New hippocampal neurons are continuously generated in the adult brain. Here, we demonstrate that lipopolysaccharide-induced inflammation, which gives rise to microglia activation in the area where ...the new neurons are born, strongly impairs basal hippocampal neurogenesis in rats. The increased neurogenesis triggered by a brain insult is also attenuated if it is associated with microglia activation caused by tissue damage or lipopolysaccharide infusion. The impaired neurogenesis in inflammation is restored by systemic administration of minocycline, which inhibits microglia activation. Our data raise the possibility that suppression of hippocampal neurogenesis by activated microglia contributes to cognitive dysfunction in aging, dementia, epilepsy, and other conditions leading to brain inflammation.
The endeavor of exploiting arrays of vertical one-dimensional (1D) nanostructures (NSs) for cellular applications has recently been experiencing a pronounced surge of activity. The interest is rooted ...in the intrinsic properties of high-aspect-ratio NSs. With a height comparable to a mammalian cell, and a diameter 100-1000 times smaller, NSs should intuitively reach far into a cell and, due to their small diameter, do so without compromising cell health. Single NSs would thus be expedient for measuring and modifying cell response. Further organization of these structures into arrays can provide up-scaled and detailed spatiotemporal information on cell activity, an achievement that would entail a massive leap forward in disease understanding and drug discovery. Numerous proofs-of-principle published recently have expanded the large toolbox that is currently being established in this rapidly advancing field of research. Encouragingly, despite the diversity of NS platforms and experimental conditions used thus far, general trends and conclusions from combining cells with NSs are beginning to crystallize. This review covers the broad spectrum of NS materials and dimensions used; the observed cellular responses with specific focus on adhesion, morphology, viability, proliferation, and migration; compares the different approaches used in the field to provide NSs with the often crucial cytosolic access; covers the progress toward biological applications; and finally, envisions the future of this technology. By maintaining the impressive rate and quality of recent progress, it is conceivable that the use of vertical 1D NSs may soon be established as a superior choice over other current techniques, with all the further benefits that may entail.
The perspectives offered by vertical arrays of nanowires for biosensing applications in living cells depend on the access of individual nanowires to the cell interior. Recent results on electrical ...access and molecular delivery suggest that direct access is not always obtained. Here, we present a generic approach to directly visualize the membrane conformation of living cells interfaced with nanowire arrays, with single nanowire resolution. The method combines confocal z-stack imaging with an optimized cell membrane labelling strategy which was applied to HEK293 cells interfaced with 2-11 μm long and 3-7 μm spaced nanowires with various surface coatings (bare, aminosilane-coated or polyethyleneimine-coated indium arsenide). We demonstrate that, for all commonly used nanowire lengths, spacings and surface coatings, nanowires generally remain enclosed in a membrane compartment, and are thereby not in direct contact with the cell interior.
Neural progenitors in the adult dentate gyrus continuously produce new functional granule cells. Here we used whole-cell patch-clamp recordings to explore whether a pathological environment ...influences synaptic properties of new granule cells labeled with a GFP-retroviral vector. Rats were exposed to a physiological stimulus, i.e., running, or a brain insult, i.e., status epilepticus, which gave rise to neuronal death, inflammation, and chronic seizures. Granule cells formed after these stimuli exhibited similar intrinsic membrane properties. However, the new neurons born into the pathological environment differed with respect to synaptic drive and short-term plasticity of both excitatory and inhibitory afferents. The new granule cells formed in the epileptic brain exhibited functional connectivity consistent with reduced excitability. We demonstrate a high degree of plasticity in synaptic inputs to adult-born new neurons, which could act to mitigate pathological brain function.
Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine, acting through the TNF-R1 and TNF-R2 receptors. The two receptors have been proposed to mediate distinct TNF-alpha effects in ...the CNS, TNF-R1 contributing to neuronal damage and TNF-R2 being neuroprotective. Whether TNF-alpha and its receptors play any role for neurogenesis in the adult brain is unclear. Here we used mouse models with loss of TNF-R1 and TNF-R2 function to establish whether signaling through these receptors could influence hippocampal neurogenesis in vivo under basal conditions, as well as after status epilepticus (SE), which is associated with inflammation and elevated TNF-alpha levels. Notably, in the intact brain, the number of new, mature hippocampal neurons was elevated in TNF-R1(-/-) and TNF-R1/R2(-/-) mice, whereas no significant changes were detected in TNF-R2(-/-) mice. Also after SE, the TNF-R1(-/-) and TNF-R1/R2(-/-) mice produced more new neurons. In contrast, the TNF-R2(-/-) mice showed reduced SE-induced neurogenesis. Cell proliferation in the dentate subgranular zone was elevated in TNF-R1(-/-) and TNF-R1/R2(-/-) mice both under basal conditions and after SE. The TNF-R2(-/-) mice either showed no change or minor decrease of cell proliferation. TNF-R1 and TNF-R2 receptors were expressed by hippocampal progenitors, as assessed with reverse transcription-PCR on sorted or cultured cells and immunocytochemistry on cultures. Our data reveal differential actions of TNF-R1 and TNF-R2 signaling in adult hippocampal neurogenesis and identify for the first time TNF-R1 as a negative regulator of neural progenitor proliferation in both the intact and pathological brain.
