Prolyl-4-hydroxylase domain protein 2 controls NF-κB/p65 transactivation and enhances the catabolic effects of inflammatory cytokines on cells of the nucleus pulposus.

Prolyl-4-hydroxylase (PHD) proteins are key in sensing tissue hypoxia. In nucleus pulposus (NP) cells, our previous work demonstrated that PHD isoforms have a differential contribution in controlling hypoxia-inducible factor (HIF)-α degradation and activity. Recently we have shown that a regulatory relationship exists between PHD3 and inflammatory cytokines in NP cells. With respect to PHD2, the most abundant PHD isoform in NP cells, very little is known concerning its function and regulation under inflammatory conditions that characterize intervertebral disc degeneration. Here, we show that PHD2 is a potent regulator of the catabolic activities of TNF-α; silencing of PHD2 significantly decreased TNF-α-induced expression of catabolic markers including SDC4, MMP-3, MMP-13, and ADAMTS5, as well as several inflammatory cytokines and chemokines, while partially restoring aggrecan and collagen II expression. Use of NF-κB reporters with ShPHD2, SiHIF-1α, as well as p65(-/-), PHD2(-/-), and PHD3(-/-) cells, shows that PHD2 serves as a co-activator of NF-κB/p65 signaling in HIF-1-independent fashion. Immunoprecipitation of endogenous and exogenously expressed tagged proteins, as well as fluorescence microscopy, indicates that following TNF-α treatment, PHD2 interacts and co-localizes with p65. Conversely, loss of function experiments using lentivirally delivered Sh-p65, Sh-IKKß, and NF-κB inhibitor confirmed that cytokine-dependent PHD2 expression in NP cells requires NF-κB signaling. These findings clearly demonstrate that PHD2 forms a regulatory circuit with TNF-α via NF-κB and thereby plays an important role in enhancing activity of this cytokine. We propose that during disc degeneration PHD2 may offer a therapeutic target to mitigate the deleterious actions of TNF-α, a key proinflammatory cytokine.

Loss of the oxygen sensor PHD3 enhances the innate immune response to abdominal sepsis.

Hypoxia and HIFs (HIF-1α and HIF-2α) modulate innate immune responses in the setting of systemic inflammatory responses and sepsis. The HIF prolyl hydroxylase enzymes PHD1, PHD2 and PHD3 regulate the mammalian adaptive response to hypoxia; however, their significance in the innate immune response has not been elucidated. We demonstrate in this study that deficiency of PHD3 (PHD3(-/-)) specifically shortens the survival of mice subjected to various models of abdominal sepsis because of an overwhelming innate immune response, leading to premature organ dysfunction. By contrast, this phenotype was absent in mice deficient for PHD1 (PHD1(-/-)) or PHD2 (PHD2(+/-)). In vivo, plasma levels of proinflammatory cytokines were enhanced, and recruitment of macrophages to internal organs was increased in septic PHD3-deficient mice. Reciprocal bone marrow transplantation in sublethally irradiated mice revealed that enhanced susceptibility of PHD3-deficient mice to sepsis-related lethality was specifically caused by loss of PHD3 in myeloid cells. Several in vitro assays revealed enhanced cytokine production, migration, phagocytic capacity, and proinflammatory activation of PHD3-deficient macrophages. Increased proinflammatory activity of PHD3-deficient macrophages occurred concomitantly with enhanced HIF-1α protein stabilization and increased NF-κB activity, and interference with the expression of HIF-1α or the canonical NF-κB pathway blunted their proinflammatory phenotype. It is concluded that impairment of PHD3 enzyme function aggravates the clinical course of abdominal sepsis via HIF-1α- and NF-κB-mediated enhancement of the innate immune response.

Adipocyte-derived lactate is a signalling metabolite that potentiates adipose macrophage inflammation via targeting PHD2.

