Simvastatin activates the spindle assembly checkpoint and causes abnormal cell division by modifying small GTPases

Simvastatin is an inhibitor of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, which is a rate-limiting enzyme of the cholesterol synthesis pathway. It has been used clinically as a lipid-lowering agent to reduce low-density lipoprotein (LDL) cholesterol levels. In addition, antitumor activity has been demonstrated. Although simvastatin attenuates the prenylation of small GTPases, its effects on cell division in which small GTPases play an important role, have not been examined as a mechanism underlying its cytostatic effects. In this study, we determined its effect on cell division. Cell cycle synchronization experiments revealed a delay in mitotic progression in simvastatin-treated cells at concentrations lower than the IC50. Time-lapse imaging analysis indicated that the duration of mitosis, especially from mitotic entry to anaphase onset, was prolonged. In addition, simvastatin increased the number of cells exhibiting misoriented anaphase/telophase and bleb formation. Inhibition of the spindle assembly checkpoint (SAC) kinase Mps1 canceled the mitotic delay. Additionally, the number of cells exhibiting kinetochore localization of BubR1, an essential component of SAC, was increased, suggesting an involvement of SAC in the mitotic delay. Enhancement of F-actin formation and cell rounding at mitotic entry indicates that cortical actin dynamics were affected by simvastatin. The cholesterol removal agent methyl-β-cyclodextrin (MβCD) accelerated mitotic progression differently from simvastatin, suggesting that cholesterol loss from the plasma membrane is not involved in the mitotic delay. Of note, the small GTPase RhoA, which is a critical factor for cortical actin dynamics, exhibited upregulated expression. In addition, Rap1 was likely not geranylgeranylated. Our results demonstrate that simvastatin affects actin dynamics by modifying small GTPases, thereby activating the spindle assembly checkpoint and causing abnormal cell division.

H2S Regulates the Phenotypic Transformation of Astrocytes Following Cerebral Ischemia/Reperfusion via Inhibiting the RhoA/ROCK Pathway

The role of hydrogen sulfide (H2S) on the phenotypic change of astrocytes following cerebral ischemia/reperfusion (I/R) in mice was investigated in present study. We tested the expression of glial fibrillary acidic protein (GFAP), A2 phenotype marker S100a10, and A1 phenotype marker C3 protein and assessed the change of BrdU/GFAP-positive cells, GFAP/C3-positive cells, and GFAP/S100a10-positive cells in mice hippocampal tissues to evaluate the change of astrocyte phenotypes following cerebral I/R. The role of H2S on the phenotypic change of astrocytes following cerebral I/R in mice was investigated by using H2S synthase cystathionine-γ-lyase (CSE) knockout mice (KO). The results revealed that cerebral I/R injury promoted the astrocytes proliferation of both A1 and A2 phenotypes, which were more significant in mice of H2S synthase CSE KO than in mice of wild type (WT). Interestingly, supplement with H2S could inhibit the A1 phenotype proliferation but promote the proliferation of A2 phenotype, suggesting that H2S could regulate the transformation of astrocytes to A2 phenotype following cerebral I/R, which is beneficial for neuronal recovery. Besides, we found that H2S-mediated change of astrocyte phenotype is related to inhibiting the RhoA/ROCK pathway. Furthermore, both H2S and ROCK inhibitor could ameliorate the brain injury of mice at 9 days after cerebral I/R. In conclusion, H2S regulates the phenotypic transformation of astrocytes to A2 phenotype following the cerebral I/R via inhibiting RhoA/ROCK pathway and then exerts the neuroprotective effect against the subacute brain injury.

Dynamic light-responsive RhoA activity regulates mechanosensitive stem cell fate decision in 3D matrices

The behavior of stem cells is regulated by mechanical cues in their niche that continuously vary due to extracellular matrix (ECM) remodeling, pulsated mechanical stress exerted by blood flow, and/or cell migration. However, it is still unclear how dynamics of mechanical cues influence stem cell lineage commitment, especially in a 3D microenvironment where mechanosensing differs from that in a 2D microenvironment. In the present study, we investigated how temporally varying mechanical signaling regulates expression of the early growth response 1 gene (Egr1), which we recently discovered to be a 3D matrix-specific mediator of mechanosensitive neural stem cell (NSC) lineage commitment. Specifically, we temporally controlled the activity of Ras homolog family member A (RhoA), which is known to have a central role in mechanotransduction, using our previously developed Arabidopsis thaliana cryptochrome-2-based optoactivation system. Interestingly, pulsed RhoA activation induced Egr1 upregulation in stiff 3D gels only, whereas static light stimulation induced an increase in Egr1 expression across a wide range of 3D gel stiffnesses. Actin assembly inhibition limited Egr1 upregulation upon RhoA activation, implying that RhoA signaling requires an actin-involved process to upregulate Egr1. Consistently, static-light RhoA activation rather than pulsed-light activation restricted neurogenesis in soft gels. Our findings indicate that the dynamics of RhoA activation influence Egr1-mediated stem cell fate within 3D matrices in a matrix stiffness-dependent manner.

Urotensin II receptor deficiency ameliorates ligation-induced carotid intimal hyperplasia partially through the RhoA-YAP1 pathway

Intimal hyperplasia (IH) is a common pathological feature of vascular proliferative diseases, such as atherosclerosis and restenosis after angioplasty. Urotensin II (UII) and its receptor (UTR) are widely expressed in cardiovascular tissues. However, it remains unclear whether the UII/UTR system is involved in IH. Right unilateral common carotid artery ligation was performed and maintained for 21 days to induce IH in UTR knockout (UTR-/-) and wild-type (WT) mice. Histological analysis revealed that compared with WT mice, UTR-deficient mice exhibited a decreased neointimal area, angiostenosis and intima-media ratio. Immunostaining revealed fewer smooth muscle cells (SMCs), endothelial cells and macrophages in the lesions of UTR-/- mice than in those of WT mice. Protein interaction analysis suggested that the UTR may affect cell proliferation by regulating YAP and its downstream target genes. In vitro experiments revealed that UII can promote the proliferation and migration of SMCs, and western blotting also revealed that UII increased the protein expression of RhoA, CTGF, Cyclin D1 and PCNA and downregulated p-YAP protein expression, while these effects could be partly reversed by urantide. To evaluate the translational value of UTRs in IH management, WT mice were also treated with two doses of urantide, a UTR antagonist, to confirm the benefit of UTR blockade in IH progression. A high dose of urantide (600 μg/kg/day), rather than a low dose (60 μg/kg/day), successfully improved ligation-induced IH compared with that in mice receiving vehicle. The results of the present study suggested that the UII/UTR system may regulate IH partly through the RhoA-YAP signaling pathway.

The Roles of RhoA/ROCK/NF-κB Pathway in Microglia Polarization Following Ischemic Stroke

Ischemic stroke is the leading cause of death and disability worldwide. Nevertheless, there still lacks the effective therapies for ischemic stroke. Microglia are resident macrophages of the central nervous system (CNS) and can initiate immune responses and monitor the microenvironment. Microglia are activated and polarize into proinflammatory or anti‑inflammatory phenotype in response to various brain injuries, including ischemic stroke. Proinflammatory microglia could generate immunomodulatory mediators, containing cytokines and chemokines, these mediators are closely associated with secondary brain damage following ischemic stroke. On the contrary, anti-inflammatory microglia facilitate recovery following stroke. Regulating the activation and the function of microglia is crucial in exploring the novel treatments for ischemic stroke patients. Accumulating studies have revealed that RhoA/ROCK pathway and NF-κB are famous modulators in the process of microglia activation and polarization. Inhibiting these key modulators can promote the polarization of microglia to anti-inflammatory phenotype. In this review, we aimed to provide a comprehensive overview on the role of RhoA/ROCK pathway and NF-κB in the microglia activation and polarization, reveal the relationship between RhoA/ROCK pathway and NF-κB in the pathological process of ischemic stroke. In addition, we likewise discussed the drug modulators targeting microglia polarization.

RVG29 Peptide-Modified Exosomes Loaded with Mir-133b Mediate the RhoA-ROCK Pathway to Improve Motor and Neurological Symptoms in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder worldwide. Drug delivery to the brain through the blood-brain barrier (BBB) is a significant challenge in PD treatment. Exosomes, which can efficiently traverse the BBB, which many drugs cannot penetrate, are ideal natural carriers for drug delivery. In this study, the BBB shuttle peptide was modified on the exosome surfaces. Three types of exosomes were constructed, each modified with a distinct peptide (RVG29, TAT, or Ang2) and loaded with miR-133b. The safety and brain-targeting capabilities of these peptide-modified exosomes were then evaluated. Finally, the mechanism by which RVG29-Exo-133b regulates the RhoA-ROCK signaling pathway was investigated. The findings indicate that the three peptide-modified exosomes were adequately tolerated, safe, and effectively assimilated in vivo and ex vivo, with RVG29 exhibiting superior targeting to the brain. Furthermore, RVG29-Exo-133b decreased the phosphorylation level of the Tau protein by targeting the RhoA-ROCK signaling pathway. It also enhanced the motor function in mice with PD, thereby reducing the degree of depression, improving dopaminergic neuron function, and attenuating 6-OHDA-induced nerve damage. In this study, we developed a stable drug delivery mechanism that targets the intracerebral region using exosomes. Furthermore, a novel strategy was developed to manage PD and can potentially serve as a preclinical basis for utilizing exosomes in the diagnosis and treatment of neurodegenerative conditions.

