About

Steven S. An is a professor in the Department of Pharmacology at Rutgers University, with research interests spanning cancer biology, cytoskeleton, drug discovery, nanobiology/nanotechnology, and signaling. His lab develops new technologies to modulate and visualize physical forces in living cells, utilizing methods such as Fourier transform traction microscopy, magnetic twisting cytometry, and spontaneous nanoscale tracer motions. These live-cell micromechanical techniques are applicable across various cell types and serve research at the interface of engineering, cell biology, and medicine, aiming to understand mechanobiology and its implications for tissue growth, contraction, movement, invasion, and remodeling. His work includes the development of a micro-physiological system called the 'bronchi-chip,' which reconstitutes 3D co-cultures of human airway smooth muscle cells and airway epithelial cells, enabling real-time interrogation of chemical and physical cues influencing asthma-like phenotypes. His research explores sensory physiology, particularly the role of sensory GPCRs such as TAS2Rs and olfactory receptors expressed on human bronchi smooth muscle, which can reverse bronchoconstriction and influence cytoskeletal remodeling and cell proliferation. These findings suggest new avenues for disease-modifying therapeutics for asthma and investigate the function of sensory receptors in cardiovascular diseases, aging, and cancer.

Research topics

• Biology
• Cell biology
• Genetics
• Medicine
• Pathology
• Immunology
• Environmental health
• Internal medicine
• Anatomy
• Chemistry

Selected publications

• Characterizing the Effects of Antimuscarinics on RhoA Signaling

  Oxford Academix (Oxford) · 2026-02-02

  article

  Purpose: Airway hyperresponsiveness in asthma is driven by acetylcholine-mediated activation of the muscarinic acetylcholine 3 receptor (M3R), promoting bronchoconstriction, mucus hypersecretion, and airway remodeling. Despite directly targeting this pathway, antimuscarinics remain adjunctive rather than first-line therapy, suggesting a disconnect between biological rationale and clinical efficacy. Recent work from the Scott Lab at Thomas Jefferson University demonstrates that M3R in human airway smooth muscle (HASM) cells drives muscle shortening through G12/13–driven RhoA signaling rather than through Gq/11-dependent calcium flux. We therefore investigated whether clinically prescribed antimuscarinics effectively inhibit G12/13-dependent RhoA signaling in HASM cells. Methods: Human telomerase reverse transcriptase immortalized HASM cells with Renilla luciferase under the control of a serum response element (hTERT-SRE) were used to evaluate ligand-dependent RhoA activation. Cells were stimulated for 5 hours with drug, either alone or combined with 100 µM acetylcholine. Luciferase activity was measured and normalized to the maximal acetylcholine response, using 3-parameter nonlinear regression to determine residual RhoA activation. Results: Ipratropium bromide, revefenacin, tiotropium bromide and umeclidinium bromide exhibited partial agonism of the M3R-dependent RhoA signaling pathway that governs HASM contraction. In preliminary studies, glycopyrrolate appears to behave as a neutral antagonist of M3R signaling. Partial agonism by erstwhile muscarinic antagonists may sustain pro-contractile signaling despite receptor blockade. Conclusions: These findings suggest that many anticholinergics inadvertently preserve G12/13–RhoA signaling, limiting their bronchoprotective efficacy. Defining this signaling bias across antimuscarinic agents provides a framework for developing next-generation therapies that more effectively suppress the G12/13–RhoA axis to control airway hyperresponsiveness and hypertrophy.

  Publisher

• Biased signaling of the proton‐sensing receptor OGR1 by benzodiazepines

  UNC Libraries · 2026-01-13

  articleOpen access

  GPCRs have diverse signaling capabilities, based on their ability to assume various conformations. Moreover, it is now appreciated that certain ligands can promote distinct receptor conformations and thereby bias signaling toward a specific pathway to differentially affect cell function. The recently deorphanized G protein-coupled receptor OGR1 [ovarian cancer G protein-coupled receptor 1 ( GPR68)] exhibits diverse signaling events when stimulated by reductions in extracellular pH. We recently demonstrated airway smooth muscle cells transduce multiple signaling events, reflecting a diverse capacity to couple to multiple G proteins. Moreover, we recently discovered that the benzodiazepine lorazepam, more commonly recognized as an agonist of the γ-aminobutyric acid A (GABA_A) receptor, can function as an allosteric modulator of OGR1 and, similarly, can promote multiple signaling events. In this study, we demonstrated that different benzodiazepines exhibit a range of biases for OGR1, with sulazepam selectively activating the canonical Gs of the G protein signaling pathway, in heterologous expression systems, as well as in several primary cell types. These findings highlight the potential power of biased ligand pharmacology for manipulating receptor signaling qualitatively, to preferentially activate pathways that are therapeutically beneficial.

