Differential Regulation of Behavioral Tolerance to WIN55,212-2 by GASP1

Abstract

Cannabinoid agonists have shown some promise clinically as analgesics, in particular for cancer pain where they have the additional benefit of decreasing nausea. However, as for most other drugs, the long-term use of cannabinoids is limited by the development of tolerance. Several molecular mechanisms have been proposed to explain drug tolerance including receptor downregulation. Cannabinoid CB1 receptors can be downregulated in vitro through an interaction with the G protein-coupled receptor associated sorting protein1, GASP1, which targets CB1 receptors for degradation after their agonist-mediated endocytosis. To investigate whether GASP1-mediated post-endocytic sorting of the CB1 receptor contributes to tolerance to cannabinoid drugs in vivo, we generated a mouse with a disruption of GASP1. In wild-type mice, repeated administration of the cannabinoid agonist WIN55,212-2 promoted downregulation of CB1 receptor levels and concomitant tolerance to the effects of drug on antinociception, motor incoordination, and locomotor hypoactivity. In contrast, GASP1 knock-out mice did not develop tolerance to any of these effects and showed no significant receptor down-regulation. Taken together, this study provides evidence that GASP1 regulates CB1 receptor downregulation in vivo, and that post-endocytic receptor trafficking plays a key role in development of tolerance to WIN55,212-2.

Cannabinoid Receptor–Interacting Protein 1a Modulates CB1 Receptor Signaling and Regulation

“…Interestingly, our results showed that CRIP 1a overexpression interfered with CB 1 R downregulation (degradation) but not desensitization (uncoupling from G-protein activation). These findings suggest that CRIP 1a might interfere with GASP1 association with CB 1 Rs (Martini et al, 2007(Martini et al, , 2010) or with C-terminal CB 1 R phosphorylation at sites that mediate internalization (Jin et al, 1999;Daigle et al, 2008;) but not at sites that mediate desensitization (Jin et al, 1999;Morgan et al, 2014). Regional differences in CB 1 R downregulation after repeated cannabinoid administration have been observed in the CNS of rodents (Sim-Selley, 2003;Sim-Selley et al, 2006) and humans (Villares, 2007;Hirvonen et al, 2012).…”

Dopamine D3 Receptors Are Down-regulated following Heterologous Endocytosis by a Specific Interaction with G Protein-coupled Receptor-associated Sorting Protein-1

“…Post-endocytic degradation of GPCRs by GASP-1 has been shown to have behavioral relevance in vivo. For example, GASP-1 knock-out mice show reduced tolerance to the cannabinoid WIN5,212-2 as a consequence of reduced CB1 down-regulation (11). In addition, GASP-1 knockout mice also show reduced sensitization to the locomotor activating effects of repeated cocaine as a consequence of reduced D 2 receptor degradation (12).…”

Reduced Antinociceptive Effect of Repeated Treatment with a Cannabinoid Receptor Type 2 Agonist in Cannabinoid-Tolerant Rats Following Spinal Nerve Transection

“…Therefore, neuronal and glial interactions may contribute to the effects of CP55940-induced tolerance on JWH015's antinociceptive effectiveness. Cannabinoid tolerance depends on CB receptor availability (Tappe-Theodor et al, 2007;Martini et al, 2010) and/or sensitivity (Jin et al, 1999;Selley et al, 2004). These receptor properties may change following peripheral insults such as paw incision (Alkaitis et al, 2010), peripheral nerve injury (Lim et al, 2003) or sustained activation by endogenous (Falenski et al, 2010;Schlosburg et al, 2010) or exogenous cannabinoids (Gardell et al, 2002;Hama and Sagen, 2009).…”

“…In contrast, we (Romero-Sandoval and Eisenach, 2007;Romero-Sandoval et al, 2008a) and others (Yao et al, 2009) have shown that spinal CB2 receptor agonists (such as JWH015) relieve postoperative and neuropathic pain in rodent models without inducing neurological side effects or antinociceptive tolerance. Despite advancements in the molecular mechanisms involved in cannabinoid tolerance (Martini et al, 2010), a better understanding of the respective roles of CB1 and CB2 receptors is required to design effective therapies that do not induce tolerance. Further advances in this area may also guide clinical treatment of patients who have already developed tolerance through prior exposure to non-selective cannabinoid agonists for recreational or medical purposes.…”