The Paraventricular Thalamic Nucleus and Its Projections in Regulating Reward and Context Associations.

The paraventricular thalamic nucleus (PVT) is a brain region that mediates aversive and reward-related behaviors as shown in animals exposed to fear conditioning, natural rewards, or drugs of abuse. However, it is unknown whether manipulations of the PVT, in the absence of external factors or stimuli (e.g., fear, natural rewards, or drugs of abuse), are sufficient to drive reward-related behaviors. Additionally, it is unknown whether drugs of abuse administered directly into the PVT are sufficient to drive reward-related behaviors. Here, using behavioral as well as pathway and cell-type specific approaches, we manipulate PVT activity as well as the PVT-to-nucleus accumbens shell (NAcSh) neurocircuit to explore reward phenotypes. First, we show that bath perfusion of morphine (10 µM) caused hyperpolarization of the resting membrane potential, increased rheobase, and decreased intrinsic membrane excitability in PVT neurons that project to the NAcSh. Additionally, we found that direct injections of morphine (50 ng) in the PVT of mice were sufficient to generate conditioned place preference (CPP) for the morphine-paired chamber. Mimicking the inhibitory effect of morphine, we employed a chemogenetic approach to inhibit PVT neurons that projected to the NAcSh and found that pairing the inhibition of these PVT neurons with a specific context evoked the acquisition of CPP. Lastly, using brain slice electrophysiology, we found that bath-perfused morphine (10 µM) significantly reduced PVT excitatory synaptic transmission on both dopamine D1 and D2 receptor-expressing medium spiny neurons in the NAcSh, but that inhibiting PVT afferents in the NAcSh was not sufficient to evoke CPP.

Iron inhibits glioblastoma cell migration and polarization.

Glioblastoma is one of the deadliest malignancies facing modern oncology today. The ability of glioblastoma cells to diffusely spread into neighboring healthy brain makes complete surgical resection nearly impossible and contributes to the recurrent disease faced by most patients. Although research into the impact of iron on glioblastoma has addressed proliferation, there has been little investigation into how cellular iron impacts the ability of glioblastoma cells to migrate-a key question, especially in the context of the diffuse spread observed in these tumors. Herein, we show that increasing cellular iron content results in decreased migratory capacity of human glioblastoma cells. The decrease in migratory capacity was accompanied by a decrease in cellular polarization in the direction of movement. Expression of CDC42, a Rho GTPase that is essential for both cellular migration and establishment of polarity in the direction of cell movement, was reduced upon iron treatment. We then analyzed a single-cell RNA-seq dataset of human glioblastoma samples and found that cells at the tumor periphery had a gene signature that is consistent with having lower levels of cellular iron. Altogether, our results suggest that cellular iron content is impacting glioblastoma cell migratory capacity and that cells with higher iron levels exhibit reduced motility.

IL-21 from high-affinity CD4 T cells drives differentiation of brain-resident CD8 T cells during persistent viral infection.

Development of tissue-resident memory (TRM) CD8 T cells depends on CD4 T cells. In polyomavirus central nervous system infection, brain CXCR5hi PD-1hi CD4 T cells produce interleukin-21 (IL-21), and CD8 T cells lacking IL-21 receptors (IL21R-/-) fail to become bTRM IL-21+ CD4 T cells exhibit elevated T cell receptor (TCR) affinity and higher TCR density. IL21R-/- brain CD8 T cells do not express CD103, depend on vascular CD8 T cells for maintenance, are antigen recall defective, and lack TRM core signature genes. CD4 T cell-deficient and IL21R-/- brain CD8 T cells show similar deficiencies in expression of genes for oxidative metabolism, and intrathecal delivery of IL-21 to CD4 T cell-depleted mice restores expression of electron transport genes in CD8 T cells to wild-type levels. Thus, high-affinity CXCR5hi PD-1hi CD4 T cells in the brain produce IL-21, which drives CD8 bTRM differentiation in response to a persistent viral infection.

The Nrf2-mediated defense mechanism associated with HFE genotype limits vulnerability to oxidative stress-induced toxicity.

