Mitochondrial dysfunction reactivates α-fetoprotein expression that drives copper-dependent immunosuppression in mitochondrial disease models

Signaling circuits crucial to systemic physiology are widespread, yet uncovering their molecular underpinnings remains a barrier to understanding the etiology of many metabolic disorders. Here, we identified a copper-linked signaling circuit activated by disruption of mitochondrial function in the murine liver or heart that resulted in atrophy of the spleen and thymus and caused a peripheral white blood cell deficiency. We demonstrated that the leukopenia was caused by α-fetoprotein, which required copper and the cell surface receptor CCR5 to promote white blood cell death. We further showed that α-fetoprotein expression was upregulated in several cell types upon inhibition of oxidative phosphorylation. Collectively, our data argue that α-fetoprotein may be secreted by bioenergetically stressed tissue to suppress the immune system, an effect that may explain the recurrent or chronic infections that are observed in a subset of mitochondrial diseases or in other disorders with secondary mitochondrial dysfunction.

Protracted neuronal maturation in a long-lived, highly social rodent

Naked mole-rats are a long-lived rodent species (current lifespan >37 years) and an increasingly popular biomedical model. Naked mole-rats exhibit neuroplasticity across their long lifespan. Previous studies have begun to investigate their neurogenic patterns. Here, we test the hypothesis that neuronal maturation is extended in this long-lived rodent. We characterize cell proliferation and neuronal maturation in established rodent neurogenic regions over 12 months following seven days of consecutive BrdU injection. Given that naked mole-rats are eusocial (high reproductive skew where only a few socially-dominant individuals reproduce), we also looked at proliferation in brain regions relevant to the social-decision making network. Finally, we measured co-expression of EdU (newly-born cells), DCX (immature neuron marker), and NeuN (mature neuron marker) to assess the timeline of neuronal maturation in adult naked mole-rats. This work reaffirms the subventricular zone as the main source of adult cell proliferation and suggests conservation of the rostral migratory stream in this species. Our profiling of socially-relevant brain regions suggests that future work which manipulates environmental context can unveil how newly-born cells integrate into circuitry and facilitate adult neuroplasticity. We also find naked mole-rat neuronal maturation sits at the intersection of rodents and long-lived, non-rodent species: while neurons can mature by 3 weeks (rodent-like), most neurons mature at 5 months and hippocampal neurogenic levels are low (like long-lived species). These data establish a timeline for future investigations of longevity- and socially-related manipulations of naked mole-rat adult neurogenesis.

Homeostatic control of nuclear-encoded mitochondrial gene expression by the histone variant H2A.Z is essential for neuronal survival

Histone variants are crucial regulators of chromatin structure and gene transcription, yet their functions within the brain remain largely unexplored. Here, we show that the H2A histone variant H2A.Z is essential for neuronal survival. Mice lacking H2A.Z in GABAergic neurons or Purkinje cells (PCs) present with a progressive cerebellar ataxia accompanied by widespread degeneration of PCs. Ablation of H2A.Z in other neuronal subtypes also triggers cell death. H2A.Z binds to the promoters of key nuclear-encoded mitochondrial genes to regulate their expression and promote organelle function. Bolstering mitochondrial activity genetically or by organelle transplant enhances the survival of H2A.Z-ablated neurons. Changes in bioenergetic status alter H2A.Z occupancy at the promoters of nuclear-encoded mitochondrial genes, an adaptive response essential for cell survival. Our results highlight that H2A.Z fulfills a key, conserved role in neuronal survival by acting as a transcriptional rheostat to regulate the expression of genes critical to mitochondrial function.

Early Metazoan Origin and Multiple Losses of a Novel Clade of RIM Presynaptic Calcium Channel Scaffolding Protein Homologs

The precise localization of Ca_V2 voltage-gated calcium channels at the synapse active zone requires various interacting proteins, of which, Rab3-interacting molecule or RIM is considered particularly important. In vertebrates, RIM interacts with Ca_V2 channels in vitro via a PDZ domain that binds to the extreme C-termini of the channels at acidic ligand motifs of D/E-D/E/H-WC-_COOH, and knockout of RIM in vertebrates and invertebrates disrupts Ca_V2 channel synaptic localization and synapse function. Here, we describe a previously uncharacterized clade of RIM proteins bearing domain architectures homologous to those of known RIM homologs, but with some notable differences including key amino acids associated with PDZ domain ligand specificity. This novel RIM emerged near the stem lineage of metazoans and underwent extensive losses, but is retained in select animals including the early-diverging placozoan Trichoplax adhaerens, and molluscs. RNA expression and localization studies in Trichoplax and the mollusc snail Lymnaea stagnalis indicate differential regional/tissue type expression, but overlapping expression in single isolated neurons from Lymnaea. Ctenophores, the most early-diverging animals with synapses, are unique among animals with nervous systems in that they lack the canonical RIM, bearing only the newly identified homolog. Through phylogenetic analysis, we find that Ca_V2 channel D/E-D/E/H-WC-_COOH like PDZ ligand motifs were present in the common ancestor of cnidarians and bilaterians, and delineate some deeply conserved C-terminal structures that distinguish Ca_V1 from Ca_V2 channels, and Ca_V1/Ca_V2 from Ca_V3 channels.

SOX2-Dependent Transcription in Clock Neurons Promotes the Robustness of the Central Circadian Pacemaker

Clock neurons within the mammalian suprachiasmatic nuclei (SCN) encode circadian time using interlocked transcription-translation feedback loops (TTFLs) that drive rhythmic gene expression. However, the contributions of other transcription factors outside of the circadian TTFLs to the functionality of the SCN remain obscure. Here, we report that the stem and progenitor cell transcription factor, sex-determining region Y-box 2 (SOX2), is expressed in adult SCN neurons and positively regulates transcription of the core clock gene, Period2. Mice lacking SOX2 selectively in SCN neurons display imprecise, poorly consolidated behavioral rhythms that do not entrain efficiently to environmental light cycles and that are highly susceptible to constant light-induced arrhythmicity. RNA sequencing revealed that Sox2 deficiency alters the SCN transcriptome, reducing the expression of core clock genes and neuropeptide-receptor systems. By defining the transcriptional landscape within SCN neurons, SOX2 enables the generation of robust, entrainable circadian rhythms that accurately reflect environmental time.

miR-132/212 Modulates Seasonal Adaptation and Dendritic Morphology of the Central Circadian Clock

The central circadian pacemaker, the suprachiasmatic nucleus (SCN), encodes day length information by mechanisms that are not well understood. Here, we report that genetic ablation of miR-132/212 alters entrainment to different day lengths and non-24 hr day-night cycles, as well as photoperiodic regulation of Period2 expression in the SCN. SCN neurons from miR-132/212-deficient mice have significantly reduced dendritic spine density, along with altered methyl CpG-binding protein (MeCP2) rhythms. In Syrian hamsters, a model seasonal rodent, day length regulates spine density on SCN neurons in a melatonin-independent manner, as well as expression of miR-132, miR-212, and their direct target, MeCP2. Genetic disruption of Mecp2 fully restores the level of dendritic spines of miR-132/212-deficient SCN neurons. Our results reveal that, by regulating the dendritic structure of SCN neurons through a MeCP2-dependent mechanism, miR-132/212 affects the capacity of the SCN to encode seasonal time.