Tumor necrosis factor-inducible gene 6 protein ameliorates chronic liver damage by promoting autophagy formation in mice

Exploring the roles of non-coding RNAs in liver regeneration

Liver regeneration (LR) is a complex process encompassing three distinct phases: priming, proliferation phase and restoration, all influenced by various regulatory factors. After liver damage or partial resection, the liver tissue demonstrates remarkable restorative capacity, driven by cellular proliferation and repair mechanisms. The essential roles of non-coding RNAs (ncRNAs), predominantly microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNA (circRNA), in regulating LR have been vastly studied. Additionally, the impact of ncRNAs on LR and their abnormal expression profiles during this process have been extensively documented. Mechanistic investigations have revealed that ncRNAs interact with genes involved in proliferation to regulate hepatocyte proliferation, apoptosis and differentiation, along with liver progenitor cell proliferation and migration. Given the significant role of ncRNAs in LR, an in-depth exploration of their involvement in the liver's self-repair capacity can reveal promising therapeutic strategies for LR and liver-related diseases. Moreover, understanding the unique regenerative potential of the adult liver and the mechanisms and regulatory factors of ncRNAs in LR are crucial for improving current treatment strategies and exploring new therapeutic approaches for various liver-related diseases. This review provides a brief overview of the LR process and the ncRNA expression profiles during this process. Furthermore, we also elaborate on the specific molecular mechanisms through which multiple key ncRNAs regulate the LR process. Finally, based on the expression characteristics of ncRNAs and their interactions with proliferation-associated genes, we explore their potential clinical application, such as developing predictive indicators reflecting liver regenerative activity and manipulating LR processes for therapeutic purposes.

LINE-1 RNA triggers matrix formation in bone cells via a PKR-mediated inflammatory response

Transposable elements (TEs) are mobile genetic modules of viral derivation that have been co-opted to become modulators of mammalian gene expression. TEs are a major source of endogenous dsRNAs, signaling molecules able to coordinate inflammatory responses in various physiological processes. Here, we provide evidence for a positive involvement of TEs in inflammation-driven bone repair and mineralization. In newly fractured mice bone, we observed an early transient upregulation of repeats occurring concurrently with the initiation of the inflammatory stage. In human bone biopsies, analysis revealed a significant correlation between repeats expression, mechanical stress and bone mineral density. We investigated a potential link between LINE-1 (L1) expression and bone mineralization by delivering a synthetic L1 RNA to osteoporotic patient-derived mesenchymal stem cells and observed a dsRNA-triggered protein kinase (PKR)-mediated stress response that led to strongly increased mineralization. This response was associated with a strong and transient inflammation, accompanied by a global translation attenuation induced by eIF2α phosphorylation. We demonstrated that L1 transfection reshaped the secretory profile of osteoblasts, triggering a paracrine activity that stimulated the mineralization of recipient cells.

Tumor necrosis factor-inducible gene 6 protein and its derived peptide ameliorate liver fibrosis by repressing CD44 activation in mice with alcohol-related liver disease

BACKGROUND

Alcohol-related liver disease (ALD) is a major health concern worldwide, but effective therapeutics for ALD are still lacking. Tumor necrosis factor-inducible gene 6 protein (TSG-6), a cytokine released from mesenchymal stem cells, was shown to reduce liver fibrosis and promote successful liver repair in mice with chronically damaged livers. However, the effect of TSG-6 and the mechanism underlying its activity in ALD remain poorly understood.

METHODS

To investigate its function in ALD mice with fibrosis, male mice chronically fed an ethanol (EtOH)-containing diet for 9 weeks were treated with TSG-6 (EtOH + TSG-6) or PBS (EtOH + Veh) for an additional 3 weeks.

RESULTS

Severe hepatic injury in EtOH-treated mice was markedly decreased in TSG-6-treated mice fed EtOH. The EtOH + TSG-6 group had less fibrosis than the EtOH + Veh group. Activation of cluster of differentiation 44 (CD44) was reported to promote HSC activation. CD44 and nuclear CD44 intracellular domain (ICD), a CD44 activator which were upregulated in activated HSCs and ALD mice were significantly downregulated in TSG-6-exposed mice fed EtOH. TSG-6 interacted directly with the catalytic site of MMP14, a proteolytic enzyme that cleaves CD44, inhibited CD44 cleavage to CD44ICD, and reduced HSC activation and liver fibrosis in ALD mice. In addition, a novel peptide designed to include a region that binds to the catalytic site of MMP14 suppressed CD44 activation and attenuated alcohol-induced liver injury, including fibrosis, in mice.

