Minoxidil exerts different inhibitory effects on gene expression of lysyl hydroxylase 1, 2, and 3: implications for collagen cross-linking and treatment of fibrosis

The tumor-associated fibrotic reactions in microenvironment aggravate glioma chemoresistance

Malignant gliomas are one of the most common and lethal brain tumors with poor prognosis. Most patients with glioblastoma (GBM) die within 2 years of diagnosis, even after receiving standard treatments including surgery combined with concomitant radiotherapy and chemotherapy. Temozolomide (TMZ) is the first-line chemotherapeutic agent for gliomas, but the frequent acquisition of chemoresistance generally leads to its treatment failure. Thus, it's urgent to investigate the strategies for overcoming glioma chemoresistance. Currently, many studies have elucidated that cancer chemoresistance is not only associated with the high expression of drug-resistance genes in glioma cells but also can be induced by the alterations of the tumor microenvironment (TME). Numerous studies have explored the use of antifibrosis drugs to sensitize chemotherapy in solid tumors, and surprisingly, these preclinical and clinical attempts have exhibited promising efficacy in treating certain types of cancer. However, it remains unclear how tumor-associated fibrotic alterations in the glioma microenvironment (GME) mediate chemoresistance. Furthermore, the possible mechanisms behind this phenomenon are yet to be determined. In this review, we have summarized the molecular mechanisms by which tumor-associated fibrotic reactions drive glioma transformation from a chemosensitive to a chemoresistant state. Additionally, we have outlined antitumor drugs with antifibrosis functions, suggesting that antifibrosis strategies may be effective in overcoming glioma chemoresistance through TME normalization.

Sarcoma Cells Secrete Hypoxia-Modified Collagen VI to Weaken the Lung Endothelial Barrier and Promote Metastasis

Intratumoral hypoxia correlates with metastasis and poor survival in patients with sarcoma. Using an impedance sensing assay and a zebrafish intravital microinjection model, we demonstrated here that the hypoxia-inducible collagen-modifying enzyme lysyl hydroxylase PLOD2 and its substrate collagen type VI (COLVI) weaken the lung endothelial barrier and promote transendothelial migration. Mechanistically, hypoxia-induced PLOD2 in sarcoma cells modified COLVI, which was then secreted into the vasculature. Upon reaching the apical surface of lung endothelial cells, modified COLVI from tumor cells activated integrin β1 (ITGβ1). Furthermore, activated ITGβ1 colocalized with Kindlin2, initiating their interaction with F-actin and prompting its polymerization. Polymerized F-actin disrupted endothelial adherens junctions and induced barrier dysfunction. Consistently, modified and secreted COLVI was required for the late stages of lung metastasis in vivo. Analysis of patient gene expression and survival data from The Cancer Genome Atlas (TCGA) revealed an association between the expression of both PLOD2 and COLVI and patient survival. Furthermore, high levels of COLVI were detected in surgically resected sarcoma metastases from patient lungs and in the blood of tumor-bearing mice. Together, these data identify a mechanism of sarcoma lung metastasis, revealing opportunities for therapeutic intervention.

SIGNIFICANCE

Collagen type VI modified by hypoxia-induced PLOD2 is secreted by sarcoma cells and binds to integrin β1 on endothelial cells to induce barrier dysfunction, which promotes sarcoma vascular dissemination and metastasis.

METTL3 facilitates renal cell carcinoma progression by PLOD2 m6A-methylation under prolonged hypoxia

N6-methyladenosine (m6A) is the most prevalent reversible modification in eukaryotic mRNA, and it plays a critical role in tumor progression. The purpose of this study was to investigate the function and regulatory mechanisms of the methyltransferase METTL3 in renal cell carcinoma (RCC). METTL3 expression was upregulated and predicted a poor prognosis in patients with advanced RCC. METTL3 facilitated the proliferation, migration, and invasion of RCC cells, depending on its methylase activity. METTL3 positively regulated the expression of PLOD2, and both genes were triggered under prolonged hypoxia. Mechanistically, hypoxia-induced the binding of HIF-1α to the METTL3 promoter, which enhanced its transcriptional activity. METTL3-mediated m6A modifications of PLOD2 mRNA at 3'UTR region, promoting the translation of PLOD2 protein. Furthermore, silencing METTL3 impaired RCC progression in vitro. In vivo, administration of highly potent and selective METTL3 inhibitor STM2457 showed anti-tumor effects, whereas AAV9-mediated re-transduction of PLOD2 largely abolished the above phenomenon in a subcutaneous mouse model. These findings reveal that hypoxia and HIF-driven METTL3 transcription promote RCC progression by increasing PLOD2 expression in an m6A-dependent manner, suggesting that METTL3 may serve as a novel pharmaceutical intervention for RCC.

Hypoxia-induced PLOD2 promotes clear cell renal cell carcinoma progression via modulating EGFR-dependent AKT pathway activation

Clear cell renal cell carcinoma (ccRCC) is a type of kidney cancer that is both common and aggressive, with a rising incidence in recent decades. Hypoxia is a key factor that plays a vital role in the tumorigenesis and metastasis of malignancy. However, the precise mechanisms of hypoxia driving ccRCC progression were not totally uncovered. Our study found that hypoxia level was elevated in ccRCC and might be an independent risk factor of prognosis in ccRCC patients. We identified a key protein PLOD2 was induced under hypoxic conditions and strongly associated with poor prognosis in ccRCC patients. When PLOD2 was depleted, the proliferation and migration of ccRCC cells were reduced in vitro and in vivo, while overexpression of PLOD2 had the opposite effect. Mechanically, the study further revealed that PLOD2 was transcriptionally activated by HIF1A, which binds to a specific promoter region of the PLOD2 gene. PLOD2 was also shown to interact with EGFR, leading to the phosphorylation of the receptor. Furthermore, PLOD2 was responsible for binding to the extracellular domain of EGFR, which ultimately activated the AKT signaling pathway, thus promoting the malignant progression of ccRCC. Treatment with the PLOD2 inhibitor Minoxidil significantly suppressed ccRCC progression by inactivating the EGFR/AKT signaling axis. In summary, the findings of this study shed light on the molecular mechanisms behind PLOD2 expression in ccRCC and suggest that it may serve as a potential predictor and therapeutic target for the clinical prognosis and treatment of ccRCC.

