Potential protective role of IL15Rα during inflammation

Development of circadian neurovascular function and its implications

The neurovascular system forms the interface between the tissue of the central nervous system (CNS) and circulating blood. It plays a critical role in regulating movement of ions, small molecules, and cellular regulators into and out of brain tissue and in sustaining brain health. The neurovascular unit (NVU), the cells that form the structural and functional link between cells of the brain and the vasculature, maintains the blood-brain interface (BBI), controls cerebral blood flow, and surveils for injury. The neurovascular system is dynamic; it undergoes tight regulation of biochemical and cellular interactions to balance and support brain function. Development of an intrinsic circadian clock enables the NVU to anticipate rhythmic changes in brain activity and body physiology that occur over the day-night cycle. The development of circadian neurovascular function involves multiple cell types. We address the functional aspects of the circadian clock in the components of the NVU and their effects in regulating neurovascular physiology, including BBI permeability, cerebral blood flow, and inflammation. Disrupting the circadian clock impairs a number of physiological processes associated with the NVU, many of which are correlated with an increased risk of dysfunction and disease. Consequently, understanding the cell biology and physiology of the NVU is critical to diminishing consequences of impaired neurovascular function, including cerebral bleeding and neurodegeneration.

Circadian rhythms in the blood-brain barrier: impact on neurological disorders and stress responses

Circadian disruption has become more prevalent in society due to the increase in shift work, sleep disruption, blue light exposure, and travel via different time zones. The circadian rhythm is a timed transcription-translation feedback loop with positive regulators, BMAL1 and CLOCK, that interact with negative regulators, CRY and PER, to regulate both the central and peripheral clocks. This review highlights the functions of the circadian rhythm, specifically in the blood-brain barrier (BBB), during both healthy and pathological states. The BBB is a highly selective dynamic interface composed of CNS endothelial cells, astrocytes, pericytes, neurons, and microglia that form the neurovascular unit (NVU). Circadian rhythms modulate BBB integrity through regulating oscillations of tight junction proteins, assisting in functions of the NVU, and modulating transporter functions. Circadian disruptions within the BBB have been observed in stress responses and several neurological disorders, including brain metastasis, epilepsy, Alzheimer's disease, and Parkinson's disease. Further understanding of these interactions may facilitate the development of improved treatment options and preventative measures.

Schizophrenia Patient Shows a Rare Interleukin 15 Receptor alpha Variant Disrupting Signal Transduction

BACKGROUND

Schizophrenia is a complex and debilitating mental disorder with strong heritability. Its pathogenesis involves immune dysregulation. Interleukin 15 and interleukin 15 receptor alpha(IL-15Rα) are classical immune molecules. They also help maintain normal brain function, leading to our hypothesis that IL-15Rα gene(IL- 15RA) variants contribute to the pathogenesis of schizophrenia.

OBJECTIVE

We determine whether the genetic variants of IL-15RA are associated with the development and progression of schizophrenia and whether IL-15RA single nucleotide polymorphism(SNP) plays a key role in downstream signaling transduction.

METHODS AND RESULTS

We sequenced IL-15RA exon from 132 Chinese schizophrenic patients and identified a rare variant(rs528238821) in a patient diagnosed with catatonic schizophrenia and ankylosing spondylitis(AS). We overexpressed this missense variant in cells driven by pBI-CMV vector. The cells showed attenuated STAT3 phosphorylation in response to interleukin15.

CONCLUSION

IL-15RA mutation is rare in schizophrenic patients but interfered with IL- 15Rα intracellular signal transduction. Given the similarity of symptoms of catatonic schizophrenia and the known phenotype of IL-15Rα knockout mice, gene variation might offer diagnostic value for sub-types of schizophrenia.

