Background: Intestinal acute radiation syndrome (IARS) represents a life-threatening component of acute radiation syndrome with limited effective countermeasures. Understanding molecular determinants governing intestinal epithelial resilience to ionizing radiation is critical for developing radiation toxicity mitigation strategies. Objectives: This study investigates the role of PIKfyve, a phosphoinositide kinase essential for endolysosomal homeostasis, in modulating radiation-induced intestinal toxicity. Methods: We utilized an inducible intestinal epithelial-specific PIKfyve-knockout mouse model (PIKfyve cKO) subjected to 10 Gy abdominal irradiation. Intestinal toxicity was assessed through histopathology, barrier permeability (FD4 assay), apoptosis markers, and transcriptomic profiling. Small intestinal organoids were employed for mechanistic validation. Results: PIKfyve deletion alone did not perturb normal gut architecture but precipitated severe post-irradiation toxicity, including villous atrophy, crypt hypoplasia, and massive crypt-cell apoptosis. Barrier dysfunction was evidenced by elevated serum FD4 and heightened systemic pro-inflammatory cytokines, culminating in markedly increased mortality. Transcriptomic analysis revealed potentiated DNA-damage signaling and amplified inflammatory cascades in PIKfyve-deficient intestines. Conclusions: These findings identify PIKfyve as a critical guardian of intestinal epithelial integrity against radiation toxicity. Given emerging PIKfyve inhibitors in cancer therapy, our results raise important safety considerations for clinical radiotherapy and position PIKfyve as a potential target for radiation toxicity mitigation.

Background: Intestinal acute radiation syndrome (IARS) represents a life-threatening component of acute radiation syndrome with limited effective countermeasures. Under-standing molecular determinants governing intestinal epithelial resilience to ionizing ra-diation is critical for developing radiation toxicity mitigation strategies. Objectives: This study investigates the role of PIKfyve, a phosphoinositide kinase essential for endolysosomal homeostasis, in modulating radiation-induced intestinal toxicity. Methods: We utilized an inducible intestinal epithelial-specific PIKfyve-knockout mouse model (PIKfyve cKO) subjected to 10 Gy abdominal irradiation. Intestinal toxicity was as-sessed through histopathology, barrier permeability (FD4 assay), apoptosis markers, and transcriptomic profiling. Small intestinal organoids were employed for mechanistic vali-dation. Results: PIKfyve deletion alone did not perturb normal gut architecture but precipitated severe post-irradiation toxicity, including villous atrophy, crypt hypoplasia, and massive crypt-cell apoptosis. Barrier dysfunction was evidenced by elevated serum FD4 and heightened systemic pro-inflammatory cytokines, culminating in markedly increased mortality. Transcriptomic analysis revealed potentiated DNA-damage signaling and am-plified inflammatory cascades in PIKfyve-deficient intestines. Conclusions: These findings identify PIKfyve as a critical guardian of intestinal epithelial integrity against radiation toxicity. Given emerging PIKfyve inhibitors in cancer therapy, our results raise important safety considerations for clinical radiotherapy and position PIKfyve as a potential target for radiation toxicity mitigation.

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder in which enhanced platelet destruction and impaired platelet production coexist, and a substantial proportion of patients remain refractory to available therapies. Here, we evaluated 2B9-Fc, a thrombopoietin (TPO) mimetic peptide engineered from a cyclic peptide with high affinity for both human and mouse c-MPL, in passive (anti-CD41 monoclonal antibody R300) and active (guinea pig anti-mouse platelet serum, GP-APS) immunization male C57BL/6J and humanized c-MPL receptor transgenic mouse models of ITP. 2B9-Fc (500 μg/kg, subcutaneously) significantly elevated peripheral platelet counts in both models (p < 0.01), without affecting WBC, RBC, or hemoglobin, and alleviated skin purpura and bleeding scores in the active model. In addition, 2B9-Fc treatment was associated with a reduced splenic M1/M2 macrophage ratio, increased regulatory T cells (Tregs), downregulated IL-6 and iNOS while upregulating TGF-β1 and Foxp3, and suppressed STAT1 phosphorylation. In humanized c-MPL receptor transgenic (MT) mice, 2B9-Fc promoted CD41⁺ megakaryocyte generation in vitro and sustained platelet recovery in vivo through day 14. These results indicate that 2B9-Fc ameliorates ITP and is associated with promotion of megakaryocyte maturation and restoration of immune tolerance, likely involving inhibition of STAT1-mediated M1 polarization and Treg expansion, supporting its potential for clinical translation.