Recent studies of the low abundant signaling lipid, phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2), reveal an intriguingly diverse list of downstream pathways, the intertwined relationship between PI(3,5)P2 and PI5P, as well as links to neurodegenerative diseases. Derived from the structural lipid phosphatidylinositol, PI(3,5)P2 is dynamically generated on multiple cellular compartments where interactions with an increasing list effectors regulate many cellular pathways. A complex of proteins that includes Fab1/PIKfyve, Vac14 and Fig4/Sac3 mediates the biosynthesis of PI(3,5)P2, and mutations that disrupt complex function and/or formation cause profound consequences in cells. Surprisingly, mutations in this pathway are linked with neurological diseases, including Charcot-Marie-Tooth Syndrome and Amyotrophic Lateral Sclerosis. Future studies of PI(3,5)P2 and PI5P are likely to expand the roles of these lipids in regulation of cellular functions, as well as provide new approaches for treatment of some neurological diseases.

SUMMARY Synaptojanin 1 (SJ1) is a major presynaptic phosphatase that couples synaptic vesicle endocytosis to the dephosphorylation of PI(4,5)P2, a reaction needed for the shedding of endocytic factors from their membranes. While the role of SJ1’s 5-phosphatase module in this process is well established, the contribution of its Sac phosphatase domain, whose preferred substrate is PI4P, remains unclear. Recently a homozygous mutation in its Sac domain was identified in early-onset Parkinsonism patients. We show that mice carrying this mutation developed neurological manifestations similar to those of human patients. Synapses of these mice displayed endocytic defects and a striking accumulation of clathrin coated intermediates strongly implicating Sac domain’s activity in endocytic protein dynamics. Mutant brains had elevated auxilin (PARK19) and parkin (PARK2) levels. Moreover, dystrophic axonal terminal changes were selectively observed in dopaminergic axons in the dorsal striatum. These results strengthen evidence for a link between synaptic endocytic dysfunction and Parkinson’s disease.

SUMMARY Homeostatic synaptic plasticity is important for maintaining stability of neuronal function, but heterogeneous expression mechanisms suggest that distinct facets of neuronal activity may shape the manner in which compensatory synaptic changes are implemented. Here, we demonstrate that local presynaptic activity gates a retrograde form of homeostatic plasticity induced by blockade of AMPA receptors (AMPARs) in cultured hippocampal neurons. We show that AMPAR blockade produces rapid (< 3 hrs) protein synthesis-dependent increases in both presynaptic and postsynaptic function, and that the induction of presynaptic, but not postsynaptic, changes requires coincident local activity in presynaptic terminals. This “state-dependent” modulation of presynaptic function requires postsynaptic release of brain-derived neurotrophic factor (BDNF) as a retrograde messenger, which is locally synthesized in dendrites in response to AMPAR blockade. Taken together, our results reveal a local cross-talk between active presynaptic terminals and postsynaptic signaling that dictates the manner by which homeostatic plasticity is implemented at synapses.

Dynamic regulation of phosphoinositide lipids (PIPs) is crucial for diverse cellular functions, and, in neurons, PIPs regulate membrane trafficking events that control synapse function. Neurons are particularly sensitive to the levels of the low abundant PIP, phosphatidylinositol 3,5-bisphosphate [PI(3,5)P 2 ], because mutations in PI(3,5)P 2 -related genes are implicated in multiple neurological disorders, including epilepsy, severe neuropathy, and neurodegeneration. Despite the importance of PI(3,5)P 2 for neural function, surprisingly little is known about this signaling lipid in neurons, or any cell type. Notably, the mammalian homolog of yeast vacuole segregation mutant (Vac14), a scaffold for the PI(3,5)P 2 synthesis complex, is concentrated at excitatory synapses, suggesting a potential role for PI(3,5)P 2 in controlling synapse function and/or plasticity. PI(3,5)P 2 is generated from phosphatidylinositol 3-phosphate (PI3P) by the lipid kinase PI3P 5-kinase (PIKfyve). Here, we present methods to measure and control PI(3,5)P 2 synthesis in hippocampal neurons and show that changes in neural activity dynamically regulate the levels of multiple PIPs, with PI(3,5)P 2 being among the most dynamic. The levels of PI(3,5)P 2 in neurons increased during two distinct forms of synaptic depression, and inhibition of PIKfyve activity prevented or reversed induction of synaptic weakening. Moreover, altering neuronal PI(3,5)P 2 levels was sufficient to regulate synaptic strength bidirectionally, with enhanced synaptic function accompanying loss of PI(3,5)P 2 and reduced synaptic strength following increased PI(3,5)P 2 levels. Finally, inhibiting PI(3,5)P 2 synthesis alters endocytosis and recycling of AMPA-type glutamate receptors (AMPARs), implicating PI(3,5)P 2 dynamics in AMPAR trafficking. Together, these data identify PI(3,5)P 2 -dependent signaling as a regulatory pathway that is critical for activity-dependent changes in synapse strength.PIKfyve | Fab1 | phosphatidylinositol lipids | synaptic plasticity | Vac14 P hosphorylated phosphoinositide lipids (PIPs) regulate diverse cellular processes (reviewed in refs. 1, 2). These seven interconvertible PIP species are synthesized and turned over by highly regulated lipid kinases and phosphatases. PIPs likely assemble complex protein machines on membrane subdomains through binding of specific downstream protein effectors, which provides tight spatial and temporal control of cellular processes. Such precision is likely critical for complex cellular functions, including regulation of synaptic strength in the CNS.Pleiotropic defects are associated with impairments in phosphatidylinositol 3,5-bisphosphate [PI(3,5)P 2 ] synthesis (reviewed in ref.3). Mutations in FIG4, the gene that encodes a positive regulator of PI(3,5)P 2 (4-10), are linked to several neurological disorders, including Charcot-Marie-Tooth type 4J (CMT4J) (4, 11), ALS, and primary lateral sclerosis (12), familial epilepsy with polymicrogyria (13) and Yunis-Varón syndrome (14). Little is known about how pert...

