Cyclic AMP regulates extracellular matrix gene expression and metabolism in cultured primary rat chondrocytes

Rapamycin-Induced Autophagy Promotes the Chondrogenic Differentiation of Synovium-Derived Mesenchymal Stem Cells in the Temporomandibular Joint in Response to IL-1β

Cartilage defects in temporomandibular disorders (TMD) lead to chronic pain and seldom heal. Synovium-derived mesenchymal stem cells (SMSCs) exhibit superior chondrogenesis and have become promising seed cells for cartilage tissue engineering. However, local inflammatory conditions that affect the repair of articular cartilage by SMSCs present a challenge, and the specific mechanism through which the function remains unclear. Thus, it is important to explore the chondrogenesis of SMSCs under inflammatory conditions of TMD such that they can be used more effectively in clinical treatment. In this study, we obtained SMSCs from TMD patients with severe cartilage injuries. In response to stimulation with IL-1β, which is well known as one of the most prevalent cytokines in TMD, MMP13 expression increased, while that of SOX9, aggrecan, and collagen II decreased during chondrogenic differentiation. At the same time, IL-1β upregulated the expression of mTOR and decreased the ratio of LC3-II/LC3-I and the formation of autophagosomes. Further study revealed that rapamycin pretreatment promoted the migration of SMSCs and the expression of chondrogenesis-related markers in the presence of IL-1β by inducing autophagy. 3-Benzyl-5-((2-nitrophenoxy)methyl)-dihydrofuran-2(3H)-one (3BDO), a new activator of mTOR, inhibited autophagy and increased the expression of p-GSK3βser9 and β-catenin, simulating the effect of IL-1β stimulation. Furthermore, rapamycin reduced the expression of mTOR, whereas the promotion of LC3-II/LC3-I was blocked by the GSK3β inhibitor TWS119. Taken together, these results indicate that rapamycin enhances the chondrogenesis of SMSCs by inducing autophagy, and GSK3β may be an important regulator in the process of rapamycin-induced autophagy. Thus, inducing autophagy may be a useful approach in the chondrogenic differentiation of SMSCs in the inflammatory microenvironment and may represent a novel TMD treatment.

Differential Effects of Hormones on Cellular Metabolism in Keratoconus In Vitro

Keratoconus (KC) is a corneal thinning disease with an onset commonly immediately post-puberty and stabilization by 40 to 50 years of age. The role of hormones in regulating corneal tissue structure in homeostatic and pathological conditions is unknown. Our group recently linked altered hormone levels to KC. Our current study sought to investigate and delineate the effects of exogenous hormones, such as androgen, luteotropin, and estrogen, on corneal stroma bioenergetics. We utilized our established 3D in vitro model to characterize the effects of DHEA, prolactin, 17β-estradiol on insulin-growth factor-1 and -2 (IGF-1, -2) signaling and metabolic function in primary corneal fibroblasts from healthy controls (HCFs) and KC patients (HKCs). Our data showed that exogenous DHEA significantly downregulated IGF-1 and its receptor in both HCFs and HKCs with HKCs showing consistently lower basal pentose phosphate flux. Prolactin caused no significant change in IGF-1 levels and an increase in IGF-2 in HKCs correlating with an increase in ATP and NADH levels. 17β-estradiol led to a significant upregulation in pentose phosphate flux and glycolytic intermediates in HCFs. Our results identified hormone-specific responses regulated in HKCs compared to HCFs revealing a novel role for hormones on bioenergetics in KC.

Glycogen synthase kinase 3 inhibition stimulates human cartilage destruction and exacerbates murine osteoarthritis

OBJECTIVE

To assess the role of glycogen synthase kinase 3 (GSK-3) as a regulator of cartilage destruction in human tissue and a murine model of osteoarthritis (OA).

METHODS

Surgical destabilization of the medial meniscus (DMM) was performed to induce experimental murine OA, and joint damage was assessed histologically. Bovine nasal and human OA cartilage samples were incubated with interleukin-1 (IL-1) plus oncostatin M (OSM) and GSK-3 inhibitor. Collagen and proteoglycan release was assessed by hydroxyproline measurement and dye binding assay, collagenase activity was assessed by bioassay, and gene expression was analyzed by real-time polymerase chain reaction. Human articular chondrocytes were isolated by enzymatic digestion and cultured prior to gene silencing and immunoblotting of cell lysates and nuclear fractions.

RESULTS

Mice treated with GSK-3 inhibitor exhibited significantly greater cartilage damage compared with sham-operated control mice. GSK-3 inhibition in bovine cartilage dramatically accelerated IL-1 plus OSM-stimulated degradation, concomitant with a profound increase in collagenase activity. GSK-3 inhibitor induced collagen release from human OA cartilage in the presence of IL-1 plus OSM and increased proteoglycan loss. Gene expression profiling of resorbing OA cartilage revealed a marked procatabolic switch in gene expression upon GSK-3 inhibition. This was mirrored in human articular chondrocytes following GSK3 silencing, particularly with the GSK-3β isoform. GSK-3 inhibition or silencing led to enhanced IL-1 plus OSM-stimulated abundance and activity of Jun, and silencing of c-jun ameliorated GSK-3 inhibitor-mediated procatabolic gene expression.

CONCLUSION

GSK-3 is an important regulator of matrix metalloproteinase (MMP)-mediated joint destruction, the inhibition of which by proinflammatory stimuli de-represses catabolic gene expression. Therapeutic strategies that maintain cartilage GSK-3 activity may therefore help curtail aberrant MMP activity during pathologic joint destruction.

Profiling insulin like factor 3 (INSL3) signaling in human osteoblasts

BACKGROUND

Young men with mutations in the gene for the INSL3 receptor (Relaxin family peptide 2, RXFP2) are at risk of reduced bone mass and osteoporosis. Consistent with the human phenotype, bone analyses of Rxfp2(-/-) mice showed decreased bone volume, alterations of the trabecular bone, reduced mineralizing surface, bone formation, and osteoclast surface. The aim of this study was to elucidate the INSL3/RXFP2 signaling pathways and targets in human osteoblasts.

METHODOLOGY/PRINCIPAL FINDINGS

Alkaline phosphatase (ALP) production, protein phosphorylation, intracellular calcium, gene expression, and mineralization studies have been performed. INSL3 induced a significant increase in ALP production, and Western blot and ELISA analyses of multiple intracellular signaling pathway molecules and their phosphorylation status revealed that the MAPK was the major pathway influenced by INSL3, whereas it does not modify intracellular calcium concentration. Quantitative Real Time PCR and Western blotting showed that INSL3 regulates the expression of different osteoblast markers. Alizarin red-S staining confirmed that INSL3-stimulated osteoblasts are fully differentiated and able to mineralize the extracellular matrix.

CONCLUSIONS/SIGNIFICANCE

Together with previous findings, this study demonstrates that the INSL3/RXFP2 system is involved in bone metabolism by acting on the MAPK cascade and stimulating transcription of important genes of osteoblast maturation/differentiation and osteoclastogenesis.