Rationale: Stem cells self-organize to form organoids that generate mini-organs that resemble the physiologically-developed ones. The mechanism by which the stem cells acquire the initial potential for generating mini-organs remains elusive. Here we used skin organoids as an example to study how mechanical force drives initial epidermal-dermal interaction which potentiates skin organoids to regenerate hair follicles. Methods: Live imaging analysis, single-cell RNA-sequencing analysis, and immunofluorescence were used to analyze the contractile force of dermal cells in skin organoids. Bulk RNA-sequencing analysis, calcium probe detection, and functional perturbations were used to verify that calcium signaling pathways respond to the contractile force of dermal cells. In vitro mechanical loading experiment was used to prove that the stretching force triggers the epidermal Piezo1 expression which negatively regulates dermal cell attachment. Transplantation assay was used to test the regenerative ability of skin organoids. Results: We found that dermal cell-derived contraction force drives the movement of dermal cells surrounding the epidermal aggregates to trigger initial mesenchymal-epithelial interaction (MEI). In response to dermal cell contraction force, the arrangement of the dermal cytoskeleton was negatively regulated by the calcium signaling pathway which further influences dermal-epidermal attachment. The native contraction force generated from the dermal cell movement exerts a stretching force on the adjacent epidermal cells, activating the stretching force sensor Piezo1 in the epidermal basal cells during organoid culture. Epidermal Piezo1 in turn drives strong MEI to negatively regulate dermal cell attachment. Proper initial MEI by mechanical-chemical coupling during organoid culture is required for hair regeneration upon transplantation of the skin organoids into the back of the nude mice. Conclusion: Our study demonstrated that mechanical-chemical cascade drives the initial event of MEI during skin organoid development, which is fundamental to the organoid, developmental, and regenerative biology fields.
In the transforming growth factor-β(TGF-β) superfamily, bone morphogenetic proteins (BMPs) are one of the largest subfamily, among which BMP-2 and BMP-4 are the most powerful molecules in biological activities. They have been shown to be involved in follicle development of ovary in mammals. However, whether these factors are involved in folliculogenesis in rabbit is still unknown. This study was performed to determine the relationships between ovarian development and the expression of BMP (BMP-2,-4) mRNAs in rabbit. Ovaries were removed from different development stages of rabbits (30-, 60-, 120-, 180-day age and 6-day encyesis), and method of RT-PCR was used for the cloning. The relative transcript levels of BMP-2,-4 genes were measured by real-time quantitative PCR, with GAPDH as an internal control. Known from the results, the BMP-2,-4 genes showed similar but also different expression patterns during ovarian development; they both increased significantly (p < 0.05) in the ovary on 60-day compared with 120-day and 6-day encyesis, and the expression of BMP-2 was always higher than that of BMP-4. The expression law of BMP-2,-4 genes presented in this study may lay the theoretical foundation for the study of BMPs' biological function.
Background Heterotopic ossification (HO) refers to a painful and complex disease. Adenosine triphosphate (ATP), as a key modulator of inflammation, is verified to promote the development of HO. However, the mechanism remains to be illustrated. The ionotropic P2X7 receptor (P2X7R) is an ATP-gated ion channel expressed in the majority of stem cells. Here, this paper hypothesizes that P2X7R may be activated by extracellular ATP and promote osteogenesis of stem cells under inflammatory condition, ending up in the formation of ectopic bone. Methods The tenotomy puncture and burn injury-induced HO model was constructed. The expression of P2X7R was found increasing at the site of injured Achilles tendon where HO occurs. Mesenchymal stem cells (MSCs) were cultivated under an inflammatory condition plus Bz-ATP treatment which mimicked a microenvironment of HO site. An induction in P2X7R expression was also observed along with an enhancement of osteogenesis. In addition, an inhibition of P2X7R expression by its specific antagonist successfully reversed the above process. Results P2X7R expression of the Achilles tendon and osteogenic capability of SCs is higher in HOG than in other two groups. Bz-ATP promoted osteogenesis under inflammation condition. BBG impeded the heterotopic bone formation in animal model. Conclusions P2X7R is a crucial mediator in ATP-signaling promotion of HO, blocking which may represent a potential therapeutic target for HO.
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