Identification of BiP as a CB₁ Receptor-Interacting Protein That Fine-Tunes Cannabinoid Signaling in the Mouse Brain

Abstract

Identification of BiP as a CB 1 receptor-interacting protein that fine-tunes cannabinoid signaling in the mouse brain

BiP Heterozigosity Aggravates Pathological Deterioration in Experimental Amyotrophic Lateral Sclerosis

“…It is important to remark that this protein interacts with many other cellular proteins and that its dysregulation has been already associated with ALS pathogenesis by mechanisms that a priori do not involve the participation of the CB 1 receptor [23][24][25], so the issue will require additional research that may test a cause-effect relationship between dysregulation in BiP function and loss of CB 1 -mediated neuroprotective effects, and vice versa. We can anticipate here that CB 1 receptor gene expression resulted to be similar in the spinal cord of wildtype or mSOD1 mice with normal or partial ablation of BiP protein, but this result was relatively expected as the recent data indicate that BiP serves as an interacting protein for the CB 1 receptor [22], so the defects in this protein should affect primarily the signaling for this receptor rather than its gene expression. In fact, the analysis of protein levels for the CB 1 receptor proved lower levels in the double mutants compared to mSOD1 mice, which may be associated with these defects in receptor signaling, although this will require additional research.…”

“…Our general objective in this study was to investigate the consequences of a heterozygous deficiency of the BiP protein, which, by potentially acting as an interacting protein, has been recently associated with CB 1 receptor function [22], in two neurodegenerative disorders in which the activation of this receptor is known to be neuroprotective: ALS [18][19][20] and PD [15][16][17]. To this end, we used an experimental approach consisting on inducing experimental ALS or PD in mice having a partial deletion in the BiP gene and their corresponding wildtype littermates, and recording the development of the pathological phenotype to determine whether BiP-deficient mice were more vulnerable or not to these experimental insults.…”

“…Again, the analysis of morphological characteristics of GFAP-positive cells also revealed a higher presence of activated cells, characterized by elevated cell body area (F(3,29) = 65.25, p < 0.0001) and their ratio with branches length (F(3,29) = 71.13, p < 0.0001), in mSOD1/BiP +/− mice compared to mSOD1 animals with normal BiP expression, with the activated cells being residual in wildtype genotypes (Figure 5A,B). Given the recently demonstrated interaction of BiP protein with the CB 1 receptor [22], we also wanted to analyze the gene expression and protein levels of this receptor in the spinal cord in the four experimental groups. Whereas we found no differences in mRNA levels (Figure 6B), our data obtained with western blotting demonstrated significantly lower levels found in mSOD1/BiP +/− mice compared to mSOD1 mice (Figure 6A).…”

“…This includes, for example, the cannabinoid receptor-interacting protein 1a (CRIP1a), β-arrestins, or GPCR-associated sorting protein (GASP) [21]. Recently, we have purified the CB 1 receptor C-terminal domain and have conducted yeast two-hybrid experiments aimed at finding new receptor interactors [22]. This approach rendered a potential CB 1 receptor-interacting protein that may be particularly attractive owing to its involvement in neurodegenerative processes: the molecular chaperone binding immunoglobulin protein (BiP), also known as 78-kDa glucose-regulated protein (GRP78) or 70-kDa heat shock protein 5 (Hspa5).…”

“…We also investigated this issue in a PD model through evaluating the consequences of unilateral lesions carried out in BiP +/− mice with the parkinsonian neurotoxin 6-OHDA, again with the objective to assess neurotoxin susceptibility in these mice compared to wildtype animals. The hypothesis derived from both paradigms is that the neuroprotective effects associated with the activation of the CB 1 receptor in experimental ALS [18][19][20], as well as those described in experimental PD [15][16][17], could be related to a modulation of CB 1 receptor function by BiP, which would be conceivable for their recently-demonstrated physical interaction [22], but this will be the objective of future work. In the present study, we wanted to set up a proof of concept that inducing ALS and/or PD pathology in mice having dysregulated BiP function would be followed by alterations in the progression of these two diseases.…”