Chronic Aroclor 1260 exposure alters the mouse liver proteome, selenoproteins, and metals in steatotic liver disease.

The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) continues to increase due in part to the obesity epidemic and to environmental exposures to metabolism disrupting chemicals. A single gavage exposure of male mice to Aroclor 1260 (Ar1260), an environmentally relevant mixture of non-dioxin-like polychlorinated biphenyls (PCBs), resulted in steatohepatitis and altered RNA modifications in selenocysteine tRNA 34 weeks post-exposure. Unbiased approaches identified the liver proteome, selenoproteins, and levels of 25 metals. Ar1260 altered the abundance of 128 proteins. Enrichment analysis of the liver Ar1260 proteome included glutathione metabolism and translation of selenoproteins. Hepatic glutathione peroxidase 4 (GPX4) and Selenoprotein O (SELENOO) were increased and Selenoprotein F (SELENOF), Selenoprotein S (SELENOS), Selenium binding protein 2 (SELENBP2) were decreased with Ar1260 exposure. Increased copper, selenium (Se), and zinc and reduced iron levels were detected. These data demonstrate that Ar1260 exposure alters the (seleno)proteome, Se, and metals in MASLD-associated pathways.

Increased expression of phosphodiesterase 4 in activated hepatic stellate cells promotes cytoskeleton remodeling and cell migration.

Activation and transdifferentiation of hepatic stellate cells (HSC) into migratory myofibroblasts is a key process in liver fibrogenesis. Cell migration requires an active remodeling of the cytoskeleton, which is a tightly regulated process coordinated by Rho-specific guanine nucleotide exchange factors (GEFs) and the Rho family of small GTPases. Rho-associated kinase (ROCK) promotes assembly of focal adhesions and actin stress fibers by regulating cytoskeleton organization. GEF exchange protein directly activated by cAMP 1 (EPAC1) has been implicated in modulating TGFß1 and Rho signaling; however, its role in HSC migration has never been examined. The aim of this study was to evaluate the role of cAMP-degrading phosphodiesterase 4 (PDE4) enzymes in regulating EPAC1 signaling, HSC migration, and fibrogenesis. We show that PDE4 protein expression is increased in activated HSCs expressing alpha smooth muscle actin and active myosin light chain (MLC) in fibrotic tissues of human nonalcoholic steatohepatitis cirrhosis livers and mouse livers exposed to carbon tetrachloride. In human livers, TGFß1 levels were highly correlated with PDE4 expression. TGFß1 treatment of LX2 HSCs decreased levels of cAMP and EPAC1 and increased PDE4D expression. PDE4 specific inhibitor, rolipram, and an EPAC-specific agonist decreased TGFß1-mediated cell migration in vitro. In vivo, targeted delivery of rolipram to the liver prevented fibrogenesis and collagen deposition and decreased the expression of several fibrosis-related genes, and HSC activation. Proteomic analysis of mouse liver tissues identified the regulation of actin cytoskeleton by the kinase effectors of Rho GTPases as a major pathway impacted by rolipram. Western blot analyses confirmed that PDE4 inhibition decreased active MLC and endothelin 1 levels, key proteins involved in cytoskeleton remodeling and contractility. The current study, for the first time, demonstrates that PDE4 enzymes are expressed in hepatic myofibroblasts and promote cytoskeleton remodeling and HSC migration. © 2023 The Pathological Society of Great Britain and Ireland.

The plasma degradome reflects later development of NASH fibrosis after liver transplant.

