Evolocumab protects mice from radiation-induced damage by affecting hematopoietic cell lineage

The hematopoietic system is extremely sensitive to ionizing radiation(IR) and is easily damaged after exposure. Recent studies [1, 2] have shown that hematopoietic lineage differentiation may play a key role in Ionizing radiation -induced acute injury.

C57BL/6 mice matched for age, sex and weight were randomly grouped and intraperitoneal injected with PBS, Evolocumab (80.0 mg/kg) or MMP9-IN (20.0 mg/kg). Survival time, body weight, pathology, hematopoietic cell differentiation changes and organoids of the mice after IR (10.0 Gy) were compared, and the mechanism of action in tissues was verified by transcriptome sequencing.

Ionizing radiation can inhibit hematopoietic cell lineage differentiation and affect cholesterol metabolism. The expression of the Pcsk9 gene was significantly upregulated after IR. Treatment with a Pcsk9 monoclonal antibody (Evolocumab) exerted significant radioprotective effects, including improving the survival rate of irradiated mice, reducing body weight loss, preserving the integrity of the bone marrow cavity, and promoting cellular proliferation. Flow cytometric analysis showed that Evolocumab significantly increased hematopoietic precursor cells and hematopoietic stem cells and promoted their differentiation into ST-LSKs and MPPs. In addition, the proportions of CMPs and GMPs were increased, whereas the proportion of MEPs was decreased. RNA sequencing results suggested that the IR-induced downregulation of Cd3e within the hematopoietic cell lineage pathway could be rescued by Evolocumab, which was further validated at the cellular level. CD3e is a T-cell-associated marker, and Evolocumab treatment was associated with an increased proportion of CD3e⁺ T cells. Analysis of previously reported hematopoiesis-related factors [3-5] indicated that Evolocumab markedly upregulated Mmp9 expression. Correlation analysis revealed that Pcsk9 was negatively correlated with Cd3e, whereas Cd3e was positively correlated with Mmp9. Following ionizing radiation, Mmp9 knockout (Mmp9 KO) mice exhibited reduced survival compared with wild-type mice. Moreover, in wild-type mice, administration of an MMP9 inhibitor (MMP9-IN) attenuated the radioprotective effects of Evolocumab, indicating that Mmp9 contributes to Evolocumab-mediated radioprotection.

Evolocumab exerts a positive effect on promoting the proliferation and differentiation of hematopoietic stem cells against IR-induced hematopoietic system injury, with its protective mechanism likely involving the activation of hematopoietic cell lineages to upregulate CD3e⁺ T cells and Mmp9 expression.