Complexity of Host Micro‐RNA Response to Cytomegalovirus Reactivation After Organ Transplantation

Human (Homo sapiens) micro‐RNAs (hsa‐miRNAs) regulate virus and host‐gene translation, but the biological impact in patients with human cytomegalovirus (hCMV) infection is not well defined in a clinically relevant model. First, we compared hsa‐miRNA expression profiles in peripheral blood mononuclear cells from 35 transplant recipients with and without CMV viremia by using a microarray chip covering 847 hsa‐miRNAs. This approach demonstrated a set of 142 differentially expressed hsa‐miRNAs. Next, we examined the effect of each of these miRNAs on viral growth by using human fibroblasts (human foreskin fibroblast‐1) infected with the hCMV Towne strain, identifying a subset of proviral and antiviral hsa‐miRNAs. miRNA‐target prediction software indicated potential binding sites within the hCMV genome (e.g., hCMV‐UL52 and ‐UL100 [UL = unique long]) and host‐genes (e.g., interleukin‐1 receptor, IRF1). Luciferase‐expressing plasmid constructs and immunoblotting confirmed several predicted miRNA targets. Finally, we determined the expression of selected proviral and antiviral hsa‐miRNAs in 242 transplant recipients with hCMV‐viremia. We measured hsa‐miRNAs before and after antiviral therapy and correlated hsa‐miRNA expression levels to hCMV‐replication dynamics. One of six antiviral hsa‐miRNAs showed a significant increase during treatment, concurrent with viral decline. In contrast, six of eight proviral hsa‐miRNAs showed a decrease during viral decline. Our results indicate that a complex and multitargeted hsa‐miRNA response occurs during CMV replication in immunosuppressed patients. This study provides mechanistic insight and potential novel biomarkers for CMV replication.     

Mathematical model of network dynamics governing mouse sleep-wake behavior

Recent work in experimental neurophysiology has identified distinct neuronal populations in the rodent brain stem and hypothalamus that selectively promote wake and sleep. Mutual inhibition between these cell groups has suggested the conceptual model of a sleep-wake switch that controls transitions between wake and sleep while minimizing time spent in intermediate states. By combining wake- and sleep-active populations with populations governing transitions between different stages of sleep, a "sleep-wake network" of neuronal populations may be defined. To better understand the dynamics inherent in this network, we created a model sleep-wake network composed of coupled relaxation oscillation equations. Mathematical analysis of the deterministic model provides insight into the dynamics underlying state transitions and predicts mechanisms for each transition type. With the addition of noise, the simulated sleep-wake behavior generated by the model reproduces many qualitative and quantitative features of mouse sleep-wake behavior. In particular, the existence of simulated brief awakenings is a unique feature of the model. In addition to capturing the experimentally observed qualitative difference between brief and sustained wake bouts, the model suggests distinct network mechanisms for the two types of wakefulness. Because circadian and other factors alter the fine architecture of sleep-wake behavior, this model provides a novel framework to explore dynamical principles that may underlie normal and pathologic sleep-wake physiology.