Although liver transplantation (LT) is an effective therapy for cirrhosis, the risk of post-LT NASH is alarmingly high and is associated with accelerated progression to fibrosis/cirrhosis, cardiovascular disease and decreased survival. Lack of risk stratification strategies hampers early intervention against development of post-LT NASH fibrosis. The liver undergoes significant remodeling during inflammatory injury. During such remodeling, degraded peptide fragments (i.e., 'degradome') of the ECM and other proteins increase in plasma, making it a useful diagnostic/prognostic tool in chronic liver disease. To investigate whether liver injury caused by post-LT NASH would yield a unique degradome profile that is predictive of severe post-LT NASH fibrosis, a retrospective analysis of 22 biobanked samples from the Starzl Transplantation Institute (12 with post-LT NASH after 5 years and 10 without) was performed. Total plasma peptides were isolated and analyzed by 1D-LC-MS/MS analysis using a Proxeon EASY-nLC 1000 UHPLC and nanoelectrospray ionization into an Orbitrap Elite mass spectrometer. Qualitative and quantitative peptide features data were developed from MSn datasets using PEAKS Studio X (v10). LC-MS/MS yielded ~ 2700 identifiable peptide features based on the results from Peaks Studio analysis. Several peptides were significantly altered in patients that later developed fibrosis and heatmap analysis of the top 25 most significantly changed peptides, most of which were ECM-derived, clustered the 2 patient groups well. Supervised modeling of the dataset indicated that a fraction of the total peptide signal (~ 15%) could explain the differences between the groups, indicating a strong potential for representative biomarker selection. A similar degradome profile was observed when the plasma degradome patterns were compared being obesity sensitive (C57Bl6/J) and insensitive (AJ) mouse strains. The plasma degradome profile of post-LT patients yielded stark difference based on later development of post-LT NASH fibrosis. This approach could yield new "fingerprints" that can serve as minimally-invasive biomarkers of negative outcomes post-LT.

The plasma degradome reflects later development of NASH fibrosis after liver transplant.

Although liver transplantation (LT) is an effective therapy for cirrhosis, the risk of post-LT NASH is alarmingly high and is associated with accelerated progression to fibrosis/cirrhosis, cardiovascular disease, and decreased survival. Lack of risk stratification strategies hamper liver undergoes significant remodeling during inflammatory injury. During such remodeling, degraded peptide fragments (i.e., 'degradome') of the ECM and other proteins increase in plasma, making it a useful diagnostic/prognostic tool in chronic liver disease. To investigate whether inflammatory liver injury caused by post-LT NASH would yield a unique degradome profile, predictive of severe post-LT NASH fibrosis, we performed a retrospective analysis of 22 biobanked samples from the Starzl Transplantation Institute (12 with post-LT NASH after 5 years and 10 without). Total plasma peptides were isolated and analyzed by 1D-LC-MS/MS analysis using a Proxeon EASY-nLC 1000 UHPLC and nanoelectrospray ionization into an Orbitrap Elite mass spectrometer. Qualitative and quantitative peptide features data were developed from MSn datasets using PEAKS Studio X (v10). LC-MS/MS yielded ∼2700 identifiable peptide features based on the results from Peaks Studio analysis. Several peptides were significantly altered in patients that later developed fibrosis and heatmap analysis of the top 25 most significantly-changed peptides, most of which were ECM-derived, clustered the 2 patient groups well. Supervised modeling of the dataset indicated that a fraction of the total peptide signal (∼15%) could explain the differences between the groups, indicating a strong potential for representative biomarker selection. A similar degradome profile was observed when the plasma degradome patterns were compared being obesity sensitive (C57Bl6/J) and insensitive (AJ) mouse strains. Both The plasma degradome profile of post-LT patients yields stark difference based on later development of post-LT NASH fibrosis. This approach could yield new "fingerprints" that can serve as minimally-invasive biomarkers of negative outcomes post-LT.

Fibrosis resolution in the mouse liver: Role of Mmp12 and potential role of calpain 1/2.

Although most work has focused on resolution of collagen ECM, fibrosis resolution involves changes to several ECM proteins. The purpose of the current study was twofold: 1) to examine the role of MMP12 and elastin; and 2) to investigate the changes in degraded proteins in plasma (i.e., the "degradome") in a preclinical model of fibrosis resolution. Fibrosis was induced by 4 weeks carbon tetrachloride (CCl4) exposure, and recovery was monitored for an additional 4 weeks. Some mice were treated with daily MMP12 inhibitor (MMP408) during the resolution phase. Liver injury and fibrosis was monitored by clinical chemistry, histology and gene expression. The release of degraded ECM peptides in the plasma was analyzed using by 1D-LC-MS/MS, coupled with PEAKS Studio (v10) peptide identification. Hepatic fibrosis and liver injury rapidly resolved in this mouse model. However, some collagen fibrils were still present 28d after cessation of CCl4. Despite this persistent collagen presence, expression of canonical markers of fibrosis were also normalized. The inhibition of MMP12 dramatically delayed fibrosis resolution under these conditions. LC-MS/MS analysis identified that several proteins were being degraded even at late stages of fibrosis resolution. Calpains 1/2 were identified as potential new proteases involved in fibrosis resolution. CONCLUSION. The results of this study indicate that remodeling of the liver during recovery from fibrosis is a complex and highly coordinated process that extends well beyond the degradation of the collagenous scar. These results also indicate that analysis of the plasma degradome may yield new insight into the mechanisms of fibrosis recovery, and by extension, new "theragnostic" targets. Lastly, a novel potential role for calpain activation in the degradation and turnover of proteins was identified.