Structural basis for the distinct roles of non-conserved Pro116 and conserved Tyr124 of BCH domain of yeast p50RhoGAP

p50RhoGAP is a key protein that interacts with and downregulates the small GTPase RhoA. p50RhoGAP is a multifunctional protein containing the BNIP-2 and Cdc42GAP Homology (BCH) domain that facilitates protein-protein interactions and lipid binding and the GAP domain that regulates active RhoA population. We recently solved the structure of the BCH domain from yeast p50RhoGAP (YBCH) and showed that it maintains the adjacent GAP domain in an auto-inhibited state through the β5 strand. Our previous WT YBCH structure shows that a unique kink at position 116 thought to be made by a proline residue between alpha helices α6 and α7 is essential for the formation of intertwined dimer from asymmetric monomers. Here we sought to establish the role and impact of this Pro116. However, the kink persists in the structure of P116A mutant YBCH domain, suggesting that the scaffold is not dictated by the proline residue at this position. We further identified Tyr124 (or Tyr188 in HBCH) as a conserved residue in the crucial β5 strand. Extending to the human ortholog, when substituted to acidic residues, Tyr188D or Tyr188E, we observed an increase in RhoA binding and self-dimerization, indicative of a loss of inhibition of the GAP domain by the BCH domain. These results point to distinct roles and impact of the non-conserved and conserved amino acid positions in regulating the structural and functional complexity of the BCH domain.

Replication competent HIV-guided CRISPR screen identifies antiviral factors including targets of the accessory protein Nef

Innate antiviral factors are essential for effective defense against viral pathogens. However, the identity of major restriction mechanisms remains elusive. Current approaches to discover antiviral factors usually focus on the initial steps of viral replication and are limited to a single round of infection. Here, we engineered libraries of >1500 replication-competent HIV-1 constructs each expressing a single gRNAs to target >500 cellular genes for virus-driven discovery of antiviral factors. Passaging in CD4+ T cells robustly enriched HIV-1 encoding sgRNAs against GRN, CIITA, EHMT2, CEACAM3, CC2D1B and RHOA by >50-fold. Using an HIV-1 library lacking the accessory nef gene, we identified IFI16 as a Nef target. Functional analyses in cell lines and primary CD4+ T cells support that the HIV-driven CRISPR screen identified restriction factors targeting virus entry, transcription, release and infectivity. Our HIV-guided CRISPR technique enables sensitive discovery of physiologically relevant cellular defense factors throughout the entire viral replication cycle.

Migrasomes from adipose derived stem cells enrich CXCL12 to recruit stem cells via CXCR4/RhoA for a positive feedback loop mediating soft tissue regeneration

BACKGROUND

Adipose-derived stem cells (ASCs) represent the most advantageous choice for soft tissue regeneration. Studies proved the recruitment of ASCs post tissue injury was mediated by chemokine CXCL12, but the mechanism by which CXCL12 is generated after tissue injury remains unclear. Migrasomes are newly discovered membrane-bound organelles that could deliver CXCL12 spatially and temporally in vivo. In this study, we sought to investigate whether migrasomes participate ASC-mediated tissue regeneration.

METHODS

Discrepant and asymmetrical soft tissue regeneration mice model were established, in which HE staining, immunofluorescent staining, western blot and qPCR were conducted to confirm the role of CXCL12 and migrasomes in ASC-mediated tissue regeneration. Characterization of ASC-derived migrasomes were carried out by confocal microscopy, scanning electron microscopy, transmission electron microscopy as well as western blot analysis. The function and mechanism of migrasomes were further testified by assisting tissue regeneration with isolated migrasomes in vivo and by in vitro transwell combined with co-culture system.

RESULTS

Here, we show for the first time that migrasomes participate in soft tissue regeneration. ASCs generate migrasomes enriched with CXCL12 to mediate tissue regeneration. Migrasomes from ASCs could promote stem cells migration by activating CXCR4/RhoA signaling in vivo and in vitro. Chemoattracted ASCs facilitate regeneration, as demonstrated by the upregulation of an adipogenesis-associated protein. This positive feed-back-loop creates a favorable microenvironment for soft tissue regeneration. Thus, migrasomes represent a new therapeutic target for ASC-mediated tissue regeneration.

CONCLUSIONS

Our findings reveal a previously unknown function of ASCs in mediating tissue regeneration by generating migrasomes. The ASC-derived migrasomes can restore tissue regeneration by recruiting stem cells, which highlighting the potential application of ASC-derived migrasomes in regenerative medicine.

Targeting osteopontin alleviates endometriosis and inflammation by inhibiting the RhoA/ROS axis and achieves non-invasive in vitro detection via menstrual blood

STUDY QUESTION

How does osteopontin (OPN) in endometriosis ectopic stromal cells (EESCs) participate in the pathogenesis of endometriosis and achieve non-invasive detection in vitro?

SUMMARY ANSWER

Targeted OPN regulates endometriosis's necroptosis and inflammatory state by inhibiting the RhoA/reactive oxygen species (ROS) axis, thereby alleviating endometriosis and enabling non-invasive detection of menstrual blood in vitro.

WHAT IS KNOWN ALREADY

Endometriosis is a chronic inflammatory disease. Recent studies have shown that OPN plays an important role in disease progression by regulating cell death and inflammation.

STUDY DESIGN, SIZE, DURATION

The study included 20 patients diagnosed with endometriosis (confirmed by laparoscopy and histology) and 10 controls without endometriosis. Endometriotic stromal cells were isolated from endometrial samples, while menstrual blood endometrial cells (MESCs) were isolated from menstrual blood. These cells were then cultured in vitro and utilized in subsequent experiments.

PARTICIPANTS/MATERIALS, SETTING, METHODS

OPN expression in EESCs was assessed using inflammatory factor sequencing, immunohistochemical staining (IHC), quantitative real-time PCR (qRT-PCR) analysis, and Western blotting (WB). The biological behavior of OPN and its effects on inflammatory factors were examined using EdU, wound-healing, Transwell, and ELISA assays. Necroptosis in EESCs and its impact on inflammatory factors were detected through qRT-PCR, WB, and Calcein-AM/PI fluorescence assays. The examination of mitochondrial stress in EESCs involved the use of the Mitochondrial Membrane Potential (ΔΨm) Assay, ROS detection, and Calcein-AM Loading/cobalt chloride Quenching. qRT-PCR, WB, and other experiments were conducted to verify the regulation of necroptosis and inflammatory factor levels in EESCs by OPN through the RhoA/ROS axis. Knockdown of OPN and its inhibitory effect on endometriosis lesion size were confirmed using AAV9 virus, IHC, qRT-PCR, WB, and other experiments. Additionally, OPN expression in MESCs was detected using transcriptome sequencing, RT-PCR, WB, and other experiments.

MAIN RESULTS AND THE ROLE OF CHANCE

In vitro assays demonstrated a significant upregulation of OPN in EESCs, and the knockdown of OPN effectively inhibited necroptosis and the release of inflammatory factors. OPN inhibited necroptosis and inflammatory factor release by mediating RhoA-dependent ROS production and blocking mixed lineage kinase domain-like protein phosphorylation at the cell membrane. In vivo, targeting of OPN can inhibit the growth of endometriosis lesions. Clinically, OPN was also significantly upregulated in the menstrual blood of patients with endometriosis.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Due to limitations in obtaining surgical specimens, our study primarily involved collecting endometriosis tissues from women during the proliferative and secretory phases of the menstrual cycle. We observed a significant overexpression of OPN in the samples used for our investigation. However, the expression of OPN in endometriosis tissues during the intermenstrual phase remains unknown.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings highlight the pivotal role of the OPN/RhoA/ROS axis in the regulation of necroptosis and the release of inflammatory factors. OPN knockdown exerts a therapeutic effect in vivo, and the high expression detection of OPN in menstrual blood in vitro. In summary, targeting OPN provides possibilities for the treatment and detection of endometriosis.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by the National Natural Science Foundation of China (82071626), the Zhejiang Province Public Welfare Technology Application Research Project (LGF21H040010), and the Clinical Research project of the Second Affiliated Hospital of Wenzhou Medical University (1010293). The authors have no conflicts of interest.

Effect of cryopreservation on Odc1 and RhoA genes expression in diapausing mouse blastocysts

The possibility of embryo cryopreservation is important for applying the genome resource banking (GRB) concept to those mammalian species that exhibit embryonal diapause in their early development. Odc1 encodes ODC1, which is a key enzyme in polyamine synthesis. RhoA is an essential part of Rho/ROCK system. Both Odc1 and RhoA play an important role in preimplantation embryo development. Studying these systems in mammalian species with obligate or experimentally designed embryonic diapause may provide insight into the molecular machinery underlying embryo dormancy and re-activation. The effect of cryopreservation procedures on the expression of the Odc1 and RhoA in diapausing embryos has not been properly studied yet. The purpose of this work is to address the possibility of cryopreservation diapausing embryos and to estimate the expression of the Odc1 and RhoA genes in diapausing and non-diapausing embryos before and after freeze-thaw procedures using ovariectomized progesterone treated mice as a model. Both diapausing and non-diapausing in vivo-derived embryos continued their development in vitro after freezing-thawing as evidenced by blastocoel re-expansion. Although cryopreservation dramatically decreased the expression of the Odc1 and RhoA genes in non-diapausing embryos, no such effects have been observed in diapausing embryos where these genes were already at the low level before freeze-thaw procedures. Future studies may attempt to facilitate the re-activation of diapausing embryos, for example frozen-thawed ones, specifically targeting Odc1 or Rho/ROCK system.

