5‐HT_2B receptor antagonists attenuate myofibroblast differentiation and subsequent fibrotic responses in vitro and in vivo

Abstract

Pulmonary fibrosis is characterized by excessive accumulation of connective tissue, along with activated extracellular matrix (ECM)‐producing cells, myofibroblasts. The pathological mechanisms are not well known, however serotonin (5‐HT) and 5‐HT class 2 (5‐HT 2) receptors have been associated with fibrosis. The aim of the present study was to investigate the role of 5‐HT 2B receptors in fibrosis, using small molecular 5‐HT 2B receptor antagonists EXT5 and EXT9, with slightly different receptor affinity. Myofibroblast differentiation [production of alpha‐smooth muscle actin (α‐SMA)] and ECM synthesis were quantified in vitro, and the effects of the receptor antagonists were evaluated. Pulmonary fibrosis was also modeled in mice by subcutaneous bleomycin administrations (under light isoflurane anesthesia), and the effects of receptor antagonists on tissue density, collagen‐producing cells, myofibroblasts and decorin expression were investigated. In addition, cytokine expression was analyzed in serum. Lung fibroblasts displayed an increased α‐SMA (P < 0.05) and total proteoglycan production (P < 0.01) when cultured with TGF‐β1 together with 5‐HT, which were significantly reduced with both receptor antagonists. Following treatment with EXT5 or EXT9, tissue density, expression of decorin, number of collagen‐producing cells, and myofibroblasts were significantly decreased in vivo compared to bleomycin‐treated mice. Receptor antagonization also significantly reduced systemic levels of TNF‐α and IL‐1β, indicating a role in systemic inflammation. In conclusion, 5‐HT 2B receptor antagonists have potential to prevent myofibroblast differentiation, in vitro and in vivo, with subsequent effect on matrix deposition. The attenuating effects of 5‐HT 2B receptor antagonists on fibrotic tissue remodeling suggest these receptors as novel targets for the treatment of pulmonary fibrosis.

Platelet activation in experimental murine neonatal pulmonary hypertension

“…The full representative blots are shown in Figure 5. The 5‐HT 2A R antibody has been previously validated (Lofdahl et al, 2016) and the SERT antibody has been validated using a transfected cell line by the manufacturer. The species‐appropriate secondary IgG antibody was used (1:2,000, Millipore).…”

Pathological Insight into 5-HT2B Receptor Activation in Fibrosing Interstitial Lung Diseases

“…More recently, agonistic activity on the 5-HT 2B receptor has been implicated in causing fibrosis, which led to the recall of fenfluramine used in the treatment of obesity, as well as pergolide, a drug used to treat Parkinson’s disease [ 31 , 32 ]. The 5-HT 2B receptor agonistic activity of these drugs has been suggested to lead to myofibroblast activation in a transforming growth factor (TGF)-β1 dependent manner, resulting in fibrosis [ 33 , 34 ]. Besides the 5-HT 2B receptor, the receptor subtypes 5-HT 2A and 5-HT 2C have also been suggested to be involved in fibrosis.…”

“…To understand the pathophysiological impact of 5-HT and the different 5-HT receptors, it is important to take into account the cellular context and the diversity in expression profile of the 5-HT receptors in different conditions. It is clear that activation of the 5-HT 2B receptor critically affects several profibrotic responses, whereby modulating its activity has been shown to attenuate fibrosis [ 34 , 38 , 39 , 40 ].…”

“…However, a dual involvement of decorin in fibrosis is described, as decorin is also shown to enhance fibroblast migration [ 48 ]. In an in vivo model of experimentally induced lung fibrosis in mice, pulmonary expression of decorin increased, which was diminished following treatment with 5-HT 2B receptor antagonists [ 34 ]. This oral, preventive treatment with 5-HT 2B receptor antagonist in bleomycin-treated mice resulted in an attenuated fibrotic development in the lung with reduced deposition of connective tissue.…”

5-HT1A Receptor Function Makes Wound Healing a Happier Process

“…There are several studies exploring the association between 5-HTR2A and 5-HTR2B antagonism in contributing to a diminished inflammatory response and fibrotic changes. Current research is still attempting to uncover the roles of different serotonin receptor subtypes (Ameisen et al, 1989; Lofdahl et al, 2016) but not particularly in the context of the role of the 5-HT1A receptor in skin wound healing. There is one study in which Buspirone has been implicated with the suppression of inflammatory effects (McAloon et al, 1995).…”