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Acute radiation syndrome (ARS) results from high-dose ionizing radiation (IR) exposure, with bone marrow (BM) being highly susceptible due to its proliferative activity. BM injury causes pancytopenia, leading to infections, anemia, and bleeding. Mesenchymal stem cells (MSCs) hold promise for ARS treatment because of their immunomodulatory, anti-inflammatory, and regenerative properties. However, challenges such as replicative senescence, poor survival, and engraftment in irradiated microenvironments limit their efficacy. This study evaluated rapamycin-preconditioned placenta-derived MSCs (rPD-MSCs) in a mouse ARS model. Rapamycin was selected for preconditioning due to its ability to induce autophagy and modulate cytokine secretion. We assessed rapamycin-dependent modulation of autophagy-related genes and proteins, as well as hematopoietic cytokines secretion in PD-MSCs, and evaluated morphological changes in blood and BM at 7 and 21 days post-irradiation in ICR/CD1 mice. Preconditioning with rapamycin alters the secretion of granulocyte colony-stimulating factor (G-CSF), stem cell factor (SCF), and Fms-related tyrosine kinase 3 ligand (Flt3LG) in PD-MSCs without affecting cell viability. rPD-MSCs better enhance hematopoietic recovery, restore bone marrow cellularity, and increase peripheral blood cell counts by elevating the secretion of hematopoietic cytokines compared to non-preconditioned cells. These results highlight rapamycin preconditioning as a promising strategy to enhance MSCs therapeutic potential for ARS, supporting further preclinical and clinical exploration.

Fibronectin (FN) is an extracellular matrix glycoprotein essential for the development and function of major vertebrate organ systems. Mutations in FN result in an autosomal dominant skeletal dysplasia termed corner fracture-type spondylometaphyseal dysplasia (SMDCF). The precise pathomechanisms through which mutant FN induces impaired skeletal development remain elusive. Here, we have generated patient-derived induced pluripotent stem cells as a cell culture model for SMDCF to investigate the consequences of FN mutations on mesenchymal stem cells (MSCs) and their differentiation into cartilage-producing chondrocytes. In line with our previous data, FN mutations disrupted protein secretion from MSCs, causing a notable increase in intracellular FN and a significant decrease in extracellular FN levels. Analyses of plasma samples from SMDCF patients also showed reduced FN in circulation. FN and endoplasmic reticulum (ER) protein folding chaperones (BIP, HSP47) accumulated in MSCs within ribosome-covered cytosolic vesicles that emerged from the ER. Massive amounts of these vesicles were not cleared from the cytosol, and a smaller subset showed the presence of lysosomal markers. The accumulation of intracellular FN and ER proteins elevated cellular stress markers and altered mitochondrial structure. Bulk RNA sequencing revealed a specific transcriptomic dysregulation of the patient-derived cells relative to controls. Analysis of MSC differentiation into chondrocytes showed impaired mesenchymal condensation, reduced chondrogenic markers, and compromised cell proliferation in mutant cells. Moreover, FN mutant cells exhibited significantly lower transforming growth factor beta-1 (TGFβ1) expression, crucial for mesenchymal condensation. Exogenous FN or TGFβ1 supplementation effectively improved the MSC condensation and promoted chondrogenesis in FN mutant cells. These findings demonstrate the cellular consequences of FN mutations in SMDCF and explain the molecular pathways involved in the associated altered chondrogenesis. The online version contains supplementary material available at 10.1007/s00018-024-05444-4.

5-Fluorouracil (5-FU) is a small, very membrane permeable drug that is poorly retained within the aqueous compartment of liposomal nanoparticles (LNP). To address this problem a novel method relying on formation of a ternary complex comprising copper, low molecular weight polyethylenimine (PEI) and 5-FU has been developed. More specifically, in the presence of entrapped copper and PEI, externally added 5-FU can be efficiently encapsulated (textgreater95%) in DSPC/Chol (1,2-Distearoyl-sn-Glycero-3-Phosphocholine/cholesterol; 55:45 mol%) liposomes (130-170 nm) to achieve drug-to-lipid ratios of 0.1 (mol:mol). Drug release studies completed using this LNP formulation of 5-FU demonstrated significant improvements in drug retention in vitro and in vivo. Plasma concentrations of 5-FU were 7- to 23-fold higher when the drug was administered intravenously to mice as the LNP 5-FU formulation compared to free 5-FU. Further, the therapeutic effects of the LNP 5-FU formulation, as determined in a HT-29 subcutaneous colorectal cancer model where treatment was given QDx5, was greater than that which could be achieved with free 5-FU when compared at equivalent doses. This is the first time an active loading method has been described for 5-FU. The use of ternary metal complexation strategy to encapsulate therapeutic agents may define a unique platform for preparation of LNP drug formulations.