CONCLUSIONS

These results demonstrate that TSG-6 attenuates alcohol-induced liver damage and fibrosis by blocking CD44 cleavage to CD44ICD and suggest that TSG-6 and TSG-6-mimicking peptide could be used as therapeutics for ALD with fibrosis.

Role of TGF-β and p38 MAPK in TSG-6 Expression in Adipose Tissue-Derived Stem Cells In Vitro and In Vivo

Mesenchymal stem cells (MSCs) regulate immune cell activity by expressing tumor necrosis factor-α (TNF-α)-stimulated gene 6 (TSG-6) in inflammatory environments; however, whether anti-inflammatory responses affect TSG-6 expression in MSCs is not well understood. Therefore, we investigated whether transforming growth factor-β (TGF-β) regulates TSG-6 expression in adipose tissue-derived stem cells (ASCs) and whether effective immunosuppression can be achieved using ASCs and TGF-β signaling inhibitor A83-01. TGF-β significantly decreased TSG-6 expression in ASCs, but A83-01 and the p38 inhibitor SB202190 significantly increased it. However, in septic C57BL/6 mice, A83-01 further reduced the survival rate of the lipopolysaccharide (LPS)-treated group and ASC transplantation did not improve the severity induced by LPS. ASC transplantation alleviated the severity of sepsis induced by LPS+A83-01. In co-culture of macrophages and ASCs, A83-01 decreased TSG-6 expression whereas A83-01 and SB202190 reduced Cox-2 and IDO-2 expression in ASCs. These results suggest that TSG-6 expression in ASCs can be regulated by high concentrations of pro-inflammatory cytokines in vitro and in vivo, and that A83-01 and SB202190 can reduce the expression of immunomodulators in ASCs. Therefore, our data suggest that co-treatment of ASCs with TGF-β or p38 inhibitors is not adequate to modulate inflammation.

Differential gene expression analysis combined with molecular dynamics simulation study to elucidate the novel potential biomarker involved in pulmonary TB

Tuberculosis (TB) is a lethal multisystem disease that attacks the lungs' first line of defense. A substantial threat to public health and a primary cause of death is pulmonary TB. This study aimed to identify and investigate the probable differentially expressed genes (DEGs) primarily involved in Pulmonary TB. Accordingly, three independent gene expression data sets, numbered GSE139825, GSE139871, and GSE54992, were utilized for this purpose. The identified DEGs were used for bioinformatics-based analysis, including physical gene interaction, Gene Ontology (GO), network analysis and pathway studies using the Kyoto Encyclopedia of Genes and Genomes pathway (KEGG). The computational analysis predicted that TNFAIP6 is the significant DEG in the gene expression profiling of TB datasets. According to gene ontology analysis, TNFAIP6 is also essential in injury and inflammation. Further, TNFA1P6 is strongly linked to arsenic poisoning, evident from the results of NetworkAnalyst, a comprehensive and interactive platform for gene expression profiling via network visual analytics. As a result, the TNFAIP6 gene was ultimately chosen as a candidate DEG and subsequently employed for in silico structural characterization studies. The tertiary structure of TNFAIP6 was modelled using the ROBETTA server, followed by validation with SAVES and ProSA webserver. Additionally, structural dynamic studies, including molecular dynamics simulation (MDS) and essential dynamics analysis, including principal component (PC) based free energy landscape (FEL) analysis, was used for checking the stability of TNFAIP6 models. The dynamics result established the structural rigidity of modelled TNFAIP6 through RMSD, RMSF and RoG results. The FEL analysis revealed the restricted conformational flexibility of TNFAIP6 by displaying a single minimum energy basin in the contour plot. The comprehensive computational analysis established that TNFAIP6 could serve as a viable biomarker to assess the severity of pulmonary TB.

Current Therapeutic Options and Potential of Mesenchymal Stem Cell Therapy for Alcoholic Liver Disease

Alcoholic liver disease (ALD) is a globally prevalent chronic liver disease caused by chronic or binge consumption of alcohol. The therapeutic efficiency of current therapies for ALD is limited, and there is no FDA-approved therapy for ALD at present. Various strategies targeting pathogenic events in the progression of ALD are being investigated in preclinical and clinical trials. Recently, mesenchymal stem cells (MSCs) have emerged as a promising candidate for ALD treatment and have been tested in several clinical trials. MSC-released factors have captured attention, as they have the same therapeutic function as MSCs. Herein, we focus on current therapeutic options, recently proposed strategies, and their limitations in ALD treatment. Also, we review the therapeutic effects of MSCs and those of MSC-related secretory factors on ALD. Although accumulating evidence suggests the therapeutic potential of MSCs and related factors in ALD, the mechanisms underlying their actions in ALD have not been well studied. Further investigations of the detailed mechanisms underlying the therapeutic role of MSCs in ALD are required to expand MSC therapies to clinical applications. This review provides information on current or possible treatments for ALD and contributes to our understanding of the development of effective and safe treatments for ALD.

