Ionizing radiation expands a p90RSK-activated patrolling monocyte subset: modulation by colchicine

Ionizing radiation (IR) is known to induce vascular injury and alter immune cell function, yet the molecular mechanisms driving these changes remain incompletely defined. In particular, the role of clonal hematopoiesis-associated proteins expression and stress-responsive signaling pathways in monocyte subsets has not been fully elucidated.

Peripheral blood mononuclear cells (PBMCs) from a single healthy human donor were pre-treated with colchicine and exposed to 2 Gy IR. After 24 h, cells were analyzed using CyTOF with a comprehensive antibody panel targeting lineage markers, DNA damage response proteins, efferocytosis receptors, and clonal hematopoiesis of indeterminate potential (CHIP) associated proteins, including DNMT3A and TET2. Data were processed using the Astrolabe platform to annotate canonical immune subsets.

While IR did not alter the overall immune cell frequency, colchicine increased the relative abundance of myeloid and B cell populations. Within CD14^-CD16⁺ monocytes, IR enhanced p90RSK activation despite reductions in proliferation and inflammatory signaling markers (e.g., Ki67, p-JAK, p-PKCζ). At the molecular level, IR reduced expression of CHIP associated proteins DNMT3A and TET2, coinciding with elevated p90RSK activity specifically in the CD14^-CD16⁺CD68^hi subset. This unique patrolling monocyte population exhibited the highest p90RSK activation and expanded significantly following IR exposure-a response not observed in other monocyte subsets. Colchicine effectively suppressed this IR-induced expansion without restoring DNMT3A or TET2 expression, indicating selective modulation of p90RSK-driven signaling.

Colchicine counteracts IR-induced immune remodeling by selectively inhibiting the expansion of CD14^-CD16⁺CD68^hi monocytes, a subset defined by reduced CHIP asscoaited proteins expression and heightened p90RSK activation. These findings suggest a novel mechanism by which colchicine may modulate radiation-responsive inflammatory signaling in monocytes in vitro, supporting a testable hypothesis that colchicine could mitigate vascular inflammation and ultimately reduce cardiovascular risk in cancer survivors.