Highlights d Fasting reduces the numbers of circulating monocytes in healthy humans and mice d Fasting also reduces monocyte metabolic and inflammatory activity d Hepatic energy-sensing regulates homeostatic monocyte numbers via CCL2 production d Fasting improves inflammatory diseases without compromising antimicrobial immunity

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*These authors contributed equally to this work.In inflammatory central nervous system conditions such as multiple sclerosis, breakdown of the blood-brain barrier is a key event in lesion pathogenesis, predisposing to oedema, excitotoxicity, and ingress of plasma proteins and inflammatory cells. Recently, we showed that reactive astrocytes drive blood-brain barrier opening, via production of vascular endothelial growth factor A (VEGFA). Here, we now identify thymidine phosphorylase (TYMP; previously known as endothelial cell growth factor 1, ECGF1) as a second key astrocyte-derived permeability factor, which interacts with VEGFA to induce blood-brain barrier disruption. The two are co-induced NFB1-dependently in human astrocytes by the cytokine interleukin 1 beta (IL1B), and inactivation of Vegfa in vivo potentiates TYMP induction. In human central nervous system microvascular endothelial cells, VEGFA and the TYMP product 2-deoxy-D-ribose cooperatively repress tight junction proteins, driving permeability. Notably, this response represents part of a wider pattern of endothelial plasticity: 2-deoxy-D-ribose and VEGFA produce transcriptional programs encompassing angiogenic and permeability genes, and together regulate a third unique cohort. Functionally, each promotes proliferation and viability, and they cooperatively drive motility and angiogenesis. Importantly, introduction of either into mouse cortex promotes blood-brain barrier breakdown, and together they induce severe barrier disruption. In the multiple sclerosis model experimental autoimmune encephalitis, TYMP and VEGFA co-localize to reactive astrocytes, and correlate with blood-brain barrier permeability. Critically, blockade of either reduces neurologic deficit, blood-brain barrier disruption and pathology, and inhibiting both in combination enhances tissue preservation. Suggesting importance in human disease, TYMP and VEGFA both localize to reactive astrocytes in multiple sclerosis lesion samples. Collectively, these data identify TYMP as an astrocyte-derived permeability factor, and suggest TYMP and VEGFA together promote blood-brain barrier breakdown.

Growth factors of the gp130 family promote oligodendrocyte differentiation, and viability, and myelination, but their mechanisms of action are incompletely understood. Here, we show that these effects are coordinated, in part, by the transcriptional activator Krüppel-like factor-6 (Klf6). Klf6 is rapidly induced in oligodendrocyte progenitors (OLP) by gp130 factors, and promotes differentiation. Conversely, in mice with lineage-selective Klf6 inactivation, OLP undergo maturation arrest followed by apoptosis, and CNS myelination fails. Overlapping transcriptional and chromatin occupancy analyses place Klf6 at the nexus of a novel gp130-Klf-importin axis, which promotes differentiation and viability in part via control of nuclear trafficking. Klf6 acts as a gp130-sensitive transactivator of the nuclear import factor importin-α5 (Impα5), and interfering with this mechanism interrupts step-wise differentiation. Underscoring the significance of this axis in vivo, mice with conditional inactivation of gp130 signaling display defective Klf6 and Impα5 expression, OLP maturation arrest and apoptosis, and failure of CNS myelination.

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Progressive multifocal leukoencephalopathy (PML) is a rapidly progressive, often fatal viral infection of the brain without a known treatment. Recently, case reports have demonstrated survival from PML with therapies that improve cell-mediated immunity, including interleukin-7 (IL-7) or the chemokine receptor type 5 (CCR5) antagonist, maraviroc (MVC). We present the first known case of a patient with PML successfully treated with both IL-7 and MVC. A 63-year-old woman presented to our center with a 6-month history of progressive left hemiparesis. Extensive laboratory testing was negative except for a severe CD4 lymphocytopenia (140/μL). Serial brain MRIs done prior to presentation revealed an enlarging, non-enhancing T2-hyperintense lesion in the right fronto-parietal white matter. PML was confirmed through detection of the JC virus by PCR in the cerebrospinal fluid and by brain biopsy, and she was started on mirtazapine and mefloquine. She continued to deteriorate and was then given a course of recombinant IL-7. Though she remained clinically stable after IL-7 treatment and serum JCV PCR decreased from 1000 copies/mL to a nadir of 238 copies/mL, a repeat MRI 3 months later showed lesion enlargement. MVC was then initiated. Now, more than 2 years after initial presentation, she remains stable and serum JCV PCR is undetectable. This case demonstrates successful treatment of PML in a patient with idiopathic CD4 lymphocytopenia and highlights the potential benefits of IL-7 and MVC in the treatment of PML. Treatment with IL-7 and MVC led to clinical stability and improvement in JC virus titers.

Inflammation of the central nervous system (CNS) induces endothelial blood–brain barrier (BBB) opening as well as the formation of a tight junction barrier between reactive astrocytes at the Glia Limitans. We hypothesized that the CNS parenchyma may acquire protection from the reactive astrocytic Glia Limitans not only during neuroinflammation but also when BBB integrity is compromised in the resting state. Previous studies found that astrocyte-derived Sonic hedgehog (SHH) stabilizes the BBB during CNS inflammatory disease, while endothelial-derived desert hedgehog (DHH) is expressed at the BBB under resting conditions. Here, we investigated the effects of endothelial Dhh on the integrity of the BBB and Glia Limitans. We first characterized DHH expression within endothelial cells at the BBB, then demonstrated that DHH is down-regulated during experimental autoimmune encephalomyelitis (EAE). Using a mouse model in which endothelial Dhh is inducibly deleted, we found that endothelial Dhh both opens the BBB via the modulation of forkhead box O1 (FoxO1) transcriptional activity and induces a tight junctional barrier at the Glia Limitans. We confirmed the relevance of this glial barrier system in human multiple sclerosis active lesions. These results provide evidence for the novel concept of “chronic neuroinflammatory tolerance” in which BBB opening in the resting state is sufficient to stimulate a protective barrier at the Glia Limitans that limits the severity of subsequent neuroinflammatory disease. In summary, genetic disruption of the BBB generates endothelial signals that drive the formation under resting conditions of a secondary barrier at the Glia Limitans with protective effects against subsequent CNS inflammation. The concept of a reciprocally regulated CNS double barrier system has implications for treatment strategies in both the acute and chronic phases of multiple sclerosis pathophysiology.

In MS, inflammatory cells accumulate within the perivascular spaces of acute and chronic lesions. Reliance on perivascular spaces as biomarkers for MS remains uncertain because various studies have reported inconsistencies in perivascular space anatomy. Distinguishing between venular and arteriolar perivascular spaces is pathophysiologically relevant in MS. In this pilot study, we leverage susceptibility-weighted imaging at 7T to better identify perivascular spaces of venular distribution on corresponding high-resolution T2 images.