Jürgen Brinckmann

Identification of PLOD2 as Telopeptide Lysyl Hydroxylase, an Important Enzyme in Fibrosis

The hallmark of fibrotic processes is an excessive accumulation of collagen. The deposited collagen shows an increase in pyridinoline cross-links, which are derived from hydroxylated lysine residues within the telopeptides. This change in cross-linking is related to irreversible accumulation of collagen in fibrotic tissues. The increase in pyridinoline cross-links is likely to be the result of increased activity of the enzyme responsible for the hydroxylation of the telopeptides (telopeptide lysyl hydroxylase, or TLH). Although the existence of TLH has been postulated, the gene encoding TLH has not been identified. By analyzing the genetic defect of Bruck syndrome, which is characterized by a pyridinoline deficiency in bone collagen, we found two missense mutations in exon 17 of PLOD2, thereby identifying PLOD2 as a putative TLH gene. Subsequently, we investigated fibroblasts derived from fibrotic skin of systemic sclerosis (SSc) patients and found that PLOD2 mRNA is highly increased indeed. Furthermore, increased pyridinoline cross-link levels were found in the matrix deposited by SSc fibroblasts, demonstrating a clear link between mRNA levels of the putative TLH gene (PLOD2) and the hydroxylation of lysine residues within the telopeptides. These data underscore the significance of PLOD2 in fibrotic processes.

Immunophenotyping of the human bulge region: the quest to define useful in situ markers for human epithelial hair follicle stem cells and their niche

Abstract:  Since the discovery of epithelial hair follicle stem cells (eHFSCs) in the bulge of human hair follicles (HFs) an important quest has started: to define useful markers. In the current study, we contribute to this by critically evaluating corresponding published immunoreactivity (IR) patterns, and by attempting to identify markers for the in situ identification of human eHFSCs and their niche. For this, human scalp skin cryosections of at least five different individuals were examined, employing standard immunohistology as well as increased sensitivity methods. Defined reference areas were compared by quantitative immunohistochemistry for the relative intensity of their specific IR.

Fibrillin-1 Interactions with Fibulins Depend on the First Hybrid Domain and Provide an Adaptor Function to Tropoelastin

Fibrillin-containing microfibrils in elastic and nonelastic extracellular matrices play important structural and functional roles in various tissues, including blood vessels, lung, skin, and bone. Microfibrils are supramolecular aggregates of several protein and nonprotein components. Recently, a large region in the N-terminal portion of fibrillin-1 was characterized as a multifunctional protein interaction site, including binding sites for fibulin-2 and -5 among others. Using a panel of recombinant fibrillin-1 swapped domain and deletion fragments, we demonstrate here that the conserved first hybrid domain in fibrillin-1 is essential for binding to fibulin-2, -4, and -5. Fibulin-3 and various isoforms of fibulin-1 did not interact with fibrillin-1. Although the first hybrid domain in fibrillin-1 is located in close vicinity to the self-assembly epitope, binding of fibulin-2, -4, and -5 did not interfere with self-assembly. However, these fibulins can associate with microfibrils at various levels of maturity. Formation of ternary complexes between fibrillin-1, fibulins, and tropoelastin demonstrated that fibulin-2 and -5 but much less fibulin-4, are able to act as molecular adaptors between fibrillin-1 and tropoelastin.

TSG-6 Released from Intradermally Injected Mesenchymal Stem Cells Accelerates Wound Healing and Reduces Tissue Fibrosis in Murine Full-Thickness Skin Wounds

Proper activation of macrophages (Mφ) in the inflammatory phase of acute wound healing is essential for physiological tissue repair. However, there is a strong indication that robust Mφ inflammatory responses may be causal for the fibrotic response always accompanying adult wound healing. Using a complementary approach of in vitro and in vivo studies, we here addressed the question of whether mesenchymal stem cells (MSCs)-due to their anti-inflammatory properties-would control Mφ activation and tissue fibrosis in a murine model of full-thickness skin wounds. We have shown that the tumor necrosis factor-α (TNF-α)-stimulated protein 6 (TSG-6) released from MSCs in co-culture with activated Mφ or following injection into wound margins suppressed the release of TNF-α from activated Mφ and concomitantly induced a switch from a high to an anti-fibrotic low transforming growth factor-β1 (TGF-β1)/TGF-β3 ratio. This study provides insight into what we believe to be a previously undescribed multifaceted role of MSC-released TSG-6 in wound healing. MSC-released TSG-6 was identified to improve wound healing by limiting Mφ activation, inflammation, and fibrosis. TSG-6 and MSC-based therapies may thus qualify as promising strategies to enhance tissue repair and to prevent excessive tissue fibrosis.