Circadian rhythm of autophagy proteins in hippocampus is blunted by sleep fragmentation

Autophagy is essential for normal cellular survival and activity. Circadian rhythms of autophagy have been studied in several peripheral organs but not yet reported in the brain. Here, we measured the circadian rhythm of autophagy-related proteins in mouse hippocampus and tested the effect of sleep fragmentation (SF). Expressions of the autophagy-related proteins microtubule-associated protein 1 light chain 3 (LC3) and beclin were determined by western blotting and immunohistochemistry. Both the hippocampal LC3 signal and the ratio of its lipid-conjugated form LC3-II to its cytosolic form LC3-I showed a 24 h rhythm. The peak was seen at ZT6 (1 pm) and the nadir at ZT16 (1 am). The LC3 immunoreactivity in hippocampal CA1 pyramidal neurons also distributed differently, with more diffuse cytoplasmic appearance at ZT16. Chronic SF had a mild effect to disrupt the 24 h rhythm of LC3 and beclin expression. Interestingly, a greater effect of SF was seen after 24 h of recovery sleep when LC3-II expression was attenuated at both the peak and trough of circadian activities. Overall, the results show for the first time that the hippocampus has a distinct rhythm of autophagy that can be altered by SF.

Diminished leptin signaling can alter circadian rhythm of metabolic activity and feeding

Leptin, a hormone mainly produced by fat cells, shows cell-specific effects to regulate feeding and metabolic activities. We propose that an important feature of metabolic dysregulation resulting in obesity is the loss of the circadian rhythm of biopotentials. This was tested in the pan-leptin receptor knockout (POKO) mice newly generated in our laboratory. In the POKO mice, leptin no longer induced pSTAT-3 signaling after intracerebroventricular injection. Three basic phenotypes were observed: the heterozygotes had similar weight and adiposity as the wild-type (WT) mice (>60% of the mice); the homozygotes were either fatter (∼30%), or rarely leaner (<5%) than the WT mice. By early adulthood, the POKO mice had higher average body weight and adiposity than their respective same-sex WT littermate controls, and this was consistent among different batches. The homozygote fat POKO showed significant reduction of midline estimating statistic of rhythm of circadian parameters, and shifts of ultradian rhythms. The blunted circadian rhythm of these extremely obese POKO mice was also seen in their physical inactivity, longer feeding bouts, and higher food intake. The extent of obesity correlated with the blunted circadian amplitude, accumulative metabolic and locomotor activities, and the severity of hyperphagia. This contrasts with the heterozygote POKO mice which showed little obesity and metabolic disturbance, and only subtle changes of the circadian rhythm of metabolic activity without alterations in feeding behavior. The results provide a novel aspect of leptin resistance, almost manifesting as an "all or none" phenomenon.

Endothelial leptin receptor mutation provides partial resistance to diet-induced obesity

Leptin, a polypeptide hormone produced mainly by adipocytes, has diverse effects in both the brain and peripheral organs, including suppression of feeding. Other than mediating leptin transport across the blood-brain barrier, the role of the endothelial leptin receptor remains unclear. We recently generated a mutant mouse strain lacking endothelial leptin receptor signaling, and showed that there is an increased uptake of leptin by brain parenchyma after its delivery by in situ brain perfusion. Here, we tested the hypothesis that endothelial leptin receptor mutation confers partial resistance to diet-induced obesity. These ELKO mice had similar body weight and percent fat as their wild-type littermates when fed with rodent chow, but blood concentrations of leptin were significantly elevated. In response to a high-fat diet, wild-type mice had a greater gain of body weight and fat than ELKO mice. As shown by metabolic chamber measurement, the ELKO mice had higher oxygen consumption, carbon dioxide production, and heat dissipation, although food intake was similar to that of the wild-type mice and locomotor activity was even reduced. This indicates that the partial resistance to diet-induced obesity was mediated by higher metabolic activity in the ELKO mice. Since neuronal leptin receptor knockout mice show obesity and diabetes, the results suggest that endothelial leptin signaling shows opposite effects from that of neuronal leptin signaling, with a facilitatory role in diet-induced obesity.