Arrays of nanowires (NWs) are currently being established as vehicles for molecule delivery and electrical- and fluorescence-based platforms in the development of biosensors. It is conceivable that ...NW-based biosensors can be optimized through increased understanding of how the nanotopography influences the interfaced biological material. Using state-of-the-art homogenous NW arrays allow for a systematic investigation of how the broad range of NW densities used by the community influences cells. Here it is demonstrated that indium arsenide NW arrays provide a cell-promoting surface, which affects both cell division and focal adhesion up-regulation. Furthermore, a systematic variation in NW spacing affects both the detailed cell morphology and adhesion properties, where the latter can be predicted based on changes in free-energy states using the proposed theoretical model. As the NW density influences cellular parameters, such as cell size and adhesion tightness, it will be important to take NW density into consideration in the continued development of NW-based platforms for cellular applications, such as molecule delivery and electrical measurements.
Inflammation influences several steps of adult neurogenesis, but whether it regulates the functional integration of the new neurons is unknown. Here, we explored, using confocal microscopy and ...whole-cell patch-clamp recordings, whether a chronic inflammatory environment affects the morphological and electrophysiological properties of new dentate gyrus granule cells, labeled with a retroviral vector encoding green fluorescent protein. Rats were exposed to intrahippocampal injection of lipopolysaccharide, which gave rise to long-lasting microglia activation. Inflammation caused no changes in intrinsic membrane properties, location, dendritic arborization, or spine density and morphology of the new cells. Excitatory synaptic drive increased to the same extent in new and mature cells in the inflammatory environment, suggesting increased network activity in hippocampal neural circuitries of lipopolysaccharide-treated animals. In contrast, inhibitory synaptic drive was more enhanced by inflammation in the new cells. Also, larger clusters of the postsynaptic GABA(A) receptor scaffolding protein gephyrin were found on dendrites of new cells born in the inflammatory environment. We demonstrate for the first time that inflammation influences the functional integration of adult-born hippocampal neurons. Our data indicate a high degree of synaptic plasticity of the new neurons in the inflammatory environment, which enables them to respond to the increase in excitatory input with a compensatory upregulation of activity and efficacy at their afferent inhibitory synapses.
Dentate gyrus (DG) neurogenesis is transiently increased during the first weeks after status epilepticus (SE). Survival of the new neurons is initially compromised by an acute inflammatory response, ...but the long‐term fate of the remaining ones in the post‐SE environment is unknown. Here adult rats were subjected to 2 h electrically evoked self‐sustained SE and perfused after 5 weeks or 6 months. Rats exhibited partial or generalized SE followed by spontaneous behavioural seizures and abnormal electroencephalographic activity during 6 months. Numbers of activated microglia in the dentate subgranular zone (SGZ)‐granule cell layer (GCL) and in the hilus declined after 5 weeks, but were still elevated at 6 months after SE, with no differences between the milder partial and the more severe generalized SE. At 6 months, partial and generalized SE rats showed a seven‐fold increase in the number of mature SGZ–GCL neurons formed during the first 2 weeks along with aberrant neurons in the hilus. Total numbers of mature neurons in SGZ–GCL were unaltered, indicating that SE‐generated neurons replaced dead granule cells. Neuroblast formation had returned to normal levels in SGZ–GCL but generation of aberrant neurons in the hilus was still ongoing at 6 months. Our data indicate that long‐term impairment of neurogenesis, as reported previously after kainic acid‐induced SE, is not a general feature of chronic epilepsy. We have found that a substantial proportion of the mature granule cells at 6 months are generated during the first 2 weeks after SE and survive despite chronic inflammation, and that SE triggers continuous production of aberrant hilar neurons.
Status epilepticus (SE) increases neurogenesis in the subgranular zone (SGZ) of the adult dentate gyrus, but many of the newborn cells die, partly through caspase-induced apoptosis. Here we provide ...immunohistochemical evidence indicating that the caspase-evoked death of the new neurons involves the mitochondrial but not the death-receptor-mediated pathway. Cytochrome c released from mitochondria was found in a subset of progenitor cell progeny, while Fas ligand and tumor necrosis factor 1 receptor-associated domain as well as the mitochondria-related, caspase-independent apoptosis-inducing factor were not detected. We also show that additional seizures, induced at different stages during neuronal differentiation of progenitor cell progeny following SE, neither potentiate cell death mechanisms in the SGZ nor compromise the survival of the new cells. Thus, we found similar expression of cytochrome c, active caspase-3, caspase-cleaved PARP, and TUNEL/Hoechst-positive DNA fragmentation, as well as numbers of new cells in the SGZ in rats exposed to additional seizures at days 6 and 7 or days 33 and 34 following SE as in control animals only subjected to SE. We propose that the degree of survival of newly generated neurons is determined primarily by the initial SE insult and the ensuing pathology in the tissue environment, whereas spontaneous seizures play a minor role.
Vertical arrays of nanostructures (NSs) are emerging as promising platforms for probing and manipulating live mammalian cells. The broad range of applications requires different types of interfaces, ...but cell settling on NS arrays is not yet fully controlled and understood. Cells are both seen to deform completely into NS arrays and to stay suspended like tiny fakirs, which have hitherto been explained with differences in NS spacing or density. Here, a better understanding of this phenomenon is provided by using a model that takes into account the extreme membrane deformation needed for a cell to settle into a NS array. It is shown that, in addition to the NS density, cell settling depends strongly on the dimensions of the single NS, and that the settling can be predicted for a given NS array geometry. The predictive power of the model is confirmed by experiments and good agreement with cases from the literature. Furthermore, the influence of cell‐related parameters is evaluated theoretically and a generic method of tuning cell settling through surface coating is demonstrated experimentally. These findings allow a more rational design of NS arrays for the numerous exciting biological applications where the mode of cell settling is crucial.
Cell settling on nanostructure (NS) arrays is modeled and the effect of geometrical and cell‐related parameters is systematically evaluated. It is found that cell settling is highly dependent on both single‐NS dimensions and NS density, and predictive tools are developed for any NS array or cell type, thus allowing a rational design of future NS arrays for biological applications.
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