Choosing the right antibody for resistin-like molecule (RELM/FIZZ) family members

Resistin predicts disease severity and survival in patients with pulmonary arterial hypertension

BACKGROUND

Abnormal remodeling of distal pulmonary arteries in patients with pulmonary arterial hypertension (PAH) leads to progressively increased pulmonary vascular resistance, followed by right ventricular hypertrophy and failure. Despite considerable advancements in PAH treatment prognosis remains poor. We aim to evaluate the potential for using the cytokine resistin as a genetic and biological marker for disease severity and survival in a large cohort of patients with PAH.

METHODS

Biospecimens, clinical, and genetic data for 1121 adults with PAH, including 808 with idiopathic PAH (IPAH) and 313 with scleroderma-associated PAH (SSc-PAH), were obtained from a national repository. Serum resistin levels were measured by ELISA, and associations between resistin levels, clinical variables, and single nucleotide polymorphism genotypes were examined with multivariable regression models. Machine-learning (ML) algorithms were applied to develop and compare risk models for mortality prediction.

RESULTS

Resistin levels were significantly higher in all PAH samples and PAH subtype (IPAH and SSc-PAH) samples than in controls (P < .0001) and had significant discriminative abilities (AUCs of 0.84, 0.82, and 0.91, respectively; P < .001). High resistin levels (above 4.54 ng/mL) in PAH patients were associated with older age (P = .001), shorter 6-min walk distance (P = .001), and reduced cardiac performance (cardiac index, P = .016). Interestingly, mutant carriers of either rs3219175 or rs3745367 had higher resistin levels (adjusted P = .0001). High resistin levels in PAH patients were also associated with increased risk of death (hazard ratio: 2.6; 95% CI: 1.27-5.33; P < .0087). Comparisons of ML-derived survival models confirmed satisfactory prognostic value of the random forest model (AUC = 0.70, 95% CI: 0.62-0.79) for PAH.

CONCLUSIONS

This work establishes the importance of resistin in the pathobiology of human PAH. In line with its function in rodent models, serum resistin represents a novel biomarker for PAH prognostication and may indicate a new therapeutic avenue. ML-derived survival models highlighted the importance of including resistin levels to improve performance. Future studies are needed to develop multi-marker assays that improve noninvasive risk stratification.

Resistin-like molecules: a marker, mediator and therapeutic target for multiple diseases

Resistin-like molecules (RELMs) are highly cysteine-rich proteins, including RELMα, RELMβ, Resistin, and RELMγ. However, RELMs exhibit significant differences in structure, distribution, and function. The expression of RELMs is regulated by various signaling molecules, such as IL-4, IL-13, and their receptors. In addition, RELMs can mediate numerous signaling pathways, including HMGB1/RAGE, IL-4/IL-4Rα, PI3K/Akt/mTOR signaling pathways, and so on. RELMs proteins are involved in wide range of physiological and pathological processes, including inflammatory response, cell proliferation, glucose metabolism, barrier defense, etc., and participate in the progression of numerous diseases such as lung diseases, intestinal diseases, cardiovascular diseases, and cancers. Meanwhile, RELMs can serve as biomarkers, risk predictors, and therapeutic targets for these diseases. An in-depth understanding of the role of RELMs may provide novel targets or strategies for the treatment and prevention of related diseases. Video abstract.

FIZZ2 as a Biomarker for Acute Exacerbation of Chronic Obstructive Pulmonary Disease

PURPOSE

Found in inflammatory zone 2 (FIZZ2) is associated with lung inflammation. The aim of the study was to investigate the expression and utility of FIZZ2 as a marker for chronic obstructive pulmonary disease (COPD).

METHODS

Immunohistochemistry was used to detect the expression of FIZZ2 in COPD. The serum concentration of FIZZ2 was measured by enzyme-linked immunosorbent assay and the episodes of acute exacerbations of COPD (AECOPD) in the following year were recorded.

RESULTS

FIZZ2 expression was elevated in bronchial epithelial cells (0.217 ± 0.021 vs 0.099 ± 0.010, p < 0.0001) and negatively correlated with the pulmonary function (FEV1/FVC%) (p = 0.0149) and positively correlated with the smoking index (p = 0.0241). Serum level of FIZZ2 in COPD were significantly higher than that in healthy controls (561.6 ± 70.71 vs 52.24 ± 20.52 pg/ml, p < 0.0001) and increased with the COPD severity. Serum levels of FIZZ2 negatively correlated with the pulmonary function [Forced Vital Capacity (FVC), Forced Expiratory Volume (FEV1), FEV1%, FEV1/FVC) (r =  - 0.3086, - 0.3529, - 0.3343, and - 0.2676, respectively, p = 0.0003, p < 0.0001, p < 0.0001, p = 0.0014). The expression of human serum FIZZ2 was positively correlated with the smoking index (r = 0.2749, p = 0.0015). There was a positive correlation between the FIZZ2 concentration and the frequency of AECOPD episodes in the following year (r = 0.7291, p < 0.0001).

