RFX1-mediated CCN3 induction that may support chondrocyte survival under starved conditions

RFX1 regulates foam cell formation and atherosclerosis by mediating CD36 expression

BACKGROUND AND AIMS

Atherosclerosis (AS) is a continuously low-grade inflammatory disease, and monocyte-derived macrophages play a vital role in AS pathogenesis. Regulatory factor X1 (RFX1) has been reported to participate in differentiation of various cells. Our previous report showed that RFX1 expression in CD14+ monocytes from AS patients was decreased and closely related to AS development. Macrophages mostly derive from monocytes and play an important role in AS plaque formation and stability. However, the functions of RFX1 in the formation of macrophage-derived foam cells and consequent AS development are unclear.

METHODS

We explored the effects of RFX1 on oxidation low lipoprotein (ox-LDL)-stimulated foam cell formation and CD36 expression by increasing or silencing Rfx1 expression in mouse peritoneal macrophages (PMAs). The ApoE-/-Rfx1f/f or ApoE-/-Rfx1f/f Lyz2-Cre mice fed a high-fat diet for 24 weeks were used to further examine the effect of RFX1 on AS pathogenesis. We then performed dual luciferase reporter assays to study the regulation of RFX1 for CD36 transcription.

RESULTS

Our results demonstrate that RFX1 expression was significantly reduced in ox-LDL induced foam cells and negatively correlated with lipid uptake in macrophages. Besides, Rfx1 deficiency in myeloid cells aggravated atherosclerotic lesions in ApoE-/- mice. Mechanistically, RFX1 inhibited CD36 expression by directly regulating CD36 transcription in macrophages.

CONCLUSIONS

The reduction of RFX1 expression in macrophages is a vital determinant for foam cell formation and the initiation of AS, proving a potential novel approach for the treatment of AS disease.

CCN3/NOV inhibition attenuates oxidative stress-induced apoptosis of mouse neural stem/progenitor cells by blocking the activation of p38 MAPK: An in vitro study

Neural stem/progenitor cells (NSPCs) hold immense promise in clinical applications, yet the harsh conditions resulting from central nervous system (CNS) injuries, particularly oxidative stress, lead to the demise of both native and transplanted NSPCs. Cellular communication network factor 3 (CCN3) exhibits a protective effect against oxidative stress in various cell types. This study investigates the impact of CCN3 on NSPCs apoptosis induced by oxidative stress. To establish models of primary cultured mouse NSPCs under oxidative stress, we exposed them to 50 μM H2O2 for 4 h. Remarkably, pre-exposing CCN3 exacerbated the H2O2-induced decline in cell viability in a concentration-dependent manner. However, employing gene-targeted siRNA to inhibit CCN3 protected NSPCs against H2O2-induced cell death. Conversely, CCN3 replenishment reversed this protective effect, as evidenced by TUNEL staining, the ratio of Cleaved-caspase-3 to Pro-caspase-3, and Bcl-2/Bax. Further investigations revealed that CCN3 pretreatment increased the phosphorylation level of p38 MAPK, while silencing CCN3 diminished p38 MAPK activation. Ultimately, the impact of changes in CCN3 protein expression on H2O2-induced apoptosis was nullified using anisomycin (a p38 activator) and SB 203580 (a p38 inhibitor). Our findings suggest that CCN3 inhibition prevents H2O2-induced cell death in cultured mouse NSPCs via the p38 pathway. These discoveries may contribute to the development of strategies aimed at enhancing the survival of both endogenous and transplanted NSPCs following CNS oxidative stress insults.

The advance of CCN3 in fibrosis

The extracellular matrix (ECM) is comprised of various extracellular macromolecules, including collagen, enzymes, and glycoproteins, which offer structural and biochemical support to neighboring cells. After tissue injury, extracellular matrix proteins deposit in the damaged tissue to promote tissue healing. However, an imbalance between ECM production and degradation can result in excessive deposition, leading to fibrosis and subsequent organ dysfunction. Acting as a regulatory protein within the extracellular matrix, CCN3 plays a crucial role in numerous biological processes, such as cell proliferation, angiogenesis, tumorigenesis, and wound healing. Many studies have demonstrated that CCN3 can reduce the production of ECM in tissues through diverse mechanisms thereby exerting an inhibitory effect on fibrosis. Consequently, CCN3 emerges as a promising therapeutic target for ameliorating fibrosis.

