MicroRNAs are being considered as a novel type of bio-markers and potential therapeutic targets for various diseases. Diverse chemical tools are being developed for the detection or regulation of microRNAs with bio-medical implications. Chemical probes have been developed for use in combination with in situ signal amplification strategies to realize sensitive detection of microRNAs of low abundance. Regulation of microRNAs aberrantly expressed in tumours represents a new approach to cancer chemotherapy. Synthetic oligonucleotides including antisense oligonucleotides and microRNA mimics have been successfully delivered into cells or tissues to inhibit or enhance the function of specific endogenous microRNAs. Small-molecule modifiers of microRNAs that modify the expression or function of endogenous microRNAs are emerging not only as useful probes to explore microRNA-involved regulatory networks, but also as potential therapeutic reagents. In this tutorial review, we discuss the strategies developed by chemists in recent years for microRNA detection and regulation, with a focus on the potential of these chemical tools in microRNA-related biomedical applications.

Photodegradable hydrogels that allow 3D encapsulation of cells are important biomaterials to modulate cellular microenvironments with temporal and spatial resolution. Herein we report a photodegradable hydrogel formed by the self-assembly of short peptides modified with a novel phototrigger. The phototrigger is a biaryl-substituted tetrazole moiety that, upon mild light irradiation, undergoes rapid intramolecular photoclick ligation to form a highly fluorescent pyrazoline moiety. Short peptides linked with a tetrazole-containing moiety, Tet(I) or Tet(II), are able to self-assemble into hydrogels, among which the Tet(I)-GFF and Tet(II)-GFRGD gels show good mechanical strength and biocompatibility for 3D encapsulation and prolonged culture of live cells. The phototriggered tetrazole-to-pyrazoline transformation generates a highly fluorescent reporter and induces the disassembly of the hydrogel matrix by disturbing the balance between hydrophilic interaction and π-π stacking of the self-assembled system. Photomodulation of cellular microenvironments was demonstrated not only for the cells grown on top of the gel but also for stem cells encapsulated inside the hydrogels.

Myogenic microRNAs (myomiRs) that are specifically expressed in cardiac and skeletal muscle are highly relevant to myogenic development and diseases. Discovery and elucidation of unknown myomiRs-involved regulatory pathways in muscle cells are important, but challenging due to the lack of proper molecular tools. We report here a miR-221/222-myoD-myomiRs regulatory pathway revealed by using a small-molecule probe that selectively inhibits myomiRs including miR-1, miR-133a, and miR-206. The small-molecule inhibitor screened from luciferase assay systems was found to inhibit myomiRs and differentiation of C2C12 cells. Using the small molecule as a probe, we found that the transcriptional factor myoD, which is upstream of myomiRs, was further regulated by miR-221/222. This miR-221/222-myoD-myomiRs regulatory pathway was confirmed by over-expressing or knockdown miR-221/222 in muscle cells, which respectively led to the inhibition or enhancement of myoD protein expression and subsequent downregulation or upregulation of myomiR expression.

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