  PublisherDOI

• TFF3 induces β2agonist hyporesponsivness in human airway smooth muscle and small airway (Abstract ID: 273696)

  Journal of Pharmacology and Experimental Therapeutics · 2026-05-01

  article
  PublisherDOI

• Pirfenidone and its Derivative: Novel Bronchodilators and Leukocyte Airway Inflammation Inhibitors

  American Journal of Respiratory Cell and Molecular Biology · 2026-03-08

  article

  Asthma, a chronic airway inflammatory disease, manifests as excessive obstruction of the airways and airway hyperresponsiveness (AHR) due to airway smooth muscle (ASM) contraction. Conventional bronchodilator treatments, such as β2-adrenergic receptor (β2-AR) agonists, often lose efficacy due to receptor desensitization, while corticosteroid-resistant neutrophilic airway inflammation remains a major challenge in severe asthma. To identify novel bronchodilators, we screened the Sigma LOPAC1280 compound library using β2-agonist-desensitized precision-cut lung slices (PCLS) as an ex vivo model and identified pirfenidone (PFD), an FDA-approved drug for idiopathic pulmonary fibrosis, as a novel bronchodilator. We then developed CXN-8, a more potent PFD derivative. Both compounds produced rapid, concentration-dependent airway relaxation in human, mouse, and rat PCLS preconstricted with multiple bronchoconstrictors, and maintained efficacy under β2-AR-insensitive conditions. CXN-8 was ∼50-fold more potent than PFD while achieving comparable maximal relaxation, with EC50 values ranging from 0.8-4.7 μM across the different bronchoconstrictors. Mechanistically, PFD and CXN-8 suppressed RhoA-mediated Ca2 + sensitization by restoring myosin light chain phosphatase activity, which reduced phosphorylation of myosin regulatory light chain (MLC20) and promoted ASM relaxation. In vivo, acute oral administration of PFD (300 mg/kg) or CXN-8 (15 mg/kg) reduced airway resistance and AHR in house dust mite-sensitized mice. Chronic oral treatment (daily, Days 14-24) further attenuated airway inflammation and remodeling, decreasing eosinophil and neutrophil infiltration, Th2 and Th17 cytokines, ASM thickening, and peribronchial collagen deposition. Collectively, these findings identify PFD and CXN-8 as dual-acting bronchodilator and anti-inflammatory agents that also alleviate airway remodeling, offering a promising therapeutic strategy for β2-agonist-insensitive and corticosteroid-resistant asthma.

  PublisherDOI

• Ovarian Cancer G protein-coupled receptor-1 signaling bias dictates anti-contractile effect of benzodiazepines on airway smooth muscle

  Respiratory Research · 2025-05-13 · 1 citations

  articleOpen access

  We recently reported that the ovarian cancer G protein-coupled receptor-1 (OGR1) can be pharmacologically biased with specific benzodiazepines to couple with distinct heterotrimeric G proteins in human airway smooth muscle (ASM) cells. Lorazepam stimulated both Gs and Gq signaling via OGR1, whereas sulazepam only stimulated Gs signaling in ASM cells. The present study sought to determine the effects of sulazepam and lorazepam on contraction of human precision cut lung slices (hPCLS), and detail the biochemical mechanisms mediating these effects. Models of histamine (His) -stimulated contraction included imaging of ex vivo human precision cut lung slices (hPCLS) and Magnetic Twisting Cytometry (MTC) analysis of human ASM cell stiffness. To explore mechanisms of regulation, we examined effects on myosin light chain (pMLC) phosphorylation and PKA activity in primary human ASM cultures, as well as actin cytoskeleton integrity as defined by changes in the ratio of F to G actin assessed by immunofluorescence. In a dose-dependent manner, sulazepam relaxed His-contracted hPCLS and reduced baseline cell stiffness. Lorazepam did not relax His-contracted hPCLS, and only at a maximal dose (100 μM) did lorazepam relax baseline cell stiffness. The Gs-biased ligand sulazepam stimulated PKA activity as evidenced by significant induction of VASP and HSP20 phosphorylation, which was associated with significant inhibition of His-induced pMLC phosphorylation. Conversely, the balanced ligand lorazepam did not significantly increase HSP20 phosphorylation or VASP phosphorylation and did not significantly inhibit His-induced MLC phosphorylation. Sulazepam was also able to inhibit histamine induced F-actin formation. The Gs-biased OGR1 ligand sulazepam relaxed contracted ASM in both tissue- and cell- based models, via inhibition of MLC phosphorylation in a PKA-dependent manner and through inhibition of actin stress fiber formation. The relative inability of the balanced ligand lorazepam to influence ASM contractile state was likely due to competitive actions of concomitant Gq and Gs signaling.

