Liver X Receptor activation delays chondrocyte hypertrophy during endochondral bone growth

Proteomic comparison of osteoarthritic and reference human menisci using data-independent acquisition mass spectrometry

OBJECTIVE

Recent research in knee osteoarthritis (OA) highlights the role of the meniscus in OA pathology. Our aim was to compare the proteomes of medial and lateral menisci from end-stage medial compartment knee OA patients, with reference menisci from knee-healthy deceased donors, using mass spectrometry.

DESIGN

Tissue plugs of Ø3 mm were obtained from the posterior horns of the lateral and medial menisci from one knee of 10 knee-healthy deceased donors and 10 patients undergoing knee replacement. Proteins were extracted and prepared for mass spectrometric analysis. Statistical analysis was conducted on abundance data that was log₂-transformed, using a linear mixed effects model and evaluated using pathway analysis.

RESULTS

We identified a total of 835 proteins in all samples, of which 331 were included in the statistical analysis. The largest differences could be seen between the medial menisci from OA patients and references, with most proteins showing higher intensities in the medial menisci from OA patients. Several matrix proteins, e.g., matrix metalloproteinase 3 (MMP3) (4.3 times higher values [95%CI 1.8, 10.6]), TIMP1 (3.5 [1.4, 8.5]), asporin (4.1 [1.7, 10.0]) and versican (4.4 [1.8, 10.9]), all showed higher abundance in medial menisci from OA patients compared to medial reference menisci. OA medial menisci also showed increased activation of several pathways involved in inflammation.

CONCLUSION

An increase in protein abundance for proteins such as MMP and TIMP1 in the medial menisci from OA patients suggests simultaneous activation of both catabolic and anabolic processes that warrants further attention.

Noonan syndrome-causing SHP2 mutants impair ERK-dependent chondrocyte differentiation during endochondral bone growth

Growth retardation is a constant feature of Noonan syndrome (NS) but its physiopathology remains poorly understood. We previously reported that hyperactive NS-causing SHP2 mutants impair the systemic production of insulin-like growth factor 1 (IGF1) through hyperactivation of the RAS/extracellular signal-regulated kinases (ERK) signalling pathway. Besides endocrine defects, a direct effect of these mutants on growth plate has not been explored, although recent studies have revealed an important physiological role for SHP2 in endochondral bone growth. We demonstrated that growth plate length was reduced in NS mice, mostly due to a shortening of the hypertrophic zone and to a lesser extent of the proliferating zone. These histological features were correlated with decreased expression of early chondrocyte differentiation markers, and with reduced alkaline phosphatase staining and activity, in NS murine primary chondrocytes. Although IGF1 treatment improved growth of NS mice, it did not fully reverse growth plate abnormalities, notably the decreased hypertrophic zone. In contrast, we documented a role of RAS/ERK hyperactivation at the growth plate level since 1) NS-causing SHP2 mutants enhance RAS/ERK activation in chondrocytes in vivo (NS mice) and in vitro (ATDC5 cells) and 2) inhibition of RAS/ERK hyperactivation by U0126 treatment alleviated growth plate abnormalities and enhanced chondrocyte differentiation. Similar effects were obtained by chronic treatment of NS mice with statins. In conclusion, we demonstrated that hyperactive NS-causing SHP2 mutants impair chondrocyte differentiation during endochondral bone growth through a local hyperactivation of the RAS/ERK signalling pathway, and that statin treatment may be a possible therapeutic approach in NS.

Nuclear receptors as potential drug targets in osteoarthritis

Osteoarthritis is amongst the major causes of disability worldwide, but no medications that can slow or stop progression of this disorder have been identified. Recent evidence suggests roles for a variety of members of the nuclear receptor family of ligand-activated transcription factors in various forms of osteoarthritis. Since nuclear receptors are amongst the major classes of drug targets, these studies suggest that modulators of nuclear receptor activity might provide novel strategies to treat osteoarthritis. This review focuses on recent advances in our understanding of the role of nuclear receptors in osteoarthritis onset and progression, as well as their therapeutic implications. Future studies should continue to examine the possible roles of additional nuclear receptors in the pathophysiology of different types of osteoarthritis.