tDCS Regulates ASBT-3-OxoLCA-PLOD2-PTEN Signaling Pathway to Confer Neuroprotection Following Rat Cerebral Ischemia-Reperfusion Injury

Humans exhibit a rich intestinal microbiome that contain high levels of bacteria capable of producing 3-oxo-lithocholic acid (3-oxoLCA) and other secondary bile acids (BAs). The molecular mechanism mediating the role of 3-oxoLCA in cerebral ischemia-reperfusion (I/R) injury remains unclear. We investigated the role of 3-oxoLCA in a rat cerebral I/R injury model. We found that the concentrations of 3-oxoLCA within the cerebrospinal fluid were increased following I/R. In the in vitro oxygen-glucose deprivation (OGD) model, the levels of intraneuronal 3-oxoLCA was elevated following OGD insult. We showed that the increase of membrane ASBT (apical sodium-dependent bile acid transporter) contributed to OGD-induced elevation of intraneuronal 3-oxoLCA. Increasing intraneuronal 3-oxoLCA promoted ischemia-induced neuronal death, whereas reducing 3-oxoLCA levels were neuroprotective. Our results revealed that PLOD2 (procollagen-lysine, 2-oxoglutarate 5-dioxygenases 2) functioned upstream of PTEN (the phosphatase and tensin homolog deleted on chromosome 10) and downstream of 3-oxoLCA to promote OGD-induced neuronal injury. We further demonstrated that direct-current stimulation (DCS) decreased the levels of intraneuronal 3-oxoLCA and membrane ASBT in OGD-insulted neurons, while bilateral transcranial DCS (tDCS) reduced brain infarct volume following I/R by inhibiting ASBT. Together, these data suggest that increased expression of ASBT promotes neuronal death via 3-oxoLCA-PLOD2-PTEN signaling pathway. Importantly, bilateral tDCS suppresses ischemia-induced increase of ASBT, thereby conferring neuroprotection after cerebral I/R injury.

Unleashing the Potential of 1,3-Diketone Analogues as Selective LH2 Inhibitors

Lysyl hydroxylase 2 (LH2) catalyzes the formation of highly stable hydroxylysine aldehyde-derived collagen cross-links (HLCCs), thus promoting lung cancer metastasis through its capacity to modulate specific types of collagen cross-links within the tumor stroma. Using 1 and 2 from our previous high-throughput screening (HTS) as lead probes, we prepared a series of 1,3-diketone analogues, 1-18, and identified 12 and 13 that inhibit LH2 with IC50's of approximately 300 and 500 nM, respectively. Compounds 12 and 13 demonstrate selectivity for LH2 over LH1 and LH3. Quantum mechanics/molecular mechanics (QM/MM) modeling indicates that the selectivity of 12 and 13 may stem from noncovalent interactions like hydrogen bonding between the morpholine/piperazine rings with the LH2-specific Arg661. Treatment of 344SQ WT cells with 13 resulted in a dose-dependent reduction in their migration potential, whereas the compound did not impede the migration of the same cell line with an LH2 knockout (LH2KO).

Novel approaches to target fibroblast mechanotransduction in fibroproliferative diseases

The ability of cells to sense and respond to changes in mechanical environment is vital in conditions of organ injury when the architecture of normal tissues is disturbed or lost. Among the various cellular players that respond to injury, fibroblasts take center stage in re-establishing tissue integrity by secreting and organizing extracellular matrix into stabilizing scar tissue. Activation, activity, survival, and death of scar-forming fibroblasts are tightly controlled by mechanical environment and proper mechanotransduction ensures that fibroblast activities cease after completion of the tissue repair process. Conversely, dysregulated mechanotransduction often results in fibroblast over-activation or persistence beyond the state of normal repair. The resulting pathological accumulation of extracellular matrix is called fibrosis, a condition that has been associated with over 40% of all deaths in the industrialized countries. Consequently, elements in fibroblast mechanotransduction are scrutinized for their suitability as anti-fibrotic therapeutic targets. We review the current knowledge on mechanically relevant factors in the fibroblast extracellular environment, cell-matrix and cell-cell adhesion structures, stretch-activated membrane channels, stress-regulated cytoskeletal structures, and co-transcription factors. We critically discuss the targetability of these elements in therapeutic approaches and their progress in pre-clinical and/or clinical trials to treat organ fibrosis.

Targeting Type I Collagen for Cancer Treatment

Collagen is the most abundant protein in animals. Interactions between tumor cells and collagen influence every step of tumor development. Type I collagen is the main fibrillar collagen in the extracellular matrix and is frequently up-regulated during tumorigenesis. The binding of type I collagen to its receptors on tumor cells promotes tumor cell proliferation, epithelial-mesenchymal transition, and metastasis. Type I collagen also regulates the efficacy of tumor therapies, such as chemotherapy, radiotherapy, and immunotherapy. Furthermore, type I collagen fragments are diagnostic markers of metastatic tumors and have prognostic value. Inhibition of type I collagen synthesis has been reported to have anti-tumor effects in animal models. However, collagen has also been shown to possess anti-tumor activity. Therefore, the roles that type I collagen plays in tumor biology are complex and tumor type-dependent. In this review, we discuss the expression and regulation of synthesis of type I collagen, as well as the role up-regulated type I collagen plays in various stages of cancer progression. We also discuss the role of collagen in tumor therapy. Finally, we highlight several recent approaches targeting type I collagen for cancer treatment. This article is protected by copyright. All rights reserved.

Lysyl hydroxylase 2 deficiency promotes filopodia formation and fibroblast migration

Lysyl hydroxylase 2 (LH2) regulates intermolecular cross-linking of collagen molecules. Accumulation of LH2-modified collagen, which is highly stable and resistant to collagenase cleavage, is one cause of fibrosis. We previously demonstrated that conventional LH2 knockout mice showed embryonic lethality. Here we established LH2 conditional knockout mice using a tamoxifen-inducible Cre system. Morphological analysis of LH2-deficient fibroblasts by microscopy showed a dramatic increase in the number of filopodia, the finger-like cell surface projections that enable cell movement. The tips and leading edges of these filopodia exhibited up-regulated expression of Myosin-X (Myo10), a regulator of filopodial integrity. Wound healing assays demonstrated that migration of LH2-deficient cells was significantly faster than that of control cells. Gene expression profiling data also supported this phenotype. Together these findings indicate that LH2 deficiency may prevent fibrosis through decreased accumulation of LH2-cross-linked collagen, and that fibroblasts with faster migration contribute to enhanced wound healing activity. In conclusion, our cellular models provide evidence that LH2 deficiency plays a critical role in cell migration mediated through filopodia formation. Understanding the precise role of this phenotype in LH2-deficient cells may be helpful to define the pathogenesis of fibrosis. As such, detailed analyses of fibrosis and wound healing using LH2-deficient mouse models are needed.

