Both the cadherin-catenin complex and Rho-family GTPases have been shown to regulate dendrite development. We show here a role for p120 catenin (p120ctn) in regulating spine and synapse formation in the developing mouse brain. p120catenin gene deletion in hippocampal pyramidal neurons in vivo resulted in reduced spine and synapse densities along dendrites. In addition, p120 catenin loss resulted in reduced cadherin levels and misregulation of Rho-family GTPases, with decreased Rac1 and increased RhoA activity. Analyses in vitro indicate that the reduced spine density reflects aberrant Rho-family GTPase signaling, whereas the effects on spine maturation appear to result from reduced cadherin levels and possibly aberrant Rho-family GTPase signaling. Thus, p120ctn acts as a signal coordinator between cadherins and Rho-family GTPases to regulate cytoskeletal changes required during spine and synapse development.

Haploinsufficiency of progranulin (PGRN) gene (GRN) causes familial frontotemporal lobar degeneration (FTLD), and modulates an innate immune response in humans and mouse models. GRN polymorphism may be linked to late-onset Alzheimer’s disease (AD). However, PRGN’s role in AD pathogenesis is unknown. Here, we show PGRN inhibits amyloid β (Aβ) deposition. Selectively reducing microglial PGRN in AD mice impaired phagocytosis and increased plaque load threefold. Lentivirus-mediated PGRN overexpression lowered plaque load in AD mice with aggressive amyloid plaque pathology. Aβ plaque load correlated negatively with levels of hippocampal PGRN, showing PGRN’s dose-dependent inhibitory effects on plaque deposition. PGRN also protected against Aβ toxicity. Reducing microglial PGRN exacerbated cognitive deficits in AD mice. Lentivirus-mediated PGRN overexpression prevented spatial memory deficits and hippocampal neuronal loss in AD mice. PGRN’s protective effects against Aβ deposition and toxicity have important therapeutic implications. We propose enhancing PGRN as a potential treatment for PGRN-deficient FTD and AD.

Deficient progranulin levels cause dose-dependent neurological syndromes: haploinsufficiency leads to frontotemporal lobar degeneration (FTLD) and nullizygosity produces adult-onset neuronal ceroid lipofuscinosis. Mechanisms controlling progranulin levels are largely unknown. To better understand progranulin regulation, we performed a genome-wide RNAi screen using an ELISA-based platform to discover genes that regulate progranulin levels in neurons. We identified 830 genes that raise or lower progranulin levels by at least 1.5-fold in Neuro2a cells. When inhibited by siRNA or some by submicromolar concentrations of small-molecule inhibitors, 33 genes of the druggable genome increased progranulin levels in mouse primary cortical neurons; several of these also raised progranulin levels in FTLD model mouse neurons. "Hit" genes regulated progranulin by transcriptional or posttranscriptional mechanisms. Pathway analysis revealed enrichment of hit genes from the autophagy-lysosome pathway (ALP), suggesting a key role for this pathway in regulating progranulin levels. Progranulin itself regulates lysosome function. We found progranulin deficiency in neurons increased autophagy and caused abnormally enlarged lysosomes and boosting progranulin levels restored autophagy and lysosome size to control levels. Our data link the ALP to neuronal progranulin: progranulin levels are regulated by autophagy and, in turn, progranulin regulates the ALP. Restoring progranulin levels by targeting genetic modifiers reversed FTLD functional deficits, opening up potential opportunities for future therapeutics development.

Localization of presynaptic components to synaptic sites is critical for hippocampal synapse formation. Cell adhesion–regulated signaling is important for synaptic development and function, but little is known about differentiation of the presynaptic compartment. In this study, we describe a pathway that promotes presynaptic development involving p120catenin (p120ctn), the cytoplasmic tyrosine kinase Fer, the protein phosphatase SHP-2, and β-catenin. Presynaptic Fer depletion prevents localization of active zone constituents and synaptic vesicles and inhibits excitatory synapse formation and synaptic transmission. Depletion of p120ctn or SHP-2 similarly disrupts synaptic vesicle localization with active SHP-2, restoring synapse formation in the absence of Fer. Fer or SHP-2 depletion results in elevated tyrosine phosphorylation of β-catenin. β-Catenin overexpression restores normal synaptic vesicle localization in the absence of Fer or SHP-2. Our results indicate that a presynaptic signaling pathway through p120ctn, Fer, SHP-2, and β-catenin promotes excitatory synapse development and function.

