Rojo, D. | Search bioRxiv

bioRxiv2024

Hypoxia disrupts circadian rhythms in astrocytes and causes synapse engulfment defects

Astrocytes are emerging as key regulators of neuronal synaptic network maturation and function, through control of synaptic pruning. This is important, because individuals with ASD have excess glutamatergic synapses in the cortex, but the biological mechanisms underlying this phenotype remain unclear. Here, we used human cortical organoids (hCO) derived from induced pluripotent stem cells (hiPSCs), to examine the effect of hypoxia on synapse engulfment in human astrocytes at postnatal-equivalent stages of development. We identified that hypoxia significantly inhibits the synaptosome phagocytosis, and that this phenotype is mediated through disruptions in the astrocytic circadian rhythm molecular pathway and subsequent decreased expression of MEGF10. Lastly, we demonstrated that circadian clock disruptions are sufficient to induce these observed phenotypes even in the absence of hypoxia, both in hCOs and within the mouse hippocampus in vivo. Our study uncovers a novel mechanistic link between hypoxia, circadian rhythms disruptions, and synapse pruning by astrocytes, and provides insight into the pathophysiology of ASD, and other neuropsychiatric diseases. Separately, the demonstration of the presence of circadian rhythms in hCOs opens an unprecedented opportunity to dissect the role of circadian clocks in normal brain development and how it contributes to specific diseases of environmental or genetic origin.

neuroscience↗

bioRxiv2022

BMAL1 loss in oligodendroglial lineage cells dysregulates myelination and sleep

Myelination depends on maintenance of oligodendrocytes that arise from oligodendrocyte precursor cells (OPCs). We show that the dynamic nature of oligodendroglia and myelination are regulated by the circadian transcription factor BMAL1. Bmal1 knockdown in OPCs during development - but not adulthood - decreases OPC proliferation, whereas BMAL1 regulates OPC morphology throughout life. OPC-specific Bmal1 deficiency impairs remyelination in an age-dependent manner, suggesting that age-associated decrements in circadian regulation of oligodendroglia may contribute to the deficient remyelination potential in demyelinating diseases like multiple sclerosis (MS). This oligodendroglial dysregulation and dysmyelination increase sleep fragmentation in OPC-specific Bmal1 knockout mice, and sleep fragmentation is causally associated with MS. These findings have broad mechanistic and therapeutic implications for numerous brain disorders that include both myelin and sleep phenotypes. One-Sentence SummaryBMAL1 regulates the homeostatic maintenance of oligodendroglia and myelin, that subsequently controls sleep architecture.

neuroscience↗

bioRxiv2020

Mouse models for V103I and I251L gain of function variants of the human MC4R display reduced adiposity and are not protected from a hypercaloric diet

ObjectiveThe melanocortin 4 receptor (MC4R) is a G protein-coupled receptor that plays major roles in the central control of energy balance. Loss-of-function mutations of MC4R constitute the most common monogenic cause of early-onset extreme obesity in humans, whereas gain-of-function mutations appear to be protective. In particular, two relatively frequent alleles carrying the non-synonymous coding mutations V103I or I251L have been associated with lower risks of obesity and type-2 diabetes. Although V103I and I251L MC4Rs showed more efficient signaling in transfected cells, their specific effects in live animals remain unexplored. Here, we investigated whether the introduction of V103I and I251L mutations into the mouse MC4R leads to a lean phenotype and provides protection against an obesogenic diet. MethodsUsing CRISPR/Cas9, we generated two novel strains of mice carrying single nucleotide mutations into the mouse Mc4r which are identical to those present in V103I and I251L MCR4 human alleles, and studied their phenotypic outcomes in mice fed with normal chow or a high- fat diet. In particular, we measured body weight progression, food intake and adiposity. In addition, we analyzed glucose homeostasis through glucose and insulin tolerance tests. ResultsWe found that homozygous V103I females displayed shorter longitudinal length and decreased abdominal white fat, whereas homozygous I251L females were also shorter and leaner due to decreased weight in all white fat pads examined. Homozygous Mc4rV103I/V103I and Mc4rI251L/I251L mice of both sexes showed improved glucose homeostasis when challenged in a glucose tolerance test, whereas Mc4rI251L/I251L females showed improved responses to insulin. Despite being leaner and metabolically more efficient, V103I and I251L mutants fed with a hypercaloric diet increased their fasting glucose levels and adiposity similar to their wild-type littermates. ConclusionsAltogether, our results demonstrate that mice carrying V103I and I251L MC4R mutations displayed gain-of-function phenotypes that were more evident in females. However, hypermorphic MC4R mutants were as susceptible as their control littermates to the obesogenic and diabetogenic effects elicited by a long-term hypercaloric diet, highlighting the importance of healthy feeding habits even under favorable genetic conditions. HighlightsO_LIIdentical single nucleotide substitutions to gain-of-function mutations of the human MC4R were introduced into the genome of inbred mice using CRISPR/Cas9 technology. C_LIO_LIHomozygous female carriers of V103I Mc4r alleles are shorter and display reduced adiposity, together with improved glucose homeostasis in both sexes. C_LIO_LIHomozygous females carrying the I251L mutation in the mouse MC4R also display shorter longitudinal length, decreased weight in all abdominal white fat pads and improved glucose clearance and insulin response. C_LIO_LIGain-of-function mutations V103I and I251L of MC4R do not protect against the diabetogenic and adipogenic effects of a high-fat diet. C_LI

genetics↗