CONCLUSION

FIZZ2 expression was elevated in patients with COPD and its serum concentration might be a potential biomarker for AECOPD.

Systemic evaluation and localization of resistin expression in normal human tissues by a newly developed monoclonal antibody

Resistin and resistin-like molecules are pleiotropic cytokines that are involved in inflammatory diseases. Our previous work suggested that resistin has the potential to be used as a biomarker and therapeutic target for human pulmonary arterial hypertension. However, data are limited on the distribution of resistin in healthy human organs. In this study, we used our newly developed anti-human resistin (hResistin) antibody to immunohistochemically detect the expression, localization, and intracellular/extracellular compartmentalization of hResistin in a full human tissue panel from healthy individuals. The potential cross reactivity of this monoclonal anti-hResistin IgG1 with normal human tissues also was verified. Results showed that hResistin is broadly distributed and principally localized in the cytoplasmic granules of macrophages scattered in the interstitium of most human tissues. Bone marrow hematopoietic precursor cells also exhibited hResistin signals in their cytoplasmic granules. Additionally, hResistin labeling was observed in the cytoplasm of nervous system cells. Notably, the cytokine activity of hResistin was illustrated by positively stained extracellular material in most human tissues. These data indicate that our generated antibody binds to the secreted hResistin and support its potential use for immunotherapy to reduce circulating hResistin levels in human disease. Our findings comprehensively document the basal expression patterns of hResistin protein in normal human tissues, suggest a critical role of this cytokine in normal and pathophysiologic inflammatory processes, and offer key insights for using our antibody in future pharmacokinetic studies and immunotherapeutic strategies.

Resistin family proteins in pulmonary diseases

The family of resistin-like molecules (RELMs) consists of four members in rodents (RELMα/FIZZ1/HIMF, RELMβ/FIZZ2, Resistin/FIZZ3, and RELMγ/FIZZ4) and two members in humans (Resistin and RELMβ), all of which exhibit inflammation-regulating, chemokine, and growth factor properties. The importance of these cytokines in many aspects of physiology and pathophysiology, especially in cardiothoracic diseases, is rapidly evolving in the literature. In this review article, we attempt to summarize the contribution of RELM signaling to the initiation and progression of lung diseases, such as pulmonary hypertension, asthma/allergic airway inflammation, chronic obstructive pulmonary disease, fibrosis, cancers, infection, and other acute lung injuries. The potential of RELMs to be used as biomarkers or risk predictors of these diseases also will be discussed. Better understanding of RELM signaling in the pathogenesis of pulmonary diseases may offer novel targets or approaches for the development of therapeutics to treat or prevent a variety of inflammation, tissue remodeling, and fibrosis-related disorders in respiratory, cardiovascular, and other systems.

RELMα Licenses Macrophages for Damage-Associated Molecular Pattern Activation to Instigate Pulmonary Vascular Remodeling

Pulmonary hypertension (PH) is a debilitating disease characterized by remodeling of the lung vasculature. In rodents, resistin-like molecule-α (RELMα, also known as HIMF or FIZZ1) can induce PH, but the signaling mechanisms are still unclear. In this study, we used human lung samples and a hypoxia-induced mouse model of PH. We found that the human homolog of RELMα, human (h) resistin, is upregulated in macrophage-like inflammatory cells from lung tissues of patients with idiopathic PH. Additionally, at PH onset in the mouse model, we observed RELMα-dependent lung accumulation of macrophages that expressed high levels of the key damage-associated molecular pattern (DAMP) molecule high-mobility group box 1 (HMGB1) and its receptor for advanced glycation end products (RAGE). In vitro, RELMα/hresistin-induced macrophage-specific HMGB1/RAGE expression and facilitated HMGB1 nucleus-to-cytoplasm translocation and extracellular secretion. Mechanistically, hresistin promoted HMGB1 posttranslational lysine acetylation by preserving the NAD⁺-dependent deacetylase sirtuin (Sirt) 1 in human macrophages. Notably, the hresistin-stimulated macrophages promoted apoptosis-resistant proliferation of human pulmonary artery smooth muscle cells in an HMGB1/RAGE-dependent manner. In the mouse model, RELMα also suppressed the Sirt1 signal in pulmonary macrophages in the early posthypoxic period. Notably, recruited macrophages in the lungs of these mice carried the RELMα binding partner Bruton tyrosine kinase (BTK). hResistin also mediated the migration of human macrophages by activating BTK in vitro. Collectively, these data reveal a vascular-immune cellular interaction in the early PH stage and suggest that targeting RELMα/DAMP-driven macrophages may offer a promising strategy to treat PH and other related vascular inflammatory diseases.

