The story of 6PPD-Q begins on the road. Every time a vehicle brakes, accelerates, or corners, its tires shed microscopic particles and a complex cocktail of chemicals into the surrounding environment. Among these chemicals, 6PPD-Q is generated by atmospheric oxidation of the tire antioxidant 6PPD and has attracted particular concern because of its extraordinary toxicity in sensitive aquatic species, most famously the acute mortality it induces in coho salmon. Environmental monitoring has since documented 6PPD-Q in air, dust, soil, road runoff, sediment, surface water, and even edible plants, creating multiple potential routes of human contact. Detection of the compound in human urine and cerebrospinal fluid indicates that environmental exposure translates into internal exposure, raising urgent questions about what such internal doses might be doing to human organs and tissues.

Previous research had already flagged the reproductive system as a potential target of 6PPD-Q. In ovarian granulosa cells, the compound has been reported to suppress PI3K/AKT/FOXO1 signaling and promote apoptosis. Chronic exposure in male mice disrupted endocrine balance, impaired sperm quality, increased germ-cell death, and altered sphingolipid signaling. An independent multi-omics study of non-obstructive azoospermia implicated oxidative injury, abnormal cell-cycle regulation, apoptosis, and loss of germ-cell homeostasis in 6PPD-Q-associated testicular damage. Growing evidence also links environmental pollution more broadly to male sexual dysfunction through oxidative stress, endocrine disruption, vascular endothelial injury, and impaired nitric oxide signaling, with occupational bisphenol A exposure, lead, arsenic, mixed heavy metals, and organophosphate metabolites all showing associations with erectile dysfunction. Yet whether 6PPD-Q directly impairs erectile function, and through what molecular mechanism, remained unclear until now.

To answer that question, the team first assembled the molecular landscape. They retrieved potential 6PPD-Q targets from SwissTargetPrediction, SEA, TargetNet, and the Comparative Toxicogenomics Database, and erectile dysfunction-associated genes from GeneCards. The intersection yielded 134 genes present in both collections, designated 6PPD-Q-ED-related genes. A protein-protein interaction network built in STRING and visualized in Cytoscape showed that these genes were mainly involved in responses to peptides and peptide hormones, responses to xenobiotic stimuli, and negative regulation of transport, while Gene Ontology and KEGG enrichment identified metabolism-, signaling-, and cancer-related pathways. The enrichment profile suggested that 6PPD-Q exposure might disrupt cellular homeostasis through mechanisms related to xenobiotic stress responses and altered transport regulation, providing the first hint of a biologically coherent link between the pollutant and cavernosal dysfunction.

The next step placed these candidate signals within the cellular architecture of the corpus cavernosum itself. Using single-cell RNA sequencing data from five human erectile tissue samples, the researchers resolved nineteen clusters and annotated six major cell types: fibroblasts, endothelial cells, smooth muscle cells, macrophages, Schwann cells, and T cells. Fibroblasts were the predominant population, accounting for 48.98 percent of all cells, followed by endothelial cells at 22.91 percent and smooth muscle cells at 22.49 percent. Gene set scoring with AUCell showed that the 6PPD-Q-ED-related gene set was relatively enriched in macrophages and moderately enriched in fibroblasts and endothelial cells, suggesting that 6PPD-Q exposure may disrupt the cavernosal microenvironment through inflammatory responses, extracellular matrix remodeling, and endothelial dysfunction, the very processes that govern penile vascular health.

To prioritize the leading candidates, the team integrated three rat corpus cavernosum transcriptomic datasets covering diabetes-associated, hypertension-associated, and neurogenic erectile dysfunction, batch-correcting the combined matrices with ComBat. Differential expression analysis identified 1,003 genes, seventeen of which overlapped with the 6PPD-Q-ED-related gene set. Two independent machine learning procedures, LASSO regression and support vector machine-recursive feature elimination, converged on four genes: ACO1, HIF1A, PDK4, and PTPN11. All four showed area under the receiver operating characteristic curve values greater than 0.70, with HIF1A reaching an AUC of 0.926. Critically, two-sample Mendelian randomization using cis-eQTL instruments from eQTLGen and erectile dysfunction summary statistics from FinnGen, comprising 1,154 cases and 94,024 controls, showed that genetically predicted HIF1A expression was significantly associated with erectile dysfunction risk, with an inverse-variance weighted odds ratio of 1.384 and a 95 percent confidence interval of 1.022 to 1.874. No significant associations were found for the other three genes, and sensitivity analyses including MR-Egger, weighted median, MR-PRESSO, and leave-one-out procedures supported the stability of the HIF1A result.