Interleukin-4 Receptor α Signaling in Myeloid Cells Controls Collagen Fibril Assembly in Skin Repair

Activation of the immune response during injury is a critical early event that determines whether the outcome of tissue restoration is regeneration or replacement of the damaged tissue with a scar. The mechanisms by which immune signals control these fundamentally different regenerative pathways are largely unknown. We have demonstrated that, during skin repair in mice, interleukin-4 receptor α (IL-4Rα)-dependent macrophage activation controlled collagen fibril assembly and that this process was important for effective repair while having adverse pro-fibrotic effects. We identified Relm-α as one important player in the pathway from IL-4Rα signaling in macrophages to the induction of lysyl hydroxylase 2 (LH2), an enzyme that directs persistent pro-fibrotic collagen cross-links, in fibroblasts. Notably, Relm-β induced LH2 in human fibroblasts, and expression of both factors was increased in lipodermatosclerosis, a condition of excessive human skin fibrosis. Collectively, our findings provide mechanistic insights into the link between type 2 immunity and initiation of pro-fibrotic pathways.

Autoantibodies to cartilage collagens in relapsing polychondritis

Relapsing polychondritis is a systemic disease associated with a destruction of cartilage in various parts of the body. Sera from six patients with relapsing polychondritis and one patient with microscopic polyarteritis nodosa as well as from six controls were analyzed by immunoblotting and ELISA. All patients had autoantibodies against native collagens II and IX. The serum from one patient showed a strong reaction with all three collagen chains of the high molecular weight fraction of collagen IX after denaturation; sera from four patients showed autoantibodies against α2 (XI) and sera from three patients showed autoantibodies against the covalently cross-linked γ component of collagen XI. The presence of autoantibodies against collagens II, IX, and XI, which form the major fibrillar scaffold in cartilage and mediate the interaction of collagen fibrils and proteoglycan, suggests that autoantibodies against cartilaginous collagen may play a crucial role in the pathogenesis of relapsing polychondritis and microscopic polyarteritis nodosa.

Lysyl Oxidases Play a Causal Role in Vascular Remodeling in Clinical and Experimental Pulmonary Arterial Hypertension

Objective—Pulmonary vascular remodeling, the pathological hallmark of pulmonary arterial hypertension, is attributed to proliferation, apoptosis resistance, and migration of vascular cells. A role of dysregulated matrix cross-linking and stability as a pathogenic mechanism has received little attention. We aimed to assess whether matrix cross-linking enzymes played a causal role in experimental pulmonary hypertension (PH). Approach and Results—All 5 lysyl oxidases were detected in concentric and plexiform vascular lesions of patients with idiopathic pulmonary arterial hypertension. Lox, LoxL1, LoxL2, and LoxL4 expression was elevated in lungs of patients with idiopathic pulmonary arterial hypertension, whereas LoxL2 and LoxL3 expression was elevated in laser-capture microdissected vascular lesions. Lox expression was hypoxia-responsive in pulmonary artery smooth muscle cells and adventitial fibroblasts, whereas LoxL1 and LoxL2 expression was hypoxia-responsive in adventitial fibroblasts. Lox expression was increased in lungs from hypoxia-exposed mice and in lungs and pulmonary artery smooth muscle cells of monocrotaline-treated rats, which developed PH. Pulmonary hypertensive mice exhibited increased muscularization and perturbed matrix structures in vessel walls of small pulmonary arteries. Hypoxia exposure led to increased collagen cross-linking, by dihydroxylysinonorleucine and hydroxylysinonorleucine cross-links. Administration of the lysyl oxidase inhibitor &bgr;-aminopropionitrile attenuated the effect of hypoxia, limiting perturbations to right ventricular systolic pressure, right ventricular hypertrophy, and vessel muscularization and normalizing collagen cross-linking and vessel matrix architecture. Conclusions—Lysyl oxidases are dysregulated in clinical and experimental PH. Lysyl oxidases play a causal role in experimental PH and represent a candidate therapeutic target. Our proof-of-principle study demonstrated that modulation of lung matrix cross-linking can affect pulmonary vascular remodeling associated with PH.