Improving Lipophagy by Restoring Rab7 Cycle: Protective Effects of Quercetin on Ethanol-Induced Liver Steatosis

Chronic alcohol consumption retards lipophagy, which contributes to the pathogenesis of liver steatosis. Lipophagy-related Rab7 has been presumed as a crucial regulator in the progression of alcohol liver disease despite elusive mechanisms. More importantly, whether or not hepatoprotective quercetin targets Rab7-associated lipophagy disorder is unknown. Herein, alcoholic fatty liver induced by chronic-plus-single-binge ethanol feeding to male C57BL/6J mice was manifested by hampering autophagosomes formation with lipid droplets and fusion with lysosomes compared with the normal control, which was normalized partially by quercetin. The GST-RILP pulldown assay of Rab7 indicated an improved GTP-Rab7 as the quercetin treatment for ethanol-feeding mice. HepG2 cells transfected with CYP2E1 showed similar lipophagy dysfunction when exposed to ethanol, which was blocked when cells were transfected with siRNA-Rab7 in advance. Ethanol-induced steatosis and autophagic flux disruption were aggravated by the Rab7-specific inhibitor CID1067700 while alleviated by transfecting with the Rab7Wt plasmid, which was visualized by immunofluorescence co-localization analysis and mCherry-GFP-LC3 transfection. Furthermore, TBC1D5, a Rab GTPase-activating protein for the subsequent normal circulation of Rab7, was downregulated after alcohol administration but regained by quercetin. Rab7 circulation retarded by ethanol and corrected by quercetin was further revealed by fluorescence recovery after photobleaching (FRAP). Altogether, quercetin attenuates hepatic steatosis by normalizing ethanol-imposed Rab7 turnover disorders and subsequent lipophagy disturbances, highlighting a novel mechanism and the promising prospect of quercetin-like phytochemicals against the crucial first hit from alcohol.

Renal Cellular Autophagy in Obesity: Boon or Bane?

Obesity is a growing human health concern worldwide and imposes adverse effects on many cell types and organ systems, including the kidneys. Obesity interferes with various cellular processes by increasing lipid accumulation and oxidation, insulin resistance, and inflammation. Autophagy is an important cellular process to maintain hemostasis and preserve resources, but might be altered in obesity. Interestingly, experimental studies have shown either an increase or a decrease in the rate of autophagy, and accumulation of byproducts and mediators of this cascade in kidneys of obese individuals. Hence, whether autophagy is beneficial or detrimental under these conditions remains unresolved. This review summarizes emerging evidence linking superfluous fat accumulation to alterations in autophagy. Elucidating the role of autophagy in the pathogenesis and complications of obesity in the kidney might help in the identification of therapeutic targets to prevent or delay the development of chronic kidney disease in obese subjects. Autophagy, kidney, obesity, lipids.

Modulation of Autophagy: A Novel "Rejuvenation" Strategy for the Aging Liver

Aging is a natural life process which leads to a gradual decline of essential physiological processes. For the liver, it leads to alterations in histomorphology (steatosis and fibrosis) and function (protein synthesis and energy generation) and affects central hepatocellular processes (autophagy, mitochondrial respiration, and hepatocyte proliferation). These alterations do not only impair the metabolic capacity of the liver but also represent important factors in the pathogenesis of malignant liver disease. Autophagy is a recycling process for eukaryotic cells to degrade dysfunctional intracellular components and to reuse the basic substances. It plays a crucial role in maintaining cell homeostasis and in resisting environmental stress. Emerging evidence shows that modulating autophagy seems to be effective in improving the age-related alterations of the liver. However, autophagy is a double-edged sword for the aged liver. Upregulating autophagy alleviates hepatic steatosis and ROS-induced cellular stress and promotes hepatocyte proliferation but may aggravate hepatic fibrosis. Therefore, a well-balanced autophagy modulation strategy might be suitable to alleviate age-related liver dysfunction. Conclusion. Modulation of autophagy is a promising strategy for "rejuvenation" of the aged liver. Detailed knowledge regarding the most devastating processes in the individual patient is needed to effectively counteract aging of the liver without causing obvious harm.

