Background: Little is known about systemic responses to joint bleeding and Factor VIII (FVIII) replacement in hemophilia.

Aims: To quantify systemic gene expression changes in wild-type and FVIII-deficient (FVIII^-/-) mice at baseline and after induced hemarthrosis, +/- FVIII replacement.

Methods: Hemarthrosis was induced by sub-patellar puncture in wild-type BALB/c (WT) mice or FVIII^-/- mice on a BALB/c background +/- recombinant human FVIII (rhFVIII) or rhFVIII-Fc prophylaxis. Spleens were harvested at baseline (FVIII^-/- mice) and day 3 or 2 weeks post-injury. Gene expression analyses were performed by RNA sequencing followed by functional enrichment analyses.

Results: Knee injury caused gross hemarthrosis in untreated FVIII^-/- mice only (day 2 hematocrit: 27 %), resulting in 5381 differentially expressed genes (DEG) on day 3 (log₂ fold-change (log2FC)>1.0 or < -1.0; p< 0.05) with enrichment of cell cycle and immune pathways. Injury in WT mice elicited 1307 DEG and the response was absent in FVIII^-/- mice administered rhFVIII(-Fc), suggesting transcriptional responses are associated with massive hemarthrosis and altered with FVIII replacement. Numerous genes (log2FC>1.5; p< 0.05) and pathways relating to hemostasis, platelet activation, and neutrophil degranulation were upregulated in WT but not FVIII^-/- mice on day 3. Moderate gene upregulation (log2FC>0.5; p< 0.05) also caused enrichment of platelet activation pathways in uninjured FVIII^-/- mice on day 3 after rhFVIII treatment. Most transcriptional responses returned to baseline by 2 weeks.

Conclusions: Hemarthrosis in FVIII^-/- mice causes a large, transient systemic transcriptional response involving immune pathways, which is altered with FVIII treatment. Differences between FVIII^-/- and WT mice suggest responses are mostly driven by bleeding rather than injury alone, and that FVIII deficiency may compromise platelet activation after joint bleeding. These findings warrant further investigations into hemostatic and immune modulatory functions of FVIII.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/differential-systemic-transcriptional-responses-to-induced-joint-bleeding-in-wild-type-and-factor-viii-deficient-mice/