Reversal of Pulmonary Hypertension in a Human-Like Model: Therapeutic Targeting of Endothelial DHFR.

BACKGROUND: Pulmonary hypertension (PH) is a progressive disorder characterized by remodeling of the pulmonary vasculature and elevated mean pulmonary arterial pressure, resulting in right heart failure. METHODS: Here, we show that direct targeting of the endothelium to uncouple eNOS (endothelial nitric oxide synthase) with DAHP (2,4-diamino 6-hydroxypyrimidine; an inhibitor of GTP cyclohydrolase 1, the rate-limiting synthetic enzyme for the critical eNOS cofactor tetrahydrobiopterin) induces human-like, time-dependent progression of PH phenotypes in mice. RESULTS: Critical phenotypic features include progressive elevation in mean pulmonary arterial pressure, right ventricular systolic blood pressure, and right ventricle (RV)/left ventricle plus septum (LV+S) weight ratio; extensive vascular remodeling of pulmonary arterioles with increased medial thickness/perivascular collagen deposition and increased expression of PCNA (proliferative cell nuclear antigen) and alpha-actin; markedly increased total and mitochondrial superoxide production, substantially reduced tetrahydrobiopterin and nitric oxide bioavailabilities; and formation of an array of human-like vascular lesions. Intriguingly, novel in-house generated endothelial-specific dihydrofolate reductase (DHFR) transgenic mice (tg-EC-DHFR) were completely protected from the pathophysiological and molecular features of PH upon DAHP treatment or hypoxia exposure. Furthermore, DHFR overexpression with a pCMV-DHFR plasmid transfection in mice after initiation of DAHP treatment completely reversed PH phenotypes. DHFR knockout mice spontaneously developed PH at baseline and had no additional deterioration in response to hypoxia, indicating an intrinsic role of DHFR deficiency in causing PH. RNA-sequencing experiments indicated great similarity in gene regulation profiles between the DAHP model and human patients with PH. CONCLUSIONS: Taken together, these results establish a novel human-like murine model of PH that has long been lacking in the field, which can be broadly used for future mechanistic and translational studies. These data also indicate that targeting endothelial DHFR deficiency represents a novel and robust therapeutic strategy for the treatment of PH.

Integration of cardiac proteome biology and medicine by a specialized knowledgebase.

RATIONALE: Omics sciences enable a systems-level perspective in characterizing cardiovascular biology. Integration of diverse proteomics data via a computational strategy will catalyze the assembly of contextualized knowledge, foster discoveries through multidisciplinary investigations, and minimize unnecessary redundancy in research efforts. OBJECTIVE: The goal of this project is to develop a consolidated cardiac proteome knowledgebase with novel bioinformatics pipeline and Web portals, thereby serving as a new resource to advance cardiovascular biology and medicine. METHODS AND RESULTS: We created Cardiac Organellar Protein Atlas Knowledgebase (COPaKB; www.HeartProteome.org), a centralized platform of high-quality cardiac proteomic data, bioinformatics tools, and relevant cardiovascular phenotypes. Currently, COPaKB features 8 organellar modules, comprising 4203 LC-MS/MS experiments from human, mouse, drosophila, and Caenorhabditis elegans, as well as expression images of 10,924 proteins in human myocardium. In addition, the Java-coded bioinformatics tools provided by COPaKB enable cardiovascular investigators in all disciplines to retrieve and analyze pertinent organellar protein properties of interest. CONCLUSIONS: COPaKB provides an innovative and interactive resource that connects research interests with the new biological discoveries in protein sciences. With an array of intuitive tools in this unified Web server, nonproteomics investigators can conveniently collaborate with proteomics specialists to dissect the molecular signatures of cardiovascular phenotypes.

Regulation of acetylation restores proteolytic function of diseased myocardium in mouse and human.