A plasma peptidomic signature reveals extracellular matrix remodeling and predicts prognosis in alcohol-related hepatitis.

Alcohol-related hepatitis (AH) is plagued with high mortality and difficulty in identifying at-risk patients. The extracellular matrix undergoes significant remodeling during inflammatory liver injury that can be detected in biological fluids and potentially used for mortality prediction. EDTA plasma samples were collected from AH patients (n= 62); Model for End-Stage Liver Disease (MELD) score defined AH severity as moderate (12-20; n=28) and severe (>20; n=34). The peptidome data was collected by high resolution, high mass accuracy UPLC-MS. Univariate and multivariate analyses identified differentially abundant peptides, which were used for Gene Ontology, parent protein matrisomal composition and protease involvement. Machine learning methods were used on patient-specific peptidome and clinical data to develop mortality predictors. Analysis of plasma peptides from AH patients and healthy controls identified over 1,600 significant peptide features corresponding to 130 proteins. These were enriched for ECM fragments in AH samples, likely related to turnover of hepatic-derived proteins. Analysis of moderate versus severe AH peptidomes showed a shift in abundance of peptides from collagen 1A1 and fibrinogen A proteins. The dominant proteases for the AH peptidome spectrum appear to be CAPN1 and MMP12. Increase in hepatic expression of these proteases was orthogonally-validated in RNA-seq data of livers from AH patients. Causal graphical modeling identified four peptides directly linked to 90-day mortality in >90% of the learned graphs. These peptides improved the accuracy of mortality prediction over MELD score and were used to create a clinically applicable mortality prediction assay. A signature based on plasma peptidome is a novel, non-invasive method for prognosis stratification in AH patients. Our results could also lead to new mechanistic and/or surrogate biomarkers to identify new AH mechanisms. Lay summary: We used degraded proteins found the blood of alcohol-related hepatitis patients to identify new potential mechanisms of injury and to predict 90 day mortality.

Dataset for proteomic analysis of arylamine N-acetyltransferase 1 knockout MDA-MB-231 breast cancer cells.

Arylamine N-acetyltransferase 1 (NAT1) is frequently upregulated in breast cancer. An unbiased analysis of proteomes of parental MDA-MB-231 breast cancer cells and two separate NAT1 knockout (KO) cell lines were performed. Among 4,890 proteins identified, 737 and 651 proteins were found significantly (p < 0.01) upregulated and downregulated, respectively, in NAT1 KO cells, compared to the parental cells. Each set of proteins was analyzed to identify Gene Ontology biological processes, molecular functions, and cellular components that were enriched in the set. Among the proteins upregulated in NAT1 KO cells, processes associated with MHC major histocompatibility complex I-mediated antigen presentation were significantly enriched. Multiple processes involved in mitochondrial functions were collectively downregulated in NAT1 KO cells, including multiple subunits of mitochondrial ATP synthase (Complex V of the electron transport chain). This was accompanied by a reduction in cell cycle-associated proteins and an increase in pro-apoptotic pathways in NAT1 KO cells. The current dataset contains additional representations of the biological processes and components that are differentially enriched in NAT1 KO MDA-MB-231 cells and will serve as a basis for generating novel hypotheses regarding the role of NAT1 in breast cancer. Data are available via ProteomeXchange with identifier PXD035953.

Quantitative Mass Spectrometry Normalization in Urine Biomarker Analysis in Nephrotic Syndrome.

