mTOR Driven Gene Transcription Is Required for Cholesterol Production in Neurons of the Developing Cerebral Cortex

The role of TSC1 and TSC2 proteins in neuronal axons

Tuberous Sclerosis Complex 1 and 2 proteins, TSC1 and TSC2 respectively, participate in a multiprotein complex with a crucial role for the proper development and function of the nervous system. This complex primarily acts as an inhibitor of the mechanistic target of rapamycin (mTOR) kinase, and mutations in either TSC1 or TSC2 cause a neurodevelopmental disorder called Tuberous Sclerosis Complex (TSC). Neurological manifestations of TSC include brain lesions, epilepsy, autism, and intellectual disability. On the cellular level, the TSC/mTOR signaling axis regulates multiple anabolic and catabolic processes, but it is not clear how these processes contribute to specific neurologic phenotypes. Hence, several studies have aimed to elucidate the role of this signaling pathway in neurons. Of particular interest are axons, as axonal defects are associated with severe neurocognitive impairments. Here, we review findings regarding the role of the TSC1/2 protein complex in axons. Specifically, we will discuss how TSC1/2 canonical and non-canonical functions contribute to the formation and integrity of axonal structure and function.

MeCP2 Is an Epigenetic Factor That Links DNA Methylation with Brain Metabolism

DNA methylation, one of the most well-studied epigenetic modifications, is involved in a wide spectrum of biological processes. Epigenetic mechanisms control cellular morphology and function. Such regulatory mechanisms involve histone modifications, chromatin remodeling, DNA methylation, non-coding regulatory RNA molecules, and RNA modifications. One of the most well-studied epigenetic modifications is DNA methylation that plays key roles in development, health, and disease. Our brain is probably the most complex part of our body, with a high level of DNA methylation. A key protein that binds to different types of methylated DNA in the brain is the methyl-CpG binding protein 2 (MeCP2). MeCP2 acts in a dose-dependent manner and its abnormally high or low expression level, deregulation, and/or genetic mutations lead to neurodevelopmental disorders and aberrant brain function. Recently, some of MeCP2-associated neurodevelopmental disorders have emerged as neurometabolic disorders, suggesting a role for MeCP2 in brain metabolism. Of note, MECP2 loss-of-function mutation in Rett Syndrome is reported to cause impairment of glucose and cholesterol metabolism in human patients and/or mouse models of disease. The purpose of this review is to outline the metabolic abnormalities in MeCP2-associated neurodevelopmental disorders that currently have no available cure. We aim to provide an updated overview into the role of metabolic defects associated with MeCP2-mediated cellular function for consideration of future therapeutic strategies.

Oxysterols are potential physiological regulators of ageing

Delaying and even reversing ageing is a major public health challenge with a tremendous potential to postpone a plethora of diseases including cancer, metabolic syndromes and neurodegenerative disorders. A better understanding of ageing as well as the development of innovative anti-ageing strategies are therefore an increasingly important field of research. Several biological processes including inflammation, proteostasis, epigenetic, oxidative stress, stem cell exhaustion, senescence and stress adaptive response have been reported for their key role in ageing. In this review, we describe the relationships that have been established between cholesterol homeostasis, in particular at the level of oxysterols, and ageing. Initially considered as harmful pro-inflammatory and cytotoxic metabolites, oxysterols are currently emerging as an expanding family of fine regulators of various biological processes involved in ageing. Indeed, depending of their chemical structure and their concentration, oxysterols exhibit deleterious or beneficial effects on inflammation, oxidative stress and cell survival. In addition, stem cell differentiation, epigenetics, cellular senescence and proteostasis are also modulated by oxysterols. Altogether, these data support the fact that ageing is influenced by an oxysterol profile. Further studies are thus required to explore more deeply the impact of the "oxysterome" on ageing and therefore this cholesterol metabolic pathway constitutes a promising target for future anti-ageing interventions.

Dysregulation of mTOR Signaling after Brain Ischemia

In this review, we provide recent data on the role of mTOR kinase in the brain under physiological conditions and after damage, with a particular focus on cerebral ischemia. We cover the upstream and downstream pathways that regulate the activation state of mTOR complexes. Furthermore, we summarize recent advances in our understanding of mTORC1 and mTORC2 status in ischemia–hypoxia at tissue and cellular levels and analyze the existing evidence related to two types of neural cells, namely glia and neurons. Finally, we discuss the potential use of mTORC1 and mTORC2 as therapeutic targets after stroke.

Robust and annotation-free analysis of alternative splicing across diverse cell types in mice

Although alternative splicing is a fundamental and pervasive aspect of gene expression in higher eukaryotes, it is often omitted from single-cell studies due to quantification challenges inherent to commonly used short-read sequencing technologies. Here, we undertake the analysis of alternative splicing across numerous diverse murine cell types from two large-scale single-cell datasets-the Tabula Muris and BRAIN Initiative Cell Census Network-while accounting for understudied technical artifacts and unannotated events. We find strong and general cell-type-specific alternative splicing, complementary to total gene expression but of similar discriminatory value, and identify a large volume of novel splicing events. We specifically highlight splicing variation across different cell types in primary motor cortex neurons, bone marrow B cells, and various epithelial cells, and we show that the implicated transcripts include many genes which do not display total expression differences. To elucidate the regulation of alternative splicing, we build a custom predictive model based on splicing factor activity, recovering several known interactions while generating new hypotheses, including potential regulatory roles for novel alternative splicing events in critical genes like Khdrbs3 and Rbfox1. We make our results available using public interactive browsers to spur further exploration by the community.

Localization and Functional Roles of Components of the Translation Apparatus in the Eukaryotic Cell Nucleus

Components of the translation apparatus, including ribosomal proteins, have been found in cell nuclei in various organisms. Components of the translation apparatus are involved in various nuclear processes, particularly those associated with genome integrity control and the nuclear stages of gene expression, such as transcription, mRNA processing, and mRNA export. Components of the translation apparatus control intranuclear trafficking; the nuclear import and export of RNA and proteins; and regulate the activity, stability, and functional recruitment of nuclear proteins. The nuclear translocation of these components is often involved in the cell response to stimulation and stress, in addition to playing critical roles in oncogenesis and viral infection. Many components of the translation apparatus are moonlighting proteins, involved in integral cell stress response and coupling of gene expression subprocesses. Thus, this phenomenon represents a significant interest for both basic and applied molecular biology. Here, we provide an overview of the current data regarding the molecular functions of translation factors and ribosomal proteins in the cell nucleus.