Proteasome complexes play essential roles in maintaining cellular protein homeostasis and serve fundamental roles in cardiac function under normal and pathological conditions. A functional detriment in proteasomal activities has been recognized as a major contributor to the progression of cardiovascular diseases. Therefore, approaches to restore proteolytic function within the setting of the diseased myocardium would be of great clinical significance. In this study, we discovered that the cardiac proteasomal activity could be regulated by acetylation. Histone deacetylase (HDAC) inhibitors (suberoylanilide hydroxamic acid and sodium valproate) enhanced the acetylation of 20S proteasome subunits in the myocardium and led to an elevation of proteolytic capacity. This regulatory paradigm was present in both healthy and acutely ischemia/reperfusion (I/R) injured murine hearts, and HDAC inhibition in vitro restored proteolytic capacities to baseline sham levels in injured hearts. This mechanism of regulation was also viable in failing human myocardium. With 20S proteasomal complexes purified from murine myocardium treated with HDAC inhibitors in vivo, we confirmed that acetylation of 20S subunits directly, at least in part, presents a molecular explanation for the improvement in function. Furthermore, using high-resolution LC-MS/MS, we unraveled the first cardiac 20S acetylome, which identified the acetylation of nine N-termini and seven internal lysine residues. Acetylation on four lysine residues and four N-termini on cardiac proteasomes were novel discoveries of this study. In addition, the acetylation of five lysine residues was inducible via HDAC inhibition, which correlated with the enhancement of 20S proteasomal activity. Taken as a whole, our investigation unveiled a novel mechanism of proteasomal function regulation in vivo and established a new strategy for the potential rescue of compromised proteolytic function in the failing heart using HDAC inhibitors.

Characterization, design, and function of the mitochondrial proteome: from organs to organisms.

Mitochondria are a common energy source for organs and organisms; their diverse functions are specialized according to the unique phenotypes of their hosting environment. Perturbation of mitochondrial homeostasis accompanies significant pathological phenotypes. However, the connections between mitochondrial proteome properties and function remain to be experimentally established on a systematic level. This uncertainty impedes the contextualization and translation of proteomic data to the molecular derivations of mitochondrial diseases. We present a collection of mitochondrial features and functions from four model systems, including two cardiac mitochondrial proteomes from distinct genomes (human and mouse), two unique organ mitochondrial proteomes from identical genetic codons (mouse heart and mouse liver), as well as a relevant metazoan out-group (drosophila). The data, composed of mitochondrial protein abundance and their biochemical activities, capture the core functionalities of these mitochondria. This investigation allowed us to redefine the core mitochondrial proteome from organs and organisms, as well as the relevant contributions from genetic information and hosting milieu. Our study has identified significant enrichment of disease-associated genes and their products. Furthermore, correlational analyses suggest that mitochondrial proteome design is primarily driven by cellular environment. Taken together, these results connect proteome feature with mitochondrial function, providing a prospective resource for mitochondrial pathophysiology and developing novel therapeutic targets in medicine.

Substrate- and isoform-specific proteome stability in normal and stressed cardiac mitochondria.

RATIONALE: Mitochondrial protein homeostasis is an essential component of the functions and oxidative stress responses of the heart. OBJECTIVE: To determine the specificity and efficiency of proteome turnover of the cardiac mitochondria by endogenous and exogenous proteolytic mechanisms. METHODS AND RESULTS: Proteolytic degradation of the murine cardiac mitochondria was assessed by 2-dimensional differential gel electrophoresis and liquid chromatography-tandem mass spectrometry. Mitochondrial proteases demonstrated a substrate preference for basic protein variants, which indicates a possible recognition mechanism based on protein modifications. Endogenous mitochondrial proteases and the cytosolic 20S proteasome exhibited different substrate specificities. CONCLUSIONS: The cardiac mitochondrial proteome contains low amounts of proteases and is remarkably stable in isolation. Oxidative damage lowers the proteolytic capacity of cardiac mitochondria and reduces substrate availability for mitochondrial proteases. The 20S proteasome preferentially degrades specific substrates in the mitochondria and may contribute to cardiac mitochondrial proteostasis.