HIMF (Hypoxia-Induced Mitogenic Factor) Signaling Mediates the HMGB1 (High Mobility Group Box 1)-Dependent Endothelial and Smooth Muscle Cell Crosstalk in Pulmonary Hypertension

OBJECTIVE

HIMF (hypoxia-induced mitogenic factor; also known as FIZZ1 [found in inflammatory zone-1] or RELM [resistin-like molecule-α]) is an etiological factor of pulmonary hypertension (PH) in rodents, but its underlying mechanism is unclear. We investigated the immunomodulatory properties of HIMF signaling in PH pathogenesis. Approach and Results: Gene-modified mice that lacked HIMF (KO [knockout]) or overexpressed HIMF human homolog resistin (hResistin) were used for in vivo experiments. The pro-PH role of HIMF was verified in HIMF-KO mice exposed to chronic hypoxia or sugen/hypoxia. Mechanistically, HIMF/hResistin activation triggered the HMGB1 (high mobility group box 1) pathway and RAGE (receptor for advanced glycation end products) in pulmonary endothelial cells (ECs) of hypoxic mouse lungs in vivo and in human pulmonary microvascular ECs in vitro. Treatment with conditioned medium from hResistin-stimulated human pulmonary microvascular ECs induced an autophagic response, BMPR2 (bone morphogenetic protein receptor 2) defects, and subsequent apoptosis-resistant proliferation in human pulmonary artery (vascular) smooth muscle cells in an HMGB1-dependent manner. These effects were confirmed in ECs and smooth muscle cells isolated from pulmonary arteries of patients with idiopathic PH. HIMF/HMGB1/RAGE-mediated autophagy and BMPR2 impairment were also observed in pulmonary artery (vascular) smooth muscle cells of hypoxic mice, effects perhaps related to FoxO1 (forkhead box O1) dampening by HIMF. Experiments in EC-specific hResistin-overexpressing transgenic mice confirmed that EC-derived HMGB1 mediated the hResistin-driven pulmonary vascular remodeling and PH.

CONCLUSIONS

In HIMF-induced PH, HMGB1-RAGE signaling is pivotal for mediating EC-smooth muscle cell crosstalk. The humanized mouse data further support clinical implications for the HIMF/HMGB1 signaling axis and indicate that hResistin and its downstream pathway may constitute targets for the development of novel anti-PH therapeutics in humans.

Hypoxia-Induced Mitogenic Factor Acts as a Nonclassical Ligand of Calcium-Sensing Receptor, Therapeutically Exploitable for Intermittent Hypoxia-Induced Pulmonary Hypertension

Hypoxia-induced mitogenic factor (HIMF) is an inflammatory cytokine playing important role(s) in the development of hypoxic pulmonary hypertension. The molecular target mediating HIMF-stimulated downstream events remains unclear. The coimmunoprecipitation screen identified extracellular calcium-sensing receptor (CaSR) as the binding partner for HIMF in pulmonary artery smooth muscle cells. The yeast 2-hybrid assay then revealed the binding of HIMF to the intracellular, not the extracellular, domain of extracellular CaSR. The binding of HIMF enhanced the activity of extracellular CaSR and mediated hypoxia-evoked proliferation of pulmonary artery smooth cells and the development of pulmonary vascular remodeling and pulmonary hypertension, all of which was specifically attenuated by a synthesized membrane-permeable peptide flanking the core amino acids of the intracellular binding domain of extracellular CaSR. Thus, HIMF induces pulmonary hypertension as a nonclassical ligand of extracellular CaSR, and the binding motif of extracellular CaSR can be therapeutically exploitable.