Chronic kidney disease (CKD) affects 30 million adults, costs ~$79 billion dollars (2016) in Medicare expenditures, and is the ninth leading cause of death in the United States. The disease is silent or undiagnosed in almost half of people with severely reduced kidney function. Urine provides an ideal biofluid that is accessible to high-sensitivity mass spectrometry-based proteomic interrogation and is an indicator of renal homeostasis. While the accurate and precise diagnosis and better disease management of CKD can be aided using urine biomarkers, their discovery in excessive protein or nephrotic urine samples can present challenges. In this work we present a mass spectrometry-based method utilizing multiplex tandem mass tag (TMT) quantification and improved protein quantification using reporter ion normalization to urinary creatinine to analyze urinary proteins from patients with a form of nephrotic syndrome (FSGS). A comparative analysis was performed for urine from patients in remission versus active disease flare. Two-dimensional LC-MS/MS TMT quantitative analysis identified over 1058 urine proteins, 580 proteins with 2 peptides or greater and quantifiable. Normalization of TMT abundance values to creatinine per ml of urine concentrated reduced variability in 2D-TMT-LC-MS/MS experiments. Univariate and multivariate analyses showed that 27 proteins were significantly increased in proteinuric disease flare. Hierarchical heatmap clustering showed that SERPINA1 and ORM1 were >1.5 fold increased in active disease versus remission urine samples. ELISA validation of SERPINA1 and ORM1 abundance agreed with our quantitative TMT proteomics analysis. These findings provide support for the utility of this method for identification of novel diagnostic markers of CKD and identify SERPINA1 and ORM1 as promising candidate diagnostic markers for FSGS.

Proteomic analysis of arylamine N-acetyltransferase 1 knockout breast cancer cells: Implications in immune evasion and mitochondrial biogenesis.

Previous studies have shown that inhibition or depletion of N-acetyltransferase 1 (NAT1) in breast cancer cell lines leads to growth retardation both in vitro and in vivo, suggesting that NAT1 contributes to rapid growth of breast cancer cells. To understand molecular and cellular processes that NAT1 contributes to and generate novel hypotheses in regard to NAT1's role in breast cancer, we performed an unbiased analysis of proteomes of parental MDA-MB-231 breast cancer cells and two separate NAT1 knockout (KO) cell lines. Among 4890 proteins identified, 737 proteins were found significantly (p < 0.01) upregulated, and 651 proteins were significantly (p < 0.01) downregulated in both NAT1 KO cell lines. We performed enrichment analyses to identify Gene Ontology biological processes, molecular functions, and cellular components that were enriched in each data set. Among the proteins upregulated in NAT1 KO cells, pathways associated with MHC (major histocompatibility complex) I-mediated antigen presentation were significantly enriched. This raises an interesting and new hypothesis that upregulation of NAT1 in breast cancer cells may aid them evade immune detection. Multiple pathways involved in mitochondrial functions were collectively downregulated in NAT1 KO cells, including multiple subunits of mitochondrial ATP synthase (Complex V of the electron transport chain). This was accompanied by a reduction in cell cycle-associated proteins and an increase in pro-apoptotic pathways in NAT1 KO cells, consistent with reported observations that NAT1 KO cells exhibit a slower growth rate both in vitro and in vivo. Thus, mitochondrial dysfunction in NAT1 KO cells likely contributes to growth retardation.

Temporal Modulation of Differential Alternative Splicing in HaCaT Human Keratinocyte Cell Line Chronically Exposed to Arsenic for up to 28 Wk.

BACKGROUND: Chronic arsenic exposure via drinking water is associated with an increased risk of developing cancer and noncancer chronic diseases. Pre-mRNAs are often subject to alternative splicing, generating mRNA isoforms encoding functionally distinct protein isoforms. The resulting imbalance in isoform species can result in pathogenic changes in critical signaling pathways. Alternative splicing as a mechanism of arsenic-induced toxicity and carcinogenicity is understudied. OBJECTIVE: This study aimed to accurately profile differential alternative splicing events in human keratinocytes induced by chronic arsenic exposure that might play a role in carcinogenesis. METHODS: Independent quadruplicate cultures of immortalized human keratinocytes (HaCaT) were maintained continuously for 28 wk with 0 or 100 nM sodium arsenite. RNA-sequencing (RNA-Seq) was performed with poly(A) RNA isolated from cells harvested at 7, 19, and 28 wk with subsequent replicate multivariate analysis of transcript splicing (rMATS) analysis to detect and quantify differential alternative splicing events. Reverse transcriptase-polymerase chain reaction (RT-PCR) for selected alternative splicing events was performed to validate RNA-Seq predictions. Functional enrichment was performed by gene ontology (GO) analysis of the differential alternative splicing event data set at each time point. RESULTS: At least 600 differential alternative splicing events were detected at each time point tested, comprising all the five main types of alternative splicing and occurring in both open reading frames (ORFs) and untranslated regions (UTRs). Based on functional relevance ELK4, SHC1, and XRRA1 were selected for validation of predicted alternative splicing events at 7 wk by RT-PCR. Densitometric analysis of RT-PCR data corroborated the rMATS predicted alternative splicing for all three events. Protein expression validation of the selected alternative splicing events was challenging given that very few isoform-specific antibodies are available. GO analysis demonstrated that the enriched terms in differential alternatively spliced mRNAs changed dynamically with the time of exposure. Notably, RNA metabolism and splicing regulation pathways were enriched at the 7-wk time point, when the greatest number of differentially alternatively spliced mRNAs are detected. Our preliminary proteomic analysis demonstrated that the expression of the canonical isoforms of the splice regulators DDX42, RMB25, and SRRM2 were induced upon chronic arsenic exposure, corroborating the splicing predictions. DISCUSSION: These results using cultures of HaCaT cells suggest that arsenic exposure disrupted an alternative splice factor network and induced time-dependent genome-wide differential alternative splicing that likely contributed to the changing proteomic landscape in arsenic-induced carcinogenesis. However, significant challenges remain in corroborating alternative splicing data at the proteomic level. https://doi.org/10.1289/EHP9676.