Increased Collagen Crosslinking in Stiff Clubfoot Tissue: Implications for the Improvement of Therapeutic Strategies

Congenital clubfoot is a complex musculoskeletal deformity, in which a stiff, contracted tissue forms in the medial part of the foot. Fibrotic changes are associated with increased collagen deposition and lysyl oxidase (LOX)-mediated crosslinking, which impair collagen degradation and increase the tissue stiffness. First, we studied collagen deposition, as well as the expression of collagen and the amount of pyridinoline and deoxypyridinoline crosslinks in the tissue of relapsed clubfoot by immunohistochemistry, real-time PCR, and enzyme-linked immunosorbent assay (ELISA). We then isolated fibroblast-like cells from the contracted tissue to study the potential inhibition of these processes in vitro. We assessed the effects of a LOX inhibitor, β-aminopropionitrile (BAPN), on the cells by a hydroxyproline assay, ELISA, and Second Harmonic Generation imaging. We also evaluated the cell-mediated contraction of extracellular matrix in 3D cell-populated collagen gels. For the first time, we have confirmed significantly increased crosslinking and excessive collagen type I deposition in the clubfoot-contracted tissue. We successfully reduced these processes in vitro in a dose-dependent manner with 10–40 µg/mL of BAPN, and we observed an increasing trend in the inhibition of the cell-mediated contraction of collagen gels. The in vitro inhibitory effects indicate that BAPN has good potential for the treatment of relapsed and resistant clubfeet.

Minoxidil decreases collagen I deposition and tissue-like contraction in clubfoot-derived cells: a way to improve conservative treatment of relapsed clubfoot?

AIM

Clubfoot is a congenital deformity affecting the musculoskeletal system, resulting in contracted and stiff tissue in the medial part of the foot. Minoxidil (MXD) has an inhibitory effect on lysyl hydroxylase, which influences the quality of extracellular matrix crosslinking, and could therefore be used to reduce the stiffness and to improve the flexibility of the tissue. We assessed the in vitro antifibrotic effects of minoxidil on clubfoot-derived cells.

METHODS

Cell viability and proliferation were quantified by xCELLigence, MTS, and LIVE/DEAD assays. The amount of collagen I deposited into the extracellular matrix was quantified using immunofluorescence with subsequent image segmentation analysis, hydroxyproline assay, and Second Harmonic Generation imaging. Extracellular matrix contraction was studied in a 3D model of cell-populated collagen gel lattices.

RESULTS

MXD concentrations of 0.25, 0.5, and 0.75 mM inhibited the cell proliferation in a concentration-dependent manner without causing a cytotoxic effect. Exposure to ≥0.5 mM MXD resulted in a decrease in collagen type I accumulation after 8 and 21 days in culture. Changes in collagen fiber assembly were observed by immunofluorescence microscopy and nonlinear optical microscopy (second harmonic generation). MXD also inhibited the contraction of cell-populated collagen lattices (0.5 mM by 22%; 0.75 mM by 28%).

CONCLUSIONS

Minoxidil exerts an in vitro inhibitory effect on the cell proliferation, collagen accumulation, and extracellular matrix contraction processes that are associated with clubfoot fibrosis. This study provides important preliminary results demonstrating the potential relevance of MXD for adjuvant pharmacological therapy in standard treatment of relapsed clubfoot.

The Collagen-Modifying Enzyme PLOD2 Is Induced and Required during L1-Mediated Colon Cancer Progression

The overactivation of Wnt/β-catenin signaling is a hallmark of colorectal cancer (CRC) development. We identified the cell adhesion molecule L1CAM (L1) as a target of β-catenin-TCF transactivation in CRC cells. The overexpression of L1 in CRC cells confers enhanced proliferation, motility, tumorigenesis and liver metastasis, and L1 is exclusively localized in the invasive areas of human CRC tissue. A number of genes are induced after L1 transfection into CRC cells by a mechanism involving the cytoskeletal protein ezrin and the NF-κB pathway. When studying the changes in gene expression in CRC cells overexpressing L1 in which ezrin levels were suppressed by shRNA to ezrin, we discovered the collagen-modifying enzyme lysyl hydroxylase 2 (PLOD2) among these genes. We found that increased PLOD2 expression was required for the cellular processes conferred by L1, including enhanced proliferation, motility, tumorigenesis and liver metastasis, since the suppression of endogenous PLOD2 expression, or its enzymatic activity, blocked the enhanced tumorigenic properties conferred by L1. The mechanism involved in increased PLOD2 expression by L1 involves ezrin signaling and PLOD2 that affect the SMAD2/3 pathway. We found that PLOD2 is localized in the colonic crypts in the stem cell compartment of the normal mucosa and is found at increased levels in invasive areas of the tumor and, in some cases, throughout the tumor tissue. The therapeutic strategies to target PLOD2 expression might provide a useful approach for CRC treatment.

Minoxidil Cannot Be Used To Target Lysyl Hydroxylases during Postnatal Mouse Lung Development: A Cautionary Note