The antiangiogenic effect of digitoxin is dependent on a ROS-elicited RhoA/ROCK pathway activation

We previously showed that digitoxin inhibits angiogenesis and cancer cell proliferation and migration and these effects were associated to protein tyrosine kinase 2 (FAK) inhibition. Considering the interactions between FAK and Rho GTPases regulating cell cytoskeleton and movement, we investigated the involvement of RhoA and Rac1 in the antiangiogenic effect of digitoxin. Phalloidin staining of human umbilical vein endothelial cells (HUVECs) showed the formation of stress fibers in cells treated with 10 nM digitoxin. By Rhotekin- and Pak1- pull down assays, detecting the GTP-bound form of GTPases, we observed that digitoxin (10-25 nM) induced sustained (0.5-6 h) RhoA activation with no effect on Rac1. Furthermore, inhibition of HUVEC migration and capillary-like tube formation by digitoxin was counteracted by hindering RhoA-ROCK axis with RhoA silencing or Y-27632 treatment. Digitoxin did not decrease p190RhoGAP phosphorylation at Tyr1105 (a site targeted by FAK), suggesting that RhoA activation was independent from FAK inhibition. Because increasing evidence points to a redox regulation of RhoA, we measured intracellular ROS and found that digitoxin treatment enhanced ROS levels in a concentration-dependent manner (1-25 nM). Notably, the flavoprotein inhibitor DPI or the pan-NADPH oxidase (NOX) inhibitor VAS-2870 antagonized both ROS increase and RhoA activation by digitoxin. Our results provide evidence that inhibition of HUVEC migration and tube formation by digitoxin is dependent on ROS production by endothelial NOX, which leads to the activation of RhoA/ROCK pathway. Digitoxin effects on proteins regulating cytoskeletal organization and cell motility could have a wider impact on cancer progression, beyond the antiangiogenic activity.

LAMB3 Promotes Myofibrogenesis and Cytoskeletal Reorganization in Endometrial Stromal Cells via the RhoA/ROCK1/MYL9 Pathway

LAMB3, a major extracellular matrix and basal membrane component, is involved in wound healing. We aimed to understand its role in Asherman's syndrome (AS), which is associated with infertility, by using bioinformatics analysis and cultured endometrial stromal cells (ESCs). MRNAs extracted from tissues obtained from control subjects and patients with severe intrauterine adhesion were sequenced and subjected to bioinformatics analysis and the RhoA/ROCK1/MYL9 pathway was implicated and this subsequently studied using cultured primary ESCs. The effects of overexpression and knockdown and activation and inhibition of LAMB3 on the mesenchymal to myofibroblastic phenotypic transformation of ECCs were assessed using PCR and western blot analysis. Phalloidin was used to localize the actin cytoskeletal proteins. Silencing of LAMB3 reversed the TGF-β-induced ESC myofibroblast phenotype conversion, whereas overexpression of LAMB3 promoted this process. Activation and silencing of LAMB3 led to remodeling of the ESC cytoskeleton. Overexpression and silencing of LAMB3 caused activation and inhibition of ESCs, respectively. Y-27632 and LPA reversed the activation and inhibition of the RhoA/ROCK1/MYL9 pathway after overexpression and silencing, respectively. These results suggest that LAMB3 can regulate ESC fibrosis transformation and cytoskeleton remodeling via the RhoA/ROCK1/MYL9 pathway. This study provides a potential new target for gene therapy and drug intervention of AS.

Berberine promotes lacteal junction zippering and ameliorates diet-induced obesity through the RhoA/ROCK signaling pathway

BACKGROUND

Obesity has emerged as a global epidemic. Recent research has indicated that diet-induced obesity can be prevented by promoting lacteal junction zippering. Berberine, which is derived from natural plants, is found to be promising in weight reduction, but the underlying mechanism remains unspecified.

PURPOSE

To determine whether berberine protects against obesity by regulating the lacteal junction and to explore potential molecular mechanisms.

METHODS

Following the induction of the diet-induced obese (DIO) model, mice were administered low and high doses of berberine for 4 weeks. Indicators associated with insulin resistance and lipid metabolism were examined. Various methods, such as Oil Red O staining, transmission electron microscopy imaging, confocal imaging and others were used to observe the effects of berberine on lipid absorption and the lacteal junction. In vitro, human dermal lymphatic endothelial cells (HDLECs) were used to investigate the effect of berberine on LEC junctions. Western Blot and immunostaining were applied to determine the expression levels of relevant molecules.

RESULTS

Both low and high doses of berberine reduced body weight in DIO mice without appetite suppression and ameliorated glucolipid metabolism disorders. We also found that the weight loss effect of berberine might contribute to the inhibition of small intestinal lipid absorption. The possible mechanism was related to the promotion of lacteal junction zippering via suppressing the ras homolog gene family member A (RhoA)/Rho-associated kinase (ROCK) signaling pathway. In vitro, berberine also promoted the formation of stable mature junctions in HDLECs, involving the same signaling pathway.

CONCLUSION

Berberine could promote lacteal junction zippering and ameliorate diet-induced obesity through the RhoA/ROCK signaling pathway.

PD-1 deficiency aggravates spinal cord injury by regulating the reprogramming of NG2 glia and activating the NgR/RhoA/ROCK signaling pathway

Spinal cord injury (SCI) is a devastating disorder and a leading cause of disability in adults worldwide. Multiple studies have reported the upregulation of programmed cell death 1 (PD-1) following SCI. However, the underlying mechanism of PD-1 deficiency in SCI is not well established. Therefore, we aimed to investigate the role and potential mechanism of PD-1 in SCI pathogenesis. PD-1 Knockout (KO) SCI mouse model was established, and PD-1 expression was evaluated in tissue samples by western blot assay. We then used a series of function gain-and-loss assays to determine the role of PD-1 in SCI pathogenesis. Moreover, mechanistic assays were performed to explore the association between PD-1, neuron-glia antigen-2 (NG2) glia cells, and miR-23b-5p and then investigated the involved signaling pathway. Results illustrated that PD-1 deficiency enhanced the inflammatory response, neuron loss, and functional impairment induced by SCI. We found that NG2 glia depletion aggravated inflammation, reduced neural survival, and suppressed locomotor recovery in murine SCI model. Further analysis indicated that NG2+ cells were increased in the spinal cord of SCI mice, and PD-1 deficiency increased the number of NG2+ cells by activating the Nogo receptor/ras homolog family member A/Rho kinase (NgR/RhoA/ROCK) signaling. Mechanistically, miR-23b-5p was identified as the negative regulator of PD-1 in NG2 glia. MiR-23b-5p deficiency reduced the expression of inflammatory cytokines, enhanced neural survival, and promoted locomotor recovery in SCI mice, which was counteracted by PD-1 deficiency. In conclusion, PD-1 deficiency exacerbates SCI in vivo by regulating reprogramming of NG2 glia and activating the NgR/RhoA/ROCK signaling.

Pulses of RhoA signaling stimulate actin polymerization and flow in protrusions to drive collective cell migration

In animals, cells often move as collectives to shape organs, close wounds, or-in the case of disease-metastasize. To accomplish this, cells need to generate force to propel themselves forward. The motility of singly migrating cells is driven largely by an interplay between Rho GTPase signaling and the actin network. Whether cells migrating as collectives use the same machinery for motility is unclear. Using the zebrafish posterior lateral line primordium as a model for collective cell migration, we find that active RhoA and myosin II cluster on the basal sides of the primordium cells and are required for primordium motility. Positive and negative feedbacks cause RhoA and myosin II activities to pulse. These pulses of RhoA signaling stimulate actin polymerization at the tip of the protrusions and myosin-II-dependent actin flow and protrusion retraction at the base of the protrusions and deform the basement membrane underneath the migrating primordium. This suggests that RhoA-induced actin flow on the basal sides of the cells constitutes the motor that pulls the primordium forward, a scenario that likely underlies collective migration in other contexts.

Molecular mechanism of regulation of RhoA GTPase by phosphorylation of RhoGDI

Rho-specific guanine nucleotide dissociation inhibitors (RhoGDIs) play a crucial role in the regulation of Rho family GTPases. They act as negative regulators that prevent the activation of Rho GTPases by forming complexes with the inactive GDP-bound state of GTPase. Release of Rho GTPase from the RhoGDI-bound complex is necessary for Rho GTPase activation. Biochemical studies provide evidence of a "phosphorylation code," where phosphorylation of some specific residues of RhoGDI selectively releases its GTPase partner (RhoA, Rac1, Cdc42, etc.). This work attempts to understand the molecular mechanism behind this specific phosphorylation-induced reduction in binding affinity. Using several microseconds long atomistic molecular dynamics simulations of the wild-type and phosphorylated states of the RhoA-RhoGDI complex, we propose a molecular-interaction-based mechanistic model for the dissociation of the complex. Phosphorylation induces major structural changes, particularly in the positively charged polybasic region (PBR) of RhoA and the negatively charged N-terminal region of RhoGDI that contribute most to the binding affinity. Molecular mechanics Poisson-Boltzmann surface area binding energy calculations show a significant weakening of interaction on phosphorylation at the RhoA-specific site of RhoGDI. In contrast, phosphorylation at a Rac1-specific site does not affect the overall binding affinity significantly, which confirms the presence of a phosphorylation code. RhoA-specific phosphorylation leads to a reduction in the number of contacts between the PBR of RhoA and the N-terminal region of RhoGDI, which manifests a reduction of the binding affinity. Using hydrogen bond occupancy analysis and energetic perturbation network, we propose a mechanistic model for the allosteric response, i.e., long-range signal propagation from the site of phosphorylation to the PBR and buried geranylgeranyl group in the form of rearrangement and rewiring of hydrogen bonds and salt bridges. Our results highlight the crucial role of specific electrostatic interactions in manifestation of the phosphorylation code.

