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Abstract: Chaperones in the endoplasmic reticulum play vital roles in the folding, assembly, and post-translational modification of secretory proteins and also recycle, refold, or initiate degradation of misfolded proteins. Chaperone deficiencies in either amount or function are implicated in the etiology or pathogenesis of Alzheimer''s disease and other protein folding disorders of the central nervous system. In this review, we discuss evidence that chaperones become pathologic through deleterious interactions with metals and then promote protein folding disorders. The “master regulator” chaperone GRP78 in the endoplasmic reticulum is a compelling subject for investigation in this context because it is located at the hub of signaling pathways in a complex chaperone network. It has therefore been studied by several laboratories in conjunction with exposure to toxic metals. The key points of this review are that metals are implicated in the etiology or pathogenesis of Alzheimer''s disease and other protein folding disorders, metals induce the expression GRP78, often associated with oxidative stress, some metals bind to GRP78, and lead (Pb) impairs GRP78 function when it binds to GRP78. If certain metals do indeed cause or promote the aggregation of toxic proteins in the central nervous system, as the available evidence indicates, the identification of the mechanisms by which they act would provide valuable leads for the development of therapies to prevent or reverse toxic protein aggregation. [Copyright &y& Elsevier]

Abstract: Copper (Cu) ion availability in tissues and cells must be closely regulated within safe limits by Cu transporters and chaperones. Astrocytes play key roles in metal homeostasis and distribution in the brain that are only partially understood. The purpose of this study was to define the role that the protein chaperone Hspa5, also known as Grp78, plays in Cu homeostasis in astrocytes. First passage cultures of primary astrocytes from neonatal rats and cultures of the C6 rat glioma cells were used as models. We found that the level of Cu accumulation in astrocyte cultures increased with Cu concentrations in the medium, and Cu treatment significantly reduced cellular levels of iron (Fe), manganese (Mn) and zinc (Zn). Cu accumulation specifically induced protein expression of Hspa5 but not metallothioneins (MTs) in astrocytes. In C6 cells, Hspa5 was identified as one component of a Cu-binding complex and shown to directly bind Cu. However, the level of Hspa5 expression was not proportional to Cu accumulation in astrocytes and C6 cells: astrocytes expressed low protein levels of Hspa5 compared to C6 cells but accumulated significantly more Cu than did C6 cells. Consistent with this finding, astrocytes expressed a lower level of the Cu-extruding protein Atp7a than did C6 cells, and depletion of Hspa5 by RNA interference resulted in significantly increased Cu accumulation and induction of MT1/2 expression. These data demonstrate that Hspa5 is involved in Cu homeostasis in astrocytes but not as a Cu storage protein. [Copyright &y& Elsevier]

Abstract: Glucose-regulated protein of 78kDa (GRP78) is an endoplasmic reticulum (ER) molecular chaperone functioning in protein folding, assembly and trafficking. GRP78 also plays a role in protection against cytotoxicity and apoptosis induced by environmental insults. Our previous study showed that lead (Pb) directly targets GRP78 by binding to the protein and increasing GRP78 levels. In this study, the effect of Pb on compartmentalized distribution of GRP78 in living cells was examined. A rat GRP78–EGFP fusion protein and EGFP were transiently expressed in astrocytoma cells exposed to 5μM Pb acetate or 50μM CuSO4 and fluorescence signals were captured. Control cells expressing EGFP showed a homogeneous distribution of EGFP that was not changed by Pb or Cu treatment. Cells expressing GRP78–EGFP showed a compartmentalized, non-homogeneous distribution of GRP78–EGFP in the cytosol. The redistribution of GRP78–EGFP fluorescent bodies was observed in cells exposed to Pb for 10h, but not 5h. Redistribution was also observed in cells exposed to 50μM Cu for 5 or 10h. To assess GRP78 function, GRP78 was depleted with dsRNAi oligos in rat C6 glioma cells. GRP78 depletion significantly increased the sensitivity of cells to Pb exposure as indicated by the generation of reactive oxygen species (ROS). These data suggest that Pb directly targets GRP78 and induces its compartmentalized redistribution in living cells and that GRP78 plays a protective role in Pb neurotoxicity. [Copyright &y& Elsevier]