Development and application of a new Silent reporter system to quantitate the activity of enhancer elements in the type II Collagen Gene

Pre-hypertrophic chondrogenic enhancer landscape of limb and axial skeleton development

Chondrocyte differentiation controls skeleton development and stature. Here we provide a comprehensive map of chondrocyte-specific enhancers and show that they provide a mechanistic framework through which non-coding genetic variants can influence skeletal development and human stature. Working with fetal chondrocytes isolated from mice bearing a Col2a1 fluorescent regulatory sensor, we identify 780 genes and 2'704 putative enhancers specifically active in chondrocytes using a combination of RNA-seq, ATAC-seq and H3K27ac ChIP-seq. Most of these enhancers (74%) show pan-chondrogenic activity, with smaller populations being restricted to limb (18%) or trunk (8%) chondrocytes only. Notably, genetic variations overlapping these enhancers better explain height differences than those overlapping non-chondrogenic enhancers. Finally, targeted deletions of identified enhancers at the Fgfr3, Col2a1, Hhip and, Nkx3-2 loci confirm their role in regulating cognate genes. This enhancer map provides a framework for understanding how genes and non-coding variations influence bone development and diseases.

Curcumin reverses erastin-induced chondrocyte ferroptosis by upregulating Nrf2

Osteoarthritis (OA) is associated with ferroptosis, a newly discovered form of programmed cell death associated with lipid peroxidation. Curcumin, the main monomer component in turmeric rhizomes, possesses antioxidant and anti-ferroptosis properties, but its effect on ferroptosis in chondrocytes of OA is unknown. This study aimed to investigate the protective effect and potential mechanism of curcumin on chondrocytes induced by erastin, a ferroptosis inducer. CCK-8 assays were used to assess cell viability in mouse primary chondrocytes treated with 3.33 μM erastin alone or in combination with different doses of curcumin. Various parameters were detected, including LDH, SOD, GSH-PX, MDA, ROS and Fe2+ contents. The ferroptosis-related proteins, such as SLC7A11, GPX4, TFR1, ACSL4, and FTH1, were examined using immunofluorescence and western blotting. Nrf2 was knocked down using siRNA to explore the molecular mechanism through which curcumin protects chondrocytes from erastin-induced ferroptosis. In a mouse model of knee ferroptosis induced by intracavity injection of 10 μL erastin (5 mg/mL), HE staining, Safranin O-Fast Green staining, and immunohistochemistry were employed to evaluate articular cartilage injury. The results demonstrated that erastin significantly suppressed the expression of SOD, GSH-PX, SLC7A11, GPX4, and FTH1 while upregulating the levels of LDH, MDA, ROS, ACSL4, and TFR1 in chondrocytes. Moreover, erastin-induced chondrocyte ferroptosis, lipid ROS, and Fe2+ production were reversed by curcumin. Additionally, curcumin significantly upregulated the expression level of the Nrf2 gene and protein. Silencing Nrf2 reversed the protective effect of curcumin on erastin-induced chondrocyte ferroptosis. In animal experiments, silencing Nrf2 counteracted the impact and damage of curcumin on erastin-induced ferroptosis of cartilage tissue in vivo, leading to significant inhibition of OA progression. Taken together, these findings suggest that curcumin can inhibit chondrocyte ferroptosis by activating the Nrf2 signaling pathway, providing further insight into the regulatory mechanism of curcumin in OA and supporting its potential therapeutic use in OA treatment.

Interleukin‑Iβ promotes cartilage degeneration by regulating forkhead box protein O4 and type Ⅱ collagen

Osteoarthritis (OA) is one of the most prevalent pain-inducing and disabling diseases globally. Aging is a primary contributing factor to the progression of OA. Forkhead box protein O4 (FOXO4) is known to be involved in the cell cycle and apoptosis regulation. The aim of the present study was to investigate the association between FOXO4 expression and chondrocyte degeneration in rats. Chondrocytes were assigned to the control (4-week-old rats), natural degeneration (16-week-old rats) or induced degeneration (IL-1β-treated chondrocytes from 4-week-old rats) groups. Immunocytochemical analysis with β-galactosidase staining revealed a greater number of stained cells present in the natural and induced degeneration groups than in the control group. PCR analysis indicated lower mRNA expression levels of collagen type II α1 chain (Col2α) and higher levels of FOXO4, and western blotting revealed reduced Col2α protein expression levels and significantly elevated FOXO4 levels in the natural and induced degeneration groups, compared with those in the control group. The results of the present study revealed that FOXO4 expression was altered in the natural and induced degeneration groups, and further research and exploration are needed to clarify the underlying mechanism.

