The AP2 clathrin adaptor protein complex regulates the abundance of GLR-1 glutamate receptors in the ventral nerve cord of Caenorhabditis elegans.

Regulation of glutamate receptor (GluR) abundance at synapses by clathrin-mediated endocytosis can control synaptic strength and plasticity. We take advantage of viable, null mutations in subunits of the clathrin adaptor protein 2 (AP2) complex in Caenorhabditis elegans to characterize the in vivo role of AP2 in GluR trafficking. In contrast to our predictions for an endocytic adaptor, we found that levels of the GluR GLR-1 are decreased at synapses in the ventral nerve cord (VNC) of animals with mutations in the AP2 subunits APM-2/µ2, APA-2/α, or APS-2/σ2. Rescue experiments indicate that APM-2/µ2 functions in glr-1-expressing interneurons and the mature nervous system to promote GLR-1 levels in the VNC. Genetic analyses suggest that APM-2/µ2 acts upstream of GLR-1 endocytosis in the VNC. Consistent with this, GLR-1 accumulates in cell bodies of apm-2 mutants. However, GLR-1 does not appear to accumulate at the plasma membrane of the cell body as expected, but instead accumulates in intracellular compartments including Syntaxin-13- and RAB-14-labeled endosomes. This study reveals a novel role for the AP2 clathrin adaptor in promoting the abundance of GluRs at synapses in vivo, and implicates AP2 in the regulation of GluR trafficking at an early step in the secretory pathway.

Complementary versus companion diagnostics: apples and oranges?

There have been several major problems that have plagued biopharmaceutical development since the end of the 1990s, but two in particular have reached the point where they are impacting the economic viability of the industry: the lack of efficacy of new drugs and increasing competition among therapeutics that broadly attack certain common diseases and disease areas. The US FDA has noted that the era of one-size-fits-all treatment may well be reaching its end days as companies increasingly adopt approaches that involve biomarkers (there are now commercial databases that purport to track over 11,000 of them). Pharmacogenomic biomarkers in particular are used to create diagnostics that help to differentiate or stratify the likely outcomes a patient will experience with a drug, which can now be said to be targeted or tailored to patients with particular traits (i.e., personalized), leading to an era of so-called precision medicine. As more is understood about diseases and the why and how of their effects on people through advances in biomarkers and genomics, personalized medicine is becoming a natural result of biomedical science and a natural trajectory for the innovation-based biopharmaceutical industry. The focus of this article is to examine an apparent divergence in that trajectory engendered by a growing differentiation in the approaches to personalized medicines in terms of their accompanying diagnostics: companion diagnostics are typically linked to a specific drug within its approved label, while complementary diagnostics are associated more broadly, usually not with a specific drug but with a class of drugs, and not confined to specific uses by labeling, with consequent ramifications for economic, regulatory and strategic considerations.