# Characterization of a Fatty Acid Amide Hydrolase (FAAH) in Hirudo verbana

## TL;DR

This study identifies and characterizes a fatty acid amide hydrolase (FAAH) in the medicinal leech, showing its role in endocannabinoid signaling and nervous system function.

## Contribution

The paper reports the first characterization of FAAH in the medicinal leech, an orthologue of vertebrate FAAH-2.

## Key findings

- Hirudo FAAH (HirFAAH) is expressed in the leech central nervous system and is an orthologue of vertebrate FAAH-2.
- HirFAAH exhibits serine hydrolase activity and hydrolyzes FAAH-specific substrates.
- URB597, a known FAAH inhibitor, blocks HirFAAH activity and potentiates synapses in leech ganglia.

## Abstract

The endocannabinoid system plays a critical role in modulating both peripheral and central nervous system function. Despite being present throughout the animal kingdom, there has been relatively little investigation of the endocannabinoid system beyond the traditional animal model systems. In this study, we report on the identification and characterization of a fatty acid aminohydrolase (FAAH) in the medicinal leech, Hirudo verbana. FAAH is the primary enzyme responsible for metabolizing the endocannabinoid signaling molecule arachidonoyl ethanolamide (anandamide or AEA) and therefore plays a critical role in regulating AEA levels in the nervous system. This Hirudo FAAH (HirFAAH) is expressed in the leech central nervous system (CNS) and is an orthologue of FAAH-2 observed in vertebrates. Functionally, HirFAAH has serine hydrolase activity based on activity-based protein profiling (ABPP) studies using the fluorophosphonate probe TAMRA-FP. HirFAAH also hydrolyzes arachidonyl 7-amino, 4-methyl coumarin amide (AAMCA), a substrate specific to FAAH. Hydrolase activity during both the ABPP and AAMCA assays was eliminated by mutation at a conserved activity-binding site. Activity was also blocked by the known FAAH inhibitor, URB597. Treatment of Hirudo ganglia with URB597 potentiated synapses made by the pressure-sensitive mechanosensory neuron (P cell), mimicking the effects of exogenously applied AEA. The Hirudo CNS has been a useful system in which to study properties of endocannabinoid modulation of nociception relevant to vertebrates. Therefore, this characterization of HirFAAH is an important contribution to comparative studies of the endocannabinoid system.