Cdc42 activity in the trailing edge is required for persistent directional migration of keratinocytes

Fibroblasts migrate discontinuously by generating transient leading-edge protrusions and irregular, abrupt retractions of a narrow trailing edge. In contrast, keratinocytes migrate persistently and directionally via a single, stable, broad protrusion paired with a stable trailing-edge. The Rho GTPases Rac1, Cdc42 and RhoA are key regulators of cell protrusions and retractions. However, how these molecules mediate cell-type specific migration modes is still poorly understood. In fibroblasts, all three Rho proteins are active at the leading edge, suggesting short-range coordination of protrusive Rac1 and Cdc42 signals with RhoA retraction signals. Here, we show that Cdc42 was surprisingly active in the trailing-edge of migrating keratinocytes. Elevated Cdc42 activity colocalized with the effectors MRCK and N-WASP suggesting that Cdc42 controls both myosin activation and actin polymerization in the back. Indeed, Cdc42 was required to maintain the highly dynamic contractile acto-myosin retrograde flow at the trailing edge of keratinocytes, and its depletion induced ectopic protrusions in the back, leading to decreased migration directionality. These findings suggest that Cdc42 is required to stabilize the dynamic cytoskeletal polarization in keratinocytes, to enable persistent, directional migration.

siRNA Mediated Downregulation of RhoA Expression Reduces Oxidative Induced Apoptosis in Retinal Ganglion Cells

BACKGROUNDS

Glaucoma is the second leading cause of blindness. Apoptosis of retinal ganglion cells (RGCs) is an important mechanism of glaucomatous optic injury. Rho kinase expression is significantly increased in apoptotic RGCs. This study aimed to investigate the role of RhoA, a Rho GTPase, on the survival of RGCs and further to explore its potential therapeutic applications.

METHODS

RGCs were treated with siRhoA for 24 hours in vitro. Knockdown of RhoA was confirmed with quantitative RT-PCR. Oxidative stress was induced by treating the RGCs with 200 μM of H2O2 for 1 hour, and apoptosis of RGCs was quantified with TUNEL assay in situ, and with flow cytometry. The mRNA expression levels of RhoA, Nogo receptor, caspase 3 and Bcl-2 were evaluated by quantitative RT-PCR, and the protein levels of RhoA, ROCK1, ROCK2, Nogo receptor, caspase 3 and Bcl-2 were evaluated by Western blot. We found siRhoA treatment efficiently downregulated the expression of RhoA in RGCs and protected against H2O2-induced injury in RGCs in vitro. Apoptosis of RGC cells under oxidative stress was quantified in situ using TUNEL assay and confirmed with flow cytometry (FCM).

RESULTS

With the knockdown of RhoA, the expression of ROCK1, ROCK2, Nogo Receptor, Casepase-3 were decreased, while the expression of Bcl-2 was increased in both mRNA and protein level. Our data indicated that siRhoA prevented H2O2-induced apoptosis in RGC cells by modulating the RhoA/ROCK pathway.

CONCLUSION

The results suggested that siRhoA may exert potentially effective neuroprotection for RGCs by reducing injury.

Advancements in the Research of GEF-H1: Biological Functions and Tumor Associations

Guanine nucleotide exchange factor H1 (GEF-H1) is a unique protein modulated by the GDP/GTP exchange. As a regulator of the Rho-GTPase family, GEF-H1 can be activated through a microtubule-depended mechanism and phosphorylation regulation, enabling it to perform various pivotal biological functions across multiple cellular activities. These include the regulation of Rho-GTPase, cytoskeleton formation, cellular barrier, cell cycle, mitosis, cell differentiation, and vesicle trafficking. Recent studies have revealed its crucial effect on the tumor microenvironment (TME) components, promoting tumor initiation and progress. Consequently, an in-depth exploration of GEF-H1's biological roles and association with tumors holds promise for its potential as a valuable molecular target in tumor treatment.

Effect of Cichoric Acid on Colorectal Cancer: Impact on Migration, Epithelial-Mesenchymal Transition, and Proliferation via RhoA/ROCK Signaling Pathway Modulation

BACKGROUND

Colorectal cancer (CRC) is a common malignancy with high morbidity and mortality. To improve CMC prognosis, research must identify safe and effective natural drugs that improve the proliferation, migration, and epithelial mesenchymal transition (EMT) processes of CRC. The purpose of this paper is to understand how cichoric acid (CA) impacts CRC proliferation, metastasis, and EMT of CRC by adjusting the Ras homolog family member A (RhoA)/RHO-associated coiled coil protein kinase (ROCK) pathway.

METHODS

Human Colon Cancer Cells (HCT116) cells were randomly divided into Control (blank medium treatment), low concentration CA (CA-L), medium concentration CA (CA-M), high concentration CA (CA-H), and high-concentration CA+RhoA activator U46619 (CA-H+U46619) groups. Cell proliferation, migration and invasion, and apoptosis were evaluated with cell counting kit-8 (CCK-8) assay, transwell assay, and flow cytometry, respectively. The expression of RhoA, ROCK, and EMT-associated proteins were detected by Western Blot. The CRC transplanted tumor model of nude mice was constructed, and the mice were grouped into low-dose CA (CA-Low, 15 mg/kg CA), high-dose CA (CA-High, 30 mg/kg CA), high-dose CA+RhoA activator U46619 (CA-High+U46619, 30 mg/kg CA+10 mM U46619), and Model groups at random, with 12 mice in each group. Tumor volume, mass, and inhibition rate were measured and calculated, and the pathological changes of tumor in nude mice were detected by hematoxylin-eosin (HE) staining.

RESULTS

Compared with Control, the optical density of cells at 450 nm (OD450) value (48 h, 72 h), cell migration number, cell invasion number, RhoA, ROCK1, N-cadherin, vimentin protein expression levels of HCT116 cells were reduced in CA-M and CA-H groups; however, E-cadherin level and apoptosis rate were increased (p < 0.05). In the CA-High group, we observed a significant decrease (p < 0.05) in both tumor volume and mass in nude mice. Additionally, the tumor tissue cells exhibited better organization, reduced size, reduced tumor and vascular tissue hyperplasia, and decreased infiltration of inflammatory cells. U46619 decreased the retardation of CA on the proliferation, EMT, and migration of CRC tumor cells as well as the growth of transplanted CRC tumors in nude mice.

CONCLUSIONS

CA may reduce CRC migration, proliferation, and EMT by inhibiting the activation of the RhoA/ROCK signaling pathway.

Rhogef17: A novel target for endothelial barrier function

ARHGEF17 encodes the protein RhoGEF17, which is highly expressed in vascular endothelial cells. It is a guanine nucleotide exchange factor (GEF) that accelerates the exchange of GDP with GTP on many small GTPases through its Dbl homology (DH) domain, enabling the activation of Rho-GTPases such as RhoA, RhoB, and RhoC. Rho GTPase-regulated changes in the actin cytoskeleton and cell adhesion kinetics are the main mechanisms mediating many endothelial cell (EC) alterations, including cell morphology, migration, and division changes, which profoundly affect EC barrier function. This review focuses on ARHGEF17 expression, activation and biological functions in ECs, linking its regulation of cellular morphology, migration, mitosis and other cellular behaviors to disease onset and progression. Understanding ARHGEF17 mechanisms of action will contribute to the design of therapeutic approaches targeting RhoGEF17, a potential drug target for the treatment of various endothelium-related diseases, Such as vascular inflammation, carcinogenesis and transendothelial metastasis of tumors.

RHOA drivers take alternate routes in gastric cancer

Oncogenic small guanosine triphosphatases (GTPases) are often characterized by a limited set of activating mutations that affect their intrinsic biochemical function, but RHOA-which is frequently mutated in gastric cancer-appears not to have read the instruction manual. Having previously characterized the Y42C RHOA mutation in gastric cancer, in this issue of Science Signaling, Schaefer et al. take on the slightly less common L57V mutation and find that individual RHOA mutations can have different and unpredictable signaling outcomes.

Novel cardiovascular protective effects of RhoA signaling and its therapeutic implications

Ras homolog gene family member A (RhoA) belongs to the Rho GTPase superfamily, which was first studied in cancers as one of the essential regulators controlling cellular function. RhoA has long attracted attention as a key molecule involved in cell signaling and gene transcription, through which it affects cellular processes. A series of studies have demonstrated that RhoA plays crucial roles under both physiological states and pathological conditions in cardiovascular diseases. RhoA has been identified as an important regulator in cardiac remodeling by regulating actin stress fiber dynamics and cytoskeleton formation. However, its underlying mechanisms remain poorly understood, preventing definitive conclusions being drawn about its protective role in the cardiovascular system. In this review, we outline the characteristics of RhoA and its related signaling molecules, and present an overview of RhoA classical function and the corresponding cellular responses of RhoA under physiological and pathological conditions. Overall, we provide an update on the novel signaling under RhoA in the cardiovascular system and its potential clinical and therapeutic targets in cardiovascular medicine.