With HIF1A prioritized, the team turned to structural biology to ask whether 6PPD-Q could physically interact with HIF-1α, the protein it encodes. Molecular docking with AutoDock Vina predicted that 6PPD-Q could bind to a pocket in HIF-1α with a binding energy of −6.8 kcal/mol, below the −5 kcal/mol threshold conventionally interpreted as suggestive of potentially favorable binding. The docked complex also showed hydrogen-bond interactions between 6PPD-Q and nearby amino acid residues. A 100-nanosecond molecular dynamics simulation in GROMACS confirmed that the complex reached a relatively stable trajectory, with root-mean-square deviation rising during early structural accommodation and subsequently fluctuating around a plateau. Radius of gyration and solvent-accessible surface area decreased modestly before stabilizing, consistent with a more compact ensemble, and intermittent hydrogen bonds persisted throughout the trajectory. The free-energy landscape contained a dominant low-energy basin, providing a computational structural basis for the proposed interaction.

The decisive evidence came from the animal experiments. Twenty-four male Sprague-Dawley rats were allocated to four groups: control, 6PPD-Q, 6PPD-Q plus PX-478, and PX-478 alone. 6PPD-Q was suspended in corn oil and given by oral gavage at 4 mg/kg once daily for six weeks, while PX-478, a HIF-1α inhibitor, was administered orally at 10 mg/kg three times per week. After the exposure period, the researchers measured erectile hemodynamics by recording intracavernosal pressure in response to electrical stimulation of the pelvic ganglion, normalizing maximum intracavernosal pressure to mean arterial pressure as the functional endpoint. Rats exposed to 6PPD-Q showed a significantly lower ICPmax/MAP ratio than controls, indicating impaired erectile function. Co-treatment with PX-478 partially restored this ratio, providing pharmacological evidence that HIF-1α activation contributes to the erectile impairment.

The molecular changes in the corpus cavernosum told a coherent story. Immunohistochemistry showed increased HIF-1α staining in endothelial and smooth muscle cells of 6PPD-Q-exposed rats, which was reduced by PX-478 treatment. Western blot analysis revealed increased HIF-1α expression alongside decreased phosphorylated eNOS, decreased total eNOS, and a reduced p-eNOS/eNOS ratio in the 6PPD-Q group. Cavernosal nitric oxide levels, measured colorimetrically, were decreased following 6PPD-Q exposure and increased after PX-478 treatment. Notably, serum testosterone levels did not differ significantly among the four groups, suggesting that the erectile impairment in this model was attributable to local vascular dysfunction rather than altered androgen levels. The eNOS/NO pathway is the core mechanism responsible for maintaining normal erectile responses, as endothelial cell-derived nitric oxide promotes relaxation of corpus cavernosum smooth muscle and sinusoidal filling, and its disruption by 6PPD-Q points directly to endothelial injury as the site of toxic action.

The findings suggest that 6PPD-Q may contribute to erectile dysfunction by activating HIF1A-related stress responses and impairing eNOS/NO-mediated endothelial relaxation. HIF-1α is a central transcriptional regulator of cellular responses to hypoxia and stress, and excessive activation may enhance the release of inflammatory mediators and activate tissue remodeling signals, contributing to endothelial injury and smooth muscle dysfunction. Previous erectile dysfunction studies have shown that cavernosal nerve injury or hypoxic conditions are accompanied by increased HIF-1α expression, elevated fibrosis-related factors, and reduced NOS expression, while interventions that improve erectile function are often associated with HIF-1α downregulation and restoration of the NOS system. The authors acknowledge important limitations: only a single dose and exposure period were evaluated, precluding dose-response assessment; the transcriptomic datasets were derived from rat models; the Mendelian randomization analysis was constrained by available public data and tissue mismatch; downstream cGMP signaling was not evaluated; and the proposed 6PPD-Q-HIF-1α interaction lacked direct biochemical validation by surface plasmon resonance or co-immunoprecipitation. Nevertheless, this study extends the reproductive toxicological effects of 6PPD-Q to penile erectile function for the first time, adding a new dimension to concerns about traffic-derived contaminants and male sexual health, and suggesting that reducing environmental 6PPD-Q exposure could become a modifiable factor in preventing vascular erectile dysfunction.

