The need for establishing best practices and gold standards in psychedelic medicine

Psychedelic substances are under investigation in several drug development programs. Controlled clinical trials are providing evidence for safe and effective use of psychedelic therapies for treating mental health conditions. With the anticipated FDA approval of MDMA-assisted therapy for posttraumatic stress disorder in 2023 and psilocybin therapy for depression disorders soon after, now is the time for the medical community to become informed on best practices and to actively participate in developing standards of care for these new treatments. Given the emergence of numerous drug sponsors and other companies developing therapeutic modalities for combination with psychedelic medications, it is essential that the medical professional field is at the forefront of communicating unbiased information related to safety and effectiveness. Gold standards have long been a part of medicine and serve to distinguish treatments and assessments as the highest quality by which all others can be compared to. For a treatment to be established as a gold standard, several factors are considered including the quantity and quality of the supporting data, the rigor of trials, and the safety and efficacy compared to other treatments. In this article, we review the origins of psychedelic-assisted therapy (PAT), minimum requirements for safe use of psychedelics, criteria for gold standards in mental health, and the nuances regarding how to establish gold standards in psychedelic medicine and guide clinical decision making.

A role of OCRL in clathrin-coated pit dynamics and uncoating revealed by studies of Lowe syndrome cells

Mutations in the inositol 5-phosphatase OCRL cause Lowe syndrome and Dent's disease. Although OCRL, a direct clathrin interactor, is recruited to late-stage clathrin-coated pits, clinical manifestations have been primarily attributed to intracellular sorting defects. Here we show that OCRL loss in Lowe syndrome patient fibroblasts impacts clathrin-mediated endocytosis and results in an endocytic defect. These cells exhibit an accumulation of clathrin-coated vesicles and an increase in U-shaped clathrin-coated pits, which may result from sequestration of coat components on uncoated vesicles. Endocytic vesicles that fail to lose their coat nucleate the majority of the numerous actin comets present in patient cells. SNX9, an adaptor that couples late-stage endocytic coated pits to actin polymerization and which we found to bind OCRL directly, remains associated with such vesicles. These results indicate that OCRL acts as an uncoating factor and that defects in clathrin-mediated endocytosis likely contribute to pathology in patients with OCRL mutations.

DOI:http://dx.doi.org/10.7554/eLife.02975.001

Oculo-Cerebro-Renal syndrome of Lowe (Lowe syndrome) is a rare genetic disorder that can cause cataracts, mental disabilities and kidney dysfunction. It is caused by mutations in the gene encoding OCRL, a protein that modifies a membrane lipid and that is found on membranes transporting molecules (cargo) into cells by a process known as endocytosis.

During endocytosis, the cell outer membrane is deformed into a pit that engulfs the cargo to be taken up by the cell. The pit then pinches off from the outer membrane to form a vesicle—a bubble-like compartment—inside the cell that transports the cargo to its destination. In one type of endocytosis, this process is mediated by a basket-like coat primarily made up from the protein clathrin that assembles at the membrane patch to be internalized. After the vesicle is released from the cell membrane, the clathrin coat is broken apart and its components are shed and recycled for use by new budding endocytic vesicles.

The OCRL protein had previously been observed associated to newly forming clathrin-coated vesicles, but the significance of this was not known. Now, Nández et al. have used a range of imaging and analytical techniques to further investigate the properties of OCRL, taking advantage of cells from patients with Lowe syndrome. These cells lack OCRL, and so allow the effect of OCRL's absence on cell function to be deduced. OCRL destroys the membrane lipid that helps to connect the clathrin coat to the membrane, and Nández et al. show that without OCRL the newly formed vesicle moves into the cell but fails to efficiently shed its clathrin coat. Thus, a large fraction of clathrin coat components remain trapped on the vesicles, reducing the amount of such components available to help new pits develop into vesicles. As a consequence, the cell has difficulty internalizing molecules.

Collectively, the findings of Nández et al. outline that OCRL plays a role in the regulation of endocytosis in addition to its previously reported actions in the control of intracellular membrane traffic. The results also help to explain some of the symptoms seen in Lowe syndrome patients.

DOI:http://dx.doi.org/10.7554/eLife.02975.002

Role of dynamin, synaptojanin, and endophilin in podocyte foot processes

Podocytes are specialized cells that play an integral role in the renal glomerular filtration barrier via their foot processes. The foot processes form a highly organized structure, the disruption of which causes nephrotic syndrome. Interestingly, several similarities have been observed between mechanisms that govern podocyte organization and mechanisms that mediate neuronal synapse development. Dynamin, synaptojanin, and endophilin are functional partners in synaptic vesicle recycling via interconnected actions in clathrin-mediated endocytosis and actin dynamics in neurons. A role of dynamin in the maintenance of the kidney filtration barrier via an action on the actin cytoskeleton of podocytes was suggested. Here we used a conditional double-KO of dynamin 1 (Dnm1) and Dnm2 in mouse podocytes to confirm dynamin's role in podocyte foot process maintenance. In addition, we demonstrated that while synaptojanin 1 (Synj1) KO mice and endophilin 1 (Sh3gl2), endophilin 2 (Sh3gl1), and endophilin 3 (Sh3gl3) triple-KO mice had grossly normal embryonic development, these mutants failed to establish a normal filtration barrier and exhibited severe proteinuria due to abnormal podocyte foot process formation. These results strongly implicate a protein network that functions at the interface between endocytosis and actin at neuronal synapses in the formation and maintenance of the kidney glomerular filtration barrier.