Metabolic labeling reveals proteome dynamics of mouse mitochondria.

Mitochondrial dysfunction is associated with many human diseases. Mitochondrial damage is exacerbated by inadequate protein quality control and often further contributes to pathogenesis. The maintenance of mitochondrial functions requires a delicate balance of continuous protein synthesis and degradation, i.e. protein turnover. To understand mitochondrial protein dynamics in vivo, we designed a metabolic heavy water ((2)H(2)O) labeling strategy customized to examine individual protein turnover in the mitochondria in a systematic fashion. Mice were fed with (2)H(2)O at a minimal level (<5% body water) without physiological impacts. Mitochondrial proteins were analyzed from 9 mice at each of the 13 time points between 0 and 90 days (d) of labeling. A novel multiparameter fitting approach computationally determined the normalized peak areas of peptide mass isotopomers at initial and steady-state time points and permitted the protein half-life to be determined without plateau-level (2)H incorporation. We characterized the turnover rates of 458 proteins in mouse cardiac and hepatic mitochondria and found median turnover rates of 0.0402 d(-1) and 0.163 d(-1), respectively, corresponding to median half-lives of 17.2 d and 4.26 d. Mitochondria in the heart and those in the liver exhibited distinct turnover kinetics, with limited synchronization within functional clusters. We observed considerable interprotein differences in turnover rates in both organs, with half-lives spanning from hours to months (≈ 60 d). Our proteomics platform demonstrates the first large-scale analysis of mitochondrial protein turnover rates in vivo, with potential applications in translational research.

Clinical characteristics of a COVID-19 cohort treated at UCLA Ronald Reagan Medical Center during the breaking phase of the pandemic: A retrospective study.

To this date, COVID-19 remains an unresolved pandemic, and the impairment of redox homeostasis dictates the severity of clinical outcomes. Here we examined initial UCLA cohort of 440 COVID-19 patients hospitalized between March 1st and April 1st, 2020, representing the first wave of the pandemic. The mean age was 58.88 ± 21.12, among which males were significantly more than females (55.5 % vs. 44.5 %), most distinctively in age group of 50-69. The age groups of 50-69 (33.6 %) and ≥70 (34.8 %) dominated. The racial composition was in general agreement with Census data with slight under-representation of Hispanics and Asians, and over-representation of Caucasians. Smoking was a significant factor (28.8 % vs. 11.0 % in LA population), likewise for obesity (BMI ≥30) (37.4 % vs. 27.7 % in LA population). Patients suffering from obesity or BMI<18.5 checked into ICU at a significantly higher rate. A 74.5 % of the patients had comorbidities including diabetes, chronic kidney disease, chronic pulmonary disease, congestive heart failure and peripheral vascular disease. The levels of d-dimer were drastically upregulated (1159.5 ng/mL), indicating hypercoagulative state. Upregulated LDH (328 IU/L) indicated significant tissue damages. A distorted redox hemeostasis is a common trait associated with these risk factors and clinical markers. A quarter of the patients received antivirals, among which Remdesivir most prescribed (23.6 %). Majority received antithrombotics (75 %), and antibiotics. Upon admission, 67 patients were intubated or received CPR; 177 patients eventually received intensive care (40.2 %). While 290 were discharged alive, 10 remained hospitalized, 73 were transferred, and 36 died with 3 palliatively discharged. In summary, our data fully characterized a Californian cohort of COVID-19 at the breaking phase of the pandemic, indicating that population demographics, biophysical characters, comorbidities and molecular pathological parameters have significant impacts on the evolvement of a pandemic. These provide critical insights into effective management of COVID-19, and future break from another pathogen.