The lysyl hydroxylases (procollagen-lysine 5-dioxygenases) PLOD1, PLOD2, and PLOD3 have been proposed as pathogenic mediators of stunted lung development in bronchopulmonary dysplasia (BPD), a common complication of preterm birth. In affected infants, pulmonary oxygen toxicity stunts lung development. Mice lacking Plod1 exhibit 15% mortality, and mice lacking Plod2 or Plod3 exhibit embryonic lethality. Therefore, to address any pathogenic role of lysyl hydroxylases in stunted lung development associated with BPD, minoxidil was administered to newborn mice in an oxygen toxicity-based BPD animal model. Minoxidil, which has attracted much interest in the management of systemic hypertension and androgenetic alopecia, can also be used to reduce lysyl hydroxylase activity in cultured cells. An in vivo pilot dosing study established 50 mg⋅kg^-1⋅day^-1 as the maximum possible minoxidil dose for intraperitoneal administration in newborn mouse pups. When administered at 50 mg⋅kg^-1⋅day^-1 to newborn mouse pups, minoxidil was detected in the lungs but did not impact lysine hydroxylation, collagen crosslinking, or lysyl hydroxylase expression in the lungs. Consistent with no impact on mouse lung extracellular matrix structures, minoxidil administration did not alter the course of normal or stunted lung development in newborn mice. At doses of up to 50 mg⋅kg⋅day^-1, pharmacologically active concentrations of minoxidil were not achieved in neonatal mouse lung tissue; thus, minoxidil cannot be used to attenuate lysyl hydroxylase expression or activity during mouse lung development. These data also highlight the need for new and specific lysyl hydroxylase inhibitors. SIGNIFICANCE STATEMENT: Extracellular matrix crosslinking is mediated by lysyl hydroxylases, which generate hydroxylated lysyl residues in procollagen peptides. Deregulated collagen crosslinking is a pathogenic component of a spectrum of diseases, and thus, there is interest in validating lysyl hydroxylases as pathogenic mediators of disease and potential "druggable" targets. Minoxidil, administered at the maximum possible dose, did not inhibit lysyl hydroxylation in newborn mouse lungs, suggesting that minoxidil was unlikely to be of use in studies that pharmacologically target lysyl hydroxylation in vivo.

Intestinal stenosis in Crohn's disease shows a generalized upregulation of genes involved in collagen metabolism and recognition that could serve as novel anti-fibrotic drug targets

BACKGROUND AND AIMS

Crohn's disease (CD) can be complicated by intestinal fibrosis. Pharmacological therapies against intestinal fibrosis are not available. The aim of this study was to determine whether pathways involved in collagen metabolism are upregulated in intestinal fibrosis, and to discuss which drugs might be suitable to inhibit excessive extracellular matrix formation targeting these pathways.

METHODS

Human fibrotic and non-fibrotic terminal ileum was obtained from patients with CD undergoing ileocecal resection due to stenosis. Genes involved in collagen metabolism were analyzed using a microfluidic low-density TaqMan array. A literature search was performed to find potential anti-fibrotic drugs that target proteins/enzymes involved in collagen synthesis, its degradation and its recognition.

RESULTS

mRNA expression of collagen type I (COL1A1, 0.76 ± 0.28 versus 37.82 ± 49.85, p = 0.02) and III (COL3A1, 2.01 ± 2.61 versus 68.65 ± 84.07, p = 0.02) was increased in fibrotic CD compared with non-fibrotic CD. mRNA expression of proteins involved in both intra- and extracellular post-translational modification of collagens (prolyl- and lysyl hydroxylases, lysyl oxidases, chaperones), collagen-degrading enzymes (MMPs and cathepsin-K), and collagen receptors were upregulated in the fibrosis-affected part. A literature search on the upregulated genes revealed several potential anti-fibrotic drugs.

CONCLUSION

Expression of genes involved in collagen metabolism in intestinal fibrosis affected terminal ileum of patients with CD reveals a plethora of drug targets. Inhibition of post-translational modification and altering collagen metabolism might attenuate fibrosis formation in the intestine in CD. Which compound has the highest potential depends on a combination anti-fibrotic efficacy and safety, especially since some of the enzymes play key roles in the physiology of collagen.

MiR-506-3p regulates autophagy and proliferation in post-burn skin fibroblasts through post-transcriptionally suppressing Beclin-1 expression

MicroRNAs (miRNAs) is involved in diverse biological processes of cells including dermal fibroblasts that contributed to wound healing and resulted in keloid scarring. MiR-506-3p has been identified as a tumor suppressor or oncogene in fibroblasts of various cancers, while the role of miR-506-3p in regulating functions of post-burn dermal fibroblasts is poorly known. In this study, miR-506-3p was confirmed to be significantly downregulated in burned tissues and heat-stimulated dermal fibroblasts. Expression levels of autophagy-related proteins suggested thermal stimulus promoting the autophagy in dermal fibroblasts. Then, miR-506-3p inhibition enhanced cell proliferation and cell cycle process in dermal fibroblasts after thermal stimulus, whereas overexpression of miR-506-3p showed the opposite effect. Western blot assay showed that inhibition of miR-506-3p resulted in the upregulation of the expression levels of LC3-II, ATG5, and structural protein collagen I, as well as the downregulation of p62. Marker proteins of intermolecular cross-links in collagen synthesis, including hydroxylysylpyridinoline (HP), lysinepyridine (LP), and lysyl hydroxylase 2 (LH2), were increased by miR-506-3p overexpression and decreased by miR-506-3p inhibition. Moreover, transfection with miR-506-3p mimic suppressed the proliferation and autophagy in heat-stimulated dermal fibroblasts in a dose-dependent manner. Subsequently, dual luciferase reporter gene assay demonstrated that Beclin-1 was a direct target of miR-506-3p, and reintroduction of Beclin-1 could antagonize the suppressive effect of miR-506-3p overexpression on fibroblast proliferation, autophagy, and the intermolecular cross-links in collagen synthesis. Taken together, our findings showed that miR-506-3p regulated autophagy and proliferation in post-burn skin fibroblasts through post-transcriptionally suppressing Beclin-1 expression.

KRAB-Induced Heterochromatin Effectively Silences PLOD2 Gene Expression in Somatic Cells and is Resilient to TGFβ1 Activation

Epigenetic editing, an emerging technique used for the modulation of gene expression in mammalian cells, is a promising strategy to correct disease-related gene expression. Although epigenetic reprogramming results in sustained transcriptional modulation in several in vivo models, further studies are needed to develop this approach into a straightforward technology for effective and specific interventions. Important goals of current research efforts are understanding the context-dependency of successful epigenetic editing and finding the most effective epigenetic effector(s) for specific tasks. Here we tested whether the fibrosis- and cancer-associated PLOD2 gene can be repressed by the DNA methyltransferase M.SssI, or by the non-catalytic Krüppel associated box (KRAB) repressor directed to the PLOD2 promoter via zinc finger- or CRISPR-dCas9-mediated targeting. M.SssI fusions induced de novo DNA methylation, changed histone modifications in a context-dependent manner, and led to 50%–70% reduction in PLOD2 expression in fibrotic fibroblasts and in MDA-MB-231 cancer cells. Targeting KRAB to PLOD2 resulted in the deposition of repressive histone modifications without DNA methylation and in almost complete PLOD2 silencing. Interestingly, both long-term TGFβ1-induced, as well as unstimulated PLOD2 expression, was completely repressed by KRAB, while M.SssI only prevented the TGFβ1-induced PLOD2 expression. Targeting transiently expressed dCas9-KRAB resulted in sustained PLOD2 repression in HEK293T and MCF-7 cells. Together, these findings point to KRAB outperforming DNA methylation as a small potent targeting epigenetic effector for silencing TGFβ1-induced and uninduced PLOD2 expression.

