Evaluation of the therapeutic potential of GDF5 mutants to treat osteoarthritis

• Main Author: Mang, Tanja
• Format: Others
• Language: en
• Published: 2019
• Online Access: https://tuprints.ulb.tu-darmstadt.de/8206/1/PhD%20Thesis%20Tanja%20Mang%20final.pdf; Mang, Tanja <http://tuprints.ulb.tu-darmstadt.de/view/person/Mang=3ATanja=3A=3A.html> (2019): Evaluation of the therapeutic potential of GDF5 mutants to treat osteoarthritis.Darmstadt, Technische Universität, [Ph.D. Thesis]

Osteoarthritis (OA) is characterized by a progressive destruction of articular cartilage. Current treatment options do not enable to heal or stop the disease progression. Consequently, there is a strong need for disease-modifying OA drugs (DMOADs). The growth and differentiation factor 5 (GDF5) is a promising DMOAD candidate. It is a key regulator of cartilage development and is involved in cartilage maintenance during adulthood. GDF5 was shown to stimulate matrix production in chondrocytes, to promote chondrogenesis in mesenchymal stem cells (MSCs) and to induce cartilage formation in an OA model [1-3]. Moreover, it was shown to exhibit anti-catabolic properties [4]. Thus, GDF5 could enable to regenerate damaged OA cartilage and to prevent further cartilage worsening in vivo. However, GDF5 was also shown to have hypertrophic and osteogenic activities [3, 5], which could result in the formation of inferior cartilage and unwanted bone formation. To reduce the hypertrophic/osteogenic properties of GDF5, different GDF5 mutants were produced and three of them (M1673, W417F, W417R) were selected. The aim of the present work was to evaluate these GDF5 mutants for their therapeutic potential in the two cells types, which can produce cartilage: chondrocytes and MSCs. Among the GDF5 mutants, M1673 was previously shown to have the strongest anabolic effect in chondrocytes from different non-human species. The first aim of this work was to confirm the anabolic effect of M1673 in human OA chondrocytes (hOAC). This was achieved with the use of a 3D culture system and modified culture conditions (slightly increased medium osmolarity). Increasing the medium osmolarity was shown to favor the chondrocytes phenotype and its matrix production. In addition, the OA characteristics (cytokine and protease production) were reduced and the expression of BMPR1a, BMPR1b and BMPR2 enhanced. With these culture conditions, M1673 was shown to exhibit anabolic and anti-catabolic effects on hOAC. Moreover, the results also suggested M1673 to be less hypertrophic in hOAC compared to GDF5. In addition, the GDF5 mutants were tested in the present work for their chondrogenic and osteogenic properties in MSCs. First, it was shown that the GDF5 mutants display a lower BMPR1a affinity compared to GDF5 but a similar BMPR1b affinity. Among the GDF5 mutants, M1673 was shown to induce the strongest chondrogenic differentiation while preventing hypertrophy. In addition, the osteogenic differentiation was delayed with M1673 compared to GDF5. Originally, it was hypothesized that chondrogenesis is mediated through BMPR1b, while osteogenesis is mediated through BMPR1a. However, in the light of the results presented here, this had to be refined: it now appears that the activation of BMPR1a is necessary for chondrogenesis as well as for osteogenesis. In addition, BMPs with a higher BMPR1a/BMPR1b ratio appear to prevent hypertrophy and delay osteogenesis. Taken together, the results of this work show that M1673 can stimulate cartilage production in both hOAC and MSCs, while having a reduced hypertrophic and osteogenic potential in comparison to GDF5. Therefore, it could be demonstrated that M1673 bear potential as a DMOAD.