The condition of having a healthy, functional proteome is known as protein homeostasis, or proteostasis. Establishing and maintaining proteostasis is the province of the proteostasis network, approximately 2,500 genes that regulate protein synthesis, folding, localization, and degradation. The proteostasis network is a fundamental entity in biology with direct relevance to many diseases of protein conformation. However, it is not well defined or annotated, which hinders its functional characterization in health and disease. In this series of manuscripts, we aim to operationally define the human proteostasis network by providing a comprehensive, annotated list of its components. Here, we provide a curated list of 959 unique genes that comprise the protein synthesis machinery, chaperones, folding enzymes, systems for trafficking proteins into and out of organelles, and organelle-specific degradation systems. In subsequent manuscripts, we will delineate the human autophagy-lysosome pathway, the ubiquitin-proteasome system, and the proteostasis networks of model organisms.

Frontotemporal dementia is the second prevalent dementia after Alzheimer's disease.• GRN mutations leading to PGRN deficiency are linked to frontotemporal dementia.• PGRN deficiency causes lysosome defects, neurodegeneration, and neuroinflammation.• Efforts to raise PGRN levels are a therapeutic strategy for frontotemporal dementia.

Progranulin (PGRN), a secreted growth factor, is a key regulator of inflammation and is genetically linked to two common and devastating neurodegenerative diseases. Haploinsufficiency mutations in , the gene encoding PGRN, cause frontotemporal dementia (FTD), and a SNP confers significantly increased risk for Alzheimer's disease (AD). Because cellular and animal data indicate that increasing PGRN can reverse phenotypes of both FTD and AD, modulating PGRN level has been proposed as a therapeutic strategy for both diseases. However, little is known about the regulation of PGRN levels. In this study, we performed an siRNA-based screen of the kinome to identify genetic regulators of PGRN levels in a rodent cell-based model system. We found that knocking down receptor-interacting serine/threonine protein kinase 1 () increased both intracellular and extracellular PGRN protein levels by increasing the translation rate of PGRN without affecting mRNA levels. We observed this effect in Neuro2a cells, wild-type primary mouse neurons, and -haploinsufficient primary neurons from an FTD mouse model. We found that the effect of RIPK1 on PGRN is independent of the kinase activity of RIPK1 and occurs through a novel signaling pathway. These data suggest that targeting RIPK1 may be a therapeutic strategy in both AD and FTD.

Autophagy activation has the potential to ameliorate neurodegenerative disease phenotypes, including protein aggregation, lipid level perturbations and axonal trafficking defects. We performed a high content imaging-based screen assessing 940,000 small molecules to identify those that accelerate lipid droplet clearance. Hits were validated in diverse cell lines and by counter-screening. Of the 77 structurally diverse validated hits, 24 increase autophagy flux. Herein, we highlight CCT020312 as a mammalian target of rapamycin (mTOR) inhibitor-independent autophagy activator, which should function without compromising human immune function. CCT020312 dose-dependently reduces cytotoxic axonal mutant prion protein aggregate levels within endosomes of primary murine hippocampal neurons and normalizes axonal trafficking deficiencies. Moreover, CCT020312 robustly clears phosphorylated insoluble tau, while reducing tau-mediated neuronal stress vulnerability in patient-derived neuronal models. CCT020312 also restores lysosomal function in neurons differentiated from sporadic Alzheimer's patients' fibroblasts bearing epigenetic marks of aging. Taken together, we describe a promising strategy to uncover novel pharmacological agents that normalize cellular neurodegenerative disease pathology.