The Non-Fibrillar Side of Fibrosis: Contribution of the Basement Membrane, Proteoglycans, and Glycoproteins to Myocardial Fibrosis

The extracellular matrix (ECM) provides structural support and a microenvironmentfor soluble extracellular molecules. ECM is comprised of numerous proteins which can be broadly classified as fibrillar (collagen types I and III) and non-fibrillar (basement membrane, proteoglycans, and glycoproteins). The basement membrane provides an interface between the cardiomyocytes and the fibrillar ECM, while proteoglycans sequester soluble growth factors and cytokines. Myocardial fibrosis was originally only linked to accumulation of fibrillar collagens, but is now recognized as the expansion of the ECM including the non-fibrillar ECM proteins. Myocardial fibrosis can be reparative to replace the lost myocardium (e.g., ischemic injury or myocardial infarction), or can be reactive resulting from pathological activity of fibroblasts (e.g., dilated or hypertrophic cardiomyopathy). Contribution of fibrillar collagens to fibrosis is well studied, but the role of the non-fibrillar ECM proteins has remained less explored. In this article, we provide an overview of the contribution of the non-fibrillar components of the extracellular space of the heart to highlight the potential significance of these molecules in fibrosis, with direct evidence for some, although not all of these molecules in their direct contribution to fibrosis.

Current and upcoming therapies to modulate skin scarring and fibrosis

Skin is the largest organ of the human body. Being the interface between the body and the outer environment, makes it susceptible to physical injury. To maintain life, nature has endowed skin with a fast healing response that invariably ends in the formation of scar at the wounded dermal area. In many cases, skin remodelling may be impaired, leading to local hypertrophic scars or keloids. One should also consider that the scarring process is part of the wound healing response, which always starts with inflammation. Thus, scarring can also be induced in the dermis, in the absence of an actual wound, during chronic inflammatory processes. Considering the significant portion of the population that is subject to abnormal scarring, this review critically discusses the state-of-the-art and upcoming therapies in skin scarring and fibrosis.

Lysyl Hydroxylase Inhibition by Minoxidil Blocks Collagen Deposition and Prevents Pulmonary Fibrosis via TGF-β₁/Smad3 Signaling Pathway

Background

Idiopathic pulmonary fibrosis (IPF) is a deadly disease characterized by excessive collagen in the extracellular matrix (ECM) of the lungs. Collagen is the primary protein component of the ECM. However, the exact mechanisms underlying the formation and deposition of collagen in the ECM under normal and pathological conditions remain unclear. Previous studies showed that lysyl hydroxylase (LH) plays a crucial role in the formation of collagen. Minoxidil is an FDA-approved anti-hypertensive agent that inhibits LH that reduces fibrosis. In this study, we investigated the functional roles of LHs (LH1, LH2, and LH3) in pulmonary fibrosis and the anti-fibrotic effects of minoxidil.

Material/Methods

Patient serum samples were examined for their expression of procollagen-lysine, 2-oxoglutarate 5-dioxygenases (PLOD) 1–3, the genes encoding LH 1–3. Mice with bleomycin (BLM 2.5 mg/kg)-induced pulmonary fibrosis were administered a minoxidil solution (30 mg/kg) by oral gavage.

Results

The PLOD mRNA levels were significantly higher in the IPF patients than in the healthy control subjects. Minoxidil suppressed the BLM-induced pulmonary fibrosis in vivo. These effects were associated with blocking TGF-β₁/Smad3 signal transduction and attenuating the expression and activity of LHs, resulting in decreased collagen formation, thus reducing the pulmonary fibrosis. The anti-fibrotic effects of minoxidil may be mediated through competitive inhibition of LHs activity, resulting in decreased pyridine cross-link formation and collagen production and deposition.

Conclusions

The results of this study suggest that LH represents a target to prevent or treat pulmonary fibrosis, and minoxidil may provide an effective agent to inhibit LHs.

The Role of Hypoxia in Glioblastoma Invasion

Glioblastoma multiforme (GBM), a grade IV astrocytoma, is the most common and deadly type of primary malignant brain tumor, with a patient's median survival rate ranging from 15 to 17 months. The current treatment for GBM involves tumor resection surgery based on MRI image analysis, followed by radiotherapy and treatment with temozolomide. However, the gradual development of tumor resistance to temozolomide is frequent in GBM patients leading to subsequent tumor regrowth/relapse. For this reason, the development of more effective therapeutic approaches for GBM is of critical importance. Low tumor oxygenation, also known as hypoxia, constitutes a major concern for GBM patients, since it promotes cancer cell spreading (invasion) into the healthy brain tissue in order to evade this adverse microenvironment. Tumor invasion not only constitutes a major obstacle to surgery, radiotherapy, and chemotherapy, but it is also the main cause of death in GBM patients. Understanding how hypoxia triggers the GBM cells to become invasive is paramount to developing novel and more effective therapies against this devastating disease. In this review, we will present a comprehensive examination of the available literature focused on investigating how GBM hypoxia triggers an invasive cancer cell phenotype and the role of these invasive proteins in GBM progression.

Hypoxia and TGF-β1 induced PLOD2 expression improve the migration and invasion of cervical cancer cells by promoting epithelial-to-mesenchymal transition (EMT) and focal adhesion formation

BACKGROUND

Intra-tumoral hypoxia and increases in extracellular level of transforming growth factor β1 (TGF-β1), which are common findings in cancer, are associated with an increased risk of metastasis and mortality. Moreover, metastasis is the leading cause of death of patients with cervical cancer. PLOD2 is an intracellular enzyme required for the biogenesis of collagen and its expression can be induced by hypoxia and TGF-β1. Specifically, PLOD2 is up-regulated in several types of cancer, including cervical cancer, and is associated with cancer metastasis. Thus, in this research, we aimed to investigate the role of PLOD2 in the motility of cervical cancer cells and to show the molecular mechanism underlying this effect.