Perioperative Changes in Plasma Nitrite and IL-6 Levels Predict Postoperative Atrial Fibrillation (POAF) and Acute Kidney Injury (AKI) after Cardiac Surgery.

Background: Postoperative atrial fibrillation (POAF) and acute kidney injury (AKI) are common yet significant complications after cardiac surgery, with incidences of up to 40% for each. Here, we assessed plasma nitrite and serum interleukin-6 (IL-6) levels before and after cardiac surgery to quantify the extent to which oxidative stress and inflammation contribute to POAF and AKI occurrence. Methods: We prospectively enrolled 206 cardiac surgical patients. Plasma nitrite and serum IL-6 levels were determined preoperatively and at 24 h, 48 h and 72 h postoperatively. The patients had continuous EKG monitoring for occurrence of POAF, while daily serum creatinine was measured for determination of stage 1 + AKI. Results: Postoperatively, 78 (38%) patients experienced AF, and 47 (23%) patients experienced stage 1 + AKI. POAF analysis: Age, ACE-inhibitor use, valve surgery and percent change in baseline plasma nitrite at 24 h postoperatively were associated with POAF in multiple logistic regression analysis. The inclusion of this new biomarker significantly improved the POAF prediction model (AUC 0.77 for clinical risk factors alone, to AUC 0.81). AKI analysis: A history of diabetes mellitus was associated with AKI in multiple logistic regression analysis, and the addition of preoperative IL-6 levels improved the prediction model for AKI occurrence (AUC 0.69 to AUC 0.74). Conclusions: We previously observed selective upregulation of NADPH oxidase isoform 4 (NOX4) in patients with AF, a critical causal role of NOX4 for AF in zebrafish and a robust inhibitory effect of nitric oxide (NO) on NOX4. Our data innovatively demonstrate that a reduction in circulating nitrite levels, likely implicative of elevated NOX4-mediated oxidative stress, independently associates with POAF and improves POAF prediction, whereas the inclusion of circulating IL-6 levels improves the prediction model for AKI. Therefore, therapeutic strategies to mitigate these pathophysiological sequalae of surgical stress may reduce the incidence of severe postoperative complications of POAF and AKI.

Post-translational modification of cardiac proteasomes: functional delineation enabled by proteomics.

Proteasomes are ubiquitously expressed multicatalytic complexes that serve as key regulators of protein homeostasis. There are several lines of evidence indicating that proteasomes exist in heterogeneous subpopulations in cardiac muscle, differentiated, in part, by post-translational modifications (PTMs). PTMs regulate numerous facets of proteasome function, including catalytic activities, complex assembly, interactions with associating partners, subcellular localization, substrate preference, and complex turnover. Classical technologies used to identify PTMs on proteasomes have lacked the ability to determine site specificity, quantify stoichiometry, and perform large-scale, multi-PTM analysis. Recent advancements in proteomic technologies have largely overcome these limitations. We present here a discussion on the importance of PTMs in modulating proteasome function in cardiac physiology and pathophysiology, followed by the presentation of a state-of-the-art proteomic workflow for identifying and quantifying PTMs of cardiac proteasomes.

Acrolein consumption exacerbates myocardial ischemic injury and blocks nitric oxide-induced PKCepsilon signaling and cardioprotection.

