Archives

  • 2018-07
  • 2019-04
  • 2019-05
  • 2019-06
  • 2019-07
  • 2019-08
  • 2019-09
  • 2019-10
  • 2019-11
  • 2019-12
  • 2020-01
  • 2020-02
  • 2020-03
  • 2020-04
  • 2020-05
  • 2020-06
  • 2020-07
  • 2020-08
  • 2020-09
  • 2020-10
  • 2020-11
  • 2020-12
  • 2021-01
  • 2021-02
  • 2021-03
  • 2021-04
  • 2021-05
  • 2021-06
  • 2021-07
  • 2021-08
  • 2021-09
  • 2021-10
  • 2021-11
  • 2021-12
  • 2022-01
  • 2022-02
  • 2022-03
  • 2022-04
  • 2022-05
  • 2022-06
  • 2022-07
  • 2022-08
  • 2022-09
  • 2022-10
  • 2022-11
  • 2022-12
  • 2023-01
  • 2023-02
  • 2023-03
  • 2023-04
  • 2023-05
  • 2023-06
  • 2023-07
  • 2023-08
  • 2023-09
  • 2023-10
  • 2023-11
  • 2023-12
  • 2024-01
  • 2024-02
  • 2024-03
  • 2024-04
  • 2024-05
  • 2024-06
  • 2024-07
  • 2024-08
  • 2024-09

    • Knockdown of CPG led to an increase in postsynaptic clathrin

    2020-07-31

    Knockdown of CPG2 led to an increase in postsynaptic clathrin-coated vesicles, some trafficking NMDA receptors, and a disruption of glutamate receptor internalization. This phenotype is similar to that seen in presynaptic terminals of organisms with mutations of endophilin or synaptojanin, where there is an accumulation of clathrin-coated vesicles and a disruption of the synaptic vesicle cycle, due to a defect in clathrin-coated vesicle uncoating Cremona et al. 1999, Harris et al. 2000, Kim et al. 2002, Verstreken et al. 2002, Verstreken et al. 2003. Since CPG2 contains multiple protein interaction motifs, including two spectrin-like repeats and several coiled coils, we propose a model in which CPG2 interacts with other proteins at the postsynaptic endocytic zone that are necessary for the downstream processing, such as the uncoating, of glutamate receptor-trafficking vesicles. According to this model, following CPG2 knockdown, the CPG2-associated protein network is disrupted, inhibiting vesicle clearance and causing their accumulation. Due to the slowed kinetics of this late step, the entire endocytic pathway is slowed, disrupting further glutamate receptor internalization. Future experiments should reveal the proteins with which CPG2 interacts at synapses and at what point they function to regulate the vesicle cycle. This would clarify whether CPG2 is an active regulator of the endocytic pathway or is a component of the overall endocytic machinery unique to the postsynaptic density. In CPG2 knockdown neurons, there is an increase in synaptic glutamate receptors, which is likely due to the disruption of glutamate receptor endocytosis. Although some reports have indicated that 85 8 sale inhibition does not affect the number of surface AMPA receptors Lledo et al. 1998, Man et al. 2000, our data are consistent with results showing that acute blockade of endocytosis causes an increase in synaptic transmission (Luscher et al., 1999). However, the increase in surface receptors is moderate (20%) despite a greater than 70% disruption in glutamate receptor internalization. This discrepancy may be due to the tight link, previously proposed, between the rates of receptor insertion into and removal from the synaptic membrane Ehlers 2000, Liang and Huganir 2001. Considering there is a decrease in glutamate receptor internalization in these neurons, there must be a compensatory decrease in glutamate receptor insertion for steady-state amount of surface receptors to remain relatively constant. Thus, CPG2 knockdown appears to slow not only the internalization, but also the insertion, of glutamate receptors, suggesting that CPG2 may be necessary for the rapid cycling of synaptic glutamate receptors. Given a disruption of membrane internalization and an increase in synaptic glutamate receptors in CPG2 knockdown neurons, one might expect an increase in dendritic spine size as membrane continues to be inserted into the spines during receptor exocytosis. However, we observed the opposite phenotype, with dendritic spines on CPG2 knockdown neurons nearly twenty percent smaller than in control neurons. According to our model of CPG2 function, the reduction in spine size may result from an increase in membrane retention within internalized clathrin-coated vesicles, as the clathrin coat cannot be removed and the membrane cannot be recovered from these vesicles. However, since the cytoskeleton is critical for both spine morphology and endocytosis Engqvist-Goldstein and Drubin 2003, Rao and Craig 2000, it is possible that CPG2 regulates the spine cytoskeleton and that its knockdown affects both spine size and endocytosis in parallel. A large proportion of AMPA receptors are inserted into the plasma membrane at extrasynaptic sites, possibly between spines (Passafaro et al., 2001). While normally there is a tight correlation between spine size and synaptic AMPA receptor numbers (Kasai et al., 2003), in CPG2 knockdown neurons, the total amount of synaptic glutamate receptors increases despite smaller spines, suggesting that CPG2 knockdown may disrupt the spine size/receptor number relationship.