METHODS

siRNA was used to knockdown PLOD2 in the cervical cancer cell lines HeLa and SiHa. The ability of cells to migrate and invade, their adhesion to type I collagen, and their capacity for epithelial-to-mesenchymal transition (ΕΜΤ) and focal adhesion formation were analyzed. Gene expression changes were validated by qRT-PCR, Western blotting and Immunocytochemistry. The morphological status of cells was examined using phalloidin staining. Differences in PLOD2 expression among patients with cervical cancer were identified by referring to public databases, including Oncomine and TCGA.

RESULTS

Hypoxia and TGF-β1 enhanced the expression of PLOD2 in HeLa and SiHa cells, and knockdown of PLOD2 inhibited cell motility and EMT. Moreover, the depletion of PLOD2 attenuated hypoxia-mediated cell migration and invasion and inhibited TGF-β1-induced phenotypic EMT-like changes by preventing β-catenin from entering the nucleus. In addition, PLOD2 depletion decreased cell adhesion to extracellular collagen by inhibiting the formation of focal adhesions. Moreover, a database analysis showed that PLOD2 expression is associated with human cervical cancer progression.

CONCLUSIONS

Overall, our results indicated that hypoxia- and TGF-β1-induced PLOD2 expression promotes the migratory, invasive and adhesive capacities of cervical cancer cells by participating in TGF-β1 induced EMT and the formation of focal adhesions.

PLOD2 in cancer research

Collagen is not only the most abundant protein providing the scaffold for assembly of the extracellular matrix (ECM), but also considered to be the "highway" for cancer cell migration and invasion depending on the different collagen organizations. The accumulation of stabilized collagen is enhanced by different covalent collagen cross-links, lysyl hydroxylases 2 (encoded by the PLOD2 gene) is the key enzyme mediating the formation of the stabilized collagen cross-link. Interestingly, PLOD2 is overexpressed in different cancers and closely related to a poor prognosis. To the best of our knowledge, only the mechanisms of PLOD2 regulated by HIF-1α, TGF-β and microRNA-26a/b have been elaborated. In addition, several pharmacologic inhibitors of PLOD2 have been confirmed to have an anti-metastasis effect. However, there have been no reviews about PLOD2 in cancer research published thus far. In brief, this review about PLOD2 will describe the function, regulatory mechanism, and the inhibitors of PLOD2 in cancer, suggesting the credible clinical evaluation of a prognostic signature in pathological examination and the possible development of therapeutic strategies targeting PLOD2 in the future.

Intratumoral oxygen gradients mediate sarcoma cell invasion

Hypoxia is a critical factor in the progression and metastasis of many cancers, including soft tissue sarcomas. Frequently, oxygen (O2) gradients develop in tumors as they grow beyond their vascular supply, leading to heterogeneous areas of O2 depletion. Here, we report the impact of hypoxic O2 gradients on sarcoma cell invasion and migration. O2 gradient measurements showed that large sarcoma mouse tumors (>300 mm(3)) contain a severely hypoxic core [≤0.1% partial pressure of O2 (pO2)] whereas smaller tumors possessed hypoxic gradients throughout the tumor mass (0.1-6% pO2). To analyze tumor invasion, we used O2-controllable hydrogels to recreate the physiopathological O2 levels in vitro. Small tumor grafts encapsulated in the hydrogels revealed increased invasion that was both faster and extended over a longer distance in the hypoxic hydrogels compared with nonhypoxic hydrogels. To model the effect of the O2 gradient accurately, we examined individual sarcoma cells embedded in the O2-controllable hydrogel. We observed that hypoxic gradients guide sarcoma cell motility and matrix remodeling through hypoxia-inducible factor-1α (HIF-1α) activation. We further found that in the hypoxic gradient, individual cells migrate more quickly, across longer distances, and in the direction of increasing O2 tension. Treatment with minoxidil, an inhibitor of hypoxia-induced sarcoma metastasis, abrogated cell migration and matrix remodeling in the hypoxic gradient. Overall, we show that O2 acts as a 3D physicotactic agent during sarcoma tumor invasion and propose the O2-controllable hydrogels as a predictive system to study early stages of the metastatic process and therapeutic targets.

Disentangling mechanisms involved in collagen pyridinoline cross-linking: The immunophilin FKBP65 is critical for dimerization of lysyl hydroxylase 2

Collagens are subjected to extensive posttranslational modifications, such as lysine hydroxylation. Bruck syndrome (BS) is a connective tissue disorder characterized at the molecular level by a loss of telopeptide lysine hydroxylation, resulting in reduced collagen pyridinoline cross-linking. BS results from mutations in the genes coding for lysyl hydroxylase (LH) 2 or peptidyl-prolyl cis-trans isomerase (PPIase) FKBP65. Given that the immunophilin FKBP65 does not exhibit LH activity, it is likely that LH2 activity is somehow dependent on FKPB65. In this report, we provide insights regarding the interplay between LH2 and FKBP65. We found that FKBP65 forms complexes with LH2 splice variants LH2A and LH2B but not with LH1 and LH3. Ablating the catalytic activity of FKBP65 or LH2 did not affect complex formation. Both depletion of FKBP65 and inhibition of FKBP65 PPIase activity reduced the dimeric (active) form of LH2 but did not affect the binding of monomeric (inactive) LH2 to procollagen Iα1. Furthermore, we show that LH2A and LH2B cannot form heterodimers with each other but are able to form heterodimers with LH1 and LH3. Collectively, our results indicate that FKBP65 is linked to pyridinoline cross-linking by specifically mediating the dimerization of LH2. Moreover, FKBP65 does not interact with LH1 and LH3, explaining why in BS triple-helical hydroxylysines are not affected. Our results provide a mechanistic link between FKBP65 and the loss of pyridinolines and may hold the key to future treatments for diseases related to collagen cross-linking anomalies, such as fibrosis and cancer.

