Prakash, Y. S.

The intestinal epithelium is exposed to diverse combinations of microbiota-derived compounds; however, the mechanisms by which the host integrates these signals remain poorly defined. Studying two highly abundant microbial metabolites, we identified the purine metabolite hypoxanthine as an effector metabolite that directly drives signaling and the short-chain fatty acid butyrate as a regulatory metabolite that conditions host responsiveness. Specifically, hypoxanthine activates the adenosine A1 receptor–TRPC4 axis in enterochromaffin (EC) cells, triggering calcium influx and serotonin release resulting in accelerated gastrointestinal transit locally and increased platelet activation systemically. In contrast, butyrate epigenetically upregulates specific G protein–coupled receptors and ion channels to enhance response to hypoxanthine and the neurotransmitters norepinephrine and dopamine. These findings define a cooperative signaling framework and highlight the role of EC cells as a distinct epithelial signaling hub that senses and integrates microbial metabolite signals to drive physiological responses. Our findings provide a mechanistic foundation for therapeutic strategies that leverage combinatorial microbial signaling.

siRNA delivery to target cellular processes is an appealing area in lung diseases such as asthma. To realize this potential requires efficient, targeted cytosolic delivery without cellular toxicity or siRNA degradation. We demonstrate the efficacy of PONI-Guan nanoparticles in accessing airway epithelial and smooth muscle cells with specific siRNA targeting of mRNAs of interest while maintaining barrier integrity and avoiding cellular toxicity.

Iron is an essential element for cellular homeostasis and functionality. Increased iron in the lung is associated with aging and asthma in the elderly (AIE). Using human airway smooth muscle cells from young versus elderly versus AIE patients, we found that dysregulated iron metabolism (more than iron accumulation), resulting in activation of antioxidant systems and increased susceptibility to ferroptosis, occurs in AIE, contributing to cell hyperplasia and matrix remodeling of aging and AIE.

Iron is an important metal element regulating biological processes such as gene expression, electron transport, cell proliferation, differentiation and division, and cellular respiration. Regulation of iron levels is therefore critical, with excess iron accumulation leading to iron-dependent lipid peroxidation and cell death (ferroptosis). Factors such as aging and environmental exposures (e.g., high/low oxygen, particulate iron) can disrupt iron homeostasis. Iron-dependent processes influence downstream pathways such as inflammation, mitochondrial energetics, and remodeling (proliferation, fibrosis), pathways involved in lung diseases particularly at the extremes of age, from hyperoxic lung injury in neonates to chronic diseases such as asthma, chronic obstructive pulmonary disease (COPD), and pulmonary fibrosis (PF) that increase with age. Although these diseases involve structural and functional changes in bronchial versus alveolar compartments, including airway hyperreactivity, altered mucus production, cell proliferation and migration, increased extracellular matrix (ECM) remodeling, senescence, and metabolic dysregulation, the casual or consequential links between iron dysregulation and disease pathology, particularly with aging, are still being investigated. The aim of this topical review is to 1) highlight current knowledge regarding iron regulation in normal lung versus lung diseases, 2) identify known roles of iron in lung homeostasis and the contribution of iron dysregulation in lung diseases with aging, and 3) explore the potential benefit of targeting iron regulation and/or ferroptosis in lung diseases.

Recognizing that antioxidant systems are impaired in the airways of premature infants, we used human fetal airway cells to explore the impact of oxygen on iron regulation and iron-mediated cell death (ferroptosis). We find moderate hyperoxia impairs antioxidant systems that prevent ferroptosis and dysregulates iron metabolism, while severe hyperoxia has a negative effect on mechanisms driving the early onset of ferroptosis. Inhibitors of ferroptosis decrease iron and lipid peroxidation, demonstrating links between oxygen and iron regulation in developing airways.

Abstract As an intrinsically mechanosensitive organ, the lung experiences a range of mechanical forces. Chronic obstructive pulmonary disease (COPD) involves abnormal macroscopic cellular and extracellular matrix (ECM) changes that impact mechanical properties of the lung. Mechanosensitive Piezo1/2 channels are expressed in the lung including on airway smooth muscle cells (ASM) that mediate cellular responses to stretch and ECM biomechanics. The expression and roles of Piezos in COPD lung ASM are not known. We hypothesized that Piezo expression and activation are altered in COPD lung ASM influencing ECM regulation. Distribution of Piezo proteins in ASM and epithelium of small airways of COPD stage II and IV vs. non-COPD controls was assessed using immunohistochemistry and ImageJ (n=10-17/group). Isolated ASM cells from control (n=6) vs. COPD stage II and IV patients (n=3 each stage) were exposed to stretch or the Piezo1 agonist Yoda1 followed by measurement of ECM gene and protein expression. Less Piezo2 staining was observed in COPD IV patients compared to controls, with lesser area and intensity of staining in the epithelial layer, and lower intensity of staining in ASM and small airways as a whole. Fura-2-based imaging of ASM Ca 2+ showed lower influx after Yoda1 exposure in COPD II compared to control and COPD IV. Gene expression of Piezo1 increased upon stretching in controls but not in COPD ASM, while Piezo2 protein expression decreased with stretching in all groups. Yoda1 treatment resulted in decreased collagen1 , fibulin1 and periostin gene and collagen 1 and periostin protein expression in ASM. Overall, these results support a role for Piezo activation in abnormal ECM-ASM cell crosstalk in COPD.