The Utility of Differential Scanning Calorimetry Curves of Blood Plasma for Diagnosis, Subtype Differentiation and Predicted Survival in Lung Cancer.

Early detection of lung cancer (LC) significantly increases the likelihood of successful treatment and improves LC survival rates. Currently, screening (mainly low-dose CT scans) is recommended for individuals at high risk. However, the recent increase in the number of LC cases unrelated to the well-known risk factors, and the high false-positive rate of low-dose CT, indicate a need to develop new, non-invasive methods for LC detection. Therefore, we evaluated the use of differential scanning calorimetry (DSC) for LC patients' diagnosis and predicted survival. Additionally, by applying mass spectrometry, we investigated whether changes in O- and N-glycosylation of plasma proteins could be an underlying mechanism responsible for observed differences in DSC curves of LC and control subjects. Our results indicate selected DSC curve features could be useful for differentiation of LC patients from controls with some capable of distinction between subtypes and stages of LC. DSC curve features also correlate with LC patients' overall/progression free survival. Moreover, the development of classification models combining patients' DSC curves with selected plasma protein glycosylation levels that changed in the presence of LC could improve the sensitivity and specificity of the detection of LC. With further optimization and development of the classification method, DSC could provide an accurate, non-invasive, radiation-free strategy for LC screening and diagnosis.

Nuclear Pyruvate Kinase M2 (PKM2) Contributes to Phosphoserine Aminotransferase 1 (PSAT1)-Mediated Cell Migration in EGFR-Activated Lung Cancer Cells.

An elevated expression of phosphoserine aminotransferase 1 (PSAT1) has been observed in multiple tumor types and is associated with poorer clinical outcomes. Although PSAT1 is postulated to promote tumor growth through its enzymatic function within the serine synthesis pathway (SSP), its role in cancer progression has not been fully characterized. Here, we explore a putative non-canonical function of PSAT1 that contributes to lung tumor progression. Biochemical studies found that PSAT1 selectively interacts with pyruvate kinase M2 (PKM2). Amino acid mutations within a PKM2-unique region significantly reduced this interaction. While PSAT1 loss had no effect on cellular pyruvate kinase activity and PKM2 expression in non-small-cell lung cancer (NSCLC) cells, fractionation studies demonstrated that the silencing of PSAT1 in epidermal growth factor receptor (EGFR)-mutant PC9 or EGF-stimulated A549 cells decreased PKM2 nuclear translocation. Further, PSAT1 suppression abrogated cell migration in these two cell types whereas PSAT1 restoration or overexpression induced cell migration along with an elevated nuclear PKM2 expression. Lastly, the nuclear re-expression of the acetyl-mimetic mutant of PKM2 (K433Q), but not the wild-type, partially restored cell migration in PSAT1-silenced cells. Therefore, we conclude that, in response to EGFR activation, PSAT1 contributes to lung cancer cell migration, in part, by promoting nuclear PKM2 translocation.

Identification and characterization of a UbK family kinase in Porphyromonas gingivalis that phosphorylates the RprY response regulator.