Hepatoprotective and Anti-fibrotic Agents: It's Time to Take the Next Step

Hepatic fibrosis and cirrhosis cause strong human suffering and necessitate a monetary burden worldwide. Therefore, there is an urgent need for the development of therapies. Pre-clinical animal models are indispensable in the drug discovery and development of new anti-fibrotic compounds and are immensely valuable for understanding and proofing the mode of their proposed action. In fibrosis research, inbreed mice and rats are by far the most used species for testing drug efficacy. During the last decades, several hundred or even a thousand different drugs that reproducibly evolve beneficial effects on liver health in respective disease models were identified. However, there are only a few compounds (e.g., GR-MD-02, GM-CT-01) that were translated from bench to bedside. In contrast, the large number of drugs successfully tested in animal studies is repeatedly tested over and over engender findings with similar or identical outcome. This circumstance undermines the 3R (Replacement, Refinement, Reduction) principle of Russell and Burch that was introduced to minimize the suffering of laboratory animals. This ethical framework, however, represents the basis of the new animal welfare regulations in the member states of the European Union. Consequently, the legal authorities in the different countries are halted to foreclose testing of drugs in animals that were successfully tested before. This review provides a synopsis on anti-fibrotic compounds that were tested in classical rodent models. Their mode of action, potential sources and the observed beneficial effects on liver health are discussed. This review attempts to provide a reference compilation for all those involved in the testing of drugs or in the design of new clinical trials targeting hepatic fibrosis.

Ziploc-ing the structure: Triple helix formation is coordinated by rough endoplasmic reticulum resident PPIases

BACKGROUND

Protein folding is crucial for proteins' specific functions and is facilitated by various types of enzymes and molecular chaperones. The peptidyl prolyl cis/trans isomerases (PPIase) are one of these families of enzymes. They ubiquitously exist inside the cell and there are eight PPIases in the rough endoplasmic reticulum (rER), a compartment where the folding of most secreted proteins occurs.

SCOPE OF REVIEW

We review the functional and structural aspects of individual rER resident PPIases. Furthermore, we specifically discuss the role of these PPIases during collagen biosynthesis, since collagen is the most abundant protein in humans, is synthesized in the rER, and contains a proportionally high number of proline residues.

MAJOR CONCLUSIONS

The rER resident PPIases recognize different sets of substrates and facilitate their folding. Although they are clearly catalysts for protein folding, they also have more broad and multifaceted functions. We propose that PPIases coordinate collagen biosynthesis in the rER.

GENERAL SIGNIFICANCE

This review expands our understanding of collagen biosynthesis by explaining the influence of novel indirect mechanisms of regulating folding and this is also explored for PPIases. We also suggest future directions of research to obtain a better understanding of collagen biosynthesis and functions of PPIases in the rER. This article is part of a Special Issue entitled Proline-directed Foldases: Cell Signaling Catalysts and Drug Targets.

Essential roles of insulin, AMPK signaling and lysyl and prolyl hydroxylases in the biosynthesis and multimerization of adiponectin

Post-translational modifications (PTMs) of the adiponectin molecule are essential for its full bioactivity, and defects in PTMs leading to its defective production and multimerization have been linked to the mechanisms of insulin resistance, obesity, and type-2 diabetes. Here we observed that, in differentiated 3T3-L1 adipocytes, decreased insulin signaling caused by blocking of insulin receptors (InsR) with an anti-InsR blocking antibody, increased rates of adiponectin secretion, whereas concomitant elevations in insulin levels counteracted this effect. Adenosine monophosphate-activated protein kinase (AMPK) signaling regulated adiponectin production by modulating the expression of adiponectin receptors, the secretion of adiponectin, and eventually the expression of adiponectin itself. We found that lysyl hydroxylases (LHs) and prolyl hydroxylases (PHs) were expressed in white-adipose tissue of ob/ob mice, wherein LH3 levels were increased compared with controls. In differentiated 3T3-L1 adipocytes, both non-specific inhibition of LHs and PHs by dipyridyl, and specific inhibition of LHs by minoxidil and of P4H with ethyl-3,4-dihydroxybenzoate, caused significant suppression of adiponectin production, more particularly of the higher-order isoforms. Transient gene knock-down of LH3 (Plod3) caused a suppressive effect, especially on the high molecular-weight (HMW) isoforms. These data indicate that PHs and LHs are both required for physiological adiponectin production and in particular are essential for the formation/secretion of the HMW isoforms.

Hypoxia-dependent modification of collagen networks promotes sarcoma metastasis

Intratumoral hypoxia and expression of hypoxia-inducible factor-1α (HIF-1α) correlate with metastasis and poor survival in patients with sarcoma. We show here that hypoxia controls sarcoma metastasis through a novel mechanism wherein HIF-1α enhances expression of the intracellular enzyme procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (PLOD2). We show that loss of HIF-1α or PLOD2 expression disrupts collagen modification, cell migration, and pulmonary metastasis (but not primary tumor growth) in allograft and autochthonous LSL-Kras(G12D/+); Trp53(fl/fl) murine sarcoma models. Furthermore, ectopic PLOD2 expression restores migration and metastatic potential in HIF-1α-deficient tumors, and analysis of human sarcomas reveals elevated HIF1A and PLOD2 expression in metastatic primary lesions. Pharmacologic inhibition of PLOD enzymatic activity suppresses metastases. Collectively, these data indicate that HIF-1α controls sarcoma metastasis through PLOD2-dependent collagen modification and organization in primary tumors. We conclude that PLOD2 is a novel therapeutic target in sarcomas and successful inhibition of this enzyme may reduce tumor cell dissemination.

SIGNIFICANCE

Undifferentiated pleomorphic sarcoma (UPS) is a commonly diagnosed and particularly aggressive sarcoma subtype in adults, which frequently and fatally metastasizes to the lung. Here, we show the potential use of a novel therapeutic target for the treatment of metastatic UPS, specifi cally the collagen-modifying enzyme PLOD2.

Impaired collagen biosynthesis and cross-linking in aorta of patients with bicuspid aortic valve

Background

Patients with bicuspid aortic valve (BAV) have an increased risk of developing ascending aortic aneurysm. In the present study, collagen homeostasis in nondilated and dilated aorta segments from patients with BAV was studied, with normal and dilated aortas from tricuspid aortic valve (TAV) patients as reference.