Adipose tissue macrophage (ATM) inflammation is involved with meta-inflammation and pathology of metabolic complications. Here we report that in adipocytes, elevated lactate production, previously regarded as the waste product of glycolysis, serves as a danger signal to promote ATM polarization to an inflammatory state in the context of obesity. Adipocyte-selective deletion of lactate dehydrogenase A (Ldha), the enzyme converting pyruvate to lactate, protects mice from obesity-associated glucose intolerance and insulin resistance, accompanied by a lower percentage of inflammatory ATM and reduced production of pro-inflammatory cytokines such as interleukin 1ß (IL-1ß). Mechanistically, lactate, at its physiological concentration, fosters the activation of inflammatory macrophages by directly binding to the catalytic domain of prolyl hydroxylase domain-containing 2 (PHD2) in a competitive manner with α-ketoglutarate and stabilizes hypoxia inducible factor (HIF-1α). Lactate-induced IL-1ß was abolished in PHD2-deficient macrophages. Human adipose lactate level is positively linked with local inflammatory features and insulin resistance index independent of the body mass index (BMI). Our study shows a critical function of adipocyte-derived lactate in promoting the pro-inflammatory microenvironment in adipose and identifies PHD2 as a direct sensor of lactate, which functions to connect chronic inflammation and energy metabolism.

Further characterization of embryonic tendon fibroblasts and the use of immunoferritin techniques to study collagen biosynthesis.

Morphological studies were carried out on fibroblasts from chick embryo tendons, cells which have been used in a number of recent studies on collagen biosynthesis. The cells were relatively rich in endoplasmic reticulum and contained a well-developed Golgi complex comprised of small vesicles, stacked membranes, and large vacuoles. Techniques were then devised for preparing cell fragments which were penetrated by ferritin-antibody conjuates but which retained the essential morphological features of the cells. Finally, the new procedures were employed to develop further information as to how collagen is synthesized. As reported elsewhere, preliminary studies with ferritin-labeled antibodies showed that prolyl hydroxylase was found in the endoplasmic reticulum of freshly isolated fibroblasts and that procollagen is found in both the cisternae of the endoplasmic reticulum and the large Golgi vacuoles. In the experiments described here, the cells were manipulated so that amino acids continued to be incorporated into polypeptide chains but assembly of the molecule was not completed because hydroxylation of prolyl and lysyl residues was prevented. The results indicated that these manipulations produced no change in the distribution of prolyl hydroxylase. Examination of the cells with ferritin conjugated to antibodies which reacted with protocollagen, the unhydroxylated form of procollagen, demonstrated that protocollagen was retained in the cisternae of the endoplasmic reticulum during inhibition of the prolyl and lysyl hydroxylases. Assays for prolyl hydroxylase with an immunologic technique demonstrated that although the enzyme is found within the endoplasmic reticulum, it is not secreted along with procollagen. The observations provided further evidence for a special role for prolyl hydroxylase in the control of collagen biosynthesis.

Opposing regulation and roles for PHD3 in lung dendritic cells and alveolar macrophages.

The prolyl hydroxylase domain-containing enzymes (PHDs) are important metabolic sensors of the cell and its environment, which might be employed to alert cells of the immune system. These enzymes regulate the expression of the hypoxia inducible factor (HIF) isoforms and NF-κB, crucial transcription factors controlling cellular metabolism and inflammation. PHD/HIF signaling is activated in the allergic lung and is proposed as a potential druggable pathway. Here, we investigated the regulation and role of the PHD isoforms in CD11c-expressing dendritic cells (DCs) and macrophages (Mϕ), sensors of the environment and crucial antigen-presenting cells in the pathogenesis of asthma. Although PHD2 and PHD3 were expressed in baseline, stimulation with house dust mite (HDM) allergen, hypoxia, and TLR4 ligands induced the expression of PHD3 in DCs. Conditional deletion or overexpression of PHD3 in CD11chi cells had minor effects on DCs and alveolar Mϕ biology in steady state. However, when put into competition with wild-type counterparts in mixed chimeric mice, alveolar Mϕ uniquely required PHD3 for optimal reconstitution of the alveolar space. Using genetic and chemical approaches, we were unable to find a clear role for PHD3 or the other PHD isoforms in DCs in asthma development. These data show cell-specific competitive advantage of PHD3 expression in antigen-presenting cells, but question whether therapeutic manipulation of PHDs in DCs would offer therapeutic benefit in asthma.