Phosphorylation of proteins is a key component of bacterial signaling systems that can control important functions such as community development and virulence. We report here the identification of a Ubiquitous bacterial Kinase (UbK) family member, designated UbK1, in the anaerobic periodontal pathogen, Porphyromonas gingivalis. UbK1 contains conserved SPT/S, Hanks-type HxDxYR, EW, and Walker A motifs, and a mutation analysis established the Walker A domain and the Hanks-type domain as required for both autophosphorylation and transphosphorylation. UbK1 autophosphorylates on the proximal serine in the SPT/S domain as well as the tyrosine residue within the HxDxYR domain and the tyrosine residue immediately proximal, indicating both serine/threonine and tyrosine specificity. The orphan two-component system response regulator (RR) RprY was phosphorylated on Y41 in the receiver domain by UbK1. The ubk1 gene is essential in P. gingivalis; however, overexpression of UbK1 showed that UbK1-mediated phosphorylation of RprY functions predominantly to augment its properties as a transcriptional enhancer. These results establish that P. gingivalis possesses an active UbK kinase in addition to a previously described Bacterial Tyrosine family kinase. The RR RprY is identified as the first transcriptional regulator controlled by a UbK enzyme.

Exosome-Like Nanoparticles From Lactobacillus rhamnosusGG Protect Against Alcohol-Associated Liver Disease Through Intestinal Aryl Hydrocarbon Receptor in Mice.

Alcohol-associated liver disease (ALD) is a major cause of mortality. Gut barrier dysfunction-induced bacterial translocation and endotoxin release contribute to the pathogenesis of ALD. Probiotic Lactobacillus rhamnosus GG (LGG) is known to be beneficial on experimental ALD by reinforcing the intestinal barrier function. In this study, we aim to investigate whether the protective effects of LGG on intestinal barrier function is mediated by exosome-like nanoparticles (ELNPs) released by LGG. Intestinal epithelial cells and macrophages were treated with LGG-derived ELNPs (LDNPs) isolated from LGG culture. LDNPs increased tight junction protein expression in epithelial cells and protected from the lipopolysaccharide-induced inflammatory response in macrophages. Three-day oral application of LDNPs protected the intestine from alcohol-induced barrier dysfunction and the liver from steatosis and injury in an animal model of ALD. Co-administration of an aryl hydrocarbon receptor (AhR) inhibitor abolished the protective effects of LDNPs, indicating that the effects are mediated, at least in part, by intestinal AhR signaling. We further demonstrated that LDNP administration increased intestinal interleukin-22-Reg3 and nuclear factor erythroid 2-related factor 2 (Nrf2)-tight junction signaling pathways, leading to the inhibition of bacterial translocation and endotoxin release in ALD mice. This protective effect was associated with LDNP enrichment of bacterial tryptophan metabolites that are AhR agonists. Conclusions: Our results suggest that the beneficial effects of LGG and their supernatant in ALD are likely mediated by bacterial AhR ligand-enriched LDNPs that increase Reg3 and Nrf2 expression, leading to the improved barrier function. These findings provide a strategy for the treatment of ALD and other gut barrier dysfunction-associated diseases.

Serine Protease HTRA1 as a Novel Target Antigen in Primary Membranous Nephropathy.

BACKGROUND: Identification of target antigens PLA2R, THSD7A, NELL1, or Semaphorin-3B can explain the majority of cases of primary membranous nephropathy (MN). However, target antigens remain unidentified in 15%-20% of patients. METHODS: A multipronged approach, using traditional and modern technologies, converged on a novel target antigen, and capitalized on the temporal variation in autoantibody titer for biomarker discovery. Immunoblotting of human glomerular proteins followed by differential immunoprecipitation and mass spectrometric analysis was complemented by laser-capture microdissection followed by mass spectrometry, elution of immune complexes from renal biopsy specimen tissue, and autoimmune profiling on a protein fragment microarray. RESULTS: These approaches identified serine protease HTRA1 as a novel podocyte antigen in a subset of patients with primary MN. Sera from two patients reacted by immunoblotting with a 51-kD protein within glomerular extract and with recombinant human HTRA1, under reducing and nonreducing conditions. Longitudinal serum samples from these patients seemed to correlate with clinical disease activity. As in PLA2R- and THSD7A- associated MN, anti-HTRA1 antibodies were predominantly IgG4, suggesting a primary etiology. Analysis of sera collected during active disease versus remission on protein fragment microarrays detected significantly higher titers of anti-HTRA1 antibody in active disease. HTRA1 was specifically detected within immune deposits of HTRA1-associated MN in 14 patients identified among three cohorts. Screening of 118 "quadruple-negative" (PLA2R-, THSD7A-, NELL1-, EXT2-negative) patients in a large repository of MN biopsy specimens revealed a prevalence of 4.2%. CONCLUSIONS: Conventional and more modern techniques converged to identify serine protease HTRA1 as a target antigen in MN.

