Serine activates JAK1-STAT3 signaling pathway to promote HSPCs proliferation and restore splenic hematopoietic function in mice with acute radiation syndrome

To investigate the reparative effects of serine on splenic hematopoiesis in a mouse model of acute radiation syndrome (ARS) and to verify the role of the JAK1-STAT3 signaling pathway in serine-mediated regulation of hematopoietic stem and progenitor cells (HSPCs) proliferation.

A total of 30 male C57BL/6 mice (aged 6 to 8 weeks, weighing 22 to 24 g) were randomly divided into a control group (received no irradiation at day 0), and an irradiation group (exposed to total body irradiation (TBI) with 7 Gy of ⁶⁰Co-γ rays to establish a severe ARS model). Body weight and spleen weight were measured at day 0 (n=6) and days 7, 14, 21, and 28 post-irradiation (n=6), and the spleen index was calculated. Flow cytometry was used to assess the proportion of HSPCs in the spleen. The morphology of spleen tissues was observed by HE staining and compared between groups. Amino acid metabolomics analysis was performed on mouse serum samples using isotope-labeled liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify differentially expressed amino acids associated with hematopoietic changes in the spleen. After 7 Gy total body irradiation, the following groups were established: radiation+PBS group (n=6), radiation+low-, medium- and high-dose serine groups (50, 150 and 450 mg/kg, n=6). Intraperitoneal injection of 100 μL PBS or equivalent volumes of different concentrations of serine was administered daily for 21 consecutive days. At the end of the experiment, the proportion of HSPCs in the spleen was detected by flow cytometry; peripheral blood cells were counted using an automated hematology analyzer; The phosphorylation levels of JAK1 and STAT3 in splenic HSPCs after serine supplementation were analyzed by Western blotting and immunofluorescence techniques. Additionally, splenic HSPCs were isolated in vitro and treated with 2 Gy of irradiation; the effects of serine on the proliferation capacity of splenic HSPCs were evaluated using the CCK-8 assay and flow cytometry.

Compared with the control group, the proportion of splenic HSPCs in the radiation group was lowest at 7 d, gradually recovered thereafter, and reached the highest value at day 21 (P<0.001), accompanied by elevated spleen index and expansion of the red pulp. Metabolomic analysis revealed that 4 amino acids (serine, alanine, proline, and sarcosine) in the serum were significantly elevated at 7 d post-radiation (P<0.0001) and decreased at 21 d. Among them, serum serine levels showed a significant negative correlation with changes in the proportion of splenic HSPCs (R=-0.78, P=0.0006). Further in vivo experiments demonstrated that, compared with the irradiation+PBS group, exogenous supplementation of 150 mg/kg serine significantly increased the proportion of splenic HSPCs (P<0.0001) and elevated peripheral blood cell counts (P<0.0001) in irradiated mice; 0.4 mol/L serine promoted HSPC proliferation (P<0.001) and enhanced their viability. At the molecular level, the phosphorylation levels of JAK1 and STAT3 in HSPCs were significantly elevated after both in vivo (150 mg/kg) and in vitro (0.4 mol/L) serine treatment compared with the control group (P<0.01).

Serine promotes the proliferation of splenic HSPCs, restores hematopoietic function in the spleens of ARS mice, and is accompanied by activation of the JAK1-STAT3 signaling pathway.