Nitric oxide mediates prolyl hydroxylase 3 expression in mesangial cells and in glomerulonephritis.

Renal mesangial cells are regarded as main players in glomerular inflammatory diseases. To investigate a possible crosstalk between inflammatory and hypoxia-driven signaling processes, we stimulated cultured mouse mesangial cells with different inflammatory agents and analyzed the expression of prolyl hydroxylase domain containing proteins (PHDs), the main regulators of hypoxia-inducible factor (HIF) stability. Administration of IL-1ß (1 nM) and TNF-α (1 nM), a combination further referred to as cytokine mix (CM), resulted in a fivefold increase in PHD3 but not PHD1 and PHD2 mRNA expression compared to untreated controls. In contrast, a combination of IL-1ß, TNF-α with lipopolysaccharide (10 µg/ml), and interferon-γ (20 ng/ml) designated as CM+ showed a high (60-fold) induction of PHD3 and a moderate (twofold) induction of PHD2 mRNA expression. Interestingly, CM+ but not CM induced the expression of inducible NO synthase and endogenously produced NO was responsible for the immense induction of PHD3 in mesangial cells treated with CM+. We found that CM+ affected PHD3 expression mainly via the NO/HIF axis, whereas PHD3 regulation by CM occurred in a NF-κB-dependent manner. In turn, silencing of PHD3 expression resulted in a decrease in the mRNA expression of ICAM-1, MIP-2, MCP-1, and CXCL-10, which are under control of NF-κB. In a rat model of mesangio-proliferative glomerulonephritis, PHD3 mRNA and protein expression was markedly induced and this effect was nearly abolished when rats were treated with the iNOS-specific inhibitor L-NIL, thus confirming our findings also in vivo. KEY MESSAGE: PHD3 expression induced by cytokines is NF-κB dependent in mesangial cells. Endogenously produced NO further augments PHD3 expression via HIF-1α. PHD3 expression is induced by NO in anti-Thy-1 glomerulonephritis.

Prolyl hydroxylase 3 (PHD3) expression augments the development of regulatory T cells.

Regulatory T cells (Tregs) are required for effective immune homeostasis by suppressing harmful immune responses against self-antigens. Transcription factor Foxp3 is required for the development of these cells. How Foxp3 is stabilised and affects Tregs development is still incompletely understood. Previous studies have suggested that hypoxia inducible factor gene HIF-1α negatively influences the development of Tregs and enhances the development of IL-17 producing Th17 cells. In this study, we reveal that prolyl hydroxylase 3 (PHD3), which is a negative regulator of HIF-1α, is upregulated in Tregs and enhances the development of Tregs. The PHD3 inhibitor dimethyl oxalylglycine (DMOG) or siRNAs-PHD3, which upregulates HIF-1α, down-regulated Foxp3 expression, and enhanced the development of Th17 cells. Our observations disclose a novel role of PHD3 in the development of Tregs.

Moabs MAS516 and 5B5, two fibroblast markers, recognize human follicular dendritic cells.

Follicular dendritic cells (FDC) are only located within follicles of secondary lymphoid tissues. The origin of this peculiar cell type is not clearly defined. To contribute to this study, we applied two monoclonal antibodies (MAS516 and 5B5) considered as specific for fibroblasts to tonsil cryosections and to isolated follicular dendritic cells. On the basis of an enzyme cocktail digestion of human tonsils and a fractionation procedure on albumin gradients, FDC can be prepared in the form of cell aggregates with associated lymphoid cells. MAS516 reacts with surface membrane molecules expressed by human fibroblasts, tissue macrophages and peripheral blood monocytes. With immunoperoxidase assays on tonsil cryosections connective tissue cells and macrophages are stained. Inside germinal centres, heavy labelling of the light zone was found. The MAS516 staining pattern is very similar to that of specific FDC markers DRC-1 or BU10. All isolated FDC reacted with MAS516 antibody. 5B5, considered as a typical fibroblast marker, reacts with human prolyl-4-hydroxylase which is an intracellular enzyme related to collagen biosynthesis. In cryosections, interfollicular and capsular areas showed 5B5 positive connective tissue fibroblasts. In germinal centres, some cells presenting features of FDC were 5B5 positive. After cell separation, 25%-50% of the isolated FDC were labelled with this antibody. This positivity of some FDC for 5B5 antibody may support the idea of their fibroblastic origin. The combination of observations realized in situ and after cell purification ensured an unequivocal recognition and identification of FDC.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunological properties of monoclonal antibodies to human and rat prolyl 4-hydroxylase.