  PublisherOA PDFDOI

• Evolution of Cell-ECM Crosstalk and Biomechanics During Arterial Aging

  Physiology · 2025-05-01

  article

  Introduction: Depending on surrounding cells, substrate mechanics, and biochemical signaling, vascular cell types – including smooth muscle cells (VSMC) – modulate their behavior to maintain short- and long-term vascular homeostasis. Aging perturbs this homeostasis, resulting in SMC dysfunction marked by pathological ECM remodeling and loss of contractile protein expression. The overall goal of this project is to obtain an integrated understanding of the molecular links between functional cellular behavior and mechanics of the vasculature and its key constituents (i.e. cells and ECM). Given that these constituents define overall in vivo stiffness, this will enable us to identify effective targets and ages for clinical intervention. Materials and Methods: Male C57Bl6/J mice aged 3mo, 6mo, 9mo, or greater than 18mo were assessed for in vivo cardiovascular function via blood pressure (BP) and pulse wave velocity (PWV). Intact and decellularized aortic segments from each age group were then subject to tensile testing to gauge bulk tissue stiffness. Mouse aortic smooth muscle cells (maSMCs) were isolated from each group and characterized for mechanical and phenotypic profile. Cell mechanics were measured using magnetic twisting cytometry/spontaneous nanoscale tracer motions (MTC/SNTM) and atomic force microscopy (AFM). Fluorescent collagen substrates were used to assess type I collagen (Col-I) integration and degradation in 2D cell culture. Cells of each age were further treated with MMP inhibitor, LOXL2 inhibitor or TGF-β1 to measure the impacts on Col-I turnover, as well as expression of relevant matricellular proteins and their associated transcripts. Results: Aortic tissue shows a steady increase in stiffness beginning at early middle-age. The aged vasculature is also more brittle, failing at lower strain values. These changes in bulk tissue mechanics are mediated by dysregulated cellular behavior, including increased expression of matrix crosslinking proteins (such as TG2) and increased cell stiffness. Collagen integration by isolated maSMCS peaks at 9mo, while collagen degradation progressively decreases with age. Treatment with LOXL2 inhibitor effectively limits collagen integration in all age groups. MMP inhibitor treatment causes a marked decrease in Col-I cleavage, though this effect is muted in the oldest maSMCs which show impaired Col-I cleavage even in the absence of MMPi. TGF-β1 treatment increases expression of stress fibers, indicating a transition to a contractile phenotype. Conclusions: There is a progressive decrease in enzymatic cleavage of Col-I by resident maSMCs with age. Col-I integration, however, is at its highest during middle-age. This implies that bulk tissue stiffening in old age is driven in large part by accumulation of crosslinked collagens that are unable to be cleared. Early in life however, changes in inherent cellular stiffness and/or cell-ECM adhesion are likely drivers of short-term tissue stiffening. Together, these data suggest EMA/middle-age is the most suitable time for clinical intervention, given that this is when cellular dysregulation begins to produce discernable increases to aortic stiffness. Financial and academic support has been provided by the NASEM Ford Foundation Fellowship, the Porter Physiology Development Fellowship and NHBLI grant R01HL148112 01 (L.S.). This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

  PublisherDOI

• Pirfenidone and Its Derivative CXN-8: Novel Dual Bronchodilators and Anti-neutrophilic Airway Inflammation Agents

