Silencing MDA5 Slows Blood Stem Cell Aging in Mice

Chronic low-grade inflammation—'inflammaging'—accelerates the decline of hematopoietic stem cells (HSCs) during aging, reducing their self-renewal, skewing differentiation toward myeloid lineages, and impairing proteostasis. Yet the molecular sensors that translate this persistent inflammatory noise into HSC dysfunction have remained poorly defined. This study identifies MDA5 (encoded by Ifih1), an intracellular innate immune RNA sensor best known for detecting viral double-stranded RNA, as a key driver of HSC aging in mice.

The researchers compared wild-type (WT) and Mda5-/- mice across young (2–3 months), middle-aged (10–14 months), and aged (18–24 months) cohorts. Bone marrow serum from aged Mda5-/- mice contained significantly lower levels of IFN-β, IL-1α, IL-1β, IL-6, and IL-10 compared to WT controls, confirming reduced inflammaging in the absence of MDA5. Phenotypically, aged Mda5-/- mice showed fewer HSCs accumulated in the bone marrow, reduced myeloid bias, and greater HSC quiescence as measured by cell-cycle analysis—all hallmarks of a younger hematopoietic system.

Functionally, aged Mda5-/- HSCs displayed superior repopulation capacity in noncompetitive transplantation experiments, outperforming aged WT HSCs in reconstituting all blood lineages. Multiomic profiling—including ATAC-seq for chromatin accessibility, bulk and single-cell transcriptomics, and metabolomics—revealed that Mda5-/- HSCs maintain open chromatin at loci associated with quiescence and stemness, express genes characteristic of younger HSCs, and sustain a more favorable metabolic state. Inflammatory gene programs that typically become hyperactivated with age were markedly attenuated.

Critically, Mda5-/- HSCs exhibited improved proteostasis, evidenced by higher levels of HSF1 (heat shock transcription factor 1) and increased phosphorylation of EIF2A—both key regulators of protein quality control. HSF1 promotes chaperone expression and stress responses that keep misfolded proteins in check, while phospho-EIF2A dampens global protein synthesis to reduce proteotoxic load and promotes autophagy. Pharmacological activation of HSF1 in aged WT HSCs partially restored youthful features, providing causal evidence that proteostasis maintenance is a downstream effector of MDA5-driven aging. The team also noted that transposable element RNAs—endogenous MDA5 ligands whose expression rises with age—may serve as the chronic sterile trigger sustaining MDA5 activity in aging HSCs.

These findings establish the RIG-I-like receptor pathway, and MDA5 in particular, as an intrinsic regulator of hematopoietic stem cell aging, mechanistically linking inflammaging to impaired proteostasis. The study opens potential therapeutic avenues: pharmacological inhibition of MDA5 or downstream inflammatory cascades, or activation of proteostasis programs like HSF1, could mitigate age-related hematopoietic decline and reduce the risk of clonal hematopoiesis and related blood disorders.