Aldehydes are common reactive constituents of food, water and air. Several food aldehydes are potentially carcinogenic and toxic; however, the direct effects of dietary aldehydes on cardiac ischemia-reperfusion (IR) injury are unknown. We tested the hypothesis that dietary consumption of aldehydes modulates myocardial IR injury and preconditioning. Mice were gavage-fed the alpha, beta-unsaturated aldehyde acrolein (5mg/kg) or water (vehicle) 24h prior to a 30-min coronary artery occlusion and 24-hour reperfusion. Myocardial infarct size was significantly increased in acrolein-treated mice, demonstrating that acute acrolein exposure worsens cardiac IR injury. Furthermore, late cardioprotection afforded by the nitric oxide (NO) donor diethylenetriamine/NO (DETA/NO; dose: 0.1mg/kg x 4, i.v.) was abrogated by the administration of acrolein 2h prior to DETA/NO treatment, indicating that oral acrolein impairs NO donor-induced late preconditioning. To examine potential intracellular targets of aldehydes, we investigated the impact of acrolein on mitochondrial PKCepsilon signaling in the heart. Acrolein-protein adducts were formed in a dose-dependent manner in isolated cardiac mitochondria in vitro and specific acrolein-PKCepsilon adducts were present in cardiac mitochondrial fractions following acrolein exposure in vivo, demonstrating that mitochondria are major targets of aldehyde toxicity. Furthermore, DETA/NO preconditioning induced both PKCepsilon translocation and increased mitochondrial PKCepsilon localization. Both of these responses were blocked by acrolein pretreatment, providing evidence that aldehydes disrupt cardioprotective signaling events involving PKCepsilon. Consumption of an aldehyde-rich diet could exacerbate cardiac IR injury and block NO donor-induced cardioprotection via mechanisms that disrupt PKCepsilon signaling.

ProteinInferencer: Confident protein identification and multiple experiment comparison for large scale proteomics projects.

Shotgun proteomics generates valuable information from large-scale and target protein characterizations, including protein expression, protein quantification, protein post-translational modifications (PTMs), protein localization, and protein-protein interactions. Typically, peptides derived from proteolytic digestion, rather than intact proteins, are analyzed by mass spectrometers because peptides are more readily separated, ionized and fragmented. The amino acid sequences of peptides can be interpreted by matching the observed tandem mass spectra to theoretical spectra derived from a protein sequence database. Identified peptides serve as surrogates for their proteins and are often used to establish what proteins were present in the original mixture and to quantify protein abundance. Two major issues exist for assigning peptides to their originating protein. The first issue is maintaining a desired false discovery rate (FDR) when comparing or combining multiple large datasets generated by shotgun analysis and the second issue is properly assigning peptides to proteins when homologous proteins are present in the database. Herein we demonstrate a new computational tool, ProteinInferencer, which can be used for protein inference with both small- or large-scale data sets to produce a well-controlled protein FDR. In addition, ProteinInferencer introduces confidence scoring for individual proteins, which makes protein identifications evaluable. This article is part of a Special Issue entitled: Computational Proteomics.

Cardiac toxic effects of trans-2-hexenal are mediated by induction of cardiomyocyte apoptotic pathways.

Aldehydes are ubiquitous pollutants with well-indicated but ill-defined cardiovascular toxicity. To investigate the direct toxic effects of environmental aldehyde exposure on the myocardium, 8-wk-old male ICR (Institute of Cancer Research) strain mice were gavage fed trans-2-hexenal (0.1, 1, 10, or 50 mg/kg/wk) or corn oil (vehicle) for 4 wk, during which cardiac function, myocardial morphology, cardiomyocyte apoptosis, and the cytochrome cmediated caspase activation apoptotic pathway were determined. Quantification by enzyme-linked immunosorbent assay (ELISA) revealed that aldehyde- protein adducts increase in mouse hearts following hexenal treatment, whereas echocardiographic analysis displayed a significant impairment of basal left-ventricular contractile function. Both histological analysis and TUNEL (terminal deoxynucleotidyl transferase-mediated nick-end labeling) staining indicated condensed nuclei and a significant increase in cardiomyocyte apoptosis in these mice, but immunohistochemistry-based confocal microscope revealed no marked myofibril disarray. Release of cytochrome c from mitochondria into the cytosol, concomitant with activation of caspase-3 and -9, was also found in hexenal-treated groups. In addition, isolated cardiac mitochondria formed hexenal-protein adducts when treated with hexenal, providing indirect evidence that the cardiac mitochondrion is one of primary subcellular targets of aldehyde toxins. These findings suggest that trans-2-hexenal exposure results in direct cardiac toxicity through, at least in part, induction of mitochondrial cytochrome c release-mediated apoptosis in cardiomyocytes, indicating that the cardiac mitochondrion is one of principal subcellular targets of aldehyde toxins.