Genetic Ablation of Mast Cells Redefines the Role of Mast Cells in Skin Wound Healing and Bleomycin-Induced Fibrosis

Conclusive evidence for the impact of mast cells (MCs) in skin repair is still lacking. Studies in mice examining the role of MC function in the physiology and pathology of skin regenerative processes have obtained contradictory results. To clarify the specific role of MCs in regenerative conditions, here we used a recently developed genetic mouse model that allows conditional MC ablation to examine MC-specific functions in skin. This mouse model is based on the cell type-specific expression of Cre recombinase in connective tissue-type MCs under control of the Mcpt5 promoter and the Cre-inducible diphtheria toxin receptor-mediated cell lineage ablation by diphtheria toxin. In response to excisional skin injury, genetic ablation of MCs did not affect the kinetics of reepithelialization, the formation of vascularized granulation tissue, or scar formation. Furthermore, genetic ablation of MCs failed to prevent the development of skin fibrosis upon bleomycin challenge. The amount of deposited collagen and the biochemistry of collagen fibril crosslinks within fibrotic lesions were comparable in MC-depleted and control mice. Collectively, our findings strongly suggest that significant reduction of MC numbers does not affect skin wound healing and bleomycin-induced fibrosis in mice, and provide to our knowledge previously unreported insight in the long-debated contribution of MCs in skin regenerative processes.

Enhanced fibrillin-2 expression is a general feature of wound healing and sclerosis: potential alteration of cell attachment and storage of TGF- β

Wound healing and sclerosis are characterized by an increase of extracellular matrix proteins, which are characteristically expressed in the embryo–fetal period. We analyzed the expression of fibrillin-2, which is typically found in embryonic tissues, but only scarcely in adult skin. In wound healing and sclerotic skin diseases such as lipodermatosclerosis and scleroderma, a marked increase of fibrillin-2 expression was found by immunohistology. Double labelling of fibrillin-2 and tenascin-C, which is also expressed in wound healing and sclerosis, showed co-localization of both proteins. Solid-phase and slot blot-overlay assays showed a dose-dependent binding of the recombinant N-terminal half of fibrillin-2 (rFBN2-N) to tenascin-C. Real-time PCR showed an increase of the fibrillin-2 gene expression in cell culture triggered by typical mediators for fibroblast activation such as serum, IL-4, and TGF-β. By contrast, prolonged hypoxia is not associated with changes in fibrillin-2 expression. Tenascin-C is an anti-adhesive substrate for fibroblasts, whereas fibrillin-2 stimulates cell attachment. Attachment assays using mixed substrates showed decreased cell attachment when tenascin-C and rFBN2-N were coated together, compared with the attachment to rFBN2-N alone. Fibrillins are involved in storage and activation of TGF-β. Immunohistology with an antibody against the latency-associated peptide (LAP (TGF-β1)) showed a marked increase of inactive LAP-bound TGF-β1 in wound healing and sclerotic skin whereas normal skin showed only a weak expression. Double immunofluorescence confirmed a partial colocalization of both proteins. In conclusion, we show that a stimulation of the fibrillin-2 expression is a characteristic feature of fibroblasts present in wound healing and sclerosis, which may be involved in the alteration of cell attachment and storage of inactive TGF-β in the matrix.

Changes with age in the urinary excretion of hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP).

There is increasing evidence that the measurement of urinary hydroxylysylpyridinoline (HP or PYD) and lysylpyridinoline (LP or DPD) by HPLC (high performance liquid chromatography) is potentially useful in clinical and pharmacological studies. HP and LP are promising markers of bone resorption because their levels in urine reflect the breakdown of mature collagen fibrils mainly of skeletal tissues. HP and LP are two non-reducible cross-links of mature collagen which are formed by a sequence of post-translational modifications. HP is a derivative of three residues of hydroxylysine and is present in almost all mature tissues (e.g. tendon. vessel walls, cartilage, dentine and bone). LP is a derivative of two residues of hydroxylysine and one residue of lysine and is present mainly in dentine and bone. Neither cross-link is found in normal human skin. We have isolated and purified HP and LP from commercially available bone gelatine by a preparative reverse-phase column HPLC. These two components were used as external standards for sample analysis. In the present study we analysed the urinary excretion of HP and LP in a group of 264 male and 279 female healthy subjects aged from 6 months to 65 years. A continuous decline of both cross-link components during childhood paralleled by a decrease of the HP:LP-ratio was observed. The levels of HP and LP were 2.5-5 times higher in infants (0.5-1 year) than in children (5-10 years) and 15-20 times higher than in adults (26-65 years). After the age of 17 years, both parameters remained at low levels. These data allow a precise quantitative monitoring of bone resorption in patients with metabolic bone diseases or during pharmacological interventions.