Targeting of protease activator receptor-2 (PAR-2) antagonist FSLLRY-NH2 as an asthma adjuvant therapy

FSLLRY-NH2, a protease-activated receptor 2 (PAR2) antagonist, activates mas-related G protein-coupled receptor C11 (MrgprC11) to induce scratching behaviors in mice

AIMS

Protease-activated receptor 2 (PAR2), a type of G protein-coupled receptor (GPCR), plays a significant role in pathophysiological conditions such as inflammation. A synthetic peptide SLIGRL-NH₂ (SLIGRL) can activate PAR2, while FSLLRY-NH₂ (FSLLRY) is an antagonist. A previous study showed that SLIGRL activates both PAR2 and mas-related G protein-coupled receptor C11 (MrgprC11), a different type of GPCR expressed in sensory neurons. However, the impact of FSLLRY on MrgprC11 and its human ortholog MRGPRX1 was not verified. Hence, the present study aims to verify the effect of FSLLRY on MrgprC11 and MRGPRX1.

METHODS

The calcium imaging technique was applied to determine the effect of FSLLRY in HEK293T cells expressing MrgprC11/MRGPRX1 or dorsal root ganglia (DRG) neurons. Scratching behavior was also investigated in wild-type and PAR2 knockout mice after injecting FSLLRY.

KEY FINDINGS

It was surprisingly discovered that FSLLRY specifically activates MrgprC11 in a dose-dependent manner, but not other MRGPR subtypes. Furthermore, FSLLRY also moderately activated MRGPRX1. FSLLRY stimulates downstream pathways including Gα_q/11, phospholipase C, IP₃ receptor, and TRPC ion channels to evoke an increase in the intracellular calcium levels. The molecular docking analysis predicted that FSLLRY interacts with the orthosteric binding pocket of MrgprC11 and MRGPRX1. Finally, FSLLRY activated primary cultures of mouse sensory neurons, and induced scratching behaviors in mice.

SIGNIFICANCE

The present study has revealed that FSLLRY is capable of triggering itch sensation through activation of MrgprC11. This finding highlights the importance of considering the unexpected activation of MRGPRs in future therapeutic approaches aimed at the inhibition of PAR2.

PAR2: The Cornerstone of Pancreatic Diseases

It has been 30 years since the first member of the protease-activated receptor (PAR) family was discovered. This was followed by the discovery of three other receptors, including PAR2. PAR2 is a G protein-coupled receptor activated by trypsin site-specific proteolysis. The process starts with serine proteases acting between arginine and serine, creating an N-terminus that functions as a tethered ligand that binds, after a conformational change, to the second extracellular loop of the receptor, leading to activation of G-proteins. The physiological and pathological functions of this ubiquitous receptor are still elusive. This review focuses on PAR2 activation and its distribution under physiological and pathological conditions, with a particular focus on the pancreas, a significant producer of trypsin, which is the prototype activator of the receptor. The role in acute or chronic pancreatitis, pancreatic cancer, and diabetes mellitus will be highlighted.

The immune response to airway mycosis

The allergic airway diseases chronic rhinosinusitis (CRS), allergic fungal rhinosinusitis (AFRS), asthma, allergic bronchopulmonary mycosis/aspergillosis (ABPM/A), and cystic fibrosis (CF) share a common immunological signature marked by T_H2 and T_H17 cell predominant immune responses, the production of IgE antibody, and a typical inflammatory cell infiltrate that includes eosinophils and other innate immune effector cells. Severe forms of these disorders have long been recognized as being related to hypersensitivity reactions to environmental fungi. Increasingly however,environmental fungi are assuming a more primary role in the etiology of these disorders, with airway mycosis, a type of non-invasive airway fungal infection, recognized as an essential driving factor in at least severe subsets of allergic airway diseases. In this review, we consider recent progress made in understanding the immune mechanisms that drive airway mycosis-related diseases, improvements in immune-based diagnostic strategies, and therapeutic approaches that target key immune pathways.