The CNS is regarded as an immunoprivileged organ, evading routine immune surveillance; however, the coordinated development of immune responses profoundly influences outcomes after brain injury. Innate lymphoid cells (ILCs) are cytokine-producing cells that are critical for the initiation, modulation, and resolution of inflammation, but the functional relevance and mechanistic regulation of ILCs are unexplored after acute brain injury. We demonstrate increased proliferation of all ILC subtypes within the meninges for up to 1 year after experimental traumatic brain injury (TBI) while ILCs were present within resected dura and elevated within cerebrospinal fluid (CSF) of moderate-to-severe TBI patients. In line with energetic derangements after TBI, inhibition of the metabolic regulator, AMPK, increased meningeal ILC expansion, whereas AMPK activation suppressed proinflammatory ILC1/ILC3 and increased the frequency of IL-10–expressing ILC2 after TBI. Moreover, intracisternal administration of IL-33 activated AMPK, expanded ILC2, and suppressed ILC1 and ILC3 within the meninges of WT and Rag1 ^–/– mice, but not Rag1 ^–/– IL2rg ^–/– mice. Taken together, we identify AMPK as a brake on the expansion of proinflammatory, CNS-resident ILCs after brain injury. These findings establish a mechanistic framework whereby immunometabolic modulation of ILCs may direct the specificity, timing, and magnitude of cerebral immunity.

Traumatic brain injury (TBI) is a major source of worldwide morbidity and mortality. Patients suffering from TBI exhibit a higher susceptibility to bone loss and an increased rate of bone fractures; however, the underlying mechanisms remain poorly defined. Herein, we observed significantly lower bone quality and elevated levels of inflammation in bone and bone marrow niche after controlled cortical impact-induced TBI in in vivo CD-1 mice. Further, we identified dysregulated NF-κB signaling, an established mediator of osteoclast differentiation and bone loss, within the bone marrow niche of TBI mice. Ex vivo studies revealed increased osteoclast differentiation in bone marrow-derived cells from TBI mice, as compared to sham injured mice. We also found bone marrow derived extracellular vesicles (EVs) from TBI mice enhanced the colony forming ability and osteoclast differentiation efficacy and activated NF-κB signaling genes in bone marrow-derived cells. Additionally, we showed that miRNA-1224 up-regulated in bone marrow-derived EVs cargo of TBI. Taken together, we provide evidence that TBI-induced inflammatory stress on bone and the bone marrow niche may activate NF-κB leading to accelerated bone loss. Targeted inhibition of these signaling pathways may reverse TBI-induced bone loss and reduce fracture rates.

The glymphatic system, an analog of the peripheral lymphatic system in the brain, and the meningeal lymphatic system are critical to central nervous system health. The glymphatic system functions to distribute cerebrospinal fluid and important compounds throughout the brain and to remove metabolic waste. The flow of cerebrospinal fluid through this system is affected by changes in cerebral blood flow, intracranial pressure, and vascular tone. Cetaceans experience profound cardiorespiratory alterations while diving that can directly affect cerebrospinal fluid and blood flow and, thus, glymphatic function. Our goal was to investigate glymphatic and lymphatic system structures, including perivascular spaces, aquaporin-4 water channels, meningeal lymphatic, and dural venous sinus vessels in the common dolphin (Delphinus delphis), using immunofluorescent labeling, histochemical staining, and postmortem computed tomography (CT) angiography. We highlight perivascular spaces and aquaporin-4 water channels surrounding blood vessels in the parenchyma and demonstrate evidence of meningeal lymphatic vessels and associated dural venous sinuses. These results demonstrate that common dolphins possess the key anatomical structures required for functional glymphatic and meningeal lymphatic systems. Future studies can build upon these anatomical discoveries to study the function and role of these systems in brain health in this species.

Alzheimer’s disease (AD) is increasingly recognized as a neurodegenerative disorder characterized by central insulin resistance and cerebral hypometabolism. The steroid hormone, 17β-estradiol (E2), interacts closely with insulin signaling pathways and is locally synthesized in the brain by the enzyme aromatase. However, the spatial and temporal dynamics of brain aromatase during AD progression and its relationship to central insulin resistance remain poorly understood. Using the 5xFAD mouse model, we examined whole-brain, regional, and neuron/astrocyte-specific alterations in aromatase expression along disease progression. Whole-brain aromatase expression remained unchanged at 2 months of age but progressively declined at 5 and 9 months, inversely correlating with amyloid-β plaque burden. Regional analysis of the cortex, hippocampal CA1, and hypothalamus revealed progressive aromatase loss in all regions; notably, the hypothalamus exhibited a significant decline at the earliest disease stage examined, preceding comparable changes in the cortex and hippocampus, while an age-related decline cannot be fully excluded, as only a single-aged wild-type (WT) control was used. Cell-level analysis revealed a progressive reduction in neuronal aromatase expression, whereas astrocytic aromatase displayed a biphasic response, increasing during early disease stages before declining at later stages. In parallel, neuronal insulin-resistance signaling increased progressively with disease advancement and was negatively correlated with neuronal aromatase expression across all regions examined (r = −0.82 to −0.87). Collectively, these findings demonstrate progressive regional and neuron/astrocyte-specific alterations in brain aromatase during the progression of amyloid pathology, identifying early hypothalamic vulnerability as a feature of AD-associated altered insulin signaling.