Curcumin Attenuates Environment-Derived Osteoarthritis by Sox9/NF-kB Signaling Axis

Inflammation has a fundamental impact on the pathophysiology of osteoarthritis (OA), a common form of degenerative arthritis. It has previously been established that curcumin, a component of turmeric (Curcuma longa), has anti-inflammatory properties. This research evaluates the potentials of curcumin on the pathophysiology of OA in vitro. To explore the anti-inflammatory efficacy of curcumin in an inflamed joint, an osteoarthritic environment (OA-EN) model consisting of fibroblasts, T-lymphocytes, 3D-chondrocytes is constructed and co-incubated with TNF-α, antisense oligonucleotides targeting NF-kB (ASO-NF-kB), or an IkB-kinase (IKK) inhibitor (BMS-345541). Our results show that OA-EN, similar to TNF-α, suppresses chondrocyte viability, which is accompanied by a significant decrease in cartilage-specific proteins (collagen II, CSPG, Sox9) and an increase in NF-kB-driven gene proteins participating in inflammation, apoptosis, and breakdown (NF-kB, MMP-9, Cox-2, Caspase-3). Conversely, similar to knockdown of NF-kB at the mRNA level or at the IKK level, curcumin suppresses NF-kB activation, NF-kB-promotes gene proteins derived from the OA-EN, and stimulates collagen II, CSPG, and Sox9 expression. Furthermore, co-immunoprecipitation assay shows that curcumin reduces OA-EN-mediated inflammation and chondrocyte apoptosis, with concomitant chondroprotective effects, due to modulation of Sox-9/NF-kB signaling axis. Finally, curcumin selectively hinders the interaction of p-NF-kB-p65 directly with DNA—this association is disrupted through DTT. These results suggest that curcumin suppresses inflammation in OA-EN via modulating NF-kB-Sox9 coupling and is essential for maintaining homeostasis in OA by balancing chondrocyte survival and inflammatory responses. This may contribute to the alternative treatment of OA with respect to the efficacy of curcumin.

Gene expression of type II collagen is regulated by direct interaction with Kruppel-like factor 4 and AT-rich interactive domain 5B

We have previously found and characterized two pairs of enhancer elements, E1 and E2, in the type II collagen alpha 1 chain (COL2A1) gene. Subsequent studies have suggested that these enhancers function differently in the regulation of gene expression. For example, histone deacetylase 10 modifies only the E2 enhancer region to affect gene expression. Therefore, in this study, we aimed to clarify the transcriptional complex formed at each enhancer region by identifying transcription factors that specifically bind to each enhancer element. To this end, we used chondrocytic cell lines established using our unique silent reporter system and overexpressed candidate transcription factors in these cells. We found two transcription factors, other than the SOX trio, that directly bound to COL2A1 and regulated its expression. The first was Kruppel-like factor-4 (KLF4), which bound to the promoter proximal region, and the second was AT-rich interactive domain 5B (ARID5B) which bound to the E1 enhancer element. Further studies are needed to identify factors that specifically bind to the E2 enhancer element. In any case, our findings provide an important insight into the molecular mechanisms underlying the regulation of COL2A1. In this paper, we reevaluated the previous analysis of transcription factors involved in the regulation of COL2A1 expression.

Therapeutic potential of hyaluronic acid/chitosan nanoparticles for the delivery of curcuminoid in knee osteoarthritis and an in vitro evaluation in chondrocytes

Knee osteoarthritis (OA) is the main cause of leg pain in middle-aged and elderly individuals. Hyaluronic acid (HA), as well as curcuminoid, has been used in the treatment of knee OA. In the present study, HA/chitosan nanoparticles (CNPs) were prepared for the delivery of curcuminoid, in order to investigate whether HA and curcuminoid can act synergistically as a better treatment option. The knee OA model was established by the Hulth method, and a knee OA chondrocyte model was constructed by the co-induction of interleukin-1β and tumor necrosis factor (TNF)-α. The drug loading capacity of HA/CNP for the delivery of curcuminoid was measured by an ultraviolet assay, and the cytotoxicity to chondrocytes was measured by an MTT assay. Collagen II was detected by immunofluorescence, and the expression levels of nuclear factor (NF)-κB and inflammation-related genes in cartilage tissue and chondrocytes were detected. Chondrocyte proliferation was determined by an EdU assay, and chondrocyte apoptosis was determined by flow cytometry. The Mankin pathological score of the Outerbridge classification was obtained. The results demonstrated that the optimum drug loading capacity of HA/CNP for the delivery of curcuminoid was 38.44%, with a good sustained release function. HA/CNP treatment resulted in inhibition of the NF-κB pathway, as well as the expression of matrix metalloproteinase (MMP)-1 and MMP-13, but it increased collagen II expression. HA/CNP for the delivery of curcuminoid significantly decreased the Outerbridge classification and Mankin pathological scores to close to normal until the 4th week. Furthermore, it was also observed that all the effects of HA/CNP on the delivery of curcuminoid were more prominent compared with the effects of HA or curcuminoid treatment individually. Taken together, these findings demonstrated that HA/CNP for the delivery of curcuminoid may suppress inflammation and chondrocyte apoptosis in knee OA via repression of the NF-κB pathway.