Subject of Research: Mechanistic evidence linking the tire-derived environmental contaminant 6PPD-quinone to erectile dysfunction through dysregulation of the HIF-1α/eNOS/nitric oxide axis

Article Title: 6PPD-quinone exposure impairs erectile function through dysregulation of the HIF-1α/eNOS/NO axis: multi-omics and in vivo evidence

Article References: Meng, C., Li, Y., Zhu, X., Li, Y., Du, Y., & Xia, Z. (2026). 6PPD-quinone exposure impairs erectile function through dysregulation of the HIF-1α/eNOS/NO axis: multi-omics and in vivo evidence. Frontiers in Endocrinology, 17, Article 1912092. https://doi.org/10.3389/fendo.2026.1912092

Image Credits: AI Generated

DOI: 10.3389/fendo.2026.1912092

Keywords: 6PPD-quinone, erectile dysfunction, HIF-1α, eNOS, nitric oxide, environmental contaminant, tire rubber pollutant, corpus cavernosum, network toxicology, single-cell RNA sequencing, Mendelian randomization, molecular docking

The biological target of the study is a population of cells known as corpus cavernosum smooth muscle cells, or CCSMCs, which form the muscular scaffolding of the erectile tissue. During an erection, these cells must relax in a coordinated fashion to allow the spongy chambers of the penis to fill with blood, and their ability to do so depends on maintaining what biologists call a contractile phenotype, a differentiated state in which the cell is packed with the contractile proteins that respond to vascular signals. Under the chronic oxidative stress of diabetes, however, these cells can undergo what researchers term phenotypic switching, abandoning their contractile identity in favor of a synthetic state characterized by proliferation, migration and the production of extracellular matrix. In the synthetic state, the cells lose the very proteins, such as alpha-smooth muscle actin and smooth muscle myosin heavy chain, that give them their mechanical function, and they instead express markers like osteopontin and proliferating cell nuclear antigen. This transition is increasingly recognized as a pivotal event in the progression of diabetes-related erectile dysfunction, but the regulatory circuits that connect diabetic stress to this switch have remained poorly understood.

To probe those circuits, the team began by examining the corpus cavernosum of rats made diabetic through injection of streptozotocin, a chemical that selectively destroys insulin-producing cells and produces a model of type 1 diabetes widely used in erectile dysfunction research. In these animals, the researchers found that expression of ARHGAP10, a member of the Rho GTPase-activating protein family, was significantly reduced compared with healthy controls. ARHGAP10 is known to function as a brake on Rho GTPase signaling, a pathway that governs cytoskeletal dynamics and smooth muscle contraction, so its loss in diabetic tissue immediately suggested a possible contributor to the erosion of contractile function.

The researchers then tested whether restoring ARHGAP10 could reverse the damage. Using adenoviral vectors delivered directly into the erectile tissue, they overexpressed the Arhgap10 gene in the cavernous tissue of diabetic rats and assessed erectile function by measuring intracavernosal pressure relative to mean arterial pressure, the standard physiological readout of erection quality in rodent models. The results were striking: animals receiving the ARHGAP10 vector showed measurably improved erectile responses compared with diabetic controls, and molecular analysis of their cavernous tissue revealed a marked suppression of the synthetic phenotypic switch, with contractile markers preserved and synthetic markers held in check.

To understand how ARHGAP10 exerts these effects, the team turned to RNA sequencing of primary CCSMCs grown in the laboratory. This transcriptomic survey identified G0S2, the G0/G1 switch gene 2, as a key downstream effector of ARHGAP10. G0S2 is a small protein with established roles in cell cycle control and lipid metabolism, best known in other contexts for its interaction with adipose triglyceride lipase, but its involvement in smooth muscle phenotypic regulation had not been appreciated. Co-immunoprecipitation assays then confirmed that ARHGAP10 and G0S2 physically interact, forming a protein complex within the cells. This physical association proved to be more than a curiosity; it was the mechanistic linchpin of the entire pathway.

The connection to mitochondria emerged when the researchers examined the organelles themselves. Mitochondria are the power plants of the cell, and their functional state is routinely assessed by measuring membrane potential, the electrical charge across the inner mitochondrial membrane that drives energy production, along with the generation of reactive oxygen species, the chemically reactive molecules that accumulate when the electron transport chain falters, and the ultrastructural appearance of the organelles under transmission electron microscopy. In diabetic conditions, CCSMCs showed the classic signature of mitochondrial dysfunction: collapsed membrane potential, excessive mitochondrial reactive oxygen species production and damaged ultrastructure. Remarkably, restoring ARHGAP10, through its interaction with G0S2, rescued all three parameters, restoring membrane potential, taming the overproduction of mitochondrial ROS and improving the structural integrity of the organelles.

