BMP4 signaling plays critical roles in self-renewal of R2i mouse embryonic stem cells.

Mouse embryonic stem cells (mESCs) can be maintained in a pluripotent state under R2i culture conditions that inhibit the TGF-ß and ERK signaling pathways. BMP4 is another member of the TGF-ß family that plays a crucial role in maintaining the pluripotency state of mESCs. It has been reported that inhibition of BMP4 caused the death of R2i-grown cells. In this study, we used the loss-of-function approach to investigate the role of BMP4 signaling in mESC self-renewal. Inhibition of this pathway with Noggin and dorsomorphin, two bone morphogenetic protein (BMP) antagonists, elicited a quick death of the R2i-grown cells. We showed that the canonical pathway of BMP4 (BMP/SMAD) was dispensable for self-renewal and maintaining pluripotency of these cells. Transcriptome analysis of the BMPi-treated cells revealed that the p53 signaling and two adhesion (AD) and apoptotic mitochondrial change (MT) pathways could be involved in the cell death of the BMPi-treated cells. According to our results, inhibition of BMP4 signaling caused a decrease in cell adhesion and ECM detachment, which triggered anoikis in the R2i-grown cells. Altogether, these findings demonstrate that endogenous BMP signaling is required for the survival of mESCs under the R2i condition.

Iron Accumulation and Changes in Cellular Organelles in WDR45 Mutant Fibroblasts.

Iron overload in the brain, defined as excess stores of iron, is known to be associated with neurological disorders. In neurodegeneration accompanied by brain iron accumulation, we reported a specific point mutation, c.974-1G>A in WD Repeat Domain 45 (WDR45), showing iron accumulation in the brain, and autophagy defects in the fibroblasts. In this study, we investigated whether fibroblasts with mutated WDR45 accumulated iron, and other effects on cellular organelles. We first identified the main location of iron accumulation in the mutant fibroblasts and then investigated the effects of this accumulation on cellular organelles, including lipid droplets, mitochondria and lysosomes. Ultrastructure analysis using transmission electron microscopy (TEM) and confocal microscopy showed structural changes in the organelles. Increased numbers of lipid droplets, fragmented mitochondria and increased numbers of lysosomal vesicles with functional disorder due to WDR45 deficiency were observed. Based on correlative light and electron microscopy (CLEM) findings, most of the iron accumulation was noted in the lysosomal vesicles. These changes were associated with defects in autophagy and defective protein and organelle turnover. Gene expression profiling analysis also showed remarkable changes in lipid metabolism, mitochondrial function, and autophagy-related genes. These data suggested that functional and structural changes resulted in impaired lipid metabolism, mitochondrial disorder, and unbalanced autophagy fluxes, caused by iron overload.