Hydrogen sulfide attenuates the recruitment of CD11b⁺Gr-1⁺ myeloid cells and regulates Bax/Bcl-2 signaling in myocardial ischemia injury.

Hydrogen sulfide, an endogenous signaling molecule, plays an important role in the physiology and pathophysiology of the cardiovascular system. Using a mouse model of myocardial infarction, we investigated the anti-inflammatory and anti-apoptotic effects of the H2S donor sodium hydrosulfide (NaHS). The results demonstrated that the administration of NaHS improved survival, preserved left ventricular function, limited infarct size, and improved H2S levels in cardiac tissue to attenuate the recruitment of CD11b(+)Gr-1(+) myeloid cells and to regulate the Bax/Bcl-2 pathway. Furthermore, the cardioprotective effects of NaHS were enhanced by inhibiting the migration of CD11b(+)Gr-1(+) myeloid cells from the spleen into the blood and by attenuating post-infarction inflammation. These observations suggest that the novel mechanism underlying the cardioprotective function of H2S is secondary to a combination of attenuation the recruitment of CD11b(+)Gr-1(+) myeloid cells and regulation of the Bax/Bcl-2 apoptotic signaling.

Lysine ubiquitination and acetylation of human cardiac 20S proteasomes.

PURPOSE: Altered proteasome functions are associated with multiple cardiomyopathies. While the proteasome targets polyubiquitinated proteins for destruction, it itself is modifiable by ubiquitination. We aim to identify the exact ubiquitination sites on cardiac proteasomes and examine whether they are also subject to acetylations. EXPERIMENTAL DESIGN: Assembled cardiac 20S proteasome complexes were purified from five human hearts with ischemic cardiomyopathy, then analyzed by high-resolution MS to identify ubiquitination and acetylation sites. We developed a library search strategy that may be used to complement database search in identifying PTM in different samples. RESULTS: We identified 63 ubiquitinated lysines from intact human cardiac 20S proteasomes. In parallel, 65 acetylated residues were also discovered, 39 of which shared with ubiquitination sites. CONCLUSION AND CLINICAL RELEVANCE: This is the most comprehensive characterization of cardiac proteasome ubiquitination to date. There are significant overlaps between the discovered ubiquitination and acetylation sites, permitting potential crosstalk in regulating proteasome functions. The information presented here will aid future therapeutic strategies aimed at regulating the functions of cardiac proteasomes.

A novel spectral library workflow to enhance protein identifications.

The innovations in mass spectrometry-based investigations in proteome biology enable systematic characterization of molecular details in pathophysiological phenotypes. However, the process of delineating large-scale raw proteomic datasets into a biological context requires high-throughput data acquisition and processing. A spectral library search engine makes use of previously annotated experimental spectra as references for subsequent spectral analyses. This workflow delivers many advantages, including elevated analytical efficiency and specificity as well as reduced demands in computational capacity. In this study, we created a spectral matching engine to address challenges commonly associated with a library search workflow. Particularly, an improved sliding dot product algorithm, that is robust to systematic drifts of mass measurement in spectra, is introduced. Furthermore, a noise management protocol distinguishes spectra correlation attributed from noise and peptide fragments. It enables elevated separation between target spectral matches and false matches, thereby suppressing the possibility of propagating inaccurate peptide annotations from library spectra to query spectra. Moreover, preservation of original spectra also accommodates user contributions to further enhance the quality of the library. Collectively, this search engine supports reproducible data analyses using curated references, thereby broadening the accessibility of proteomics resources to biomedical investigators. This article is part of a Special Issue entitled: From protein structures to clinical applications.