Editorial Expression of Concern: Tumor necrosis factor-inducible gene 6 protein ameliorates chronic liver damage by promoting autophagy formation in mice

An Editorial Expression of Concern to this paper has been published: https://doi.org/10.1038/s12276-021-00554-6

Lactobacillus reuteri DSM 17938 alleviates d-galactosamine-induced liver failure in rats

Liver failure is a serious hepatic dysfunction with high mortality. This work aimed to investigate the effect of a famous probiotic and drug, Lactobacillus reuteri DSM 17938, on liver failure in rats. Sprague-Dawley rats were gavaged with 3 × 109 CFU of DSM 17938 for 7 days. d-galactosamine was intraperitoneally injected to induce acute liver failure on the eighth day. Samples were collected to determine the liver function, serum cytokines levels, terminal ileum and liver histology, gut microbiota, metabolome and transcriptome. Our results showed that pretreatment with DSM 17938 not only reduced the elevation in serum alanine aminotransferase, aspartate aminotransferase, gamma-glutamyl transferase, IL-1α, IL-2, IL-18, M-CSF, and MIP-3α levels but also alleviated histological abnormalities of both the terminal ileum and liver induced by d-galactosamine. Additionally, DSM 17938 reduced d-galactosamine-induced enrichment of some taxa of gut Actinobacteria or Firmicutes, including abundant pathogens such as Actinomycetales, Coriobacteriaceae, Staphylococcaceae and Enterococcaceae. Furthermore, DSM 17938 reduced the d-galactosamine-induced increase in not only fecal metabolites such as trisaminol and lithocholic acid but also the transcription of liver inflammatory genes, such as Ccl2, Ccl7, Ccl11, Ccl12, Il6, Il11, Il20rb, Mmp3 and Mmp10. Downregulation of retinol metabolism and PPAR signaling pathway as well as upregulation of viral protein interaction with cytokine and cytokine receptor and central carbon metabolism in cancer signaling pathway were involved in the mechanism of L. reuteri DSM 17938 alleviating liver failure. Our findings suggested that DSM 17938 is a potential probiotic for the prevention or treatment of liver failure.

Bone marrow-derived humoral factors suppress oxidative phosphorylation, upregulate TSG-6, and improve therapeutic effects on liver injury of mesenchymal stem cells

Mesenchymal stem cells, which have the potential to be used in regenerative medicine, require improvements in quality for patient use. To maintain stemness of cultured bone marrow-derived mesenchymal stem cells, we focused on the bone marrow microenvironment, generated a conditioned medium of whole bone marrow cells (BMC-CM), and assessed its effects on bone marrow-derived mesenchymal stem cells. BMC-CM suppressed morphological deterioration and proliferative decline in cultured bone marrow-derived mesenchymal stem cells, suppressed mitochondrial oxidative phosphorylation activity, a stemness indicator, and upregulated suppressors of oxidative phosphorylation such as hypoxia-inducible factor-1 alpha, Sirtuin 3, 4, and 5. Furthermore, BMC-CM upregulated TNF-stimulated gene 6 and ameliorated the therapeutic effects of cells on liver injury in carbon tetrachloride-administered rats. Since the elimination of 20-220-nm particles attenuated the effects of BMC-CM, we further analyzed exosomal microRNAs produced by whole bone marrow cells. Among the 49 microRNAs observed to be upregulated during the preparation of BMC-CM, several were identified that were associated with suppression of oxidative phosphorylation, upregulation of TNF-stimulated gene 6, and the pathogenesis of liver diseases. Thus, bone marrow-derived humoral factors including exosomal microRNAs may help to improve the therapeutic quality of bone marrow-derived mesenchymal stem cells for liver regenerative therapy.

Liver-targeted delivery of TSG-6 by calcium phosphate nanoparticles for the management of liver fibrosis

Mesenchymal stem cells (MSCs) transplantation is a promising antifibrotic strategy but facing clinical controversies. Inspired by advances in nanomedicine, we aimed to bypass these clinical barriers of MSCs by identifying the key antifibrotic molecule of MSCs and developing a specific liver-targeting nanocarrier.

Methods: Cytokines secreted by MSCs were examined with serum stimulation of cirrhotic patients. Immunohistochemistry, microarray, immunoblotting, and quantitative real-time PCR (qRT-PCR) were applied to identify the critical antifibrotic cytokine and to discover its role in modulating antifibrotic effects. Biomineralization method was used to prepare calcium phosphate nanoparticles (NPs). The targeting and therapeutic efficiency of NPs were evaluated by in vivo imaging and biochemical studies on fibrotic mice induced by CCl₄.

