Evaluation of reference genes for human chondrocytes cultured in several different thermal environments

Periodic mild heat stimuli diminish extracellular matrix synthesis in pellet cultured human chondrocytes

Objective

This study aimed to clarify the effects of periodic mild heat stimuli on extracellular matrix (ECM) synthesis of adult human chondrocytes in 3-dimensional pellet culture.

Results

Human articular chondrocytes were subjected to pellet culture at 37 °C for 3 days. Thereafter, the pellets were divided into three groups: 32 °C group which was cultured at 32 °C without heat stimuli, 32 °C + Heat group which was cultured at 32 °C and applied periodic heat stimuli, 37 °C group which was cultured at 37 °C. Heat stimuli were given by transferring the pellets into a CO₂ incubator set at 41 °C for 20 min/day, 6 times/week. ECM synthesis ability was evaluated by analyzing the mRNA expressions. Additionally, the collagen and proteoglycan content in the pellet was quantified. DNA content was also measured for estimating the cell amount. We found that there were no significant differences in the mRNA expression of COL2A1, COL1A1, and ACAN between the 32 °C group and 32 °C + Heat group. However, the collagen content per cell and DNA content were significantly lower in the 32 °C + Heat group compared to other groups. Our results indicate that periodic mild heat stimuli may diminish ECM synthesis due to inhibition of collagen production and loss of cells.

Electronic supplementary material

The online version of this article (10.1186/s13104-019-4058-x) contains supplementary material, which is available to authorized users.

Gene expression profiles and molecular mechanism of cultured human chondrocytes' exposure to T-2 toxin and deoxynivalenol

T-2 toxin and deoxynivalenol (DON) are secondary metabolites produced by Fusarium fungi and are commonly found on food and feed. Although T-2 toxin and DON have been suggested as the etiology of Kashin-Beck disease (KBD), an endemic osteochondropathy, little is known about the mechanism when human chondrocytes are exposed to T-2 toxin and DON. The purpose of this study is to identify the gene expression differences and underlying molecular changes modulated by T-2 toxin and DON in vitro in human chondrocytes. After the experiments of cell viability, the gene expression profiles were analyzed in cells that were treated with 0.01 μg/ml T-2 toxin and 1.0 μg/ml DON for 72 h by Affymetrix Human Gene Chip. The array results showed that 882 and 2118 genes were differentially expressed for T-2 toxin and DON exposure, respectively. Enrichment analysis revealed that diverse cellular processes including DNA damage, cell cycle regulation and metabolism of extracellular matrix were affected when human chondrocytes were exposed to T-2 toxin and DON. These results demonstrate the gene expression differences and molecular mechanism of cultured human chondrocytes exposure to T-2 toxin and DON, and provide a new insight into future research in the etiology of KBD.

Serum availability affects expression of common house-keeping genes in colon adenocarcinoma cell lines: implications for quantitative real-time PCR studies

Careful selection of housekeeping genes (HKG) is prerequisite to yield sound qPCR results. HKG expression varies in response to hypoxia but the effect of manipulations of serum availability, a common experimental procedure, remains unknown. Also, no data on HKG expression stability across colon adenocarcinoma lines that would aid selection of normalizers suitable for studies involving several lines are available. Thus, we evaluated the effect of serum availability on the expression of commonly used HKG (ACTB, B2M, GAPDH, GUSB, HPRT1, IPO8, MRPL19, PGK1, PPIA, RPLP0, RPS23, SDHA, TBP, UBC, and YWHAZ) in seven colon adenocarcinoma cell lines (Caco-2, DLD-1, HCT116, HT29, Lovo, SW480, and SW620). Sets of stably expressed line-specific and pan-line HKG were validated against absolutely quantified CDKN1A, TP53, and MDK transcripts. Both serum availability and line type affected HKG expression. UBC was fourfold down-regulated and HPRT1 1.75-fold up-regulated in re-fed HT29 cultures. Line-to-line variability in HKG expression was more pronounced than that caused by altering serum availability and could be found even between isogenic cell lines. PPIA, RPLP0, YWHAZ, and IPO8 were repeatedly highly ranked while ACTB, B2M, UBC, and PGK1 were ranked poorly. Normalization against PPIA/RPLP0/SDHA was found optimal for studies involving various colon adenocarcinoma cell lines subjected to manipulations of serum availability. We found HKG expression to vary, more pronouncedly by line type than growth conditions with significant differences also between isogenic cell lines. Although using line-specific normalizers remains optimal, a set of pan-line HKG that yields good estimation of relative expression of target genes was proposed.

Culture temperature affects human chondrocyte messenger RNA expression in monolayer and pellet culture systems

Cell-based therapy has been explored for articular cartilage regeneration. Autologous chondrocyte implantation is a promising cell-based technique for repairing articular cartilage defects. However, there are several issues such as chondrocyte de-differentiation. While numerous studies have been designed to overcome some of these issues, only a few have focused on the thermal environment that can affect chondrocyte metabolism and phenotype. In this study, the effects of different culture temperatures on human chondrocyte metabolism- and phenotype-related gene expression were investigated in 2D and 3D environments. Human chondrocytes were cultured in a monolayer or in a pellet culture system at three different culture temperatures (32°C, 37°C, and 41°C) for 3 days. The results showed that the total RNA level, normalized to the threshold cycle value of internal reference genes, was higher at lower temperatures in both culture systems. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and citrate synthase (CS), which are involved in glycolysis and the citric acid cycle, respectively, were expressed at similar levels at 32°C and 37°C in pellet cultures, but the levels were significantly lower at 41°C. Expression of the chondrogenic markers, collagen type IIA1 (COL2A1) and aggrecan (ACAN), was higher at 37°C than at 32°C and 41°C in both culture systems. However, this phenomenon did not coincide with SRY (sex-determining region Y)-box 9 (SOX9), which is a fundamental transcription factor for chondrogenesis, indicating that a SOX9-independent pathway might be involved in this phenomenon. In conclusion, the expression of chondrocyte metabolism-related genes at 32°C was maintained or enhanced compared to that at 37°C. However, chondrogenesis-related genes were further induced at 37°C in both culture systems. Therefore, manipulating the culture temperature may be an advantageous approach for regulating human chondrocyte metabolic activity and chondrogenesis.

Culture temperature affects redifferentiation and cartilaginous extracellular matrix formation in dedifferentiated human chondrocytes

To date, there have been few studies on how temperature affects the phenotype and metabolism of human chondrocytes. Thus, the purpose of this study was to elucidate the effects of culture temperature on chondrocyte redifferentiation and extracellular matrix (ECM) formation using dedifferentiated mature human chondrocytes in vitro. Dedifferentiated chondrocytes were cultured in a pellet culture system for up to 21 days. The pellets were randomly divided into three groups with different culture temperature (32, 37, and 41°C). Chondrocyte redifferentiation and ECM formation were evaluated by wet weight, messenger ribonucleic acid (mRNA), histological, and biochemical analyses. The results showed that the wet weight and the mRNA expressions of collagen type II A1 and cartilage oligomeric matrix protein at 37°C were higher than the corresponding values at 32°C. The histological and biochemical analyses revealed that the syntheses of type II collagen and proteoglycan were promoted at 37°C compared to those at 32°C, whereas they were considerably inhibited at 41°C. In conclusion, the results obtained herein indicated that temperature affects chondrocyte redifferentiation and ECM formation, and modulation of temperature might thus represent an advantageous means to regulate the phenotype and biosynthetic activity of chondrocytes.