  American Journal of Respiratory and Critical Care Medicine · 2025-05-01

  article

  Abstract RATIONALE: Asthma is a chronic inflammatory disease characterized by airway hyperresponsiveness (AHR) and inflammation. While β2-adrenergic receptor (β2-AR) agonists and inhaled corticosteroids are standard treatments, prolonged use of β2-agonists can lead to β2-AR desensitization, reducing their effectiveness. Additionally, a significant proportion of severe asthma patients, particularly those with corticosteroid-insensitive neutrophilic airway inflammation (NAI), remain difficult to treat. New therapeutic strategies are urgently needed to overcome this resistance. METHODS: To identify novel bronchodilators, we screened the Sigma Compound Library in mouse precision-cut lung slices (PCLS). The effects of identified candidates on myosin regulatory light chain (MLC2) phosphorylation, intracellular [Ca²⁺] levels, and RhoA activation were evaluated in human asthmatic airway smooth muscle (ASM) cells. Therapeutic efficacy was further assessed in LPS/ovalbumin-induced and HDM-induced mouse asthma models. AHR was assessed using a FinePointe apparatus, and inflammation was assessed through leukocyte counts in bronchoalveolar lavage fluid and histological analysis of lung tissue. RESULTS: Pirfenidone (PFD), a drug approved for idiopathic pulmonary fibrosis, was identified as a novel bronchodilator. We then developed a more potent derivative, CXN-8. Both PFD and CXN-8 demonstrated rapid (<2 min) and dose-dependent airway relaxation in mouse, rat, and human PCLS preconstricted with bronchoconstrictors acetylcholine, serotonin, histamine, and U46619, maintaining efficacy even after β2-AR desensitization. CXN-8 exhibited 50-fold greater potency than PFD, with an EC50 of 5 µM. Both compounds significantly counteract bronchoconstriction and ameliorate AHR in mice. Mechanistically, PFD and CXN-8 attenuated RhoA activation, restored myosin light chain kinase phosphatase (MLCP) activity, and reduced MLC2 phosphorylation without significantly altering intracellular [Ca²⁺] levels, indicating modulation of calcium sensitization pathways in ASM cells. Moreover, both compounds significantly alleviate corticosteroid-insensitive NAI of asthmatic mice. CONCLUSIONS: This study shows that PFD and its derivative CXN-8 act as dual bronchodilators and anti-inflammatory agents, targeting key pathways in airway constriction and inflammation. These compounds offer a promising approach for treating severe asthma, particularly with β2-agonist-insensitivity and corticosteroid-resistance, with CXN-8 showing high potential for clinical use.

  PublisherDOI

• Distinct mural cells and fibroblasts promote pathogenic plasma cell accumulation in idiopathic pulmonary fibrosis

  European Respiratory Journal · 2025-02-20 · 15 citations

  article

  BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is characterised by significant but poorly understood immune and antibody responses. This study examines the spatial transcriptomes and microenvironmental niches of antibody-producing plasma cells and tertiary lymphoid structures in IPF lungs, and the molecular pathways influencing antibody accumulation and pulmonary fibrosis. METHODS: Explant lung tissues from IPF patients and control normal lungs were used for spatial transcriptome assays and validating RNAscope and immunofluorescence assays. Fibroblasts derived from IPF and control lungs were examined for their ability to attract plasma cells. Neutralising antibodies were administered to investigate molecules affecting pulmonary plasma cell accumulation and fibrosis in bleomycin-treated mice. RESULTS: Human IPF lungs exhibited a remarkably widespread distribution of plasma cells and local antibodies in the fibrotic regions, disseminating from plasma cell-generating tertiary lymphoid structures. Novel mural cells wrapped the vessels in tertiary lymphoid structure regions, expressing C-C motif chemokine receptor 7 (CCR7) ligands that attracted T-cells into tertiary lymphoid structures to promote plasma cell generation. Distinct IPF-associated fibroblasts further secreted C-X-C motif chemokine ligand 12 (CXCL12), providing an extramedullary niche to foster the dissemination and accumulation of plasma cells in the fibrotic regions. Neutralisation of CCR7 ligands or CXCL12 reduced plasma cell and local antibody accumulation in the lungs of bleomycin-treated mice, leading to reduced transforming growth factor β concentrations and alleviated pulmonary fibrosis. CONCLUSIONS: Plasma cells and local antibodies are widely distributed in the fibrotic regions of IPF lungs. Distinct subsets of IPF-associated mural cells and fibroblasts promote pathological plasma cell and antibody accumulation. These findings have potential implications for strategies aimed at targeting immune and antibody responses to combat IPF.

  PublisherDOI

• Atovaquone Inhibits ABCC1 and Decreases Camp Egress in Human Airway Smooth Muscle Cells