Results: The stimulated MSCs exhibited high-level expression of Tumor necrosis factor (TNF)-stimulated gene 6 (TSG-6). On animal study, exogenous administration of TSG-6 alone can ameliorate liver fibrosis while TSG-6 knocked MSCs (Lv-TSG-6 MSCs) lost antifibrotic effects. Further studies verified the importance of TSG-6 and identified its antifibrotic mechanism by modulating M2 macrophages and increasing matrix metalloproteinase 12 (MMP12) expression. Additionally, we found a feedback loop between TSG-6, MMP12 and pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β), which may improve our understanding of the aggravating process of cirrhosis and antifibrotic mechanisms of TSG-6 and MSCs. Based on these findings, we developed calcium phosphate nanoparticles (CaP@BSA NPs) by biomineralization method using bovine serum albumin (BSA) as the biotemplate. Imaging tracking and drug loading studies showed specific liver targeting and high TSG-6 loading efficacy of as-prepared CaP@BSA NPs. In vivo therapeutic study further demonstrated the improved therapeutic effects of TSG-6 loaded CaP@BSA.

Conclusions: TSG-6 was a major antifibrotic cytokine of MSCs, TSG-6 loaded CaP@BSA NPs showed specific liver accumulation and improved therapeutic effects, which indicated translational potentials of CaP@BSA as a promising drug carrier for the liver disease management.

Autophagy promotes hepatic differentiation of hepatic progenitor cells by regulating the Wnt/β-catenin signaling pathway

Hepatic progenitor cells (HPCs) can be activated when the liver suffers persistent and severe damage and can differentiate into hepatocytes to maintain liver regeneration and homeostasis. However, the molecular mechanism underlying the hepatic differentiation of HPCs is unclear. Therefore, in this study, we aimed to investigate the roles of autophagy and the Wnt/β-catenin signaling pathway during hepatic differentiation of HPCs in vivo and in vitro. First, immunohistochemistry, immunofluorescence and electron microscopy showed that Atg5 and β-catenin were highly expressed in human fibrotic liver and mouse liver injury induced by feeding a 50% choline-deficient diet plus 0.15% ethionine solution in drinking water (CDE diet) for 21 days; in addition, these factors were expressed in CK19-positive HPCs. Second, Western blotting and immunofluorescence confirmed that CK19-positive HPCs incubated in differentiation medium for 7 days can differentiate into hepatocytes and that differentiated HPCs were able to take up ICG and secrete albumin and urea. Further investigation via Western blotting, immunofluorescence and electron microscopy revealed autophagy and the Wnt/β-catenin pathway to be activated during hepatic differentiation of HPCs. Next, we found that inhibiting autophagy by downregulating Atg5 gene expression impaired hepatic differentiation of HPCs and inhibited activation of the Wnt/β-catenin pathway, which was rescued by overexpression of the β-catenin gene. Moreover, downregulating β-catenin gene expression without inhibiting autophagy still impeded the differentiation of HPCs. Finally, coimmunoprecipitation demonstrated that P62 forms a complex with phosphorylated glycogen synthase kinase 3 beta (pGSK3β). Third, in mouse CDE-induced liver injury, immunohistochemistry and immunofluorescence confirmed that downregulating Atg5 gene expression inhibited autophagy, thus impeding hepatic differentiation of HPCs and inhibiting activation of the Wnt/β-catenin pathway. As observed in vitro, overexpression of β-catenin rescued this phenomenon caused by autophagy inhibition, though decreasing β-catenin levels without autophagy inhibition still impeded HPC differentiation. We also found that HPCs differentiated into hepatocytes in human fibrotic liver tissue. Collectively, these results demonstrate that autophagy promotes HPC differentiation by regulating Wnt/β-catenin signaling. Our results are the first to identify a role for autophagy in promoting the hepatic differentiation of HPCs.

TSG-6: A multifunctional protein with anti-inflammatory and tissue-protective properties

Tumor necrosis factor- (TNF) stimulated gene-6 (TSG-6) is an inflammation-associated secreted protein that has been implicated as having important and diverse tissue protective and anti-inflammatory properties, e.g. mediating many of the immunomodulatory and beneficial activities of mesenchymal stem/stromal cells. TSG-6 is constitutively expressed in some tissues, which are either highly metabolically active or subject to challenges from the environment, perhaps providing protection in these contexts. The diversity of its functions are dependent on the binding of TSG-6 to numerous ligands, including matrix molecules such as glycosaminoglycans, as well as immune regulators and growth factors that themselves interact with these linear polysaccharides. It is becoming apparent that TSG-6 can directly affect matrix structure and modulate the way extracellular signalling molecules interact with matrix. In this review, we focus mainly on the literature for TSG-6 over the last 10 years, summarizing its expression, structure, ligand-binding properties, biological functions and highlighting TSG-6's potential as a therapeutic for a broad range of disease indications.