Do not overwork: cellular communication network factor 3 for life in cartilage

Cellular communication network factor (CCN) 3, which is one of the founding members of the CCN family, displays diverse functions. However, this protein generally represses the proliferation of a variety of cells. Along with skeletal development, CCN3 is produced in cartilaginous anlagen, growth plate cartilage and epiphysial cartilage. Interestingly, CCN3 is drastically induced in the growth plates of mice lacking CCN2, which promotes endochondral ossification. Notably, chondrocytes in these mutant mice with elevated CCN3 production also suffer from impaired glycolysis and energy metabolism, suggesting a critical role of CCN3 in cartilage metabolism. Recently, CCN3 was found to be strongly induced by impaired glycolysis, and in our study, we located an enhancer that mediated CCN3 regulation via starvation. Subsequent investigations specified regulatory factor binding to the X-box 1 (RFX1) as a transcription factor mediating this CCN3 regulation. Impaired glycolysis is a serious problem, resulting in an energy shortage in cartilage without vasculature. CCN3 produced under such starved conditions restricts energy consumption by repressing cell proliferation, leading chondrocytes to quiescence and survival. This CCN3 regulatory system is indicated to play an important role in articular cartilage maintenance, as well as in skeletal development. Furthermore, CCN3 continues to regulate cartilage metabolism even during the aging process, probably utilizing this regulatory system. Altogether, CCN3 seems to prevent "overwork" by chondrocytes to ensure their sustainable life in cartilage by sensing energy metabolism. Similar roles are suspected to exist in relation to systemic metabolism, since CCN3 is found in the bloodstream.

Cellular Fluorescence Imaging for the Evaluation of Bioactivity of CCN Family Proteins

The method of labeling proteins of interest with fluorescent dyes that can specifically stain organelles in living cells provides a tool for investigating various cellular processes under a microscope. Visualization (imaging) of the cells using fluorescence has many advantages, including the ability to stain multiple cell organelles and intracellular proteins simultaneously and discriminately, and is used in many research fields. In this chapter, we describe the observation of cell organelles using fluorescence staining to analyze the functions of CCN family proteins involved in various cellular events.

Elevated Expression of CCN3 in Articular Cartilage Induces Osteoarthritis in Hip Joints Irrespective of Age and Weight Bearing

Osteoarthritis (OA) occurs not only in the knee but also in peripheral joints throughout the whole body. Previously, we have shown that the expression of cellular communication network factor 3 (CCN3), a matricellular protein, increases with age in knee articular cartilage, and the misexpression of CCN3 in cartilage induces senescence-associated secretory phenotype (SASP) factors, indicating that CCN3 promotes cartilage senescence. Here, we investigated the correlation between CCN3 expression and OA degenerative changes, principally in human femoral head cartilage. Human femoral heads obtained from patients who received total hip arthroplasty were categorized into OA and femoral neck fracture (normal) groups without significant age differences. Gene expression analysis of RNA obtained from femoral head cartilage revealed that CCN3 and MMP-13 expression in the non-weight-bearing part was significantly higher in the OA group than in the normal group, whereas the weight-bearing OA parts and normal cartilage showed no significant differences in the expression of these genes. The expression of COL10A1, however, was significantly higher in weight-bearing OA parts compared with normal weight-bearing parts, and was also higher in weight-bearing parts compared with non-weight-bearing parts in the OA group. In contrast, OA primary chondrocytes from weight-bearing parts showed higher expression of CCN3, p16, ADAMTS4, and IL-1β than chondrocytes from the corresponding normal group, and higher ADAMTS4 and IL-1β in the non-weight-bearing part compared with the corresponding normal group. Acan expression was significantly lower in the non-weight-bearing group in OA primary chondrocytes than in the corresponding normal chondrocytes. The expression level of CCN3 did not show significant differences between the weight-bearing part and non-weight-bearing part in both OA and normal primary chondrocytes. Immunohistochemical analysis showed accumulated CCN3 and aggrecan neoepitope staining in both the weight-bearing part and non-weight-bearing part in the OA group compared with the normal group. The CCN3 expression level in cartilage had a positive correlation with the Mankin score. X-ray analysis of cartilage-specific CCN3 overexpression mice (Tg) revealed deformation of the femoral and humeral head in the early stage, and immunohistochemical analysis showed accumulated aggrecan neoepitope staining as well as CCN3 staining and the roughening of the joint surface in Tg femoral and humeral heads. Primary chondrocytes from the Tg femoral head showed enhanced expression of Ccn3, Adamts5, p16, Il-6, and Tnfα, and decreased expression of Col2a1 and -an. These findings indicate a correlation between OA degenerative changes and the expression of CCN3, irrespective of age and mechanical loading. Furthermore, the Mankin score indicates that the expression level of Ccn3 correlates with the progression of OA.