  American Journal of Respiratory and Critical Care Medicine · 2025-05-01

  article

  Abstract RATIONALE: Evidence suggests that atovaquone and mefloquine, anti-malarial drugs, modulate the activity of ATP-binding cassette (ABC) transport proteins. We previously showed that ABCC1, a member of ABC transporter family, promotes the egress of intracellular cAMP in human airway smooth muscle (HASM) cells and that inhibition of ABCC1 expression or activity decreases basal tone and enhances HASM relaxation in response to β2-agonists. In this study, we posit that atovaquone and mefloquine enhance β2-agonist-induced cAMP signaling by blocking ABCC1 activity in HASM cells. METHODS: Primary HASM cells were treated for 30 min with or without atovaquone (1-10μM) or mefloquine (1-10μM) and then stimulated with 10μM isoproterenol (ISO). Using a highly sensitive cAMP ELISA, we measured both intracellular and extracellular cAMP levels. HSP20 phosphorylation level was also determined by immunoblot as a measure of PKA (protein kinase A) activity. RESULTS: Compared to untreated cells, cells treated with atovaquone showed ∼15-40% reduction in cAMP efflux and increased HSP20 phosphorylation in response to ISO. Mefloquine had little effect on ISO-induced cAMP efflux or HSP20 phosphorylation. These data suggest that similarly structured anti-malaria drugs may interact differently to ABC transport proteins and manifest differential effects on inhibiting ABCC1-induced cAMP efflux and PKA activation. CONCLUSION: Atovaquone inhibits ABCC1 activity in HASM cells, offering a new approach to repurpose anti-malaria drugs to enhance cAMP signaling and PKA-dependent HASM relaxation in the treatment of airflow obstruction in asthma.

  PublisherDOI

• The 18 KDA Mitochondrial Translocator Protein TSPO in Regulating Airway Smooth Muscle Cell Contraction

  American Journal of Respiratory and Critical Care Medicine · 2025-05-01

  article

  Abstract Rationale: The 18 kDa translocator protein (TSPO, aka peripheral benozdiazepine receptor) in an outer mitochondrial membrane protein, previously reported to have a role in cholesterol transport and neurosteroid synthesis. Preliminary research in our laboratory indicates that TSPO may play a role in the regulation of smooth muscle function. Herein, we examined the physiological role for TSPO in airway smooth muscle (ASM) biology and the actions of putative TSPO ligands on ASM function. Methods: We applied siRNA-based approach to knockdown TSPO expression (TSPO KD, ∼ 80% knock down efficiency) in cultured primary human ASM cells and applied a suite of biochemical approaches and functional studies to examine TSPOs role in ASM cells. Results: Using confocal imaging, we show that TSPO localization is not exclusive to mitochondria (Mitotracker Red CMXRos), also colocalizing with endoplasmic reticulum (ER; calnexin). TSPO KD did not have any observable effect on ASM cell growth when compared to ASMs transfected with control siRNA (scrambled, Scr) or ASM cell migration. Further, TSPO KD had no effect (compared to Scr group) on mitochondrial structural features, and baseline mitochondrial membrane potential (Scr 634.39 ± 45.04 S.E. vs TSPO KD TMRE fluorescence 577.88 ± 29.16 S.E.). Contractile agonist-induced intracellular (cytosolic; Fluo-4 AM and mitochondrial; Rhod-2 AM) calcium flux in ASM cells was unaffected from TSPO KD. In functional studies, using magnetic twisting cytometry (MTC), we observed that TSPO KD had no effect on baseline cell stiffness (Scr 0.89 ± 0.076 S.E. vs TSPO KD 0.818 ± 0.082 S.E.) or histamine-induced cell stiffness (Scr 1.377 ± 0.076 S.E. vs TSPO KD 1.32 ± 0.057 S.E.). In gel contraction studies, TSPO KD and Scr ASM cells showed comparable contraction (36-40%) in response to histamine. Ligands of TSPO relax airway tissues from mice (tracheal rings, ∼80%) and humans (precision cut lung slices, ∼50%). In cultured ASM cells, we show that TSPO ligands regulate pMLC20 (∼50% reduction PK11195, Ro5-4864, AC 5216 and 95% etifoxine) explaining the mechanism of relaxation. TSPO ligands evoke intracellular calcium flux in ASM cells and differentially activate protein kinase A substrates with no evidence of cellular cAMP accumulation (∼2-3% max response), suggesting involvement of unique signaling networks in regulation of ASM function by TSPO ligands. Conclusion: In summary, our studies indicate that while TSPO is not relevant in regulating ASM contractile state, ligands of TSPO evoke airway relaxation through mechanisms yet to be determined.

  PublisherDOI

Recent grants

• Nrf2 as a critical determinant of smooth muscle function

  NIH · $2.0M · 2011–2017

Frequent coauthors

• Paula J. Hurley

  Vanderbilt University Medical Center

  58 shared

• Phuoc T. Tran

  University of Maryland, Baltimore

  52 shared

• Reynold A. Panettieri

  Rutgers, The State University of New Jersey

  50 shared

• Brian W. Simons

  49 shared

• Jessie Huang

  Boston University

  48 shared

• Edward M. Schaeffer

  47 shared

• Rajendra P. Gajula

  University of Baltimore

  47 shared

• Elana J. Fertig

  Sidney Kimmel Comprehensive Cancer Center

  45 shared

Education

• PhD, Physiology

  Brown University

  2000