A peripheral CB2 cannabinoid receptor mechanism suppresses chemotherapy-induced peripheral neuropathy: evidence from a CB2 reporter mouse

Abstract

CB 2 cannabinoid receptors (CB 2 ) are a promising therapeutic target that lacks unwanted side effects of CB 1 activation. However, the cell types expressing CB 2 that mediate these effects remain poorly understood. We used transgenic mice with CB 2 promoter-driven expression of enhanced green fluorescent protein (EGFP) to study cell types that express CB 2 and suppress neuropathic nociception in a mouse model of chemotherapy-induced peripheral neuropathy. Structurally distinct CB 2 agonists (AM1710 and LY2828360) suppressed paclitaxel-induced mechanical and cold allodynia in CB 2 EGFP reporter mice with established neuropathy. Antiallodynic effects of AM1710 were blocked by SR144528, a CB 2 antagonist with limited CNS penetration. Intraplantar AM1710 administration suppressed paclitaxel-induced neuropathic nociception in CB 2 EGFP but not CB 2 knockout mice, consistent with a local site of antiallodynic action. mRNA expression levels of the anti-inflammatory cytokine interleukin-10 were elevated in the lumbar spinal cord after intraplantar AM1710 injection along with the proinflammatory cytokine tumor necrosis factor alpha and chemokine monocyte chemoattractant protein-1. CB 2 EGFP , but not wildtype mice, exhibited anti-GFP immunoreactivity in the spleen. However, the anti-GFP signal was below the threshold for detection in the spinal cord and brain of either vehicle-treated or paclitaxel-treated CB 2 EGFP mice. EGFP fluorescence was coexpressed with CB 2 immunolabeling in stratified patterns among epidermal keratinocytes. EGFP fluorescence was also expressed in dendritic cells in the dermis, Langerhans cells in the epidermis, and Merkel cells. Quantification of the EGFP signal revealed that Langerhans cells were dynamically increased in the epidermis after paclitaxel treatment. Our studies implicate CB 2 expressed in previously unrecognized populations of skin cells as a potential target for suppressing chemotherapy-induced neuropathic nociception.

Peripheral sensory neuron CB2 cannabinoid receptors are necessary for both CB2-mediated antinociceptive efficacy and sparing of morphine tolerance in a mouse model of neuropathic pain

“…In fact, using the same CB2 f/f mouse used here, we recently showed that CB2 EGFP in Langerhans cells and keratinocytes are dynamically regulated by paclitaxel in peripheral paw tissue under conditions in which only scattered axonal labeling of large diameter fibers were observed (14). These latter effects are consistent with likely localization of CB2 on Aβ fibers whereas thinly myelinated and unmyelinated epidermal nerve fibers lacked CB2 EGFP labeling (14). CB2 agonist administered locally in the paw also suppressed paclitaxel-induced allodynia and increases spinal IL-10 mRNA levels (14).…”

“…Both CB2 and GFP mRNA were decreased in the DRG of advillin Cre/+ ;CB2 f/f mice, but not in the spleen or spinal cord relative to CB2 f/f mice, indicating that deletion of CB2 receptors by advillin Cre/+ selectively decreased mRNAs for both markers of CB2 receptor transcription in the cell bodies of peripheral sensory neurons. Additionally, local administration of CB2 receptor agonists in the paw decrease mechanical and cold allodynia induced by the chemotherapeutic drug paclitaxel, and CB2 EGFP is detected in keratinocytes, Langerhans cells and dendritic cells within the epidermis (14). In fact, using the same CB2 f/f mouse used here, we recently showed that CB2 EGFP in Langerhans cells and keratinocytes are dynamically regulated by paclitaxel in peripheral paw tissue under conditions in which only scattered axonal labeling of large diameter fibers were observed (14).…”

“…Additionally, local administration of CB2 receptor agonists in the paw decrease mechanical and cold allodynia induced by the chemotherapeutic drug paclitaxel, and CB2 EGFP is detected in keratinocytes, Langerhans cells and dendritic cells within the epidermis (14). In fact, using the same CB2 f/f mouse used here, we recently showed that CB2 EGFP in Langerhans cells and keratinocytes are dynamically regulated by paclitaxel in peripheral paw tissue under conditions in which only scattered axonal labeling of large diameter fibers were observed (14). These latter effects are consistent with likely localization of CB2 on Aβ fibers whereas thinly myelinated and unmyelinated epidermal nerve fibers lacked CB2 EGFP labeling (14).…”

“…Cold allodynia was assessed by applying a droplet of acetone to the midplantar surface of the hind paw and measuring the amount of time spent attending to the stimulated paw (i.e. licking, shaking, and lifting of the paw) in triplicate for each paw (14,22,(69)(70)(71).…”

“…Identification of cell types expressing CB2 that mediate the therapeutic benefits of CB2 ligands has remained problematic given the lack of reliable antibodies for CB2 and low levels of CB2 expression in central nervous system (10)(11)(12). To circumvent CB2 antibody specificity issues, the current studies employed a recently developed CB2 reporter mouse (CB2 f/f ) to aid in identification of cell types within nociceptive circuitry which express CB2 (13,14). In this mouse line, the entire cnr2 coding region is flanked by loxP sites, allowing for cell-type specific deletion 3 i.p.)…”