Visualizing the subcellular localization of RHOB-GTP and GTPase-Effector complexes using a split-GFP/nanobody labelling assay

Small GTPases are highly regulated proteins that control essential signaling pathways through the activity of their effector proteins. Among the RHOA subfamily, RHOB regulates peculiar functions that could be associated with the control of the endocytic trafficking of signaling proteins. Here, we used an optimized assay based on tripartite split-GFP complementation to localize GTPase-effector complexes with high-resolution. The detection of RHOB interaction with the Rhotekin Rho binding domain (RBD) that specifically recognizes the active GTP-bound GTPase, is performed in vitro by the concomitant addition of recombinant GFP1-9 and a GFP nanobody. Analysis of RHOB-RBD complexes localization profiles combined with immunostaining and live cell imaging indicated a serum-dependent reorganization of the endosomal and membrane pool of active RHOB. We further applied this technology to the detection of RHO-effector complexes that highlighted their subcellular localization with high resolution among the different cellular compartments.

PAR1 regulates sepsis-induced vascular endothelial barrier dysfunction by mediating ERM phosphorylation via the RhoA/ROCK signaling pathway

Sepsis begins with vascular endothelial barrier breakdown and causes widespread organ failure. Protease-activated receptor 1 (PAR1) is an important target for modulating vascular endothelial permeability; however, little research has been undertaken in sepsis, and its putative molecular mechanism remains unknown. The vascular endothelial permeability was examined by detecting FITC-dextran flux. F-actin was examined by immunofluorescence (IF). PAR1, ERM phosphorylation, and RhoA/ROCK signaling pathway expression in lipopolysaccharide (LPS)-stimulated human umbilical vein endothelial cells (HUVECs) line were examined by IF and Western blot. To develop the sepsis model, cecal ligation and puncture (CLP) were conducted. The PAR1 inhibitor SCH79797 was utilized to inhibit PAR1 expression in vivo. Vascular permeability in main organs weres measured by Evans blue dye extravasation. The pathological changes in main organs were examined by HE staining. The expression of PAR1, ERM phosphorylation, and the RhoA/ROCK signaling pathway was examined using IF, immunohistochemical and WB in CLP mice. In vitro, in response to LPS stimulation of HUVECs, PAR1 mediated the phosphorylation of ERM, promoted F-actin rearrangement, and increased endothelial hyperpermeability, all of which were prevented by inhibiting PAR1 or RhoA. Additionally, inhibiting PAR1 expression reduced RhoA and ROCK expression. In vivo, we showed that inhibiting PAR1 expression will reduce ezrin/radixin/moesin (ERM) phosphorylation to relieve vascular endothelial barrier dysfunction and thereby ameliorate multiorgan dysfunction syndrome (MODS) in CLP-induced septic mice. This study revealed that PAR1-mediated phosphorylation of ERM induced endothelial barrier dysfunction, which in turn led to MODS in sepsis, and that the RhoA/ROCK signaling pathway underlay these effects.

PFTK1 kinase regulates axogenesis during development via RhoA activation

BACKGROUND

PFTK1/Eip63E is a member of the cyclin-dependent kinases (CDKs) family and plays an important role in normal cell cycle progression. Eip63E expresses primarily in postnatal and adult nervous system in Drosophila melanogaster but its role in CNS development remains unknown. We sought to understand the function of Eip63E in the CNS by studying the fly ventral nerve cord during development.

RESULTS

Our results demonstrate that Eip63E regulates axogenesis in neurons and its deficiency leads to neuronal defects. Functional interaction studies performed using the same system identify an interaction between Eip63E and the small GTPase Rho1. Furthermore, deficiency of Eip63E homolog in mice, PFTK1, in a newly generated PFTK1 knockout mice results in increased axonal outgrowth confirming that the developmental defects observed in the fly model are due to defects in axogenesis. Importantly, RhoA phosphorylation and activity are affected by PFTK1 in primary neuronal cultures. We report that GDP-bound inactive RhoA is a substrate of PFTK1 and PFTK1 phosphorylation is required for RhoA activity.

CONCLUSIONS

In conclusion, our work establishes an unreported neuronal role of PFTK1 in axon development mediated by phosphorylation and activation of GDP-bound RhoA. The results presented add to our understanding of the role of Cdks in the maintenance of RhoA-mediated axon growth and its impact on CNS development and axonal regeneration.

Genomic and Reverse Translational Analysis Discloses a Role for Small GTPase RhoA Signaling in the Pathogenesis of Schizophrenia: Rho-Kinase as a Novel Drug Target

Schizophrenia is one of the most serious psychiatric disorders and is characterized by reductions in both brain volume and spine density in the frontal cortex. RhoA belongs to the RAS homolog (Rho) family and plays critical roles in neuronal development and structural plasticity via Rho-kinase. RhoA activity is regulated by GTPase-activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs). Several variants in GAPs and GEFs associated with RhoA have been reported to be significantly associated with schizophrenia. Moreover, several mouse models carrying schizophrenia-associated gene variants involved in RhoA/Rho-kinase signaling have been developed. In this review, we summarize clinical evidence showing that variants in genes regulating RhoA activity are associated with schizophrenia. In the last half of the review, we discuss preclinical evidence indicating that RhoA/Rho-kinase is a potential therapeutic target of schizophrenia. In particular, Rho-kinase inhibitors exhibit anti-psychotic-like effects not only in Arhgap10 S490P/NHEJ mice, but also in pharmacologic models of schizophrenia (methamphetamine- and MK-801-treated mice). Accordingly, we propose that Rho-kinase inhibitors may have antipsychotic effects and reduce cognitive deficits in schizophrenia despite the presence or absence of genetic variants in small GTPase signaling pathways.

RhoA vesicle trafficking-mediated transglutaminase 2 membrane translocation promotes IgA1 mesangial deposition in IgA nephropathy

Transglutaminase 2 (TGase2) has been shown to contribute to the mesangial IgA1 deposition in a humanized mouse model of IgA nephropathy (IgAN), but the mechanism is not fully understood. In this study, we found that inhibition of TGase2 activity could dramatically decrease the amount of polymeric IgA1 (pIgA1) isolated from patients with IgAN that interacts with human mesangial cells (HMC). TGase2 was expressed both in the cytosol and on the membrane of HMC. Upon treatment with pIgA1, there were more TGase2 recruited to the membrane. Using a cell model of mesangial deposition of pIgA1, we identified 253 potential TGase2-associated proteins in the cytosolic fraction and observed a higher concentration of cellular vesicles and increased expression of Ras homolog family member A (RhoA) in HMC after pIgA1 stimulation. Both the amount of pIgA1 deposited on HMC and membrane TGase2 level were decreased by inhibition of the vesicle trafficking pathway. Mechanistically, TGase2 was found to be coprecipitated with RhoA in the cellular vesicles. Membrane TGase2 expression was greatly increased by overexpression of RhoA, while it was reduced by knockdown of RhoA. Our in vitro approach demonstrated that TGase2 was transported from the cytosol to the membrane through a RhoA-mediated vesicle-trafficking pathway that can facilitate pIgA1 interaction with mesangium in IgAN.

Fidgetin-like 2 depletion enhances cell migration by regulating GEF-H1, RhoA, and FAK

The microtubule (MT) cytoskeleton and its dynamics play an important role in cell migration. Depletion of the microtubule-severing enzyme Fidgetin-like 2 (FL2), a regulator of MT dynamics at the leading edge of migrating cells, leads to faster and more efficient cell migration. Here we examine how siRNA knockdown of FL2 increases cell motility. Förster resonance energy transfer biosensor studies shows that FL2 knockdown decreases activation of the p21 Rho GTPase, RhoA, and its activator GEF-H1. Immunofluorescence studies reveal that GEF-H1 is sequestered by the increased MT density resulting from FL2 depletion. Activation of the Rho GTPase, Rac1, however, does not change after FL2 knockdown. Furthermore, FL2 depletion leads to an increase in focal adhesion kinase activation at the leading edge, as shown by immunofluorescence studies, but no change in actin dynamics, as shown by fluorescence recovery after photobleaching. We believe these results expand our understanding of the role of MT dynamics in cell migration and offer new insights into RhoA and Rac1 regulation.

Rho MultiBinder, a fluorescent biosensor that reports the activity of multiple GTPases

Imaging two or more fluorescent biosensors in the same living cell can reveal the spatiotemporal coordination of protein activities. However, using multiple Förster resonance energy transfer (FRET) biosensors together is challenging due to toxicity and the need for orthogonal fluorophores. Here we generate a biosensor component that binds selectively to the activated conformation of three different proteins. This enabled multiplexed FRET with fewer fluorophores, and reduced toxicity. We generated this MultiBinder (MB) reagent for the GTPases RhoA, Rac1, and Cdc42 by combining portions of the downstream effector proteins Pak1 and Rhotekin. Using FRET between mCherry on the MB and YPet or mAmetrine on two target proteins, the activities of any pair of GTPases could be distinguished. The MB was used to image Rac1 and RhoA together with a third, dye-based biosensor for Cdc42. Quantifying effects of biosensor combinations on the frequency, duration, and velocity of cell protrusions and retractions demonstrated reduced toxicity. Multiplexed imaging revealed signaling hierarchies between the three proteins at the cell edge where they regulate motility.

Growth differentiation factor 5 inhibits lipopolysaccharide-mediated pyroptosis of nucleus pulposus mesenchymal stem cells via RhoA signaling pathway

BACKGROUND

Degenerative disc disease(DDD)is one of the most important causes of low back pain (LBP). Programmed death of human nucleus pulposus mesenchymal stem cells (NPMSCs) plays an important role in the progression of DDD. Growth differentiation factor-5 (GDF-5) is a protein that promotes chondrogenic differentiation, and has been reported to slow the expression of inflammatory factors in nucleus pulposus cells. Compared with those in normal rats, MRI T2-weighted images show hypointense in the central nucleus pulposus region of the intervertebral disc in GDF-5 knockout rats.