Methods and Results

Ascending aortas from 56 patients were used for biochemical and morphological analyses of collagen. mRNA expression was analyzed in 109 patients. Collagen turnover rates were similar in nondilated and dilated aortas of BAV patients, showing that aneurysmal formation in BAV is, in contrast to TAV, not associated with an increased collagen turnover. However, BAV in general was associated with an increased aortic collagen turnover compared with nondilated aortas of TAV patients. Importantly, the ratio of hydroxylysyl pyridinoline (HP) to lysyl pyridinoline (LP), 2 distinct forms of collagen cross‐linking, was lower in dilated aortas from patients with BAV, which suggests that BAV is associated with a defect in the posttranslational collagen modification. This suggests a deficiency at the level of lysyl hydroxylase (PLOD1), which was confirmed by mRNA and protein analyses that showed reduced PLOD1 expression but normal lysyl oxidase expression in dilated aortas from patients with BAV. This suggests that impaired collagen cross‐linking in BAV patients may be attributed to changes in the expression and/or activity of PLOD1.

Conclusions

Our results demonstrate an impaired biosynthesis and posttranslational modification of collagen in aortas of patients with BAV, which may explain the increased aortic aneurysm formation in BAV patients.

Lysyl hydroxylase 3 glucosylates galactosylhydroxylysine residues in type I collagen in osteoblast culture

Lysyl hydroxylase 3 (LH3), encoded by Plod3, is the multifunctional collagen-modifying enzyme possessing LH, hydroxylysine galactosyltransferase (GT), and galactosylhydroxylysine-glucosyltransferase (GGT) activities. Although an alteration in type I collagen glycosylation has been implicated in several osteogenic disorders, the role of LH3 in bone physiology has never been investigated. To elucidate the function of LH3 in bone type I collagen modifications, we used a short hairpin RNA technology in a mouse osteoblastic cell line, MC3T3-E1; generated single cell-derived clones stably suppressing LH3 (short hairpin (Sh) clones); and characterized the phenotype. Plod3 expression and the LH3 protein levels in the Sh clones were significantly suppressed when compared with the controls, MC3T3-E1, and the clone transfected with an empty vector. In comparison with controls, type I collagen synthesized by Sh clones (Sh collagen) showed a significant decrease in the extent of glucosylgalactosylhydroxylysine with a concomitant increase of galactosylhydroxylysine, whereas the total number of hydroxylysine residues was essentially unchanged. In an in vitro fibrillogenesis assay, Sh collagen showed accelerated fibrillogenesis compared with the controls. In addition, when recombinant LH3-V5/His protein was generated in 293 cells and subjected to GGT/GT activity assay, it showed GGT but not GT activity against denatured type I collagen. The results from this study clearly indicate that the major function of LH3 in osteoblasts is to glucosylate galactosylhydroxylysine residues in type I collagen and that an impairment of this LH3 function significantly affects type I collagen fibrillogenesis.

A connective tissue disorder caused by mutations of the lysyl hydroxylase 3 gene

Lysyl hydroxylase 3 (LH3, encoded by PLOD3) is a multifunctional enzyme capable of catalyzing hydroxylation of lysyl residues and O-glycosylation of hydroxylysyl residues producing either monosaccharide (Gal) or disaccharide (Glc-Gal) derivatives, reactions that form part of the many posttranslational modifications required during collagen biosynthesis. Animal studies have confirmed the importance of LH3, particularly in biosynthesis of the highly glycosylated type IV and VI collagens, but to date, the functional significance in vivo of this enzyme in man is predominantly unknown. We report here a human disorder of LH3 presenting as a compound heterozygote with recessive inheritance. One mutation dramatically reduced the sugar-transfer activity of LH3, whereas another abrogated lysyl hydroxylase activity; these changes were accompanied by reduced LH3 protein levels in cells. The disorder has a unique phenotype causing severe morbidity as a result of features that overlap with a number of known collagen disorders.

Biochemistry and functional significance of collagen cross-linking

The biophysical characteristics of vascular tissues are dependent largely on the properties of fibrillar collagens. Considering the predominant structural component, collagen type I, the present review describes the mechanisms of formation and maturation of lysyl oxidase-mediated cross-linking, leading to an understanding of how intracellular collagen-modifying enzymes affect the patterns of cross-links produced. An important distinction is made between the enzyme-mediated cross-linking, essential for optimum tissue function, and the non-enzymatic aging processes that generally lead to structural changes deleterious to function. Finally, the extracellular matrix of vascular tissue is a multicomponent system and the role of other major constituents, such as elastin and glycosaminoglycans, in modifying tissue properties should be considered. Some details of newer methods being developed to quantify these constituents will be presented.

Post-translational modifications of the four conserved lysine residues within the collagenous domain of adiponectin are required for the formation of its high molecular weight oligomeric complex

Adiponectin is a multifunctional adipokine that circulates as several oligomeric complexes in the blood stream. However, the molecular basis that regulates the production of the adiponectin oligomers remains largely elusive. We have shown previously that several conserved lysine residues (positions 68, 71, 80, and 104) within the collagenous domain of adiponectin are modified by hydroxylation and glycosylation (Wang, Y., Xu, A., Knight, C., Xu, L. Y., and Cooper, G. J. (2002) J. Biol. Chem. 277, 19521-19529). Here, we investigated the potential roles of these post-translational modifications in oligomeric complex formation of adiponectin. Gel filtration chromatography revealed that adiponectin produced from mammalian cells formed trimeric, hexameric, and high molecular weight (HMW) oligomeric complexes. These three oligomeric forms were differentially glycosylated, with the HMW oligomer having the highest carbohydrate content. Disruption of hydroxylation and glycosylation by substitution of the four conserved lysines with arginines selectively abrogated the intracellular assembly of the HMW oligomers in vitro as well as in vivo. In type 2 diabetic patients, both the ratios of HMW to total adiponectin and the degree of adiponectin glycosylation were significantly decreased compared with healthy controls. Functional studies of adiponectin-null mice revealed that abrogation of lysine hydroxylation/glycosylation markedly decreased the ability of adiponectin to stimulate phosphorylation of AMP-activated protein kinase in liver tissue. Chronic treatment of db/db diabetic mice with wild-type adiponectin alleviated hyperglycemia, hypertriglyceridemia, hepatic steatosis, and insulin resistance, whereas full-length adiponectin without proper post-translational modifications and HMW oligomers showed substantially decreased activities. Taken together, these data suggest that hydroxylation and glycosylation of the lysine residues within the collagenous domain of adiponectin are critically involved in regulating the formation of its HMW oligomeric complex and consequently contribute to the insulin-sensitizing activity of adiponectin in hepatocytes.