Summary Reprogramming somatic cells to induced pluripotent stem cells (iPSCs), resets their identity back to an embryonic age, and thus presents a significant hurdle for modeling late-onset disorders. In this study, we describe a strategy for inducing aging-related features in human iPSC-derived lineages and apply it to the modeling of Parkinson’s disease (PD). Our approach involves expression of progerin, a truncated form of lamin A associated with premature aging. We found that expression of progerin in iPSC-derived fibroblasts and neurons induces multiple aging-related markers and characteristics, including dopamine-specific phenotypes such as neuromelanin accumulation. Induced aging in PD-iPSC-derived dopamine neurons revealed disease phenotypes that require both aging and genetic susceptibility, such as pronounced dendrite degeneration, progressive loss of tyrosine-hydroxylase (TH) expression and enlarged mitochondria or Lewy body-precursor inclusions. Thus, our study suggests that progerin-induced aging can be used to reveal late-onset age-related disease features in hiPSC-based disease models.

Pro- and mature brain-derived neurotrophic factor (BDNF) activate two distinct receptors: p75 neurotrophin receptor (p75(NTR)) and TrkB. Mature BDNF facilitates hippocampal synaptic potentiation through TrkB. Here we report that proBDNF, by activating p75(NTR), facilitates hippocampal long-term depression (LTD). Electron microscopy showed that p75(NTR) localized in dendritic spines, in addition to afferent terminals, of CA1 neurons. Deletion of p75(NTR) in mice selectively impaired the NMDA receptor-dependent LTD, without affecting other forms of synaptic plasticity. p75(NTR-/-) mice also showed a decrease in the expression of NR2B, an NMDA receptor subunit uniquely involved in LTD. Activation of p75(NTR) by proBDNF enhanced NR2B-dependent LTD and NR2B-mediated synaptic currents. These results show a crucial role for proBDNF-p75(NTR) signaling in LTD and its potential mechanism, and together with the finding that mature BDNF promotes synaptic potentiation, suggest a bidirectional regulation of synaptic plasticity by proBDNF and mature BDNF.

A central question in Alzheimer's disease concerns the mechanism by which beta-amyloid contributes to neuropathology, and in particular whether intracellular versus extracellular beta-amyloid plays a critical role. Alzheimer transgenic mouse studies demonstrate brain dysfunction, as beta-amyloid levels rise, months before the appearance of beta-amyloid plaques. We have now used immunoelectron microscopy to determine the subcellular site of neuronal beta-amyloid in normal and Alzheimer brains, and in brains from Alzheimer transgenic mice. We report that beta-amyloid 42 localized predominantly to multivesicular bodies of neurons in normal mouse, rat, and human brain. In transgenic mice and human Alzheimer brain, intraneuronal beta-amyloid 42 increased with aging and beta-amyloid 42 accumulated in multivesicular bodies within presynaptic and especially postsynaptic compartments. This accumulation was associated with abnormal synaptic morphology, before beta-amyloid plaque pathology, suggesting that intracellular accumulation of beta-amyloid plays a crucial role in Alzheimer's disease.

Multiple lines of evidence implicate ␤-amyloid (A␤) in the pathogenesis of Alzheimer's disease (AD), but the mechanisms whereby A␤ is involved remain unclear. Addition of A␤ to the extracellular space can be neurotoxic. Intraneuronal A␤42 accumulation is also associated with neurodegeneration. We reported previously that in Tg2576 amyloid precursor protein mutant transgenic mice, brain A␤42 localized by immunoelectron microscopy to, and accumulated with aging in, the outer membranes of multivesicular bodies, especially in neuronal processes and synaptic compartments. We now demonstrate that primary neurons from Tg2576 mice recapitulate the in vivo localization and accumulation of A␤42 with time in culture. Furthermore, we demonstrate that A␤42 aggregates into oligomers within endosomal vesicles and along microtubules of neuronal processes, both in Tg2576 neurons with time in culture and in Tg2576 and human AD brain. These A␤42 oligomer accumulations are associated with pathological alterations within processes and synaptic compartments in Tg2576 mouse and human AD brains.

Background and Purpose Intracerebral hemorrhage (ICH) leads to disability or death with few established treatments. Adverse outcomes following ICH result from irreversible damage to neurons resulting from primary and secondary injury. Secondary injury has been attributed to hemoglobin and its oxidized product hemin from lysed red blood cells. The aim of this study was to identify the underlying cell death mechanisms attributable to secondary injury by hemoglobin and hemin to broaden treatment options. Methods We investigated cell death mechanisms in cultured neurons exposed to hemoglobin or hemin. Chemical inhibitors implicated in all known cell death pathways were employed. Identified cell death mechanisms were confirmed using molecular markers and electron microscopy. Results Chemical inhibitors of ferroptosis and necroptosis protected against hemoglobin- and hemin-induced toxicity. By contrast, inhibitors of caspase-dependent apoptosis, protein or mRNA synthesis, autophagy, mitophagy or parthanatos had no effect. Accordingly, molecular markers of ferroptosis and necroptosis were increased following ICH in vitro and in vivo. Electron microscopy showed that hemin induced a necrotic phenotype. Necroptosis and ferroptosis inhibitors each abrogated death by greater than 80% and had similar therapeutic windows in vitro. Conclusion Experimental ICH shares features of ferroptotic and necroptotic cell death, but not caspase-dependent apoptosis or autophagy. We propose that ferroptosis or necroptotic signaling induced by lysed blood is sufficient to reach a threshold of death that leads to neuronal necrosis and that inhibition of either one of these pathways can bring cells below that threshold to survival.

