Nachweis und isoformspezifische Funktion von HMGB1-Protein im osteoarthritischen Knorpel und chondrogenen Progenitorzellen
Detection and isoform-specific function of high mobility group box protein 1 (HMGB1) in human osteoarthritic cartilage and chondrogenic progenitor cells.
by Christoph Lehmann
Date of Examination:2020-06-29
Date of issue:2020-07-06
Advisor:Prof. Dr. Nicolai Miosge
Referee:Prof. Dr. Rainer Mausberg
Referee:Prof. Dr. Arndt Schilling
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EnglishOsteoarthritis (OA) is a common musculoskeletal disease in the elderly, characterized by painful aseptic inflammation, destruction of the joint surface and subchondral sclerosis. In late-stage OA, human articular cartilage harbors a unique progenitor cell population (CPCs) with stem cell characteristics such as multipotency and migratory activity. The aim of the present study was to analyze the HMGB1 distribution in OA cartilage and its effect on CPCs. HMGB1 protein is expressed by all eukaryotic cells and it is named for its rapid mobility on electrophoresis gels. HMGB1 was originally identified as a DNA binding protein. Extracellular HMGB1 play significantly different roles in inflammation, injury and infection response and cell migration depending on post-translational modifications. Oxidized HMGB1 (also called disulfide HMGB1) is a pro-inflammatory cytokine, whereas by contrast reduced HMGB1 (fully-reduced HMGB1) activates cell migration. The immunohistochemical study demonstrated that the HMGB1 protein level is increased in deep layers of OA cartilage. Breaks in tidemark packed with blood vessels that had vascularized into the cartilage tissue stained HMGB1 positive in IHC. Immuncytochemistry (ICC) identified HMGB1 in chondrocyte nuclear and cytoplasm. In CPCs, the signal was limited to the nuclear region. Western blot analysis for HMGB1 indicated a high level of HMGB1 protein in OA chondrocytes, whereas healthy chondrocytes and CPCs shown a lower HMGB1 protein expression. ICC also identified extracellular receptors such as RAGE (Receptor for Advanced Glycation Endproducts) and TLR4 (Toll-like receptor 4) on the CPC membrane. CPC migration assay identified fully-reduced HMGB1 as a pro-migratory cytokine. CPC stimulation with disulfide HMGB1 did not enhance the expression of pro-inflammatory cytokines such as IL6 and TNFα.
Keywords: Osteoarthritis; HMGB1; Chondrogenic Progenior Cells