Development of a new co-culture system, the "separable-close co-culture system," to enhance stem-cell-to-chondrocyte differentiation

Use of 2D and co-culture cell models to assess the toxicity of zein nanoparticles loading insect repellents icaridin and geraniol

After the latest dengue and Zika outbreaks, the fight against mosquito vectors has become an emerging area of research. One tool for this combat is repellents; however, these products are composed of different toxic agents. Botanical compounds with repellent potential are an alternative; however these compounds are highly volatile. Thus, the present study aimed to synthesize zein-based polymeric nanoparticles as an efficient carrier system for the sustained release of the repellents icaridin and geraniol and evaluate the toxicity of these nanorepellents comparing two different cell models. In vitro tests were carried out due to current Brazilian legislation prohibiting animal testing for cosmetics (current classification of repellents). The cytotoxicity and genotoxicity of the nanoparticles were evaluated in 2D and co-culture cell models (A549/lung epithelium, HaCaT/keratinocytes, HT-29/intestinal epithelium, and THP-1/peripheral blood monocytes). Cell viability by mitochondrial activity, cell membrane integrity, damage to genetic material, and expression of genes involved in the allergic/inflammatory system were evaluated. The results of cytotoxicity evaluation showed cell viability above 70% in both cell models. No differences were observed in genotoxicity assessment between cells exposed to nanorepellents and controls. In contrast, gene expression analysis showed increased cytokine expression for the emulsion compounds in 2D cell cultures compared to co-cultures. These findings open perspectives that zein-based nanorepellents have potential applications due to the reduced toxicity observed when the compounds are encapsulated and emerge as an alternative for arbovirus control. In addition, the study demonstrated that depending on the analysis, different results might be observed when comparing 2D and co-culture cell models to evaluate the toxicity of new nanosystems.

Chasing Chimeras - The elusive stable chondrogenic phenotype

The choice of the best-suited cell population for the regeneration of damaged or diseased cartilage depends on the effectiveness of culture conditions (e.g. media supplements, three-dimensional scaffolds, mechanical stimulation, oxygen tension, co-culture systems) to induce stable chondrogenic phenotype. Herein, advances and shortfalls in in vitro, preclinical and clinical setting of various in vitro microenvironment modulators on maintaining chondrocyte phenotype or directing stem cells towards chondrogenic lineage are critically discussed. Chondrocytes possess low isolation efficiency, limited proliferative potential and rapid phenotypic drift in culture. Mesenchymal stem cells are relatively readily available, possess high proliferation potential, exhibit great chondrogenic differentiation capacity, but they tend to acquire a hypertrophic phenotype when exposed to chondrogenic stimuli. Embryonic and induced pluripotent stem cells, despite their promising in vitro and preclinical data, are still under-investigated. Although a stable chondrogenic phenotype remains elusive, recent advances in in vitro microenvironment modulators are likely to develop clinically- and commercially-relevant therapies in the years to come.

The trans-well coculture of human synovial mesenchymal stem cells with chondrocytes leads to self-organization, chondrogenic differentiation, and secretion of TGFβ

Background

Synovial mesenchymal stem cells (SMSC) possess a high chondrogenic differentiation potential, which possibly supports natural and surgically induced healing of cartilage lesions. We hypothesized enhanced chondrogenesis of SMSC caused by the vicinity of chondrocytes (CHDR).

Methods

Human SMSC and CHDR interactions were investigated in an in-vitro trans-well monolayer coculture over a time period of up to 21 days. Protein expression was analyzed using histology, immunostaining, or enzyme-linked immunosorbent assay. Additionally, mRNA expression was assessed by quantitative PCR.

Results

After 7 days, phase-contrast microscopy revealed cell aggregation of SMSC in coculture with CHDR. Afterwards, cells formed spheres and lost adherence. However, this phenomenon was not observed when culturing SMSC alone. Fluorescence labeling showed concurrent collagen type II expression. Addition of transforming growth factor beta (TGFβ) to the cocultures induced SMSC aggregation in less time and with higher intensity. Additionally, alcian blue staining demonstrated enhanced glycosaminoglycan expression around SMSC aggregates after 1 and 2 weeks. Although TGFβ mRNA was expressed in all SMSC, the protein was measured with constantly increasing levels over 21 days only in supernatants of the cocultures. Considering the enhanced mRNA levels following supplementation with TGFβ, a positive feedback mechanism can be supposed. In line with the development of a chondrogenic phenotype, aggrecan mRNA expression increased after 7 and 14 days in the cocultures with and without TGFβ. Coculture conditions also amplified collagen type II mRNA expression after 2 weeks without and already after 1 week with TGFβ. There was no difference in collagen type I and type X expression between SMSC alone and the coculture with CHDR. Expression of both collagens increased following addition of TGFβ. mRNA data correlated with the intensity of immunofluorescence staining.

Conclusions

Paracrine effects of CHDR induce a chondrogenic phenotype in SMSC possibly mimicking joint homeostasis. Coculture approaches may lead to a better understanding of cellular interactions with potential implications for cartilage repair procedures.

Hypoxia enhances tenocyte differentiation of adipose-derived mesenchymal stem cells by inducing hypoxia-inducible factor-1α in a co-culture system

OBJECTIVES

Tissue engineering is a promising approach for repair of tendon injuries. Adipose-derived mesenchymal stem cells (ADMSCs) have gained increasing research interest for their potential in improving healing and regeneration of injured tendons. The present study aimed to investigate effects of O2 tension and potential signalling pathways on AMDSC differentiation into tenocytes, in an indirect co-culture system.

MATERIALS AND METHODS

Human ADMSCs were co-cultured under normoxia (20% O2 ) and also under hypoxia (2% O2 ). Tenocyte differentiation of AMDSCs and expression of hypoxia-inducible factor-1 (HIF-1α) were analysed by reverse transcription-PCR, Western blotting and immunohistochemistry. Furthermore, HIF-1α inhibitor and inducer (FG-4592) effects on differentiation of AMDSCs were studied using qPCR, immunofluorescence and Western blotting.

RESULTS

Indirect co-culture with tenocytes increased differentiation of ADMSCs into tenocytes; furthermore, hypoxia further enhanced tenocyte differentiation of AMDSCs, accompanied by increased expression of HIF-1α. HIF-1α inhibitor attenuated effects of hypoxia on differentiation of ADMSCs; in contrast, FG-4592 increased differentiation of ADMSCs under both hypoxia and normoxia.

CONCLUSIONS

Taken together, we found that growing ADMSCs under hypoxia, or activating expression of HIF-1α to be important in differentiation of ADMSCs, which provides a foundation for application of ADMSCs in vivo for tendon regeneration.