Transferrin Receptor Is Necessary for Proper Oligodendrocyte Iron Homeostasis and Development

Role of iron in brain development, aging, and neurodegenerative diseases

It is now understood that iron crosses the blood-brain barrier via a complex metabolic regulatory network and participates in diverse critical biological processes within the central nervous system, including oxygen transport, energy metabolism, and the synthesis and catabolism of myelin and neurotransmitters. During brain development, iron is distributed throughout the brain, playing a pivotal role in key processes such as neuronal development, myelination, and neurotransmitter synthesis. In physiological aging, iron can selectively accumulate in specific brain regions, impacting cognitive function and leading to intracellular redox imbalance, mitochondrial dysfunction, and lipid peroxidation, thereby accelerating aging and associated pathologies. Furthermore, brain iron accumulation may be a primary contributor to neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Comprehending the role of iron in brain development, aging, and neurodegenerative diseases, utilizing iron-sensitive Magnetic Resonance Imaging (MRI) technology for timely detection or prediction of abnormal neurological states, and implementing appropriate interventions may be instrumental in preserving normal central nervous system function.

SRSF10 regulates oligodendrocyte differentiation during mouse central nervous system development by modulating pre-mRNA splicing

We characterized the role and regulation mechanism of a pre-mRNA splicing factor, SRSF10, in the development of oligodendrocyte lineage cells (OLCs) and the myelination process during mouse central nervous system (CNS) development. We found that depletion of SRSF10 specifically in OLCs induces hypomyelination and a decrease in OLCs in the developing mouse CNS, whereas depletion of SRSF10 only in differentiated OLCs does not significantly affect these processes. More detailed in vivo and in vitro analyses revealed that SRSF10 primarily regulates the earlier differentiation stages of OLCs, while the proliferation and apoptosis of OLCs were not affected. Mechanistically, RNA-seq and RIP-Seq transcript analyses identified a series of genes whose alternative splicing (AS) was directly regulated by SRSF10. Among these genes, compensating for the AS phenotype of Myo5a using antisense oligonucleotides (ASOs) reversed the inhibition of OLCs differentiation induced by SRSF10 depletion. In summary, we revealed for the first time that SRSF10 is a key regulator in the early differentiation of OLCs, likely via modulating the AS patterns of target genes such as Myo5a. This research provides significant implications for understanding OLC development and exploring potential therapeutic strategies for dysmyelination-related diseases.

Transferrin receptors

The transferrin receptor (TfR) is one of the key proteins involved in cellular iron uptake. TfR-mediated endocytosis of transferrin-bound iron is the major pathway for iron acquisition by most cells in the body. Over the past three decades, the studies on TfR have made significant progress, and also, our knowledge on cell iron uptake has greatly been improved. Here we focus on recent advances in the studies on TfR and a brief discussion of the structures and functions of four different types of TfR, namely TfR1 (transferrin receptor 1), TfR2 (transferrin receptor 2), TfR3 (glyceraldehyde-3-phosphate dehydrogenase) and TfR4 (cubilin). These proteins work in different cells or organs and at different times, ensuring that cells and tissues get the iron they need. Their normal expression and function are fundamental to the body's iron homeostasis.

Functional Annotation of Bipolar Disorder 2 Risk Location Implicates Novel Susceptibility Genes

INTRODUCTION

Bipolar 2 disorder (BD2) is an independent disease with specific familial aggregation, significant functional impairment, specific treatment challenges, and several distinctive clinical features. However, unlike bipolar 1 disorder, studies investigating causal and functional genes are lacking. This study aimed to identify and prioritize causal genetic variants and genes for BD2 by analysing brain-specific gene expression markers, improve the understanding of its genetic underpinnings, and support advancements in diagnosis, treatment, and prognosis.

METHOD

We used FUMA, a genome-wide association study (GWAS) annotation tool, to pinpoint potential causal variants and genes from the largest BD2 GWAS data. Candidate causal variants most likely affecting brain gene expression were prioritized using the following criteria: (1) variants identified as eSNPs in any brain region within any brain expression quantitative trait loci (eQTL) dataset; (2) variants annotated in the Regulome database with a score <5, indicating likely functional localization; (3) the most common 15-core chromatin state across all cell types in the Roadmap Epigenomics data being ≤7, reflecting an open chromatin state; (4) localization in genomic regions with evidence of 3D chromatin interactions, as such interactions mediate genetic effects on gene expression.