Abstract The lung, one the largest branching organs in our body and vital for survival at first breath, is commonly known as the gas-exchange organ. Recent novel findings on lung sensing cells, molecules, and lung-brain crosstalk in the emerging discipline of interoception have highlighted the consideration of the lung as a sensory organ. Acknowledging the central importance of lung sensing to human health and disease, NHLBI convened a workshop to synthesize the past, current, and future of lung sensing research, with in-person presentations by ∼20 interdisciplinary experts and a large virtual audience. Here, we highlight the key topics discussed and summarize a blueprint for the future in this important field.

Abstract Endothelial-to-mesenchymal transition (EndMT) is a biological process through which lung vascular endothelial cells (ECs) transdifferentiate into mesenchymal-like cells. EndMT has recently been implicated in the development and progression of pulmonary vascular remodeling in pulmonary hypertension (PH); however, its underlying regulatory mechanisms remain incompletely understood. MicroRNAs (miRNAs) are key post-transcriptional regulators of EC gene expression and cellular responses to various stimuli. Notably, microRNA-153 (miR-153) has been shown to directly target SNAI1 to modulate epithelial-to-mesenchymal transition (EMT), a process closely related to EndMT and extensively studied in cancer. Whether miR-153 also participates in EndMT regulation, however, remains unknown. In this study, we demonstrate that 72-hour hypoxic exposure induces SNAI1-mediated EndMT in human lung vascular ECs. Hypoxia also increased cell proliferation and disrupted intercellular junctions, leading to enhanced endothelial permeability. Reduced miR-153 expression was observed in both hypoxia- and TGF-β1-induced EndMT, as well as in ECs isolated from PH patients exhibiting an EndMT phenotype. Similar to hypoxia, TGF-β1 promoted EC permeability. Loss of miR-153 enhanced SNAI1-mediated EndMT, endothelial survival, and permeability under normoxic conditions, whereas miR-153 overexpression attenuated EndMT induced by hypoxia or TGF-β1. However, miR-153 restoration did not completely restore endothelial barrier integrity disrupted by these stimuli. In vitro findings were validated in experimental PH model. In conclusion, miR-153 serves as a critical regulator of EndMT, maintaining endothelial identity and barrier function. Therapeutic delivery of miR-153 may therefore represent a novel strategy to inhibit EndMT and attenuate pulmonary vascular remodeling in PH.

Rationale: Pulmonary hypertension (PH) is a fatal disease characterized by a sustained elevated pulmonary vascular resistance that results in right heart failure. Despite therapeutic advances, no treatment provides disease progression reversion, resulting in poor long-term survival. Identifying new therapeutic targets for PH therefore requires a deeper understanding of its mechanisms. A defining feature of PH is pulmonary vascular remodeling, a result from excessive proliferation, migration, and apoptosis resistance of pulmonary artery smooth muscle cells (PASMC). SNAI1, a transcription factor regulating cell proliferation and differentiation during development and disease, has recently been implicated in endothelial dysfunction and endothelial-to-mesenchymal transition in PH. However, its role within PASMC remains unknown. Here, we aimed to define the contribution of SNAI1 in PASMC to the pathogenesis of PH. Methods: Normal human PASMC were exposed to normoxia (21% O 2 ) or hypoxia (3% O 2 ) for 72 hours. PASMC were also isolated from patients with or without PH. Cell proliferation and migration were assessed by EdU incorporation and wound scratch assays respectively. Mice were exposed to hypoxia (10% O 2 ) or Sugen5416/hypoxia (10% O 2 plus Sugen5416 20mg/kg, i.p., weekly) for 6 weeks. PH phenotype was characterized by right heart catheterization, right ventricle (RV) hypertrophy by Fulton index and pulmonary artery (PA) remodeling by H&E staining of lung tissues. Pharmacological blocker GN-25 was used to inhibit SNAI1 in vitro and in vivo. Results: SNAI1 expression was markedly increased in hypoxic PASMC and in PASMC from patients with PH. Hypoxia also upregulated HIF-1alpha, Vimentin, p-AKT, PCNA at the protein level in PASMC. EdU incorporation and migration rates were significantly higher in hypoxic cells as well as in PASMC isolated from PH patients compared with controls. In vitro, GN-25 (100 nM) abolished hypoxia-induced PASMC proliferation and migration. Right ventricular systolic pressure (RVSP), a surrogate measurement of PA systolic pressure, estimated mean PAP (mPAP), and RV contractility (RV-±dP/dtmax) were significantly increased in both PH models compared with controls. Additionally, Sugen5416/hypoxia-treated mice exhibited higher RVSP, mPAP and RV-±dP/dtmax compared to hypoxia-treated animals. The Fulton index (weight of RV vs. left ventricle and septum), was increased in both PH groups indicating development of RV hypertrophy in PH compared to control. PH mice lost body weight by 5-10%. Additionally, when Fulton index was normalized by body weight, RV hypertrophy was significantly higher in Sugen5416/hypoxia-treated mice compared with hypoxic animals. Lung tissues from PH mice exhibit PA hypertrophy (media remodeling) with some PA partially or completely occluded. Additionally, we detected protein upregulation of Snai1 and Vimentin in lung tissues of PH mice in both groups. Treatment of PH mice with GN-25 (20 mg/kg, daily, for the last 3 weeks under PH stimuli) in reversal experiments attenuated PH phenotype in both animal models by decreasing hemodynamic parameters, right ventricle hypertrophy and pulmonary vascular remodeling. Conclusions: Our findings identify a key role for SMC SNAI1 in the pathogenesis of lung vascular remodeling during hypoxia-induced PH. Inhibition of SNAI1 in PASMC may constitute a new therapeutic strategy for the treatment of PH. This abstract was presented at the American Physiology Summit 2026 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.