DREADD not the designer compound: Designer receptors exclusively activated by designer drugs (DREADDs) constitute a powerful chemogenetic strategy that can modulate nerve cell activity in freely moving animal preparations. Gomez et al. used radioligand receptor occupancy measurements and in vivo positron emission tomography to show that DREADDs expressed in the brain are not activated by the designer compound CNO (clozapine N -oxide). Instead, they are activated by the CNO metabolite clozapine, a drug with multiple endogenous targets. This may have important implications for the interpretation of results obtained with this popular technology. Science , this issue p. 503

Mesencephalic astrocyte-derived neurotrophic factor (MANF) is an endoplasmic reticulum (ER) stress-responsive protein with neuroprotective effects in animal models of neurodegeneration, but the underlying mechanism is not understood. We constructed a set of lentiviral vectors that contain or lack the highly conserved final four amino acids of MANF (“RTDL”), which resemble the canonical ER retention signal (“KDEL”), to study MANF regulation in neuroblastoma cells and rat primary cortical neurons. The RTDL sequence was required for both ER retention and secretory response to ER stress. Overexpression of KDEL receptor paralogs (KDELRs) differentially reduced MANF secretion but had no effect on MANF lacking RTDL. MANF binding to the plasma membrane also required the RTDL sequence and was inhibited with a peptide known to interact with KDELRs, suggesting MANF binds KDELRs at the surface. We detected surface localization of FLAG-tagged KDELRs, with levels increasing following ER stress. Our study provides new insight into the regulation of MANF trafficking and has implications for other secreted proteins containing a KDEL-like retention signal.

Astaxanthin (ATX) is a dietary carotenoid of crustaceans and fish that contributes to their coloration. Dietary ATX is important for development and survival of salmonids and crustaceans and has been shown to reduce cardiac ischemic injury in rodents. The purpose of this study was to examine whether ATX can protect against ischemic injury in the mammalian brain. Adult rats were injected intracerebroventricularly with ATX or vehicle prior to a 60‐min middle cerebral artery occlusion (MCAo). ATX was present in the infarction area at 70‐75 min after onset of MCAo. Treatment with ATX, compared to vehicle, increased locomotor activity in stroke rats and reduced cerebral infarction at 2 d after MCAo. To evaluate the protective mechanisms of ATX against stroke, brain tissues were assayed for free radical damage, apoptosis, and excitoxicity. ATX antagonized ischemia‐mediated loss of aconitase activity and reduced glutamate release, lipid peroxidation, translocation of cytochrome c, and TUNEL labeling in the ischemic cortex. ATX did not alter physiological parameters, such as body temperature, brain temperature, cerebral blood flow, blood gases, blood pressure, and pH. Collectively, our data suggest that ATX can reduce ischemia‐related injury in brain tissue through the inhibition of oxidative stress, reduction of glutamate release, and antiapoptosis. ATX may be clinically useful for patients vulnerable or prone to ischemic events.—Shen, H., Kuo, C.‐C., Chou, J., Delvolve, A., Jackson, S.N., Post, J., Woods, A.S., Hoffer, B.J., Wang, Y., Harvey, B.K. Astaxanthin reduces ischemic brain injury in adult rats. FASEB J. 23, 1958–1968 (2009)

Retention of critical endoplasmic reticulum (ER) luminal proteins needed to carry out diverse functions (e.g., protein synthesis and folding, lipid metabolism) is mediated through a carboxy-terminal ER retention sequence (ERS) and its interaction with KDEL receptors. Here, we demonstrate that depleting ER calcium causes mass departure of ERS-containing proteins from cells by overwhelming KDEL receptors. In addition, we provide evidence that KDELR2 and KDELR3, but not KDELR1, are unfolded protein response (UPR) genes upregulated as an adaptive response to counteract the loss of ERS-containing proteins, suggesting previously unknown isoform-specific functions of the KDEL receptors. Overall, our findings establish that decreases in ER calcium change the composition of the ER luminal proteome and secretome, which can impact cellular functions and cell viability. The redistribution of the ER proteome from inside the cell to the outside has implications for dissecting the complex relationship of ER homeostasis with diverse disease pathologies.