The Alphaviral Capsid Protein Inhibits IRAK1-Dependent TLR Signaling.

Alphaviruses are arthropod-borne RNA viruses which can cause either mild to severe febrile arthritis which may persist for months, or encephalitis which can lead to death or lifelong cognitive impairments. The non-assembly molecular role(s), functions, and protein-protein interactions of the alphavirus capsid proteins have been largely overlooked. Here we detail the use of a BioID2 biotin ligase system to identify the protein-protein interactions of the Sindbis virus capsid protein. These efforts led to the discovery of a series of novel host-pathogen interactions, including the identification of an interaction between the alphaviral capsid protein and the host IRAK1 protein. Importantly, this capsid-IRAK1 interaction is conserved across multiple alphavirus species, including arthritogenic alphaviruses SINV, Ross River virus, and Chikungunya virus; and encephalitic alphaviruses Eastern Equine Encephalitis virus, and Venezuelan Equine Encephalitis virus. The impact of the capsid-IRAK1 interaction was evaluated using a robust set of cellular model systems, leading to the realization that the alphaviral capsid protein specifically inhibits IRAK1-dependent signaling. This inhibition represents a means by which alphaviruses may evade innate immune detection and activation prior to viral gene expression. Altogether, these data identify novel capsid protein-protein interactions, establish the capsid-IRAK1 interaction as a common alphavirus host-pathogen interface, and delineate the molecular consequences of the capsid-IRAK1 interaction on IRAK1-dependent signaling.

Patients with Proliferative Lupus Nephritis Have Autoantibodies That React to Moesin and Demonstrate Increased Glomerular Moesin Expression.

Kidney involvement in systemic lupus erythematosus (SLE)-termed lupus nephritis (LN)-is a severe manifestation of SLE that can lead to end-stage kidney disease (ESKD). LN is characterized by immune complex deposition and inflammation in the glomerulus. We tested the hypothesis that autoantibodies targeting podocyte and glomerular cell proteins contribute to the development of immune complex formation in LN. We used Western blotting with SLE sera from patients with and without LN to identify target antigens in human glomerular and cultured human-derived podocyte membrane proteins. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), we identified the proteins in the gel regions corresponding to reactive bands observed with sera from LN patients. We identified 102 proteins that were present in both the podocyte and glomerular samples. We identified 10 high-probability candidates, including moesin, using bioinformatic analysis. Confirmation of moesin as a target antigen was conducted using immunohistochemical analysis (IHC) of kidney biopsy tissue and enzyme-linked immunosorbent assay (ELISA) to detect circulating antibodies. By IHC, biopsies from patients with proliferative lupus nephritis (PLN, class III/IV) demonstrated significantly increased glomerular expression of moesin (p < 0.01). By ELISA, patients with proliferative LN demonstrated significantly increased antibodies against moesin (p < 0.01). This suggests that moesin is a target glomerular antigen in lupus nephritis.

Effect of Epidermal Growth Factor Treatment and Polychlorinated Biphenyl Exposure in a Dietary-Exposure Mouse Model of Steatohepatitis.

BACKGROUND: Polychlorinated biphenyls (PCBs) are signaling disrupting chemicals that exacerbate nonalcoholic steatohepatitis (NASH) in mice. They are epidermal growth factor receptor (EGFR) inhibitors that enhance hepatic inflammation and fibrosis in mice. OBJECTIVES: This study tested the hypothesis that epidermal growth factor (EGF) administration can attenuate PCB-related NASH by increasing hepatic EGFR signaling in a mouse model. METHODS: C57BL/6 male mice were fed a 42% milk fat diet and exposed to Aroclor 1260 (20mg/kg) or vehicle for 12 wk. EGF (0.2µg/g) or vehicle were administered daily for 10 d starting at study week 10. Liver and metabolic phenotyping were performed. The EGF dose was selected based on results of an acute dose-finding study (30 min treatment of EGF at 0.2, 0.02, 0.002µg/g of via intraperitoneal injection). Hepatic phosphoproteomic analysis was performed using liver tissue from this acute study to understand EGFR's role in liver physiology. RESULTS: Markers of EGFR signaling were higher in EGF-treated mice. EGF+PCB-exposed mice had lower hepatic free fatty acids, inflammation, and fibrosis relative to PCB-only exposed mice. EGF-treated mice had higher plasma lipids, with no improvement in hepatic steatosis, and an association with higher LXR target gene expression and de novo lipogenesis. EGF-treated mice showed more severe hyperglycemia associated with lower adiponectin levels and insulin sensitivity. EGF-treated mice had higher hepatic HNF4α, NRF2, and AhR target gene expression but lower constitutive androstane receptor and farnesoid X receptor target gene expression. The hepatic EGF-sensitive phosphoproteome demonstrated a role for EGFR signaling in liver homeostasis. DISCUSSION: These results validated EGFR inhibition as a causal mode of action for PCB-related hepatic inflammation and fibrosis in a mouse model of NASH. However, observed adverse effects may limit the clinical translation of EGF therapy. More data are required to better understand EGFR's underinvestigated roles in liver and environmental health. https://doi.org/10.1289/EHP8222.

