Mouse mast cells and mast cell proteases do not play a significant role in acute tissue injury pain induced by formalin

Abstract

Subcutaneous formalin injections are used as a model for tissue injury-induced pain where formalin induces pain and inflammation indirectly by crosslinking proteins and directly through activation of the transient receptor potential A1 receptor on primary afferents. Activation of primary afferents leads to both central and peripheral release of neurotransmitters. Mast cells are found in close proximity to peripheral sensory nerve endings and express receptors for neurotransmitters released by the primary afferents, contributing to the neuro/immune interface. Mast cell proteases are found in large quantities within mast cell granules and are released continuously in small amounts and upon mast cell activation. They have a wide repertoire of proposed substrates, including Substance P and calcitonin gene-related peptide, but knowledge of their in vivo function is limited. We evaluated the role of mouse mast cell proteases (mMCPs) in tissue injury pain responses induced by formalin, using transgenic mice lacking either mMCP4, mMCP6, or carboxypeptidase A3 (CPA3), or mast cells in their entirety. Further, we investigated the role of mast cells in heat hypersensitivity following a nerve growth factor injection. No statistical difference was observed between the respective mast cell protease knockout lines and wild-type controls in the formalin test. Mast cell deficiency did not have an effect on formalin-induced nociceptive responses nor nerve growth factor-induced heat hypersensitivity. Our data thus show that mMCP4, mMCP6, and CPA3 as well as mast cells as a whole, do not play a significant role in the pain responses associated with acute tissue injury and inflammation in the formalin test. Our data also indicate that mast cells are not essential to heat hypersensitivity induced by nerve growth factor.

Mast cell stabilizer ketotifen fumarate reverses inflammatory but not neuropathic-induced mechanical pain in mice

“…The contribution of MCs to pain via its proteases is also debatable, as they were found not to be essential for acute pain response in the formalin model. 44 Our preclinical findings are supported by a case series of patients with CWP treated with KF, who achieved substantial symptom improvement. This is in line with reports of cases of patients with long-lasting sickle cell anemia pain that improved after the inhibition of MC activation.…”

“…Although the link between NGF and MC activation has been extensively implicated in different models of hyperalgesia, 36 , 39 , 59 , 67 , 80 recent studies have shown that selective depletion of MCs does not reduce NGF-induced peripheral sensitization in vivo, 41 , 44 nor is NGF capable of activating MCs, as they do not express NGF receptors. 41 These studies also showed that CFA-induced mechanical and thermal allodynia 41 and formalin-induced thermal allodynia 44 were not different between selectively MC-depleted and wild-type animals, suggesting that MCs contribute little to the sensitization of peripheral nociceptors. The contribution of MCs to pain via its proteases is also debatable, as they were found not to be essential for acute pain response in the formalin model.…”

“…The contribution of MCs to pain via its proteases is also debatable, as they were found not to be essential for acute pain response in the formalin model. 44 …”

Involvement of Mast Cells in the Pathophysiology of Pain

“…Taken as a whole, the results indicate that MCs play an important role in different painful conditions, although some studies showed that depletion or stabilization of MC did not display pain-relieving effect in models induced by complete Freund’s adjuvant, carrageenan, formalin, NGF, or nociceptin/orphanin (McDougall and Larson, 2006 ; Xanthos et al, 2011 ; Lopes et al, 2017 ; Magnusdottir et al, 2018 ). Whether MC plays a critical role in nociceptive processing remains to be elucidated.…”

Neurotransmitter and neuropeptide regulation of mast cell function: a systematic review

“…NGF treatment in vitro does not lead to increased levels of TNF-α in bone marrow-derived MCs, and qRT-PCR data indicate that MCs express negligible levels of NGF receptors, thereby explaining their lack of response to NGF [ 131 ]. Mouse MCs are not essential to heat hypersensitivity induced by NGF [ 132 ].…”