{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,24]],"date-time":"2026-09-24T00:03:22Z","timestamp":1790208202189,"version":"4.1.0"},"reference-count":51,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2019,2,13]],"date-time":"2019-02-13T00:00:00Z","timestamp":1550016000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Seventh Framework Programme","award":["305815"],"award-info":[{"award-number":["305815"]}]},{"name":"Reumafonds","award":["LLP14"],"award-info":[{"award-number":["LLP14"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>During standard expansion culture (i.e., plasma osmolarity, 280 mOsm) human articular chondrocytes dedifferentiate, making them inappropriate for autologous chondrocyte implantation to treat cartilage defects. Increasing the osmolarity of culture media to physiological osmolarity levels of cartilage (i.e., 380 mOsm), increases collagen type II (COL2A1) expression of human articular chondrocytes in vitro, but the underlying molecular mechanism is not fully understood. We hypothesized that TGF-\u03b2 superfamily signaling may drive expression of COL2A1 under physiological osmolarity culture conditions. Human articular chondrocytes were cultured in cytokine-free medium of 280 or 380 mOsm with or without siRNA mediated TGF-\u03b22 knockdown (RNAi). Expression of TGF-\u03b2 isoforms, and collagen type II was evaluated by RT-qPCR and immunoblotting. TGF-\u03b22 protein secretion was evaluated using ELISA and TGF-\u03b2 bioactivity was determined using an established reporter assay. Involvement of BMP signaling was investigated by culturing human articular chondrocytes in the presence or absence of BMP inhibitor dorsomorphin and BMP bioactivity was determined using an established reporter assay. Physiological cartilage osmolarity (i.e., physosmolarity) most prominently increased TGF-\u03b22 mRNA expression and protein secretion as well as TGF-\u03b2 bioactivity. Upon TGF-\u03b22 isoform-specific knockdown, gene expression of chondrocyte marker COL2A1 was induced. TGF-\u03b22 RNAi under physosmolarity enhanced TGF-\u03b2 bioactivity. BMP bioactivity increased upon physosmotic treatment, but was not related to TGF-\u03b22 RNAi. In contrast, dorsomorphin inhibited COL2A1 mRNA expression in human articular chondrocytes independent of the osmotic condition. Our data suggest a role for TGF-\u03b2 superfamily member signaling in physosmolarity-induced mRNA expression of collagen type II. As physosmotic conditions favor the expression of COL2A1 independent of our manipulations, contribution of other metabolic, post-transcriptional or epigenetic factors cannot be excluded in the underlying complex and interdependent regulation of marker gene expression. Dissecting these molecular mechanisms holds potential to further improve future cell-based chondral repair strategies.<\/jats:p>","DOI":"10.3390\/ijms20040795","type":"journal-article","created":{"date-parts":[[2019,2,14]],"date-time":"2019-02-14T03:21:46Z","timestamp":1550114506000},"page":"795","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":23,"title":["Increased TGF-\u03b2 and BMP Levels and Improved Chondrocyte-Specific Marker Expression In Vitro under Cartilage-Specific Physiological Osmolarity"],"prefix":"10.3390","volume":"20","author":[{"given":"Ufuk","family":"Tan Timur","sequence":"first","affiliation":[{"name":"Laboratory for Experimental Orthopedics, Department of Orthopaedic Surgery, Maastricht University Medical Centre+, 6229 HX Maastricht, The Netherlands"},{"name":"Institute of Anatomy and Cell Biology, RWTH Aachen University, 52074 Aachen, Germany."}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marjolein","family":"Caron","sequence":"additional","affiliation":[{"name":"Laboratory for Experimental Orthopedics, Department of Orthopaedic Surgery, Maastricht University Medical Centre+, 6229 HX Maastricht, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Guus","family":"van den Akker","sequence":"additional","affiliation":[{"name":"Laboratory for Experimental Orthopedics, Department of Orthopaedic Surgery, Maastricht University Medical Centre+, 6229 HX Maastricht, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6244-7946","authenticated-orcid":false,"given":"Anna","family":"van der Windt","sequence":"additional","affiliation":[{"name":"Department of Orthopaedics, Erasmus MC, University Medical Center, 3000 CA Rotterdam, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7182-3571","authenticated-orcid":false,"given":"Jenny","family":"Visser","sequence":"additional","affiliation":[{"name":"Department of Internal Medicine, Erasmus MC, University Medical Center, 3000 CA Rotterdam, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lodewijk","family":"van Rhijn","sequence":"additional","affiliation":[{"name":"Laboratory for Experimental Orthopedics, Department of Orthopaedic Surgery, Maastricht University Medical Centre+, 6229 HX Maastricht, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Harrie","family":"Weinans","sequence":"additional","affiliation":[{"name":"Department of Orthopaedics, University Medical Center Utrecht, 3508 GA Utrecht, The Netherlands"},{"name":"Department of Rheumatology &amp; Clinical Immunology, University Medical Center Utrecht, 3508 GA Utrecht, The Netherlands"},{"name":"Department of Biomechanical Engineering, Delft University of Technology, 2628 CD Delft, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tim","family":"Welting","sequence":"additional","affiliation":[{"name":"Laboratory for Experimental Orthopedics, Department of Orthopaedic Surgery, Maastricht University Medical Centre+, 6229 HX Maastricht, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Pieter","family":"Emans","sequence":"additional","affiliation":[{"name":"Laboratory for Experimental Orthopedics, Department of Orthopaedic Surgery, Maastricht University Medical Centre+, 6229 HX Maastricht, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Holger","family":"Jahr","sequence":"additional","affiliation":[{"name":"Laboratory for Experimental Orthopedics, Department of Orthopaedic Surgery, Maastricht University Medical Centre+, 6229 HX Maastricht, The Netherlands"},{"name":"Institute of Anatomy and Cell Biology, RWTH Aachen University, 52074 Aachen, Germany."}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2019,2,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Brittberg, M. 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