Tantawy, M. | bioRxiv Science

bioRxiv2025

A Novel Proteoglycan-4 Isoform Drives Skeletal Regeneration

Proteoglycan 4 (PRG4) is an extracellular matrix protein best known for its lubricating role in articular cartilage. Using a murine model of tibial fracture, we performed RNA-seq across multiple post-fracture timepoints and observed high Prg4 expression during the first week of healing, coinciding with the initial inflammatory phase. Single-cell RNA-seq of the fracture callus localized Prg4 expression to a stem cell population with key roles in repair. Analysis of alternative splicing in callus RNA identified a unique Prg4 isoform lacking three coding exons (hereafter termed Prg4-S). In vivo knockdown of Prg4-S using locally delivered siRNA produced multiple defects that culminated in impaired bone formation. Together, these findings uncover an unanticipated osteogenic role for a unique Prg4 splicing isoform and highlight its potential for translational applications.

molecular biology↗

bioRxiv2021

Itaconate and derivatives reduce interferon responses and inflammation in influenza A infection

Itaconate has recently emerged as a metabolite with immunomodulatory properties. We evaluated effects of endogenous itaconate and exogenous itaconate, dimethyl-, and 4-octyl-itaconate on host responses to influenza A virus infection. Infection induced ACOD1 (the enzyme catalyzing itaconate synthesis) mRNA in monocytes and macrophages, which correlated with viral replication and was abrogated by itaconate treatment. Pulmonary inflammation and weight loss were greater in Acod1-/- than wild-type mice, and ectopic synthesis of itaconate in human epithelial cells reduced infection-induced inflammation. The compounds induced different recruitment programs in infected human macrophages, and transcriptome profiling revealed that they reversed infection-triggered interferon responses and modulated inflammation in cell lines, PBMC, and lung tissue. Single-cell RNA sequencing of PBMC revealed that infection induced ACOD1 exclusively in monocytes, whereas treatment silenced IFN-responses in monocytes, lymphocytes, and NK cells. Viral replication did not increase under treatment despite the dramatically repressed IFN responses, but 4-octyl itaconate inhibited viral transcription in PBMC. The results reveal dramatic reprogramming of host responses by itaconate and derivatives and their potential as adjunct treatments for hyperinflammation in viral infection.

immunology↗