasome and signal via toll-like receptors. Dysfunctional apoA-I or its low abundance may cause accumulation of cholesterol mass in alveolar macrophages, leading to the formation of foam cells. Increased numbers of foam cells have been noted in the lungs of mice after experimental exposure to cigarette smoke, silica, or bleomycin and in the lungs of patients suffering from different types of lung fibrosis, including idiopathic pulmonary fibrosis (IPF). This suggests that dysregulation of lipid metabolism may be a common event in the pathogenesis of interstitial lung diseases. Recognition of the emerging role of cholesterol in the regulation of lung inflammation and remodeling provides a challenging concept for understanding lung diseases and offers novel and exciting avenues for therapeutic development. Accordingly, a number of preclinical studies demonstrated decreased expression of inflammatory and profibrotic mediators and preserved lung tissue structure following the administration of the apoA-I or its mimetic peptides. This review highlights the role of apoA-I in lung fibrosis and provides evidence for its potential use in the treatment of this pathological condition.

A20 binding and inhibitor of nuclear factor kappa B (NF-κB)-1 (ABIN-1): a novel modulator of mitochondrial autophagy.

A20 binding inhibitor of nuclear factor kappa B (NF-κB)-1 (ABIN-1), a polyubiquitin-binding protein, is a signal-induced autophagy receptor that attenuates NF-κB-mediated inflammation and cell death. The present study aimed to elucidate the potential role of ABIN-1 in mitophagy, a biological process whose outcome is decisive in diverse physiological and pathological settings. Microtubule-associated proteins 1A/1B light chain 3B-II (LC3B-II) was found to be in complex with ectopically expressed hemagglutinin (HA)-tagged-full length (FL)-ABIN-1. Bacterial expression of ABIN-1 and LC3A and LC3B showed direct binding of ABIN-1 to LC3 proteins, whereas mutations in the LC3-interacting region (LIR) 1 and 2 motifs of ABIN-1 abrogated ABIN-1/LC3B-II complex formation. Importantly, induction of autophagy in HeLa cells resulted in colocalization of ABIN-1 with LC3B-II in autophagosomes and with lysosomal-associated membrane protein 1 (LAMP-1) in autophagolysosomes, leading to degradation of ABIN-1 with p62. Interestingly, ABIN-1 was found to translocate to damaged mitochondria in HeLa-mCherry-Parkin transfected cells. In line with this observation, clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)-mediated deletion of ABIN-1 significantly inhibited the degradation of the mitochondrial outer membrane proteins voltage-dependent anion-selective channel 1 (VDAC-1), mitofusin-2 (MFN2), and translocase of outer mitochondrial membrane (TOM)20. In addition, short interfering RNA (siRNA)-mediated knockdown of ABIN-1 significantly decreased lysosomal uptake of mitochondria in HeLa cells expressing mCherry-Parkin and the fluorescence reporter mt-mKEIMA. Collectively, our results identify ABIN-1 as a novel and selective mitochondrial autophagy regulator that promotes mitophagy, thereby adding a new player to the complex cellular machinery regulating mitochondrial homeostasis.

Circulating hyaluronic acid signature in CAP and ARDS - the role of pneumolysin in hyaluronic acid shedding.

Shedding of hyaluronan (HA), the component of endothelial cell (EC) glycocalyx, has been associated with acute lung injury. HA degradation allows plasma proteins and fluid to penetrate across the vascular wall leading to lung edema formation and leukocyte recruitment. Here, we analyzed sHA levels and size in patients with community-acquired pneumonia (CAP) and acute respiratory distress syndrome (ARDS), correlated them to disease severity, and evaluated the impact of pneumolysin (PLY), the Streptococcus pneumoniae (S.p.) exotoxin, on HA shedding from human pulmonary microvascular EC (HPMVEC). sHA levels were elevated in CAP and ARDS and correlated with the CRB65 severity score and with markers of inflammation (interleukin-6), EC activation (E-selectin), and basement membrane destruction (collagen IV). Furthermore, sHA levels were associated with an increase in 28-day mortality. Small and large sHA fragments were detected in plasma of most severe CAP or ARDS patients, and the presence of large sHA fragments was accompanied by the elevated levels of circulating collagen IV. In vitro, PLY induced sHA release from HPMVEC. This effect was dependent on reactive oxygen species (ROS) production and was not associated with endothelial barrier dysfunction. Conversely, HA shedding was impaired following HPMVEC infection with a S.p. PLY-deficient mutant. Our study identifies association between the severity of CAP and ARDS and the levels and size of sHA in plasma. It links sHA levels with, inflammation, EC activation status and basement membrane disassembly in ARDS and provides insights into the mechanism of HA shedding during infection.

Sphingosine 1-Phosphate Receptor 5 (S1P5) Knockout Ameliorates Adenine-Induced Nephropathy.

S1P and its receptors have been reported to play important roles in the development of renal fibrosis. Although S1P5 has barely been investigated so far, there are indications that it can influence inflammatory and fibrotic processes. Here, we report the role of S1P5 in renal inflammation and fibrosis. Male S1P5 knockout mice and wild-type mice on a C57BL/6J background were fed with an adenine-rich diet for 7 days or 14 days to induce tubulointerstitial fibrosis. The kidneys of untreated mice served as respective controls. Kidney damage, fibrosis, and inflammation in kidney tissues were analyzed by real-time PCR, Western blot, and histological staining. Renal function was assessed by plasma creatinine ELISA. The S1P5 knockout mice had better renal function and showed less kidney damage, less proinflammatory cytokine release, and less fibrosis after 7 days and 14 days of an adenine-rich diet compared to wild-type mice. S1P5 knockout ameliorates tubular damage and tubulointerstitial fibrosis in a model of adenine-induced nephropathy in mice. Thus, targeting S1P5 might be a promising goal for the pharmacological treatment of kidney diseases.

EGFR Signaling in Lung Fibrosis.

In this review article, we will first provide a brief overview of the ErbB receptor-ligand system and its importance in developmental and physiological processes. We will then review the literature regarding the role of ErbB receptors and their ligands in the maladaptive remodeling of lung tissue, with special emphasis on idiopathic pulmonary fibrosis (IPF). Here we will focus on the pathways and cellular processes contributing to epithelial-mesenchymal miscommunication seen in this pathology. We will also provide an overview of the in vivo studies addressing the efficacy of different ErbB signaling inhibitors in experimental models of lung injury and highlight how such studies may contribute to our understanding of ErbB biology in the lung. Finally, we will discuss what we learned from clinical applications of the ErbB1 signaling inhibitors in cancer in order to advance clinical trials in IPF.