Several lines of evidence indicate that estrogen affects hippocampal synaptic plasticity through rapid nongenomic mechanisms, possibly by binding to plasma membrane estrogen receptors (ERs). We have previously shown that ERalpha immunoreactivity (ir) is in select interneuron nuclei and in several extranuclear locations, including dendritic spines and axon terminals, within the rat hippocampal formation (Milner et al., [2001] J Comp Neurol 429:355). The present study sought to determine the cellular and subcellular locations of ERbeta-ir. Coronal hippocampal sections from diestrus rats were immunolabeled with antibodies to ERbeta and examined by light and electron microscopy. By light microscopy, ERbeta-ir was primarily in the perikarya and proximal dendrites of pyramidal and granule cells. ERbeta-ir was also in a few nonprincipal cells and scattered nuclei in the ventral subiculum and CA3 region. Ultrastructural analysis revealed ERbeta-ir at several extranuclear sites in all hippocampal subregions. ERbeta-ir was affiliated with cytoplasmic organelles, especially endomembranes and mitochondria, and with plasma membranes primarily of principal cell perikarya and proximal dendrites. ERbeta-ir was in dendritic spines, many arising from pyramidal and granule cell dendrites. In both dendritic shafts and spines, ERbeta-ir was near the perisynaptic zone adjacent to synapses formed by unlabeled terminals. ERbeta-ir was in preterminal axons and axon terminals, associated with clusters of small, synaptic vesicles. ERbeta-labeled terminals formed both asymmetric and symmetric synapses with dendrites. ERbeta-ir also was detected in glial profiles. The cellular and subcellular localization of ERbeta-ir was generally similar to that of ERalpha, except that ERbeta was more extensively found at extranuclear sites. These results suggest that ERbeta may serve primarily as a nongenomic transducer of estrogen actions in the hippocampal formation.

SUMMARY The prognosis of patients with glioblastoma (GBM) remains dismal, with a median survival of approximately 15 months. Current preclinical GBM models are limited by the lack of a “normal” human microenvironment and the inability of many tumor cell lines to accurately reproduce GBM biology. To address these limitations, we have established a model system whereby we can retro-engineer patient-specific GBMs using patient-derived glioma stem cells (GSCs) and human embryonic stem cell (hESC)-derived cerebral organoids. Our cerebral organoid glioma (GLICO) model shows that GSCs home toward the human cerebral organoid and deeply invade and proliferate within the host tissue, forming tumors that closely phenocopy patient GBMs. Furthermore, cerebral organoid tumors form rapidly and are supported by an interconnected network of tumor micro-tubes that aids in the invasion of normal host tissue. Our GLICO model provides a system for modeling primary human GBM ex vivo and for high-throughput drug screening.

We have investigated the potential role of contactin and contactin-associated protein (Caspr) in the axonal–glial interactions of myelination. In the nervous system, contactin is expressed by neurons, oligodendrocytes, and their progenitors, but not by Schwann cells. Expression of Caspr, a homologue of Neurexin IV, is restricted to neurons. Both contactin and Caspr are uniformly expressed at high levels on the surface of unensheathed neurites and are downregulated during myelination in vitro and in vivo. Contactin is downregulated along the entire myelinated nerve fiber. In contrast, Caspr expression initially remains elevated along segments of neurites associated with nascent myelin sheaths. With further maturation, Caspr is downregulated in the internode and becomes strikingly concentrated in the paranodal regions of the axon, suggesting that it redistributes from the internode to these sites. Caspr expression is similarly restricted to the paranodes of mature myelinated axons in the peripheral and central nervous systems; it is more diffusely and persistently expressed in gray matter and on unmyelinated axons. Immunoelectron microscopy demonstrated that Caspr is localized to the septate-like junctions that form between axons and the paranodal loops of myelinating cells. Caspr is poorly extracted by nonionic detergents, suggesting that it is associated with the axon cytoskeleton at these junctions. These results indicate that contactin and Caspr function independently during myelination and that their expression is regulated by glial ensheathment. They strongly implicate Caspr as a major transmembrane component of the paranodal junctions, whose molecular composition has previously been unknown, and suggest its role in the reciprocal signaling between axons and glia.