Differentiating Staphylococcus infection-associated glomerulonephritis and primary IgA nephropathy: a mass spectrometry-based exploratory study.

Staphylococcus infection-associated glomerulonephritis (SAGN) and primary IgA nephropathy (IgAN) are separate disease entities requiring different treatment approaches. However, overlapping histologic features may cause a diagnostic dilemma. An exploratory proteomic study to identify potential distinguishing biomarkers was performed on formalin fixed paraffin embedded kidney biopsy tissue, using mass spectrometry (HPLC-MS/MS) (n = 27) and immunohistochemistry (IHC) (n = 64), on four main diagnostic groups-SAGN, primary IgAN, acute tubular necrosis (ATN) and normal kidney (baseline transplant biopsies). Spectral counts modeled as a negative binomial distribution were used for statistical comparisons and in silico pathway analysis. Analysis of variance techniques were used to compare groups and the ROC curve to evaluate classification algorithms. The glomerular proteomes of SAGN and IgAN showed remarkable similarities, except for significantly higher levels of monocyte/macrophage proteins in SAGN-mainly lysozyme and S100A9. This finding was confirmed by IHC. In contrast, the tubulointerstitial proteomes were markedly different in IgAN and SAGN, with a lower abundance of metabolic pathway proteins and a higher abundance of extracellular matrix proteins in SAGN. The stress protein transglutaminase-2 (TGM2) was also significantly higher in SAGN. IHC of differentially-expressed glomerular and tubulointerstitial proteins can be used to help discriminate between SAGN and IgAN in ambiguous cases.

Proteomic Analysis Identifies Distinct Glomerular Extracellular Matrix in Collapsing Focal Segmental Glomerulosclerosis.

BACKGROUND: The mechanisms leading to extracellular matrix (ECM) replacement of areas of glomerular capillaries in histologic variants of FSGS are unknown. This study used proteomics to test the hypothesis that glomerular ECM composition in collapsing FSGS (cFSGS) differs from that of other variants. METHODS: ECM proteins in glomeruli from biopsy specimens of patients with FSGS not otherwise specified (FSGS-NOS) or cFSGS and from normal controls were distinguished and quantified using mass spectrometry, verified and localized using immunohistochemistry (IHC) and confocal microscopy, and assessed for gene expression. The analysis also quantified urinary excretion of ECM proteins and peptides. RESULTS: Of 58 ECM proteins that differed in abundance between cFSGS and FSGS-NOS, 41 were more abundant in cFSGS and 17 in FSGS-NOS. IHC showed that glomerular tuft staining for cathepsin B, cathepsin C, and annexin A3 in cFSGS was significantly greater than in other FSGS variants, in minimal change disease, or in membranous nephropathy. Annexin A3 colocalized with cathepsin B and C, claudin-1, phosphorylated ERK1/2, and CD44, but not with synaptopodin, in parietal epithelial cells (PECs) infiltrating cFSGS glomeruli. Transcripts for cathepsins B and C were increased in FSGS glomeruli compared with normal controls, and urinary excretion of both cathepsins was significantly greater in cFSGS compared with FSGS-NOS. Urinary excretion of ECM-derived peptides was enhanced in cFSGS, although in silico analysis did not identify enhanced excretion of peptides derived from cathepsin B or C. CONCLUSIONS: ECM differences suggest that glomerular sclerosis in cFSGS differs from that in other FSGS variants. Infiltration of activated PECs may disrupt ECM remodeling in cFSGS. These cells and their cathepsins may be therapeutic targets.