Investigating peripheral blood monocyte and T-cell subsets as non-invasive biomarkers for asymptomatic hepatic steatosis: results from the Multi-Ethnic Study of Atherosclerosis.

Background: Circulating immune cells have gained interest as biomarkers of hepatic steatosis. Data on the relationships between immune cell subsets and early-stage steatosis in population-based cohorts are limited. Methods: This study included 1,944 asymptomatic participants of the Multi-Ethnic Study of Atherosclerosis (MESA) with immune cell phenotyping and computed tomography measures of liver fat. Participants with heavy alcohol use were excluded. A liver-to-spleen ratio Hounsfield units (HU) <1.0 and liver attenuation <40 HU were used to diagnose liver fat presence and >30% liver fat content, respectively. Logistic regression estimated cross-sectional associations of immune cell subsets with liver fat parameters adjusted for risk factors. We hypothesized that higher proportions of non-classical monocytes, Th1, Th17, and memory CD4+ T cells, and lower proportions of classical monocytes and naive CD4+ T cells, were associated with liver fat. Exploratory analyses evaluated additional immune cell phenotypes (n = 19). Results: None of the hypothesized cells were associated with presence of liver fat. Higher memory CD4+ T cells were associated with >30% liver fat content, but this was not significant after correction for multiple hypothesis testing (odds ratio (OR): 1.31, 95% confidence interval (CI): 1.03, 1.66). In exploratory analyses unadjusted for multiple testing, higher proportions of CD8+CD57+ T cells were associated with liver fat presence (OR: 1.21, 95% CI: 1.02, 1.44) and >30% liver fat content (OR: 1.34, 95% CI: 1.07, 1.69). Conclusions: Higher circulating memory CD4+ T cells may reflect liver fat severity. CD8+CD57+ cells were associated with liver fat presence and severity, but replication of findings is required.

Effects of early life seizures on coordination of hippocampal-prefrontal networks: Influence of sex and dynamic brain states.

OBJECTIVE: Early life seizures (ELSs) alter activity-dependent maturation of neuronal circuits underlying learning and memory. The pathophysiological mechanisms underpinning seizure-induced cognitive impairment are not fully understood, and critical variables such as sex and dynamic brain states with regard to cognitive outcomes have not been explored. We hypothesized that in comparison to control (CTL) rats, ELS rats would exhibit deficits in spatial cognition correlating with impaired dynamic neural signal coordination between the hippocampus and medial prefrontal cortex (mPFC). METHODS: Male and female rat pups were given 50 flurothyl-induced seizures over 10 days starting at postnatal Day 15. As adults, spatial cognition was tested through active avoidance on a rotating arena. Microwire tetrodes were implanted in the mPFC and CA1 subfield. Single cells and local field potentials were recorded and analyzed in each region during active avoidance and sleep. RESULTS: ELS males exhibited avoidance impairments, whereas female rats were unaffected. During avoidance, hippocampus-mPFC coherence was higher in CTL females than CTL males across bandwidths. In comparison to CTL males, ELS male learners exhibit increased coherence within theta bandwidth as well as altered burst-timing in mPFC cell activity. Hippocampus-mPFC coherence levels are predictive of cognitive outcome in the active avoidance spatial task. SIGNIFICANCE: Spatial cognitive outcome post-ELS is sex-dependent, as females fare better than males. ELS males that learn the task exhibit increased mPFC coherence levels at low-theta frequency, which may compensate for ELS effects on mPFC cell timing. These results suggest that coherence may serve as a biomarker for spatial cognitive outcome post-ELS and emphasize the significance of analyzing sex and dynamic cognition as variables in understanding seizure effects on the developing brain.

Disruption of hippocampal rhythms via optogenetic stimulation during the critical period for memory development impairs spatial cognition.

BACKGROUND: Hippocampal oscillations play a critical role in the ontogeny of allocentric memory in rodents. During the critical period for memory development, hippocampal theta is the driving force behind the temporal coordination of neuronal ensembles underpinning spatial memory. While known that hippocampal oscillations are necessary for normal spatial cognition, whether disrupted hippocampal oscillatory activity during the critical period impairs long-term spatial memory is unknown. Here we investigated whether disruption of normal hippocampal rhythms during the critical period have enduring effects on allocentric memory in rodents. OBJECTIVE/HYPOTHESIS: We hypothesized that disruption of hippocampal oscillations via artificial regulation of the medial septum during the critical period for memory development results in long-standing deficits in spatial cognition. METHODS: After demonstrating that pan-neuronal medial septum (MS) optogenetic stimulation (465 nm activated) regulated hippocampal oscillations in weanling rats we used a random pattern of stimulation frequencies to disrupt hippocampal theta rhythms for either 1Hr or 5hr a day between postnatal (P) days 21-25. Non-stimulated and yellow light-stimulated (590 nm) rats served as controls. At P50-60 all rats were tested for spatial cognition in the active avoidance task. Rats were then sacrificed, and the MS and hippocampus assessed for cell loss. Power spectrum density of the MS and hippocampus, coherences and voltage correlations between MS and hippocampus were evaluated at baseline for a range of stimulation frequencies from 0.5 to 110 Hz and during disruptive hippocampal stimulation. Unpaired t-tests and ANOVA were used to compare oscillatory parameters, behavior and cell density in all animals. RESULTS: Non-selective optogenetic stimulation of the MS in P21 rats resulted in precise regulation of hippocampal oscillations with 1:1 entrainment between stimulation frequency (0.5-110 Hz) and hippocampal local field potentials. Across bandwidths MS stimulation increased power, coherence and voltage correlation at all frequencies whereas the disruptive stimulation increased power and reduced coherence and voltage correlations with most statistical measures highly significant (p < 0.001, following correction for false detection). Rats receiving disruptive hippocampal stimulation during the critical period for memory development for either 1Hr or 5hr had marked impairment in spatial learning as measured in active avoidance test compared to non-stimulated or yellow light-control rats (p < 0.001). No cell loss was measured between the blue-stimulated and non-stimulated or yellow light-stimulated controls in either the MS or hippocampus. CONCLUSION: The results demonstrated that robust regulation of hippocampal oscillations can be achieved with non-selective optogenetic stimulation of the MS in rat pups. A disruptive hippocampal stimulation protocol, which markedly increases power and reduces coherence and voltage correlations between the MS and hippocampus during the critical period of memory development, results in long-standing spatial cognitive deficits. This spatial cognitive impairment is not a result of optogenetic stimulation-induced cell loss.