Molecular and Genetic Interactions between CCN2 and CCN3 behind Their Yin-Yang Collaboration

Cellular communication network factor (CCN) 2 and 3 are the members of the CCN family that conduct the harmonized development of a variety of tissues and organs under interaction with multiple biomolecules in the microenvironment. Despite their striking structural similarities, these two members show contrastive molecular functions as well as temporospatial emergence in living tissues. Typically, CCN2 promotes cell growth, whereas CCN3 restrains it. Where CCN2 is produced, CCN3 disappears. Nevertheless, these two proteins collaborate together to execute their mission in a yin–yang fashion. The apparent functional counteractions of CCN2 and CCN3 can be ascribed to their direct molecular interaction and interference over the cofactors that are shared by the two. Recent studies have revealed the mutual negative regulation systems between CCN2 and CCN3. Moreover, the simultaneous and bidirectional regulatory system of CCN2 and CCN3 is also being clarified. It is of particular note that these regulations were found to be closely associated with glycolysis, a fundamental procedure of energy metabolism. Here, the molecular interplay and metabolic gene regulation that enable the yin–yang collaboration of CCN2 and CCN3 typically found in cartilage development/regeneration and fibrosis are described.

Dynamic nucleosome organization after fertilization reveals regulatory factors for mouse zygotic genome activation

Chromatin remodeling is essential for epigenome reprogramming after fertilization. However, the underlying mechanisms of chromatin remodeling remain to be explored. Here, we investigated the dynamic changes in nucleosome occupancy and positioning in pronucleus-stage zygotes using ultra low-input MNase-seq. We observed distinct features of inheritance and reconstruction of nucleosome positioning in both paternal and maternal genomes. Genome-wide de novo nucleosome occupancy in the paternal genome was observed as early as 1 h after the injection of sperm into ooplasm. The nucleosome positioning pattern was continually rebuilt to form nucleosome-depleted regions (NDRs) at promoters and transcription factor (TF) binding sites with differential dynamics in paternal and maternal genomes. NDRs formed more quickly on the promoters of genes involved in zygotic genome activation (ZGA), and this formation is closely linked to histone acetylation, but not transcription elongation or DNA replication. Importantly, we found that NDR establishment on the binding motifs of specific TFs might be associated with their potential pioneer functions in ZGA. Further investigations suggested that the predicted factors MLX and RFX1 played important roles in regulating minor and major ZGA, respectively. Our data not only elucidate the nucleosome positioning dynamics in both male and female pronuclei following fertilization, but also provide an efficient method for identifying key transcription regulators during development.

Cellular communication network factor 3 in cartilage development and maintenance

Cellular communication network factor (CCN) 3 is one of the classical members of the CCN family, which are characterized by common molecular structures and multiple functionalities. Although this protein was discovered as a gene product overexpressed in a truncated form in nephroblastoma, recent studies have revealed its physiological roles in the development and homeostasis of mammalian species, in addition to its pathological association with a number of diseases. Cartilage is a tissue that creates most of the bony parts and cartilaginous tissues that constitute the human skeleton, in which CCN3 is also differentially produced to exert its molecular missions therein. In this review article, after the summary of the molecular structure and function of CCN3, recent findings on the regulation of ccn3 expression and the roles of CCN3 in endochondral ossification, cartilage development, maintenance and disorders are introduced with an emphasis on the metabolic regulation and function of this matricellular multifunctional molecule.