METHODS AND RESULTS

We aimed to evaluate the role of GDF-5 and Ras homolog family member A (RhoA) in NPMSCs. We used lipopolysaccharide (LPS) to simulate the inflammatory environment in degenerative disc disease, and performed related experiments on the effects of GDF-5 on NPMSCs, including the effects of pyroptosis, RhoA protein, and the expression of extracellular matrix components, and the effects of GDF-5, on NPMSCs. In addition, the effect of GDF-5 on chondroid differentiation of NPMSCs was included. The results showed that the addition of GDF-5 inhibited the LPS-induced pyroptosis of NPMSCs, and further analysis of its mechanism showed that this was achieved by activating the RhoA signaling pathway.

CONCLUSION

These findings suggest that GDF-5 plays an important role in inhibiting the pyroptosis of NPMSCs and GDF-5 may have potential for degenerative disc disease gene-targeted therapy in the future.

CLIC4 Regulates Endothelial Barrier Control by Mediating PAR1 Signaling via RhoA

BACKGROUND

Endothelial CLICs (chloride intracellular channel proteins) CLIC1 and CLIC4 are required for the GPCRs (G-protein-coupled receptors) S1PR1 (sphingosine-1-phosphate receptor 1) and S1PR3 to activate the small GTPases Rac1 (Ras-related C3 botulinum toxin substrate 1) and RhoA (Ras homolog family member A). To determine whether CLIC1 and CLIC4 function in additional endothelial GPCR pathways, we evaluated CLIC function in thrombin signaling via the thrombin-regulated PAR1 (protease-activated receptor 1) and downstream effector RhoA.

METHODS

We assessed the ability of CLIC1 and CLIC4 to relocalize to cell membranes in response to thrombin in human umbilical vein endothelial cells (HUVEC). We examined CLIC1 and CLIC4 function in HUVEC by knocking down expression of each CLIC protein and compared thrombin-mediated RhoA or Rac1 activation, ERM (ezrin/radixin/moesin) phosphorylation, and endothelial barrier modulation in control and CLIC knockdown HUVEC. We generated a conditional murine allele of Clic4 and examined PAR1-mediated lung microvascular permeability and retinal angiogenesis in mice with endothelial-specific loss of Clic4.

RESULTS

Thrombin promoted relocalization of CLIC4, but not CLIC1, to HUVEC membranes. Knockdown of CLIC4 in HUVEC reduced thrombin-mediated RhoA activation, ERM phosphorylation, and endothelial barrier disruption. Knockdown of CLIC1 did not reduce thrombin-mediated RhoA activity but prolonged the RhoA and endothelial barrier response to thrombin. Endothelial-specific deletion of Clic4 in mice reduced lung edema and microvascular permeability induced by PAR1 activating peptide.

CONCLUSIONS

CLIC4 is a critical effector of endothelial PAR1 signaling and is required to regulate RhoA-mediated endothelial barrier disruption in cultured endothelial cells and murine lung endothelium. CLIC1 was not critical for thrombin-mediated barrier disruption but contributed to the barrier recovery phase after thrombin treatment.

A YAP/TAZ-ARHGAP29-RhoA Signaling Axis Regulates Podocyte Protrusions and Integrin Adhesions

Glomerular disease due to podocyte malfunction is a major factor in the pathogenesis of chronic kidney disease. Identification of podocyte-specific signaling pathways is therefore a prerequisite to characterizing relevant disease pathways and developing novel treatment approaches. Here, we employed loss of function studies for EPB41L5 (Yurt) as a central podocyte gene to generate a cell type-specific disease model. Loss of Yurt in fly nephrocytes caused protein uptake and slit diaphragm defects. Transcriptomic and proteomic analysis of human EPB41L5 knockout podocytes demonstrated impaired mechanotransduction via the YAP/TAZ signaling pathway. Further analysis of specific inhibition of the YAP/TAZ-TEAD transcription factor complex by TEADi led to the identification of ARGHAP29 as an EPB41L5 and YAP/TAZ-dependently expressed podocyte RhoGAP. Knockdown of ARHGAP29 caused increased RhoA activation, defective lamellipodia formation, and increased maturation of integrin adhesion complexes, explaining similar phenotypes caused by loss of EPB41L5 and TEADi expression in podocytes. Detection of increased levels of ARHGAP29 in early disease stages of human glomerular disease implies a novel negative feedback loop for mechanotransductive RhoA-YAP/TAZ signaling in podocyte physiology and disease.

Src stimulates Abl-dependent phosphorylation of the guanine exchange factor Net1A to promote its cytosolic localization and cell motility

The neuroepithelial cell transforming gene 1 (Net1) is a guanine nucleotide exchange factor for the small GTPase RhoA that promotes cancer cell motility and metastasis. Two isoforms of Net1 exist, Net1 and Net1A, both of which are sequestered in the nucleus in quiescent cells to prevent aberrant RhoA activation. Many cell motility stimuli drive cytosolic relocalization of Net1A, but mechanisms controlling this event are not fully understood. Here, we demonstrate that epithelial growth factor stimulates protein kinase Src- and Abl1-dependent phosphorylation of Net1A to promote its cytosolic localization. We show that Abl1 efficiently phosphorylates Net1A on Y373, and that phenylalanine substitution of Y373 prevents Net1A cytosolic localization. Furthermore, we found that Abl1-driven cytosolic localization of Net1A does not require S52, which is a phosphorylation site of a different kinase, c-Jun N-terminal kinase, that inhibits nuclear import of Net1A. However, we did find that MKK7-stimulated cytosolic localization of Net1A does require Y373. We also demonstrate that aspartate substitution at Y373 is sufficient to promote Net1A cytosolic accumulation, and expression of Net1A Y373D potentiates epithelial growth factor-stimulated RhoA activation, downstream myosin light chain 2 phosphorylation, and F-actin accumulation. Moreover, we show that expression of Net1A Y373D in breast cancer cells also significantly increases cell motility and Matrigel invasion. Finally, we show that Net1A is required for Abl1-stimulated cell motility, which is rescued by expression of Net1A Y373D, but not Net1A Y373F. Taken together, this work demonstrates a novel mechanism controlling Net1A subcellular localization to regulate RhoA-dependent cell motility and invasion.

RHOA, a small G-protein, signals to mitophagy through regulation of PINK1 protein stability and protects cardiomyocytes against ischemia

RHOA (ras homolog family member A) is a small G-protein that regulates a range of cellular processes including cell growth and survival. RHOA is a proximal downstream effector of G protein-coupled receptors coupling to GNA12/Gα12-GNA13/Gα13 proteins, and is activated in response to stretch and oxidative stress, functioning as a stress-response molecule. It has been demonstrated that RHOA signaling provides cardioprotection through inhibition of mitochondrial death pathways. Mitochondrial integrity is preserved not only by inhibition of mitochondrial death pathways but also by mitochondrial quality control mechanisms including mitophagy. One of the most well-established mechanisms of mitophagy is the mitochondrial membrane depolarization-dependent PINK1-PRKN/Parkin pathway. However, depolarization of the mitochondrial membrane potential is a late-stage event that occurs just before cell death, and additional intracellular mechanisms that enhance the PINK1-PRKN pathway have not been fully determined. We recently discovered that RHOA activation engages a unique mechanism to regulate PINK1 protein stability without inducing mitochondrial membrane depolarization, leading to increased mitophagy and protection against ischemia in cardiomyocytes. Our results suggest regulation of RHOA signaling as a potential strategy to enhance protective mitophagy against stress without compromising mitochondrial functions.

Mechanosensitive stem cell fate choice is instructed by dynamic fluctuations in activation of Rho GTPases

During the intricate process by which cells give rise to tissues, embryonic and adult stem cells are exposed to diverse mechanical signals from the extracellular matrix (ECM) that influence their fate. Cells can sense these cues in part through dynamic generation of protrusions, modulated and controlled by cyclic activation of Rho GTPases. However, it remains unclear how extracellular mechanical signals regulate Rho GTPase activation dynamics and how such rapid, transient activation dynamics are integrated to yield long-term, irreversible cell fate decisions. Here, we report that ECM stiffness cues alter not only the magnitude but also the temporal frequency of RhoA and Cdc42 activation in adult neural stem cells (NSCs). Using optogenetics to control the frequency of RhoA and Cdc42 activation, we further demonstrate that these dynamics are functionally significant, where high- vs. low-frequency activation of RhoA and Cdc42 drives astrocytic vs. neuronal differentiation, respectively. In addition, high-frequency Rho GTPase activation induces sustained phosphorylation of the TGFβ pathway effector SMAD1, which in turn drives the astrocytic differentiation. By contrast, under low-frequency Rho GTPase stimulation, cells fail to accumulate SMAD1 phosphorylation and instead undergo neurogenesis. Our findings reveal the temporal patterning of Rho GTPase signaling and the resulting accumulation of an SMAD1 signal as a critical mechanism through which ECM stiffness cues regulate NSC fate.