The causal chain was then tested from both directions. When the researchers knocked down G0S2 in cultured cells, the protective effects of ARHGAP10 on the contractile phenotype were abolished, demonstrating that G0S2 is necessary for ARHGAP10 to work. Conversely, when G0S2 alone was overexpressed in the cavernous tissue of diabetic rats, without any ARHGAP10 manipulation, the treatment effectively reproduced the therapeutic benefits of ARHGAP10, restoring erectile function and preserving the contractile phenotype of the smooth muscle cells. This sufficiency experiment is particularly significant because it elevates G0S2 from a mere correlate to a genuine therapeutic target, one that sits downstream of ARHGAP10 and could potentially be manipulated directly by drugs.

The clinical context of these findings is important. Current first-line therapy for erectile dysfunction consists of phosphodiesterase type 5 inhibitors, the drug class that includes sildenafil, which work by amplifying the nitric oxide signaling that drives blood flow into the penis. These drugs are effective for many patients, but a substantial fraction of men with diabetes respond poorly to them, largely because diabetes ravages the nerves, blood vessels and smooth muscle that the drugs depend upon. By targeting the underlying cellular degeneration rather than the downstream signaling, an ARHGAP10-G0S2-based strategy would represent a fundamentally different approach, one that aims to preserve or restore the contractile machinery of the erectile tissue itself rather than simply coax more blood through a failing system.

Several technical details of the study strengthen its conclusions. The use of both in vivo adenoviral gene delivery and in vitro primary cell culture allowed the team to triangulate their findings across experimental systems, and the comprehensive mitochondrial assessment, spanning membrane potential measured with the JC-1 fluorescent probe, reactive oxygen species quantification and transmission electron microscopy of organelle ultrastructure, provided converging evidence that mitochondrial rescue is the operative mechanism. The team also traced the pathway’s connection to canonical smooth muscle contraction signaling, examining the RhoA pathway and its downstream effector MYPT1, thereby situating ARHGAP10 within the broader Rho signaling architecture that governs smooth muscle tone. Supplementary experiments further showed that ARHGAP10 overexpression attenuates the proliferation and migration of CCSMCs induced by platelet-derived growth factor-BB, a potent driver of phenotypic switching, and that pharmacological knockdown of G0S2 promotes switching on its own, reinforcing the necessity of this gene for maintaining the contractile state.

As with any preclinical rodent study, the road from these findings to human therapy is long, involving the development of deliverable interventions, safety testing and clinical trials. Gene therapy approaches for erectile dysfunction have been explored for decades without reaching routine clinical use, and the adenoviral vectors employed here are research tools rather than ready-made medicines. Nevertheless, the identification of a necessary and sufficient downstream mediator in G0S2 offers a concrete molecular handle that small molecules or other modalities could eventually target. The work also adds to a growing appreciation that mitochondrial dysfunction is not merely a byproduct of diabetic tissue damage but an active driver of it, and that restoring mitochondrial health can reverse pathological cellular reprogramming. For the millions of men whose diabetes has eroded both their vascular health and their quality of life, the demonstration that a single protein interaction can restore erectile function in a disease model is a compelling proof of concept, and a reminder that some of the most promising advances in medicine come from following the molecular threads wherever they lead, even into the smallest organelles of the body’s most private machinery.

Subject of Research: The role of the ARHGAP10-G0S2 protein interaction in preserving mitochondrial function and contractile phenotype of corpus cavernosum smooth muscle cells to ameliorate diabetic erectile dysfunction

Article Title: ARHGAP10-G0S2 interaction attenuates phenotypic switching of corpus cavernosum smooth muscle cells by restoring mitochondrial function, thereby ameliorating erectile dysfunction in diabetic rats

Article References: Liao, Z.-Q., Luo, J.-Q., Xiang, Y.-R., Liu, Y.-H., Lu, B.-X., Luo, C.-Y., He, H.-Y., Zhou, X.-C., Pan, M.-X., He, S.-H., Wei, A.-Y., & Zhang, H.-B. (2026). ARHGAP10-G0S2 interaction attenuates phenotypic switching of corpus cavernosum smooth muscle cells by restoring mitochondrial function, thereby ameliorating erectile dysfunction in diabetic rats. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-08942-0

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08942-0

Keywords: erectile dysfunction, diabetes, ARHGAP10, G0S2, mitochondrial dysfunction, phenotypic switching, smooth muscle cells, corpus cavernosum, reactive oxygen species, diabetic rats, Journal of Translational Medicine, Rho signaling