There is considerable interest in gene and environment interactions in neurodegenerative diseases. The HFE (homeostatic iron regulator) gene variant (H63D) is highly prevalent in the population and has been investigated as a disease modifier in multiple neurodegenerative diseases. We have developed a mouse model to interrogate the impact of this gene variant in a model of paraquat toxicity. Using primary astrocytes, we found that the H67D-Hfe(equivalent of the human H63D variant) astrocytes are less vulnerable than the WT-Hfe astrocytes to paraquat-induced cell death, mitochondrial damage, and cellular senescence. We hypothesized that the Hfe variant-associated protection is a result of the activation of the Nrf2 antioxidant defense system and found a significant increase in Nrf2 levels after paraquat exposure in the H67D-Hfe astrocytes than the WT-Hfe astrocytes. Moreover, decreasing Nrf2 by molecular or pharmaceutical manipulation resulted in increased vulnerability to paraquat in the H67D-Hfe astrocytes. To further elucidate the role of Hfe variant genotype in neuroprotection mediated by astrocytes, we added media from the paraquat-treated astrocytes to differentiated SH-SY5Y neuroblastoma cells and found a significantly larger reduction in the viability when treated with WT-Hfe astrocyte media than the H67D-Hfe astrocyte media possibly due to higher secretion of IL-6 observed in the WT-Hfe astrocytes. To further explore the mechanism of Nrf2 protection, we measured NQO1, the Nrf2-mediated antioxidant, in primary astrocytes and found a significantly higher NQO1 level in the H67D-Hfe astrocytes. To consider the translational potential of our findings, we utilized the PPMI (Parkinson's Progression Markers Initiative) clinical database and found that, consistent with the mouse study, H63D-HFE carriers had a significantly higher NQO1 level in the CSF than the WT-HFE carriers. Consistent with our previous reports on H63D-HFE in disease, these data further suggest that HFE genotype in the human population impacts the antioxidant defense system and can therefore alter pathogenesis.

A novel mouse model for the study of endogenous neural stem and progenitor cells after traumatic brain injury.

Traumatic brain injury (TBI) is a leading cause of death and disability in the US. Neural stem/progenitor cells (NSPCs) persist in the adult brain and represent a potential cell source for tissue regeneration and wound healing after injury. The Notch signaling pathway is critical for embryonic development and adult brain injury response. However, the specific role of Notch signaling in the injured brain is not well characterized. Our previous study has established a Notch1CR2-GFP reporter mouse line in which the Notch1CR2 enhancer directs GFP expression in NSPCs and their progeny. In this study, we performed closed head injury (CHI) in the Notch1CR2-GFP mice to study the response of injury-activated NSPCs. We show that CHI induces neuroinflammation, cell death, and the expression of typical TBI markers (e.g., ApoE, Il1b, and Tau), validating the animal model. In addition, CHI induces cell proliferation in GFP+ cells expressing NSPC markers, e.g., Notch1 and Nestin. A significant higher percentage of GFP+ astrocytes and GABAergic neurons was observed in the injured brain, with no significant change in oligodendrocyte lineage between the CHI and sham animal groups. Since injury is known to activate astrogliosis, our results suggest that injury-induced GFP+ NSPCs preferentially differentiate into GABAergic neurons. Our study establishes that Notch1CR2-GFP transgenic mouse is a useful tool for the study of NSPC behavior in vivo after TBI. Unveiling the potential of NSPCs response to TBI (e.g., proliferation and differentiation) will identify new therapeutic strategy for the treatment of brain trauma.

Iron uptake at the blood-brain barrier is influenced by sex and genotype.

Iron transport to the brain is a critically important and highly regulated process necessary for proper brain function. This review aims to summarize iron uptake mechanisms in the brain and the importance of sex and genotype on this uptake. In restless legs syndrome (RLS), brain iron uptake has been hypothesized to be dysregulated, leading to the clinically observed brain iron deficiency, so this review specifically comments on this disorder. The review covers transferrin-bound transport and the more recently discovered role of ferritin in brain iron delivery. Studies on the impact of sex, MEIS1 (associated with RLS), and H63D gene variants have revealed critical regulatory mechanisms and driving factors that significantly impact iron transport that may considerably affect the clinical treatment of RLS. RLS has provided insights into the gaps in knowledge underlying brain iron uptake mechanisms and their regulation, which in turn have provided insights into the pathophysiology of RLS.