Septin-mediated RhoA activation engages the exocyst complex to recruit the cilium transition zone

Septins are filamentous GTPases that play important but poorly characterized roles in ciliogenesis. Here, we show that SEPTIN9 regulates RhoA signaling at the base of cilia by binding and activating the RhoA guanine nucleotide exchange factor, ARHGEF18. GTP-RhoA is known to activate the membrane targeting exocyst complex, and suppression of SEPTIN9 causes disruption of ciliogenesis and mislocalization of an exocyst subunit, SEC8. Using basal body-targeted proteins, we show that upregulating RhoA signaling at the cilium can rescue ciliary defects and mislocalization of SEC8 caused by global SEPTIN9 depletion. Moreover, we demonstrate that the transition zone components, RPGRIP1L and TCTN2, fail to accumulate at the transition zone in cells lacking SEPTIN9 or depleted of the exocyst complex. Thus, SEPTIN9 regulates the recruitment of transition zone proteins on Golgi-derived vesicles by activating the exocyst via RhoA to allow the formation of primary cilia.

Endothelial-Specific Targeting of RhoA Signaling via CD31 Antibody-Conjugated Nanoparticles

Existing vascular endothelial growth factor-oriented antiangiogenic approaches are known for their high potency. However, significant side effects associated with their use drive the need for novel antiangiogenic strategies. The small GTPase RhoA is an established regulator of actin cytoskeletal dynamics. Previous studies have highlighted the impact of endothelial RhoA pathway on angiogenesis. Rho-associate kinase (ROCK), a direct RhoA effector, is potently inhibited by Fasudil, a clinically relevant ROCK inhibitor. Here, we aimed to target the RhoA signaling in endothelial cells by generating Fasudil-encapsulated CD31-targeting liposomes as a potential antiangiogenic therapy. The liposomes presented desirable characteristics, preferential binding to CD31-expressing HEK293T cells and to endothelial cells, inhibited stress fiber formation and cytoskeletal-related morphometric parameters, and inhibited in vitro angiogenic functions. Overall, this work shows that the nanodelivery-mediated endothelial targeting of RhoA signaling can offer a promising strategy for angiogenesis inhibition in vascular-related diseases. SIGNIFICANCE STATEMENT: Systemic administration of antiangiogenic therapeutics induces side effects to non-targeted tissues. This study, among others, has shown the impact of the RhoA signaling in the endothelial cells and their angiogenic functions. Here, to minimize potential toxicity, this study generated CD31-targeting liposomes with encapsulated Fasudil, a clinically relevant Rho kinase inhibitor, and successfully targeted endothelial cells. In this proof-of-principle study, the efficient Fasudil delivery, its impact on the endothelial signaling, morphometric alterations, and angiogenic functions verify the benefits of site-targeted antiangiogenic therapy.

BAG6 supports stress fiber formation by preventing the ubiquitin-mediated degradation of RhoA

The Rho family of small GTPases is a key regulator of cytoskeletal actin polymerization. Although the ubiquitination of Rho proteins is reported to control their activity, the mechanisms by which the ubiquitination of Rho family proteins is controlled by ubiquitin ligases have yet to be elucidated. In this study, we identified BAG6 as the first factor needed to prevent the ubiquitination of RhoA, a critical Rho family protein in F-actin polymerization. We found that BAG6 is necessary for stress fiber formation by stabilizing endogenous RhoA. BAG6 deficiency enhanced the association between RhoA and Cullin-3-based ubiquitin ligases, thus promoting its polyubiquitination and subsequent degradation, leading to the abrogation of actin polymerization. In contrast, the restoration of RhoA expression through transient overexpression rescued the stress fiber formation defects induced by BAG6 depletion. BAG6 was also necessary for the appropriate assembly of focal adhesions as well as cell migration events. These findings reveal a novel role for BAG6 in maintaining the integrity of actin fiber polymerization and establish BAG6 as a RhoA-stabilizing holdase, which binds to and supports the function of RhoA.

Fluoride exposure disrupts the cytoskeletal arrangement and ATP synthesis of HT-22 cell by activating the RhoA/ROCK signaling pathway

BACKGROUND

Fluoride, an environmental contaminant, is ubiquitously present in air, water, and soil. It usually enters the body through drinking water and may cause structural and functional disorders in the central nervous system in humans and animals. Fluoride exposure affects cytoskeleton and neural function, but the mechanism is not clear.

METHODS

The specific neurotoxic mechanism of fluoride was explored in HT-22 cells. Cellular proliferation and toxicity detection were investigated by CCK-8, CCK-F, and cytotoxicity detection kits. The development morphology of HT-22 cells was observed under a light microscope. Cell membrane permeability and neurotransmitter content were determined using lactate dehydrogenase (LDH) and glutamate content determination kits, respectively. The ultrastructural changes were detected by transmission electron microscopy, and actin homeostasis was observed by laser confocal microscopy. ATP enzyme and ATP activity were determined using the ATP content kit and ultramicro-total ATP enzyme content kit, respectively. The expression levels of GLUT1 and 3 were assessed by Western Blot assays and qRT-PCR.

RESULTS

Our results showed that fluoride reduced the proliferation and survival rates of HT-22 cells. Cytomorphology showed that dendritic spines became shorter, cellular bodies became rounder, and adhesion decreased gradually after fluoride exposure. LDH results showed that fluoride exposure increased the membrane permeability of HT-22 cells. Transmission electron microscopy results showed that fluoride caused cells to swell, microvilli content decreased, cellular membrane integrity was damaged, chromatin was sparse, mitochondria ridge gap became wide, and microfilament and microtubule density decreased. Western Blot and qRT-PCR analyses showed that RhoA/ROCK/LIMK/Cofilin signaling pathway was activated by fluoride. F-actin/G-actin fluorescence intensity ratio remarkably increased in 0.125 and 0.5 mM NaF, and the mRNA expression of MAP2 was significantly decreased. Further studies showed that GLUT3 significantly increased in all fluoride groups, while GLUT1 decreased (p < 0.05). ATP contents remarkably increased, and ATP enzyme activity substantially decreased after NaF treatment with the control.

CONCLUSION

Fluoride activates the RhoA/ROCK/LIMK/Cofilin signaling pathway, impairs the ultrastructure, and depresses the connection of synapses in HT-22 cells. Moreover, fluoride exposure affects the expression of glucose transporters (GLUT1 and 3) and ATP synthesis. Sum up fluoride exposure disrupts actin homeostasis, ultimately affecting structure, and function in HT-22 cells. These findings support our previous hypothesis and provide a new perspective on the neurotoxic mechanism of fluorosis.

Activation of RhoA pathway participated in the changes of emotion, cognitive function and hippocampal synaptic plasticity in juvenile chronic stress rats

Neuropsychiatric diseases are related to early life stress (ELS), patients often have abnormal learning, memory and emotion. But the regulatory mechanism is unclear. Hippocampal synaptic plasticity (HSP) changes are important mechanism. RhoA pathway is known to regulate HSP by modulating of dendritic spines (DS), whether it's involved in HSP changes in ELS hasn't been reported. So we investigated whether and how RhoA participates in HSP regulation in ELS. The ELS model was established by separation-rearing in juvenile. Results of IntelliCage detection etc. showed simple learning and memory wasn't affected, but spatial, punitive learning and memories reduced, the desire to explore novel things reduced, the anxiety-like emotion increased. We further found hippocampus was activated, the hippocampal neurons dendritic complexities reduced, the proportion of mature DS decreased. The full-length transcriptome sequencing techniques was used to screen for differentially expressed genes involved in regulating HSP changes, we found RhoA gene was up-regulated. We detected RhoA protein, RhoA phosphorylation and downstream molecules expression changes, results shown RhoA and p-RhoA, p-ROCK2 expression increased, p-LIMK, p-cofilin expression and F-actin/G-actin ratio decreased. Our study revealed HSP changes in ELS maybe regulate by activation RhoA through ROCK2/LIMK/cofilin pathway regulated F-actin/G-actin balance and DS plasticity, affecting emotion and cognition.

Decreased B7-H3 promotes unexplained recurrent miscarriage via RhoA/ROCK2 signaling pathway and regulates the secretion of decidual NK cells†

The cause for at least 50% of recurrent miscarriages is unclear, which is defined as unexplained recurrent miscarriages. The B7-H1 (PD-L1), a molecule of the B7 family, promotes tumor development by modulating immune evasion, and recent researchers have also attached importance to the role of B7-H3, another molecule of B7 family, in tumor. Based on the similarity between growth and immune response in tumors and pregnancy, we first explored the role of B7-H3 in unexplained recurrent miscarriages. We found reduced levels of B7-H3 in the villus tissue of unexplained recurrent miscarriage patients, and it was mainly expressed on the cell membrane of extravillous trophoblasts. Further, the HTR-8/SVneo and JEG-3 cells were selected to explore the role of B7-H3 in proliferation, apoptosis, tube formation, migration, and invasion. We found that B7-H3 regulated trophoblast migration and invasion via RhoA/ROCK2 signaling pathway. Inflammatory cytokines were detected through enzyme-linked immunosorbent assay after co-culturing with decidual natural killer cells and B7-H3-knockout JEG-3. Results showed that B7-H3 inhibited IL-8 and IP-10 secretion from the decidual natural killer cells. In a CBA/J × DBA/2 abortion-prone mice model, treatment with B7-H3-Fc protein successfully reduced the rate of embryo resorption. In conclusion, our results revealed a possible mechanism by which decreased B7-H3 on trophoblasts of unexplained recurrent miscarriages inhibited trophoblast migration and invasion and increased IL-8 and IP-10 secretion from the decidual natural killer cells. Furthermore, B7-H3 may be a promising new therapeutic target in unexplained recurrent miscarriage patients.

