An Evolutionary Novelty in TRPV1 Functional Regulation: Characterization of a Dominant-Negative Isoform Exclusive to Catarrhine Primates
TRPV1, a member of the transient receptor potential (TRP) family, is a non-selective cation channel primarily known for its role in pain perception, inflammation, and thermosensation. In mammals, it responds to noxious heat (>43{degrees}C) and chemical stimuli such as capsaicin and protons. It is widely expressed in sensory neurons, notably in the dorsal root and trigeminal ganglia. However, it is also found in some non-neuronal tissues, like the skin and bladder. The human canonical variant of TRPV1 renders a protein with 839 residues. Different splice variants have been described, and some display a dominant negative effect, partially or totally inhibiting the activity of the canonical counterpart. Here, we characterize a splice variant that encodes for a channel of 850 amino acids (TRPV1850). This variant is an evolutionary novelty of catarrhine (Old World monkeys and apes) primates, incorporating an exon of 33 bp long. Both imaging of membrane expression and electrophysiological recordings suggest that TRPV1850 alone does not reach the plasma membrane. However, in cells co-expressing the canonical and TRPV1850 variants, the latter would act as a dominant negative, preventing the canonical variant from reaching the plasma membrane and rendering smaller macroscopic currents in response to capsaicin. Thus, this new isoform of the TRPV1 ion channel represents a novel form of functional regulation only present in apes and Old World monkeys. SignificanceWe identified a novel isoform of the TRPV1 ion channel, a protein essential for detecting pain and heat stimuli unique to apes and Old World monkeys. This isoform contains an additional exonic sequence encoding eleven amino acids, which originated in the common ancestor of apes and Old World monkeys. This additional exonic sequence disrupts a specific domain in the N-terminal region of the protein, resulting in functional differences. Unlike the canonical TRPV1 isoform, this variant cannot reach the plasma membrane independently. Instead, it exerts a dominant-negative effect by interfering with the canonical TRPV1 protein, reducing its ability to localize to the cell surface and diminishing its responsiveness to capsaicin, a well-known TRPV1 activator.