Resistin-Like Molecule α in Allergen-Induced Pulmonary Vascular Remodeling

Resistin-like molecule α (RELMα) has mitogenic, angiogenic, vasoconstrictive, and chemokine-like properties and is highly relevant in lung pathology. Here, we used RELMα knockout (Retnla(-/-)) mice to investigate the role of RELMα in pulmonary vascular remodeling after intermittent ovalbumin (OVA) challenge. We compared saline- and OVA-exposed wild-type (WT) mice and found that OVA induced significant increases in right ventricular systolic pressure, cardiac hypertrophy, pulmonary vascular remodeling of intra-alveolar arteries, goblet cell hyperplasia in airway epithelium, and intensive lung inflammation, especially perivascular inflammation. Genetic ablation of Retnla prevented the OVA-induced increase in pulmonary pressure and cardiac hypertrophy seen in WT mice. Histological analysis showed that Retnla(-/-) mice exhibited less vessel muscularization, less perivascular inflammation, reduced medial thickness of intra-alveolar vessels, and fewer goblet cells in upper airway epithelium (250-600 μm) than did WT animals after OVA challenge. Gene expression profiles showed that genes associated with vascular remodeling, including those related to muscle protein, contractile fibers, and actin cytoskeleton, were expressed at a lower level in OVA-challenged Retnla(-/-) mice than in similarly treated WT mice. In addition, bronchoalveolar lavage from OVA-challenged Retnla(-/-) mice had lower levels of cytokines, such as IL-1β, -1 receptor antagonist, and -16, chemokine (C-X-C motif) ligand 1, -2, -9, -10, and -13, monocyte chemoattractant protein-1, macrophage colony-stimulating factor, TIMP metallopeptidase inhibitor-1, and triggering receptor expressed on myeloid cells-1, than did that from WT mice when analyzed by cytokine array dot blots. Retnla knockout inhibited the OVA-induced T helper 17 response but not the T helper 2 response. Altogether, our results suggest that RELMα is involved in immune response-induced pulmonary vascular remodeling and the associated increase in inflammation typically observed after OVA challenge.

Sexually dimorphic characteristics of the small intestine and colon of prepubescent C57BL/6 mice

BACKGROUND

There is increasing appreciation for sexually dimorphic effects, but the molecular mechanisms underlying these effects are only partially understood. In the present study, we explored transcriptomics and epigenetic differences in the small intestine and colon of prepubescent male and female mice. In addition, the microbiota composition of the colonic luminal content has been examined.

METHODS

At postnatal day 14, male and female C57BL/6 mice were sacrificed and the small intestine, colon and content of luminal colon were isolated. Gene expression of both segments of the intestine was analysed by microarray analysis. DNA methylation of the promoter regions of selected sexually dimorphic genes was examined by pyrosequencing. Composition of the microbiota was explored by deep sequencing.

RESULTS

Sexually dimorphic genes were observed in both segments of the intestine of 2-week-old mouse pups, with a stronger effect in the small intestine. Amongst the total of 349 genes displaying a sexually dimorphic effect in the small intestine and/or colon, several candidates exhibited a previously established function in the intestine (i.e. Nts, Nucb2, Alox5ap and Retnlγ). In addition, differential expression of genes linked to intestinal bowel disease (i.e. Ccr3, Ccl11 and Tnfr) and colorectal cancer development (i.e. Wt1 and Mmp25) was observed between males and females. Amongst the genes displaying significant sexually dimorphic expression, nine genes were histone-modifying enzymes, suggesting that epigenetic mechanisms might be a potential underlying regulatory mechanism. However, our results reveal no significant changes in DNA methylation of analysed CpGs within the selected differentially expressed genes. With respect to the bacterial community composition in the colon, a dominant effect of litter origin was found but no significant sex effect was detected. However, a sex effect on the dominance of specific taxa was observed.

CONCLUSIONS

This study reveals molecular dissimilarities between males and females in the small intestine and colon of prepubescent mice, which might underlie differences in physiological functioning and in disease predisposition in the two sexes.

The Histochem Cell Biol conspectus: the year 2013 in review

Herein, we provide a brief synopsis of all manuscripts published in Histochem Cell Biol in the year 2013. For ease of reference, we have divided the manuscripts into the following categories: Advances in Methodologies; Molecules in Health and Disease; Organelles, Subcellular Structures and Compartments; Golgi Apparatus; Intermediate Filaments and Cytoskeleton; Connective Tissue and Extracellular Matrix; Autophagy; Stem Cells; Musculoskeletal System; Respiratory and Cardiovascular Systems; Gastrointestinal Tract; Central Nervous System; Peripheral Nervous System; Excretory Glands; Kidney and Urinary Bladder; and Male and Female Reproductive Systems. We hope that the readership will find this annual journal synopsis of value and serve as a quick, categorized reference guide for “state-of-the-art” manuscripts in the areas of histochemistry, immunohistochemistry, and cell biology.