Circadian and circannual timescales interact to generate seasonal changes in immune function.

Annual changes in day length enhance or suppress diverse aspects of immune function, giving rise to seasonal cycles of illness and mortality. The daily light-dark cycle also entrains circadian rhythms in immunity. Most published reports on immunological seasonality rely on measurements or interventions performed only at one point in the day. Because there can be no perfect matching of circadian phase across photoperiods of different duration, the manner in which these timescales interact to affect immunity is not understood. We examined whether photoperiodic changes in immune function reflect phenotypic changes that persist throughout the daily cycle, or merely reflect photoperiodic shifts in the circadian phase alignment of immunological rhythms. Diurnal rhythms in blood leukocyte trafficking, infection induced sickness responses, and delayed-type hypersensitivity skin inflammatory responses were examined at high-frequency sampling intervals (every 3 h) in Siberian hamsters (Phodopus sungorus) following immunological adaptation to summer or winter photoperiods. Photoperiod profoundly enhanced or suppressed immune function, in a trait-specific manner, and we were unable to identify a phase alignment of diurnal waveforms which eliminated these enhancing and suppressing effects of photoperiod. These results support the hypothesis that seasonal timescales affect immunity via mechanisms independent of circadian entrainment of the immunological circadian waveform.

The age-dependent immune response to ischemic stroke.

Stroke is a devastating cause of global morbidity and mortality. Ischemic brain injury triggers a profound local and systemic immune response that participates in stroke pathophysiology. In turn, this immune response has emerged as a potential therapeutic target. In order to maximize its therapeutic potential, it is critical to understand how the immune response to ischemic brain injury is affected by age - the strongest non-modifiable risk factor for stroke. The development of multi-omics and single-cell technologies has provided a more comprehensive characterization of transcriptional and cellular changes that occur during aging. In this review, we summarize recent advances in our understanding of how age-related immune alterations shape differential stroke outcomes in older versus younger organisms, highlighting studies in both experimental mouse models and patient cohorts. Wherever possible, we emphasize outstanding questions that present important avenues for future investigation with therapeutic value for the aging population.

Rab7a activation promotes degradation of select tight junction proteins at the blood-brain barrier after ischemic stroke.

The stability of tight junctions (TJs) between endothelial cells (ECs) is essential to maintain blood-brain barrier (BBB) function in the healthy brain. Following ischemic stroke, TJ strand dismantlement due to protein degradation leads to BBB dysfunction, yet the mechanisms driving this process are poorly understood. Here, we show that endothelial-specific ablation of Rab7a, a small GTPase that regulates endolysosomal protein degradation, reduces stroke-induced TJ strand disassembly resulting in decreased paracellular BBB permeability and improved neuronal outcomes. Two pro-inflammatory cytokines, TNFα and IL1ß, but not glucose and oxygen deprivation, induce Rab7a activation via Ccz1 in brain ECs in vitro, leading to increased TJ protein degradation and impaired paracellular barrier function. Silencing Rab7a in brain ECs in vitro reduces cytokine-driven endothelial barrier dysfunction by suppressing degradation of a key BBB TJ protein, Claudin-5. Thus, Rab7a activation by inflammatory cytokines promotes degradation of select TJ proteins leading to BBB dysfunction after ischemic stroke.

Neurovascular dynamics of repeated cortical spreading depolarizations after acute brain injury.

Cortical spreading depolarizations (CSDs) are increasingly suspected to play an exacerbating role in a range of acute brain injuries, including stroke, possibly through their interactions with cortical blood flow. We use simultaneous wide-field imaging of neural activity and hemodynamics in Thy1-GCaMP6f mice to explore the neurovascular dynamics of CSDs during and following Rose Bengal-mediated photothrombosis. CSDs are observed in all mice as slow-moving waves of GCaMP fluorescence extending far beyond the photothrombotic area. Initial CSDs are accompanied by profound vasoconstriction and leave residual oligemia and ischemia in their wake. Later, CSDs evoke variable responses, from constriction to biphasic to vasodilation. However, CSD-evoked vasoconstriction is found to be more likely during rapid, high-amplitude CSDs in regions with stronger oligemia and ischemia, which, in turn, worsens after each repeated CSD. This feedback loop may explain the variable but potentially devastating effects of CSDs in the context of acute brain injury.