Long noncoding RNA expression profiles in chondrogenic and hypertrophic differentiation of mouse mesenchymal stem cells

Long noncoding RNAs (lncRNAs) are important regulators for a variety of biological processes. Chondrogenic differentiation of mesenchymal stem cells (MSCs) is a crucial stage in chondrogenesis while chondrocyte hypertrophy is related to endochondral ossification and osteoarthritis. However, the effects of lncRNAs on chondrogenic and hypertrophic differentiation of mouse MSCs are unclear. To explore the potential mechanisms of lncRNAs during chondrogenesis and chondrocyte hypertrophy, microarray was performed to investigate the expression profiles of lncRNA and mRNA in MSCs, pre-chondrocytes, and hypertrophic chondrocytes. Then, we validated microarray data by RT-PCR and screened three lncRNAs from upregulating groups during chondrogenesis and chondrocyte hypertrophy respectively. After downregulating any of the above lncRNAs, we found that the expression of chondrogenesis-related genes such as Sox9 and Col2a1 and hypertrophy-related genes including Runx2 and Col10a1 was inhibited, respectively. Furthermore, the target genes of above lncRNAs were predicted by bioinformatics approaches. Gene ontology and Kyoto encyclopedia of genes and genome biological pathway analysis were also made to speculate the functions of above lncRNAs. In conclusion, the study first revealed the expression profile of lncRNAs in chondrogenic and hypertrophic differentiations of mouse MSCs and presented a new prospect for the underlying mechanisms of chondrogenesis and endochondral ossification.

Nuclear receptors regulate lipid metabolism and oxidative stress markers in chondrocytes

Abstract

Joint homeostasis failure can result in osteoarthritis (OA). Currently, there are no treatments to alter disease progression in OA, but targeting early changes in cellular behavior has great potential. Recent data show that nuclear receptors contribute to the pathogenesis of OA and could be viable therapeutic targets, but their molecular mechanisms in cartilage are incompletely understood. This study examines global changes in gene expression after treatment with agonists for four nuclear receptor implicated in OA (LXR, PPARδ, PPARγ, and RXR). Murine articular chondrocytes were treated with agonists for LXR, PPARδ, PPARγ, or RXR and underwent microarray, qPCR, and cellular lipid analyses to evaluate changes in gene expression and lipid profile. Immunohistochemistry was conducted to compare two differentially expressed targets (Txnip, Gsta4) in control and cartilage-specific PPARδ knockout mice subjected to surgical destabilization of the medial meniscus (DMM). Nuclear receptor agonists induced different gene expression profiles with many responses affecting lipid metabolism. LXR activation downregulated gene expression of proteases involved in OA, whereas RXR agonism decreased expression of ECM components and increased expression of Mmp13. Functional assays indicate increases in cell triglyceride accumulation after PPARγ, LXR, and RXR agonism but a decrease after PPARδ agonism. PPARδ and RXR downregulate the antioxidant Gsta4, and PPARδ upregulates Txnip. Wild-type, but not PPARδ-deficient mice, display increased staining for Txnip after DMM. Collectively, these data demonstrate that nuclear receptor activation in chondrocytes primarily affects lipid metabolism. In the case of PPARδ, this change might lead to increased oxidative stress, possibly contributing to OA-associated changes.

Key message

Nuclear receptors regulate metabolic genes in chondrocytes.

Nuclear receptors affect triglyceride levels.

PPARδ mediates regulation of oxidative stress markers.

Nuclear receptors are promising therapeutic targets for osteoarthritis.

Electronic supplementary material

The online version of this article (doi:10.1007/s00109-016-1501-5) contains supplementary material, which is available to authorized users.