Recruitment of endophilin to clathrin-coated pit necks is required for efficient vesicle uncoating after fission

Endophilin is a membrane-binding protein with curvature-generating and -sensing properties that participates in clathrin-dependent endocytosis of synaptic vesicle membranes. Endophilin also binds the GTPase dynamin and the phosphoinositide phosphatase synaptojanin and is thought to coordinate constriction of coated pits with membrane fission (via dynamin) and subsequent uncoating (via synaptojanin). We show that although synaptojanin is recruited by endophilin at bud necks before fission, the knockout of all three mouse endophilins results in the accumulation of clathrin-coated vesicles, but not of clathrin-coated pits, at synapses. The absence of endophilin impairs but does not abolish synaptic transmission and results in perinatal lethality, whereas partial endophilin absence causes severe neurological defects, including epilepsy and neurodegeneration. Our data support a model in which endophilin recruitment to coated pit necks, because of its curvature-sensing properties, primes vesicle buds for subsequent uncoating after membrane fission, without being critically required for the fission reaction itself.

Overlapping role of dynamin isoforms in synaptic vesicle endocytosis

The existence of neuron-specific endocytic protein isoforms raises questions about their importance for specialized neuronal functions. Dynamin, a GTPase implicated in the fission reaction of endocytosis, is encoded by three genes, two of which, dynamin 1 and 3, are highly expressed in neurons. We show that dynamin 3, thought to play a predominantly postsynaptic role, has a major presynaptic function. Although lack of dynamin 3 does not produce an overt phenotype in mice, it worsens the dynamin 1 KO phenotype, leading to perinatal lethality and a more severe defect in activity-dependent synaptic vesicle endocytosis. Thus, dynamin 1 and 3, which together account for the overwhelming majority of brain dynamin, cooperate in supporting optimal rates of synaptic vesicle endocytosis. Persistence of synaptic transmission in their absence indicates that if dynamin plays essential functions in neurons, such functions can be achieved by the very low levels of dynamin 2.

Coordinated actions of actin and BAR proteins upstream of dynamin at endocytic clathrin-coated pits

The GTPase dynamin, a key player in endocytic membrane fission, interacts with numerous proteins that regulate actin dynamics and generate/sense membrane curvature. To determine the functional relationship between these proteins and dynamin, we have analyzed endocytic intermediates that accumulate in cells that lack dynamin (derived from dynamin 1 and 2 double conditional knockout mice). In these cells, actin-nucleating proteins, actin, and BAR domain proteins accumulate at the base of arrested endocytic clathrin-coated pits, where they support the growth of dynamic long tubular necks. These results, which we show reflect the sequence of events in wild-type cells, demonstrate a concerted action of these proteins prior to, and independent of, dynamin and emphasize similarities between clathrin-mediated endocytosis in yeast and higher eukaryotes. Our data also demonstrate that the relationship between dynamin and actin is intimately connected to dynamin's endocytic role and that dynamin terminates a powerful actin- and BAR protein-dependent tubulating activity.

All known patient mutations in the ASH-RhoGAP domains of OCRL affect targeting and APPL1 binding

Mutations in the inositol 5-phosphatase OCRL are responsible for Lowe syndrome, an X-linked disorder characterized by bilateral cataracts, mental retardation, neonatal hypotonia, and renal Fanconi syndrome, and for Dent disease, another X-linked condition characterized by kidney reabsorption defects. We have previously described an interaction of OCRL with the endocytic adaptor APPL1 that links OCRL to protein networks involved in the disease phenotype. Here, we provide new evidence showing that among the interactions which target OCRL to membranes of the endocytic pathway, binding to APPL1 is the only one abolished by all known disease-causing missense mutations in the ASH-RhoGAP domains of the protein. Furthermore, we demonstrate that APPL1 and rab5 independently contribute to recruit OCRL to enlarged endosomes induced by the expression of constitutively active Rab5. Thus, binding to APPL1 helps localize OCRL at specific cellular sites, and disruption of this interaction may play a role in disease.

A role of the Lowe syndrome protein OCRL in early steps of the endocytic pathway

Mutations in the inositol 5-phosphatase OCRL are responsible for Lowe syndrome, whose manifestations include mental retardation and renal Fanconi syndrome. OCRL has been implicated in membrane trafficking, but disease mechanisms remain unclear. We show that OCRL visits late-stage, endocytic clathrin-coated pits and binds the Rab5 effector APPL1 on peripheral early endosomes. The interaction with APPL1, which is mediated by the ASH-RhoGAP-like domains of OCRL and is abolished by disease mutations, provides a link to protein networks implicated in the reabsorptive function of the kidney and in the trafficking and signaling of growth factor receptors in the brain. Crystallographic studies reveal a role of the ASH-RhoGAP-like domains in positioning the phosphatase domain at the membrane interface and a clathrin box protruding from the RhoGAP-like domain. Our results support a role of OCRL in the early endocytic pathway, consistent with the predominant localization of its preferred substrates, PI(4,5)P(2) and PI(3,4,5)P(3), at the cell surface.

A selective activity-dependent requirement for dynamin 1 in synaptic vesicle endocytosis

Dynamin 1 is a neuron-specific guanosine triphosphatase thought to be critically required for the fission reaction of synaptic vesicle endocytosis. Unexpectedly, mice lacking dynamin 1 were able to form functional synapses, even though their postnatal viability was limited. However, during spontaneous network activity, branched, tubular plasma membrane invaginations accumulated, capped by clathrin-coated pits, in synapses of dynamin 1-knockout mice. Synaptic vesicle endocytosis was severely impaired during strong exogenous stimulation but resumed efficiently when the stimulus was terminated. Thus, dynamin 1-independent mechanisms can support limited synaptic vesicle endocytosis, but dynamin 1 is needed during high levels of neuronal activity.