Increasing evidence has indicated that microRNAs (miRNAs/miRs) are associated with tumorigenesis and the development of numerous cancer types. Previous studies have suggested miRNA-491-5p is downregulated in osteosarcoma (OS) and functions as a tumor suppressor. However, the biological roles and underlying mechanisms associated with miR-491-5p function in OS require further exploration. In the present study, it was demonstrated by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) that miR-491-5p was downregulated in 36 pairs of OS tissues, compared with in adjacent normal bone tissues. Furthermore, CCK-8 and colony formation assays indicated that miR-491-5p mimics suppressed OS cell proliferation. However, an miR-491-5p inhibitor enhanced cell proliferation. In addition, luciferase reporter assays, RT-qPCR and western blot analysis demonstrated that PKM2 was a direct target of miR-491-5p. The miR-491-5p mimic inhibited the mRNA and protein expression of PKM2, while the miR-491-5p inhibitor promoted PKM2 mRNA and protein expression. In addition, PKM2 overexpression reversed the proliferation-inhibiting effects of miR-491-5p in OS cells. Therefore, these results indicated that miR-491-5p serves as a tumor suppressor in OS cells, which may be important in OS treatment.

Slow growth and rapid loss of chondrogenic phenotypes are the major problems affecting chronic cartilage lesions. The role of microRNA-195 (miR-195) and its detailed working mechanism in the fore-mentioned process remains unknown. Fibroblastic growth factor 18 (FGF-18) plays a key role in cartilage homeostasis; whether miR-195 could regulate FGF-18 and its downstream signal pathway in chondrocyte proliferation and maintenance of chondrogenic phenotypes still remains unclear. The present research shows elevated miR-195 but depressed FGF-18 expressed in joint fluid specimens of 20 patients with chronic cartilage lesions and in CH1M and CH3M chondrocytes when compared with that in joint fluid specimens without cartilage lesions and in CH1W and CH2W chondrocytes, respectively. The following loss of function test revealed that downregulation of miR-195 by transfection of miR-195 inhibitors promoted chondrocyte proliferation and expression of a type II collagen α I chain (Col2a1)/aggrecan. Through the online informatics analysis we theoretically predicted that miR-195 could bind to a FGF-18 3′ untranslated region (3′UTR), also, we verified that a miR-195 could regulate the FGF-18 and its downstream pathway. The constructed dual luciferase assay further confirmed that FGF-18 was a direct target of miR-195. The executed anti-sense experiment displayed that miR-195 could regulate chondrocyte proliferation and Col2a1/aggrecan expression via the FGF-18 pathway. Finally, through an in vivo anterior cruciate ligament transection (ACLT) model, downregulation of miR-195 presented a significantly protective effect on chronic cartilage lesions. Evaluating all of the outcomes of the current research revealed that a decrease of miR-195 protected chronic cartilage lesions by promoting chondrocyte proliferation and maintenance of chondrogenic phenotypes via the targeting of the FGF-18 pathway and that the miR-195/FGF-18 axis could be a potential target in the treatment of cartilage lesions.

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