NFĸB is an unexpected major mediator of interleukin-15 signaling in cerebral endothelia

Interleukin (IL)-15 and its receptors are induced by tumor necrosis factor α (TNF) in the cerebral endothelial cells composing the blood-brain barrier, but it is not yet clear how IL-15 modulates endothelial function. Contrary to the known induction of JAK/STAT3 signaling, here we found that nuclear factor (NF)- κB is mainly responsible for IL-15 actions on primary brain microvessel endothelial cells and cerebral endothelial cell lines. IL-15-induced transactivation of an NFκB luciferase reporter resulted in phosphorylation and degradation of the inhibitory subunit IκB that was followed by phosphorylation and nuclear translocation of the p65 subunit of NFκB. An IκB kinase inhibitor Bay 11-7082 only partially inhibited IL-15-induced NFκB luciferase activity. The effect of IL-15 was mediated by its specific receptor IL-15Rα, since endothelia from IL-15Rα knockout mice showed delayed nuclear translocation of p65, whereas those from knockout mice lacking a co-receptor IL-2Rγ did not show such changes. At the mRNA level, IL-15 and TNF showed similar effects in decreasing the tight junction protein claudin-2 and increasing the p65 subunit of NFκB but exerted different regulation on caveolin-1 and vimentin. Taken together, NFκB is a major signal transducer by which IL-15 affects cellular permeability, endocytosis, and intracellular trafficking at the level of the blood-brain barrier.

Rapid endocytosis of interleukin-15 by cerebral endothelia

Interleukin (IL)-15 receptors are present in the cerebral endothelia composing the blood-brain barrier where they show robust up-regulation by neuroinflammation. To determine how IL15 receptor subunits participate in the endocytosis and intracellular trafficking of IL15, we performed confocal microscopic imaging and radioactive tracer uptake assays in primary brain microvessel endothelial cells and related cell lines transfected with modulatory molecules. By immunostaining and co-localization studies with organelle markers, we showed that IL15 was rapidly endocytosed via lipid rafts and was directed to diverse intracellular pathways. During the course of intracellular trafficking, Alexa dye-conjugated IL15 was partially co-localized with both the specific receptor IL15Rα and the co-receptor IL2Rγ. However, deletion of one of the receptor subunits had only a minor effect in slowing IL15 uptake when primary brain microvessel endothelial cells from the receptor knockout mice were compared with those from wildtype mice. IL15 was trafficked to early, recycling, and late endosomes, to the Golgi, and to lysosomes. The diffuse distribution suggests that IL15 activates multiple endothelial signaling events.

Astrocytes modulate distribution and neuronal signaling of leptin in the hypothalamus of obese A vy mice

We tested the hypothesis that astrocytic activity modulates neuronal uptake and signaling of leptin in the adult-onset obese agouti viable yellow (A vy) mouse. In the immunohistochemical study, A vy mice were pretreated with the astrocyte metabolic inhibitor fluorocitrate or phosphate-buffered saline (PBS) vehicle intracerebroventricularly (icv) followed 1 h later by Alexa568-leptin. Confocal microscopy showed that fluorocitrate pretreatment reduced astrocytic uptake of Alexa568-leptin 30 min after icv while increasing neuronal uptake in the arcuate nucleus and dorsomedial hypothalamus. Fluorocitrate also induced mild astrogliosis and moderately increased pSTAT3 immunopositive neurons in response to Alexa568-leptin in the dorsomedial hypothalamus. In the Western blotting study, A vy mice were pretreated with either PBS or fluorocitrate, and received PBS or leptin 1 h later followed by determination of pSTAT3 and GFAP expression an additional 30 min afterward. The results show that fluorocitrate induced a mild pSTAT3 activation but attenuated leptin-induced pSTAT3 activation and decreased GFAP expression independently of leptin treatment. We conclude that inhibition of astrocytic activity resulted in enhanced neuronal leptin uptake and signaling. This suggests opposite roles of astrocytes and neurons in leptin's actions in the A vy mouse with adult-onset obesity.