Monoclonal antibodies to human (8 clones) and rat (12 clones) prolyl 4-hydroxylase [EC 1.14.11.2] were prepared and characterized as regards subclass, subunit specificity, inhibition and crossreactivity. Among the antibodies to the human enzyme, four clones showed the IgG1 subclass, two IgA, one IgG2b, and one IgM. Four clones reacted with the alpha subunit of the enzyme, while the others reacted with the beta subunit. The enzymatic activity was inhibited by four clones. Five clones crossreacted with the rat enzyme. One clone inhibited the rat enzyme. Among the antibodies to the rat enzyme, seven clones showed the IgG1 subclass, four IgG2a and one IgG2b. Seven clones reacted with the alpha subunit, and four with the beta subunit. One reacted with neither subunit. The enzymatic activity was inhibited by seven clones. Seven clones crossreacted with the human enzyme. Three clones inhibited the human enzyme.

Connective tissue metabolites in serum as markers of disease activity in patients with rheumatoid arthritis.

The serum levels of aminoterminal type III procollagen peptide (S-PIIINP), immunoreactive prolyl 4-hydroxylase protein (S-IRPH), 7S domain of collagen type IV (S-Col IV, 7S), and fragment P1 of laminin (S-Lam), which are associated with the metabolism of extracellular interstitial collagens and basement membranes, were measured sequentially for two years in 14 rheumatoid arthritis (RA) patients undergoing disease modifying antirheumatic drug treatment. Elevated S-PIIINP, S-IRPH, and S-Col IV, 7S levels were demonstrated in active RA. In active disease the metabolites showed some correlation with clinical and serological signs of disease activity. A high average synovial fluid/serum concentration ratio of PIIINP and of Col IV, 7S supports the concept that the increased serum levels of PIIINP and Col IV, 7S originated from the diseased joints. After 2 years of treatment a decline was observed in S-PIIINP and S-Col IV, 7S in treatment responders. However, the median levels of S-PIIINP and S-IRPH were still above the upper limit of normal, suggesting smouldering, subclinical inflammatory processes. S-Lam remained within the normal range in active and inactive disease.

Fibroblast markers in labial salivary gland biopsies in progressive systemic sclerosis.

Labial salivary gland (LSG) biopsies from 13 patients were studied. Three were normal glands, five showed fibrosis induced by progressive systemic sclerosis (PSS) and five more had PSS-induced fibrosis combined with and focal sialadenitis compatible with Sjögren's syndrome (SS). Monoclonal antibodies to proline-4-hydroxylase (alpha PH or 5B5-A) and the carboxyterminal domain of human type I procollagen (alpha pC or M-38) were used as fibroblast markers. Immunostaining was done with avidin-biotin-peroxidase complex (ABC). Using various sample controls (including cultured fibroblasts and specimens enriched for lymphocytes, plasma cells, granulocytes, monocytes and dendritic cells) as well as analysis of various LSG resident cells, the specificity of the alpha PH and alpha pC markers for fibroblasts was established. Cross reactions were only seen with plasma cells and acinar cells containing the beta subunit of PH or disulfide isomerase involved in SS-SH interchange reactions in these secretory cells. All fibroblasts in fibroblast monolayer cultures at their logarithmic phase of growth stained with the fibroblast markers studied, but false negative staining was seen with resting, mature fibroblasts in dense connective tissue in LSG sections. Therefore, it can be concluded that proline 4-hydroxylase and the COOH-terminal domain of type-I procollagen both indicate fibroblast involvement in collagen (type l) synthesis and thus identify active but not resting fibroblasts. PH+ fibroblast-like cells and pC+ fibroblasts were both more frequent in PSS LSGs than in normal glands, suggesting active local fibroblast involvement in PSS.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum enzymes of collagen synthesis and type III procollagen aminopropeptide in Nigerian patients with sickle cell disease.