RESULTS

We identified AGRN, ORMDL3, SLC25A39, RUNDC3A, NOS2, C1orf159, RP11-5407.18, RP11-465B22.3, RP11-5407.17 as candidate causal genes. These genes are associated with important pathways such as synapse formation, mitochondrial and oxidative metabolism, intracellular transport, neurotransmission, and lipid metabolism-related pathways.

CONCLUSION

This study provides a guide for further experimental validation of functional variants, BD2-associated genes, and novel drug targets.

Age, sex, and cell type-resolved hypothalamic gene expression across the pubertal transition in mice

BACKGROUND

The hypothalamus plays a central role in regulating puberty. However, our knowledge of the postnatal gene regulatory networks that control the pubertal transition in males and females is incomplete. Here, we investigate the age-, sex- and cell-type-specific gene regulation in the hypothalamus across the pubertal transition.

METHODS

We used RNA-seq to profile hypothalamic gene expression in male and female mice at five time points spanning the onset of puberty (postnatal days (PD) 12, 22, 27, 32, and 37). By combining this data with hypothalamic single nuclei RNA-seq data from pre- and postpubertal mice, we assigned gene expression changes to their most likely cell types of origin. In our colony, pubertal onset occurs earlier in male mice, allowing us to focus on genes whose expression is dynamic across ages and offset between sexes, and to explore the bases of sex effects.

RESULTS

Our age-by-sex pattern of expression enriched for biological pathways involved hormone production, neuronal activation, and glial maturation. Additionally, we inferred a robust expansion of oligodendrocytes precursor cells into mature oligodendrocytes spanning the prepubertal (PD12) to peri-pubertal (PD27) timepoints. Using spatial transcriptomic data from postpubertal mice, we observed the lateral hypothalamic area and zona incerta were the most oligodendrocyte-rich regions and that these cells expressed genes known to be involved in pubertal regulation.

CONCLUSION

Together, by incorporating multiple biological timepoints and using sex as a variable, we identified gene and cell-type changes that may participate in orchestrating the pubertal transition and provided a resource for future studies of postnatal hypothalamic gene regulation.

Quantitative susceptibility mapping in the brain reflects spatial expression of genes involved in iron homeostasis and myelination

Quantitative susceptibility mapping (QSM) is an MRI modality used to non-invasively measure iron content in the brain. Iron exhibits a specific anatomically varying pattern of accumulation in the brain across individuals. The highest regions of accumulation are the deep grey nuclei, where iron is stored in paramagnetic molecule ferritin. This form of iron is considered to be what largely contributes to the signal measured by QSM in the deep grey nuclei. It is also known that QSM is affected by diamagnetic myelin contents. Here, we investigate spatial gene expression of iron and myelin related genes, as measured by the Allen Human Brain Atlas, in relation to QSM images of age-matched subjects. We performed multiple linear regressions between gene expression and the average QSM signal within 34 distinct deep grey nuclei regions. Our results show a positive correlation (p < .05, corrected) between expression of ferritin and the QSM signal in deep grey nuclei regions. We repeated the analysis for other genes that encode proteins thought to be involved in the transport and storage of iron in the brain, as well as myelination. In addition to ferritin, our findings demonstrate a positive correlation (p < .05, corrected) between the expression of ferroportin, transferrin, divalent metal transporter 1, several gene markers of myelinating oligodendrocytes, and the QSM signal in deep grey nuclei regions. Our results suggest that the QSM signal reflects both the storage and active transport of iron in the deep grey nuclei regions of the brain.

Identity and Maturity of iPSC-Derived Oligodendrocytes in 2D and Organoid Systems

Oligodendrocytes originating in the brain and spinal cord as well as in the ventral and dorsal domains of the neural tube are transcriptomically and functionally distinct. These distinctions are also reflected in the ultrastructure of the produced myelin, and the susceptibility to myelin-related disorders, which highlights the significance of the choice of patterning protocols in the differentiation of induced pluripotent stem cells (iPSCs) into oligodendrocytes. Thus, our first goal was to survey the different approaches applied to the generation of iPSC-derived oligodendrocytes in 2D culture and in organoids, as well as reflect on how these approaches pertain to the regional and spatial fate of the generated oligodendrocyte progenitors and myelinating oligodendrocytes. This knowledge is increasingly important to disease modeling and future therapeutic strategies. Our second goal was to recap the recent advances in the development of oligodendrocyte-enriched organoids, as we explore their relevance to a regional specification alongside their duration, complexity, and maturation stages of oligodendrocytes and myelin biology. Finally, we discuss the shortcomings of the existing protocols and potential future explorations.