Figure 7.

PD 102807 is a biased M3 mAChR ligand that promotes GRK2/3-arrestin-dependent signaling via PKC-ι and CaMKK1. Biased M3 mAChR signaling is mediated by PKC-ι, a member of the atypical family of PKC, and the AMPK kinase, CaMKK1. AMPK then phosphorylates Raptor to inhibit the mTORC1 complex, resulting in a decrease of both phosphorylation of S6 ribosomal protein (mRNA translation pathway) and SRE-Luc activity (gene transcription pathway), leading to inhibition of TGF-β-induced a-SMA expression, a feature of ASM phenotypic modulation to a contractile ASM phenotype. MCh induces a canonical Gq/calcium-dependent M3 mAChR signaling. Though not addressed in the current study, internalization may play a role in biased M3 mAChR signaling. MCh-induced AMPK phosphorylation is transient, dependent on calcium mobilization, and mediated by both CaMKK1 and CaMKK2 isoforms and independent of PKC-ι. Due to its transient nature, MCh-induced activation of AMPK does not modulate ASM phenotype. AMPK, AMP-activated protein kinase; ASM, airway smooth muscle; CaMKK, Ca²⁺/calmodulin-dependent kinase kinases; mAChR, muscarinic acetylcholine receptor; MCh, methacholine; PKC-ι, protein kinase C iota.