Oscillatory Behaviors of microRNA Networks: Emerging Roles in Retinal Development

Circadian Biology in Obstructive Sleep Apnea-Associated Cardiovascular Disease

A dysregulated circadian system is independently associated with both Obstructive Sleep Apnea (OSA) and cardiovascular disease (CVD). OSA and CVD coexistence is often seen in patients with prolonged untreated OSA. However, the role of circadian dysregulation in their relationship is unclear. Half of the human genes, associated biological pathways, and physiological functions exhibit circadian rhythms, including blood pressure and heart rate regulation. Mechanisms related to circadian dysregulation and heart function are potentially involved in the coexistence of OSA and CVD. In this article, we provide a comprehensive overview of circadian dysregulation in OSA and associated CVD. We also discuss feasible animal models and new avenues for future research to understand their relationship. Oxygen-sensing pathways, inflammation, dysregulation of cardiovascular processes, oxidative stress, metabolic regulation, hormone signaling, and epigenetics are potential clock-regulated mechanisms connecting OSA and CVD.

Mathematical Modeling for Oscillations Driven by Noncoding RNAs

In this chapter, we first survey strategies for the mathematical modeling of gene regulatory networks for capturing physiologically important dynamics in cells such as oscillations. We focus on models based on ordinary differential equations with various forms of nonlinear functions that describe gene regulations. We next use a small system of a microRNA and its mRNA target to illustrate a recently discovered oscillator driven by noncoding RNAs. This oscillator has unique features that distinguish it from conventional biological oscillators, including the absence of an imposed negative feedback loop and the divergence of the periods. The latter property may serve crucial biological functions for restoring heterogeneity of cell populations on the timescale of days. We describe general requirements for obtaining the limit cycle oscillations in terms of underlying biochemical reactions and kinetic rate constants. We discuss future directions stemming from this minimal, noncoding RNA-based model for gene expression oscillation.

Epigenetic Switches in Retinal Homeostasis and Target for Drug Development

Retinal homeostasis, a tightly regulated process maintaining the functional integrity of the retina, is vital for visual function. Emerging research has unveiled the critical role of epigenetic regulation in controlling gene expression patterns during retinal development, maintenance, and response to mutational loads and injuries. Epigenetic switches, including DNA methylation, histone modifications, and non-coding RNAs, play pivotal roles in orchestrating retinal gene expression and cellular responses through various intracellular, extracellular, and environmental modulators. This review compiles the current knowledge on epigenetic switches in retinal homeostasis, providing a deeper understanding of their impact on retinal structural integrity and function and using them as potential targets for therapeutic interventions.

MIR204 n.37C>T variant as a cause of chorioretinal dystrophy variably associated with iris coloboma, early-onset cataracts and congenital glaucoma

Four members of a three-generation Czech family with early-onset chorioretinal dystrophy were shown to be heterozygous carriers of the n.37C>T in MIR204. The identification of this previously reported pathogenic variant confirms the existence of a distinct clinical entity caused by a sequence change in MIR204. Chorioretinal dystrophy was variably associated with iris coloboma, congenital glaucoma, and premature cataracts extending the phenotypic range of the condition. In silico analysis of the n.37C>T variant revealed 713 novel targets. Additionally, four family members were shown to be affected by albinism resulting from biallelic pathogenic OCA2 variants. Haplotype analysis excluded relatedness with the original family reported to harbour the n.37C>T variant in MIR204. Identification of a second independent family confirms the existence of a distinct MIR204-associated clinical entity and suggests that the phenotype may also involve congenital glaucoma.

Light-responsive microRNA molecules in human retinal organoids are differentially regulated by distinct wavelengths of light

Cells in the human retina must rapidly adapt to constantly changing visual stimuli. This fast adaptation to varying levels and wavelengths of light helps to regulate circadian rhythms and allows for adaptation to high levels of illumination, thereby enabling the rest of the visual system to remain responsive. It has been shown that retinal microRNA (miRNA) molecules play a key role in regulating these processes. However, despite extensive research using various model organisms, light-regulated miRNAs in human retinal cells remain unknown. Here, we aim to characterize these miRNAs. We generated light-responsive human retinal organoids that express miRNA families and clusters typically found in the retina. Using an in-house developed photostimulation device, we identified a subset of light-regulated miRNAs. Importantly, we found that these miRNAs are differentially regulated by distinct wavelengths of light and have a rapid turnover, highlighting the dynamic and adaptive nature of the human retina.

miR-9 utilizes precursor pathways in adaptation to alcohol in mouse striatal neurons

microRNA-9 (miR-9) is one of the most abundant microRNAs in the mammalian brain, essential for its development and normal function. In neurons, it regulates the expression of several key molecules, ranging from ion channels to enzymes, to transcription factors broadly affecting the expression of many genes. The neuronal effects of alcohol, one of the most abused drugs in the world, seem to be at least partially dependent on regulating the expression of miR-9. We previously observed that molecular mechanisms of the development of alcohol tolerance are miR-9 dependent. Since a critical feature of alcohol action is temporal exposure to the drug, we decided to better understand the time dependence of alcohol regulation of miR-9 biogenesis and expression. We measured the effect of intoxicating concentration of alcohol (20 mM ethanol) on the expression of all major elements of miR-9 biogenesis: three pri-precursors (pri-mir-9-1, pri-mir-9-2, pri-mir-9-3), three pre-precursors (pre-mir-9-1, pre-mir-9-2, pre-mir-9-3), and two mature microRNAs: miR-9-5p and miR-9-3p, using digital PCR and RT-qPCR, and murine primary medium spiny neurons (MSN) cultures. We subjected the neurons to alcohol based on an exposure/withdrawal matrix of different exposure times (from 15 min to 24 h) followed by different withdrawal times (from 0 h to 24 h). We observed that a short exposure increased mature miR-9-5p expression, which was followed by a gradual decrease and subsequent increase of the expression, returning to pre-exposure levels within 24 h. Temporal changes of miR-9-3p expression were complementing miR-9-5p changes. Interestingly, an extended, continuous presence of the drug caused a similar pattern. These results suggest the presence of the adaptive mechanisms of miR-9 expression in the presence and absence of alcohol. Measurement of miR-9 pre- and pri-precursors showed further that the primary effect of alcohol on miR-9 is through the mir-9-2 precursor pathway with a smaller contribution of mir-9-1 and mir-9-3 precursors. Our results provide new insight into the adaptive mechanisms of neurons to alcohol exposure. It would be of interest to determine next which microRNA-based mechanisms are involved in a transition from the acute, intoxicating effects of alcohol to the chronic, addictive effects of the drug.

Notch directs telencephalic development and controls neocortical neuron fate determination by regulating microRNA levels

The central nervous system contains a myriad of different cell types produced from multipotent neural progenitors. Neural progenitors acquire distinct cell identities depending on their spatial position, but they are also influenced by temporal cues to give rise to different cell populations over time. For instance, the progenitors of the cerebral neocortex generate different populations of excitatory projection neurons following a well-known sequence. The Notch signaling pathway plays crucial roles during this process, but the molecular mechanisms by which Notch impacts progenitor fate decisions have not been fully resolved. Here, we show that Notch signaling is essential for neocortical and hippocampal morphogenesis, and for the development of the corpus callosum and choroid plexus. Our data also indicate that, in the neocortex, Notch controls projection neuron fate determination through the regulation of two microRNA clusters that include let-7, miR-99a/100 and miR-125b. Our findings collectively suggest that balanced Notch signaling is crucial for telencephalic development and that the interplay between Notch and miRNAs is essential for the control of neocortical progenitor behaviors and neuron cell fate decisions.