Mutations that alter signaling through the mammalian target of rapamycin complex 1 (mTORC1), a well established regulator of neuronal protein synthesis, have been linked to autism and cognitive dysfunction. Although previous studies have established a role for mTORC1 as necessary for enduring changes in postsynaptic function, here, we demonstrate that dendritic mTORC1 activation in rat hippocampal neurons also drives a retrograde signaling mechanism promoting enhanced neurotransmitter release from apposed presynaptic terminals. This novel mode of synaptic regulation conferred by dendritic mTORC1 is locally implemented, requires downstream synthesis of brain-derived neurotrophic factor (BDNF) as a retrograde messenger, and is engaged in an activity-dependent fashion to support homeostatic trans-synaptic control of presynaptic function. Our findings thus reveal that mTORC1-dependent translation in dendrites subserves a unique mode of synaptic regulation, highlighting an alternative regulatory pathway that could contribute to the social and cognitive dysfunction that accompanies dysregulated mTORC1 signaling.

Modulation of synaptic function by VAC14, a protein that regulates the phosphoinositides PI(3,5)P2 and PI(5)PMice deficient for VAC14, a scaffolding protein required for PIP2 biosynthesis and linked to human neuropathies, show increased postsynaptic function due to altered AMPA receptor trafficking.

BackgroundSelective attention and memory seem to be related in human experience. This appears to be the case as well in simple model organisms such as the fly Drosophila melanogaster. Mutations affecting olfactory and visual memory formation in Drosophila, such as in dunce and rutabaga, also affect short-term visual processes relevant to selective attention. In particular, increased optomotor responsiveness appears to be predictive of visual attention defects in these mutants.Methodology/Principal FindingsTo further explore the possible overlap between memory and visual attention systems in the fly brain, we screened a panel of 36 olfactory long term memory (LTM) mutants for visual attention-like defects using an optomotor maze paradigm. Three of these mutants yielded high dunce-like optomotor responsiveness. We characterized these three strains by examining their visual distraction in the maze, their visual learning capabilities, and their brain activity responses to visual novelty. We found that one of these mutants, D0067, was almost completely identical to dunce1 for all measures, while another, D0264, was more like wild type. Exploiting the fact that the LTM mutants are also Gal4 enhancer traps, we explored the sufficiency for the cells subserved by these elements to rescue dunce attention defects and found overlap at the level of the mushroom bodies. Finally, we demonstrate that control of synaptic function in these Gal4 expressing cells specifically modulates a 20–30 Hz local field potential associated with attention-like effects in the fly brain.Conclusions/SignificanceOur study uncovers genetic and neuroanatomical systems in the fly brain affecting both visual attention and odor memory phenotypes. A common component to these systems appears to be the mushroom bodies, brain structures which have been traditionally associated with odor learning but which we propose might be also involved in generating oscillatory brain activity required for attention-like processes in the fly brain.

Phosphatidylinositol 4-kinase IIIα (PI4KIIIα/PI4KA/OMIM:600286) is a lipid kinase generating phosphatidylinositol 4-phosphate (PI4P), a membrane phospholipid with critical roles in the physiology of multiple cell types. PI4KIIIα’s role in PI4P generation requires its assembly into a heterotetrameric complex with EFR3, TTC7 and FAM126. Sequence alterations in two of these molecular partners, TTC7 (encoded by TTC7A or TCC7B) and FAM126, have been associated with a heterogeneous group of either neurological (FAM126A) or intestinal and immunological (TTC7A) conditions. Here we show that biallelic PI4KA sequence alterations in humans are associated with neurological disease, in particular hypomyelinating leukodystrophy. In addition, affected individuals may present with inflammatory bowel disease, multiple intestinal atresia and combined immunodeficiency. Our cellular, biochemical and structural modelling studies indicate that PI4KA-associated phenotypical outcomes probably stem from impairment of PI4KIIIα-TTC7-FAM126's organ-specific functions, due to defective catalytic activity or altered intra-complex functional interactions. Together, these data define PI4KA gene alteration as a cause of a variable phenotypical spectrum and provide fundamental new insight into the combinatorial biology of the PI4KIIIα-FAM126-TTC7-EFR3 molecular complex.