Decoding cellular deformation from pseudo-simultaneously observed Rho GTPase activities

Limitations in simultaneously observing the activity of multiple molecules in live cells prevent researchers from elucidating how these molecules coordinate the dynamic regulation of cellular functions. Here, we propose the motion-triggered average (MTA) algorithm to characterize pseudo-simultaneous dynamic changes in arbitrary cellular deformation and molecular activities. Using MTA, we successfully extract a pseudo-simultaneous time series from individually observed activities of three Rho GTPases: Cdc42, Rac1, and RhoA. To verify that this time series encoded information on cell-edge movement, we use a mathematical regression model to predict the edge velocity from the activities of the three molecules. The model accurately predicts the unknown edge velocity, providing numerical evidence that these Rho GTPases regulate edge movement. Data preprocessing using MTA combined with mathematical regression provides an effective strategy for reusing numerous individual observations of molecular activities.

RHOA Therapeutic Targeting in Hematological Cancers

Primarily identified as an important regulator of cytoskeletal dynamics, the small GTPase Ras homolog gene family member A (RHOA) has been implicated in the transduction of signals regulating a broad range of cellular functions such as cell survival, migration, adhesion and proliferation. Deregulated activity of RHOA has been linked to the growth, progression and metastasis of various cancer types. Recent cancer genome-wide sequencing studies have unveiled both RHOA gain and loss-of-function mutations in primary leukemia/lymphoma, suggesting that this GTPase may exert tumor-promoting or tumor-suppressive functions depending on the cellular context. Based on these observations, RHOA signaling represents an attractive therapeutic target for the development of selective anticancer strategies. In this review, we will summarize the molecular mechanisms underlying RHOA GTPase functions in immune regulation and in the development of hematological neoplasms and will discuss the current strategies aimed at modulating RHOA functions in these diseases.

RhoA-LIMK Signaling Axis Reveals Rostral-Caudal Plane and Spatial Dysregulation in the Brain of Alzheimer's Disease Mouse Models

BACKGROUND

RhoA signaling is widely reported to be dysregulated in Alzheimer's disease (AD), but its therapeutic targeting demonstrated mixed outcomes. We hypothesize that the activation and inactivation states of RhoA and LIMK are different in the cortex and in subregions of hippocampus along the rostral-caudal dimensions.

OBJECTIVE

We intended to elucidate the plane and spatial dependent RhoA signaling in association with AD.

METHODS

We applied antibody pRhoA that recognizes an inactive state of RhoA (S188 phosphorylation) and antibody pLIMK against an active state of LIMK (T508 phosphorylation) to investigate RhoA signaling in wildtype (WT) and triple transgenic AD (3xTg-AD) mouse model. We prepared serial sections from the rostral to caudal coronal planes of the entire mouse brain followed by immunofluorescence staining with pRhoA and pLIMK antibodies.

RESULTS

Both pRhoA and pLIMK elicited a shift of expression pattern from rostral to caudal planes. Additionally, pRhoA demonstrated dynamic redistribution between the nucleus and cytoplasm. pLIMK did not show such nucleus and cytoplasm redistribution but the expression level was changed from rostral to caudal planes. At some planes, pRhoA showed an increasing trend in expression in the cortex but a decreasing trend in the dentate gyrus of the 3xTg-AD mouse hippocampus. pLIMK tends to decrease in the cortex but increase in the dentate gyrus of 3xTg-AD mouse hippocampus.

CONCLUSIONS

RhoA activation is dysregulated in both human and mouse AD brains, and the RhoA-LIMK signaling axis reveals spatial dysregulation along the rostral-caudal plane dimensions.

Acupuncture Improves Synaptic Plasticity of SAMP8 Mice through the RhoA/ROCK Pathway

BACKGROUND

Studies have found synaptic plasticity damage to be an early marker of Alzheimer's disease (AD). RhoA/ROCK pathway is involved in the regulation of synaptic plasticity. Acupuncture can significantly improve the cognitive state of AD.

OBJECTIVE

We aimed to use modern biological technology to detect the changes in synaptic plasticity and RhoA/ROCK pathway in SAMP8 mice, as well as the intervention effect of acupuncture.

METHODS

Morris water maze and electrophysiological techniques were used in vivo to detect the changes in spatial memory and LTP of mice. Golgi Cox staining and CASEVIEWER2.1 software were used to quantitatively analyze the changes in the morphology and number of dendritic spines in the hippocampus of mice. The activity of RhoA and ROCK2 in the hippocampus of mice was detected, respectively, by pull-down technique and ELISA. WB technique was used to detect the protein expression of ROCK2 and phosphorylation level of MLC2, LIMK2, and CRMP2 in the hippocampus of mice.

RESULTS

The neurobehavior and synaptic plasticity of 8-month-old SAMP8 mice were found to be significantly impaired. Acupuncture could improve the spatial learning and memory ability of SAMP8 mice, and partially prevent the reduction in the number of spines on the secondary branches of the apical dendrites in the hippocampus and the attenuation of LTP. The RhoA/ROCK pathway was significantly activated in the hippocampus of 8-month-old SAMP8 mice, and acupuncture had an inhibitory effect on it.

CONCLUSION

Acupuncture can improve synaptic plasticity by inhibiting the abnormal activation of the RhoA/ROCK pathway, and improve the spatial learning and memory ability of AD, so as to achieve the purpose of treating AD.

ROCK (RhoA/Rho Kinase) Activation in Atrial Fibrillation: Molecular Pathways and Clinical Implications

Among the complex mechanisms of AF pathogenesis, intracellular calcium overload and oxidative stress play a major role, both triggered by inflammatory processes. The additional basic event taking place in AF is atrial fibrotic remodeling, again triggered by oxidative stress, which is determined by connexins rearrangement and differentiation of fibroblasts into active collagensecreting myofibroblasts. RhoA/ROCK system is the final pathway of a wide spectrum of molecular effectors such as Angiotensin II, platelet-derived growth factor, connective tissue growth factor and transforming growth factor β, that overall determine calcium dysregulation and pro-fibrotic remodeling. Both in experimental and clinical studies, RhoA/ROCK activation has been linked to superoxide ion production, fibrotic remodeling and connexins rearrangement, with important consequences for AF pathogenesis. ROCK pathway inhibition may therefore be a therapeutic or preventive target for special AF subgroups of patients.

Activation Mechanism of RhoA Caused by Constitutively Activating Mutations G14V and Q63L

RhoA, a member of Rho GTPases, regulates myriad cellular processes. Abnormal expression of RhoA has been implicated in various diseases, including cancers, developmental disorders and bacterial infections. RhoA mutations G14V and Q63L have been reported to constitutively activate RhoA. To figure out the mechanisms, in total, 1.8 μs molecular dynamics (MD) simulations were performed here on RhoA^WT and mutants G14V and Q63L in GTP-bound forms, followed by dynamic analysis. Both mutations were found to affect the conformational dynamics of RhoA switch regions, especially switch I, shifting the whole ensemble from the wild type's open inactive state to different active-like states, where T37 and Mg²⁺ played important roles. In RhoA^G14V, both switches underwent thorough state transition, whereas in RhoA^Q63L, only switch I was sustained in a much more closed conformation with additional hydrophobic interactions introduced by L63. Moreover, significantly decreased solvent exposure of the GTP-binding site was observed in both mutants with the surrounding hydrophobic regions expanded, which furnished access to water molecules required for hydrolysis more difficult and thereby impaired GTP hydrolysis. These structural and dynamic differences first suggested the potential activation mechanism of RhoA^G14V and RhoA^Q63L. Together, our findings complemented the understanding of RhoA activation at the atomic level and can be utilized in the development of novel therapies for RhoA-related diseases.

RhoA signaling increases mitophagy and protects cardiomyocytes against ischemia by stabilizing PINK1 protein and recruiting Parkin to mitochondria

Mitophagy, a mitochondria-specific form of autophagy, removes dysfunctional mitochondria and is hence an essential process contributing to mitochondrial quality control. PTEN-induced kinase 1 (PINK1) and the E3 ubiquitin ligase Parkin are critical molecules involved in stress-induced mitophagy, but the intracellular signaling mechanisms by which this pathway is regulated are unclear. We tested the hypothesis that signaling through RhoA, a small GTPase, induces mitophagy via modulation of the PINK1/Parkin pathway as a protective mechanism against ischemic stress. We demonstrate that expression of constitutively active RhoA as well as sphingosine-1-phosphate induced activation of endogenous RhoA in cardiomyocytes result in an accumulation of PINK1 at mitochondria. This is accompanied by translocation of Parkin to mitochondria and ubiquitination of mitochondrial proteins leading to recognition of mitochondria by autophagosomes and their lysosomal degradation. Expression of RhoA in cardiomyocytes confers protection against ischemia, and this cardioprotection is attenuated by siRNA-mediated PINK1 knockdown. In vivo myocardial infarction elicits increases in mitochondrial PINK1, Parkin, and ubiquitinated mitochondrial proteins. AAV9-mediated RhoA expression potentiates these responses and a concurrent decrease in infarct size is observed. Interestingly, induction of mitochondrial PINK1 accumulation in response to RhoA signaling is neither mediated through its transcriptional upregulation nor dependent on depolarization of the mitochondrial membrane, the canonical mechanism for PINK1 accumulation. Instead, our results reveal that RhoA signaling inhibits PINK1 cleavage, thereby stabilizing PINK1 protein at mitochondria. We further show that active RhoA localizes at mitochondria and interacts with PINK1, and that the mitochondrial localization of RhoA is regulated by its downstream effector protein kinase D. These findings demonstrate that RhoA activation engages a unique mechanism to regulate PINK1 accumulation, induce mitophagy and protect against ischemic stress, and implicates regulation of RhoA signaling as a potential strategy to enhance mitophagy and confer protection under stress conditions.