Serum immunoreactive prolyl hydroxylase protein (S-IRPH), galactosylhydroxylysyl glucosyltransferase activity (S-GGT), and the aminoterminal propeptide of type III procollagen (S-Pro(III)-N-P) were measured in 20 patients with sickle cell disease and the values were compared with those in 20 apparently healthy Nigerians. The means for the two enzymes and S-Pro(III)-N-P were significantly elevated in the sickle cell disease patients. Significant correlations were found between the values of the two enzymes and the protein (S-Pro(III)-N-P) within the sickle cell disease patients. The data confirm that collagen formation is found in the bone, liver, or other organs of patients with this disease. The measurement of S-GGT and S-Pro(III)-N-P in prospective studies might be helpful in predicting general and hepatic fibrogenesis in sickle cell disease.

Prolyl hydroxylase in human corpora lutea during menstrual cycle and early pregnancy.

Immunohistochemical staining for human prolyl hydroxylase revealed intense staining of the human corpora lutea (CL) parencyma during early pregnancy compared with those in the menstrual cycle. These results suggest that human prolyl hydroxylase might play an important role in determining the physiology and structure of the CL during the menstrual cycle and early pregnancy.

Interdependence of hypoxic and innate immune responses.

Hypoxia-inducible factor (HIF) is an important transcriptional regulator of cell metabolism and the adaptation to cellular stress caused by oxygen deficiency (hypoxia). Phagocytic cells have an essential role in innate immune defence against pathogens and this is a battle that takes place mainly in the hypoxic microenvironments of infected tissues. It has now become clear that HIF promotes the bactericidal activities of phagocytic cells and supports the innate immune functions of dendritic cells, mast cells and epithelial cells. In response to microbial pathogens, HIF expression is upregulated through pathways involving the key immune response regulator nuclear factor-kappaB, highlighting an interdependence of the innate immune and hypoxic responses to infection and tissue damage. In turn, HIF-driven innate immune responses have important consequences for both the pathogen and the host, such that the tissue microenvironment fundamentally influences susceptibility to infectious disease.

The assembly of tetrameric prolyl hydroxylase in tendon fibroblasts from newly synthesized alpha-subunits and from preformed cross-reacting protein.

Embryonic-chick tendon cells were incubated in suspension for 4h with (14)C-labelled amino acids, cell extracts were subjected to gel filtration, and the effluent was examined by rocket immunoelectrophoresis by using antibodies specific for the beta-subunit of chick prolyl hydroxylase. Two peaks of immunoreactive protein were found. The first peak contained 40% of the immunoreactive protein eluted from the column and 100% of the enzyme activity. Polyacrylamide-slab-gel electrophoresis in sodium dodecyl sulphate of an immunoprecipitate of this peak demonstrated that it consisted of the tetrameric form of prolyl hydroxylase, subunit composition alpha(2)beta(2) where alpha and beta are non-identical subunits. Only the alpha-subunits were labelled, indicating that they were synthesized during the 4h labelling period. The beta-subunits were unlabelled, indicating that they had been synthesized before the labelling period. The second peak eluted from the gel-filtration column contained 60% of the immunoreactive protein eluted from the column and was enzymically inactive. Polyacrylamide-slab-gel electrophoresis of an immunoprecipitate of this peak indicated that it consisted of a single labelled polypeptide chain, identified as cross-reacting protein, which was related to, but not identical with, the beta-subunit of prolyl hydroxylase. Pulse-chase experiments were performed on cultured chick tendon cells to demonstrate that alpha-subunits and cross-reacting protein had half-lives of about 60h. The half-life of beta-subunits was considerably longer, and the kinetic pattern was consistent with their being derived from a labelled precursor such as cross-reacting protein. The data presented here indicate that the active tetrameric form of prolyl hydroxylase in cells is assembled from alpha-subunits which are newly synthesized, and from beta-subunits which are derived from cross-reacting protein.