Search

The reduced oxygen concentration is a distinctive feature of osteoarthritic (OA) cartilage, whereas the mechanical friction also contributes to the inflammatory hypoxia microenvironment of OA. Herein, novel hypoxia-responsive methylprednisolone (MP) delivery microgels combining the capability of reactive oxygen species (ROS)-depletion and lubrication were constructed for regulating the microenvironment of OA. Methacrylate-modified sulfonated azocalix[4] arene (MACA) loaded with MP, the copolymers consisting of bioinspired lubricant 2-methacryloxyethyl phosphorylcholine (MPC), and polyethylene glycol-modified ROS-responsive poly(thioketal) (PEG-4PTK) were crosslinked together to construct the microgels. The zwitterionic MPC offered a lubrication effect, while the ROS-elimination was contributed by the PTK segments and the phenol groups in MACA. The microgels responsively released cargos in inflammatory environment and decreased inflammation by inhibiting the production of ROS and regulating the expression of inflammatory cytokines, and showed the lowest hypoxia-inducible factor-1α (HIF-1α) positive area and presented more deposition of glycosaminoglycans and collagen II with a smoother and integrated cartilage structure in therapy of OA in rats in vivo. [Display omitted] ● Stimuli-responsive microgels deliver anti-inflammatory and immunomodulator in response to hypoxia. ● The microgels have very low viscosity and can be precisely delivered with the clinical convenience. ● The microgels dissipate stress, and sensitively respond to the physiological stimuli of inflammatory factors, ROS and hypoxia. ● The microgels improve intra-articular lubrication and ROS-elimination to adaptively regulate the inflammation of OA. [ABSTRACT FROM AUTHOR]

Transcriptional activity of the hypoxia inducible factor (HIF) relies on the formation of a heterodimer composed of an oxygen-regulated α-subunit and a stably expressed β-subunit. Heterodimeric HIF activates expression by binding to RCGTG motifs within promoters of hypoxia-activated genes. Some hypoxia targets also possess an adjacent HIF ancillary sequence (HAS) reported to increase transcription but whose function remains obscure. Here, we investigate the contribution of the HAS element to the hypoxia response and its mechanism of action, using the HAS-containing prolyl 4-hydroxylase subunit α1 (P4HA1) as a gene model in NIH/3T3 mouse embryonic fibroblasts and HEK293 human embryonic kidney cells. Our HIF overexpression experiments demonstrate that the HAS motif is essential for full induction by hypoxia and that the presence of the tandem HAS/HIF, as opposed to HIF-only sequences, provides HIF proteins with the capacity to form complexes of stoichiometry beyond the classical heterodimer, likely tetramers, to cooperatively potentiate hypoxia-induced transcription. We also provide evidence of the crucial role played by the Fα helix of the PAS-B domain of the HIF1β subunit to support the interaction between heterodimers. Functional analysis showed that human genes containing the HAS/HIF motifs are better responders to hypoxia, and their promoters are enriched for specific transcription factor binding sites. Gene ontology enrichment revealed a predominance of HAS/HIF in genes primarily related to tissue formation and development. Our findings add an extra level of regulation of the hypoxia/HIF signaling through multimerization of HIF proteins on regulatory elements containing the HAS/HIF motifs. [Display omitted] • The HAS (HIF ancillary sequence) is essential for full induction by hypoxia. • HIFα/β heterodimers associate forming tetramers on HAS/HIF sequences. • The Fα helix of HIF1β PAS-B domain supports the interaction between heterodimers. • HAS/HIF-containing genes are better responders to hypoxia. • HAS/HIF-containing genes are primarily related to tissue formation and development. [ABSTRACT FROM AUTHOR]