Each year, 10 million people worldwide survive the neurologic injury associated with a stroke. Importantly, stroke survivors have more than twice the risk of subsequently developing dementia compared with people who have never had a stroke. The link between stroke and the later development of dementia is not understood. There are reports of oligoclonal bands in the CSF of stroke patients, suggesting that in some people a B-lymphocyte response to stroke may occur in the CNS. Therefore, we tested the hypothesis that a B-lymphocyte response to stroke could contribute to the onset of dementia. We discovered that, in mouse models, activated B-lymphocytes infiltrate infarcted tissue in the weeks after stroke. B-lymphocytes undergo isotype switching, and IgM, IgG, and IgA antibodies are found in the neuropil adjacent to the lesion. Concurrently, mice develop delayed deficits in LTP and cognition. Genetic deficiency, and the pharmacologic ablation of B-lymphocytes using an anti-CD20 antibody, prevents the appearance of delayed cognitive deficits. Furthermore, immunostaining of human postmortem tissue revealed that a B-lymphocyte response to stroke also occurs in the brain of some people with stroke and dementia. These data suggest that some stroke patients may develop a B-lymphocyte response to stroke that contributes to dementia, and is potentially treatable with FDA-approved drugs that target B cells.

The p75 neurotrophin receptor (p75(NTR)) is associated with multiple mechanisms linked to Alzheimer's disease (AD); hence, modulating its function might confer therapeutic effects. In previous in vitro work, we developed small molecule p75(NTR) ligands that inhibited amyloid-β-induced degenerative signaling and prevented neurite degeneration. In the present study, a prototype p75(NTR) ligand, LM11A-31, was administered orally to the Thy-1 hAPP(Lond/Swe) (APP(L/S)) AD mouse model. LM11A-31 reached brain concentrations known to inhibit degenerative signaling without toxicity or induction of hyperalgesia. It prevented deficits in novel object recognition after 2.5 months and, in a separate cohort, deficits in Y-maze performance after 3 months of treatment. Stereology studies found that the number and size of basal forebrain cholinergic neurons, which are normal in APP(L/S) mice, were unaffected. Neuritic dystrophy, however, was readily apparent in the basal forebrain, hippocampus and cortex, and was significantly reduced by LM11A-31, with no effect on amyloid levels. These studies reveal that p75(NTR) is an important and tractable in vivo drug target for AD, with LM11A-31 representing a novel class of therapeutic candidates.

Tumor progression is coincident with mechanochemical changes in the extracellular matrix (ECM). We hypothesized that tumor stroma stiffening, alongside a shift in the ECM composition from a basement membrane-like microenvironment toward a dense network of collagen-rich fibers during tumorigenesis, confers resistance to otherwise powerful chemotherapeutics. To test this hypothesis, we created a high-throughput drug screening platform based on our poly(ethylene glycol)-phosphorylcholine (PEG-PC) hydrogel system, and customized it to capture the stiffness and integrin-binding profile of in vivo tumors. We report that the efficacy of a Raf kinase inhibitor, sorafenib, is reduced on stiff, collagen-rich microenvironments, independent of ROCK activity. Instead, sustained activation of JNK mediated this resistance, and combining a JNK inhibitor with sorafenib eliminated stiffness-mediated resistance in triple negative breast cancer cells. Surprisingly, neither ERK nor p38 appears to mediate sorafenib resistance, and instead, either ERK or p38 inhibition rescued sorafenib resistance during JNK inhibition, suggesting negative crosstalk between these signaling pathways on stiff, collagen-rich environments. Overall, we discovered that β1 integrin and its downstream effector JNK mediate sorafenib resistance during tumor stiffening. These results also highlight the need for more advanced cell culture platforms, such as our high-throughput PEG-PC system, with which to screen chemotherapeutics.

Following stroke, the damaged tissue undergoes liquefactive necrosis, a stage of infarct resolution that lasts for months although the exact length of time is currently unknown. One method of repair involves reactive astrocytes and microglia forming a glial scar to compartmentalize the area of liquefactive necrosis from the rest of the brain. The formation of the glial scar is a critical component of the healing response to stroke, as well as other central nervous system (CNS) injuries. The goal of this study was to evaluate the toxicity of the extracellular fluid present in areas of liquefactive necrosis and determine how effectively it is segregated from the remainder of the brain. To accomplish this goal, we used a mouse model of stroke in conjunction with an extracellular fluid toxicity assay, fluorescent and electron microscopy, immunostaining, tracer injections into the infarct, and multiplex immunoassays. We confirmed that the extracellular fluid present in areas of liquefactive necrosis following stroke is toxic to primary cortical and hippocampal neurons for at least 7 weeks following stroke, and discovered that although glial scars are robust physical and endocytic barriers, they are nevertheless permeable. We found that molecules present in the area of liquefactive necrosis can leak across the glial scar and are removed by a combination of paravascular clearance and microglial endocytosis in the adjacent tissue. Despite these mechanisms, there is delayed atrophy, cytotoxic edema, and neuron loss in regions adjacent to the infarct for weeks following stroke. These findings suggest that one mechanism of neurodegeneration following stroke is the failure of glial scars to impermeably segregate areas of liquefactive necrosis from surviving brain tissue.

We report here the synthesis of a new class of hydrogels with an extremely wide range of mechanical properties suitable for cell studies. Mechanobiology has emerged as an important field in bioengineering, in part due to the development of synthetic polymer gels and fibrous protein biomaterials to control and quantify how cells sense and respond to mechanical forces in their microenvironment. To address the problem of limited availability of biomaterials, in terms of both mechanical range and optical clarity, we have prepared hydrogels that combine poly(ethylene glycol) (PEG) and phosphorylcholine (PC) zwitterions. Our goal was to create a hydrogel platform that exceeds the range of Young's moduli reported for similar hydrogels, while being simple to synthesize and manipulate. The Young's modulus of these "PEG-PC" hydrogels can be tuned over 4 orders of magnitude, much greater than commonly used hydrogels such as PEG-diacrylate, PEG-dimethacrylate, and polyacrylamide, with smaller average mesh sizes and optical clarity. We prepared PEG-PC hydrogels to study how substrate mechanical properties influence cell morphology, focal adhesion structure, and proliferation across multiple mammalian cell lines, as a proof of concept. These novel PEG-PC biomaterials represent a new and useful class of mechanically tunable hydrogels for mechanobiology.