Obesity is independently associated with septic shock, renal complications, and mortality in a multiracial patient cohort hospitalized with COVID-19.

BACKGROUND: Obesity has emerged as a risk factor for severe coronavirus disease 2019 (COVID-19) infection. To inform treatment considerations the relationship between obesity and COVID-19 complications and the influence of race, ethnicity, and socioeconomic factors deserves continued attention. OBJECTIVE: To determine if obesity is an independent risk factor for severe COVID-19 complications and mortality and examine the relationship between BMI, race, ethnicity, distressed community index and COVID-19 complications and mortality. METHODS: A retrospective cohort study of 1,019 SARS-CoV-2 positive adult admitted to an academic medical center (n = 928) and its affiliated community hospital (n-91) in New York City from March 1 to April 18, 2020. RESULTS: Median age was 64 years (IQR 52-75), 58.7% were men, 23.0% were Black, and 52.8% were Hispanic. The prevalence of overweight and obesity was 75.2%; median BMI was 28.5 kg/m2 (25.1-33.0). Over the study period 23.7% patients died, 27.3% required invasive mechanical ventilation, 22.7% developed septic shock, and 9.1% required renal replacement therapy (RRT). In the multivariable logistic regression model, BMI was associated with complications including intubation (Odds Ratio [OR]1.03, 95% Confidence Interval [CI]1.01-1.05), septic shock (OR 1.04, CI 1.01-1.06), and RRT (OR1.07, CI 1.04-1.10), and mortality (OR 1.04, CI 1.01-1.06). The odds of death were highest among those with BMI ≥ 40 kg/m2 (OR 2.05, CI 1.04-4.04). Mortality did not differ by race, ethnicity, or socioeconomic distress score, though Black and Asian patients were more likely to require RRT. CONCLUSIONS AND RELEVANCE: Severe complications of COVID-19 and death are more likely in patients with obesity, independent of age and comorbidities. While race, ethnicity, and socioeconomic status did not impact COVID-19 related mortality, Black and Asian patients were more likely to require RRT. The presence of obesity, and in some instances race, should inform resource allocation and risk stratification in patients hospitalized with COVID-19.

Clinical and electrographic features of persistent seizures and status epilepticus associated with anti-NMDA receptor encephalitis (anti-NMDARE).

Based on a multicenter cohort of people with anti-NMDA receptor encephalitis (anti-NMDARE), we describe seizure phenotypes, electroencephalographic (EEG) findings, and anti-seizure treatment strategies. We also investigated whether specific electrographic features are associated with persistent seizures or status epilepticus after acute presentation. In this retrospective cohort study, we reviewed records of children and adults with anti-NMDARE between 2010 and 2014 who were included in the Rare Epilepsy of New York City database, which included the text of physician notes from five academic medical centers. Clinical history (e.g., seizure semiology) and EEG features (e.g., background organization, slowing, epileptiform activity, seizures, sleep architecture, extreme delta brush) were abstracted. We compared clinical features associated with persistent seizures (ongoing seizures after one month from presentation) and status epilepticus, using bivariate and multivariable analyses. Among the 38 individuals with definite anti-NMDARE, 32 (84%) had seizures and 29 (76%) had seizures captured on EEG. Electrographic-only seizures were identified in five (13%) individuals. Seizures started at a median of four days after initial symptoms (IQR: 3-6 days). Frontal lobe-onset focal seizures were most common (n=12; 32%). Most individuals (31/38; 82%) were refractory to anti-seizure medications. Status epilepticus was associated with younger age (15 years [9-20] vs. 23 years [18-27]; p=0.04) and Hispanic ethnicity (30 [80%] vs. 8 [36%]; p=0.04). Persistent seizures (ongoing seizures after one month from presentation) were associated with younger age (nine years [3-14] vs. 22 years [15-28]; p<0.01). Measured electrographic features were not associated with persistent seizures. Seizures associated with anti-NMDARE are primarily focal seizures originating in the frontal lobes. Younger patients may be at increased risk of epileptogenesis and status epilepticus. Continuous EEG monitoring helps identify subclinical seizures, but specific EEG findings may not predict the severity or persistence of seizures during hospitalization.