RhoA Signaling in Immune Cell Response and Cardiac Disease

SARS-CoV-2 NSP2 specifically interacts with cellular protein SmgGDS

The novel coronavirus, SARS-CoV-2, is responsible for the ongoing global pandemic of Coronavirus disease 2019 (COVID-19). SARS-CoV-2 belongs to the Coronaviridae family, which also includes the Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and the Middle East Respiratory Syndrome Coronavirus (MERS-CoV). Recent studies using affinity purification mass spectrometry analysis have revealed that SARS-CoV-2 NSP2 may interact with cellular protein Small G-protein dissociation stimulator (SmgGDS), a guanine nucleotide exchange factor (GEF) that specifically regulates RhoA and RhoC proteins, which are involved in a range of cellular activities, including actin reorganization, cell motility and adhesion. Biochemical experiments have confirmed that NSP2 binds directly to SmgGDS and that this interaction requires the full-length NSP2. Given the low sequence conservation compared to other coronaviruses, this interaction with SmgGDS appears specific to SARS-CoV-2, with similar proteins in other coronaviruses unable to bind SmgGDS. Further studies have revealed that the binding of SARS-CoV-2 NSP2 to SmgGDS has a significant inhibitory effect on the GEF activity of SmgGDS. This inhibition disrupts the nucleotide exchange process on RhoA, impairing its function and potentially contributing to the pathogenic mechanisms of SARS-CoV-2. These findings highlight a novel pathway through which SARS-CoV-2 may influence host cellular processes, providing insights into the unique impact of coronaviruses on cellular regulation.

Mechanism and application of feedback loops formed by mechanotransduction and histone modifications

Mechanical stimulation is the key physical factor in cell environment. Mechanotransduction acts as a fundamental regulator of cell behavior, regulating cell proliferation, differentiation, apoptosis, and exhibiting specific signature alterations during the pathological process. As research continues, the role of epigenetic science in mechanotransduction is attracting attention. However, the molecular mechanism of the synergistic effect between mechanotransduction and epigenetics in physiological and pathological processes has not been clarified. We focus on how histone modifications, as important components of epigenetics, are coordinated with multiple signaling pathways to control cell fate and disease progression. Specifically, we propose that histone modifications can form regulatory feedback loops with signaling pathways, that is, histone modifications can not only serve as downstream regulators of signaling pathways for target gene transcription but also provide feedback to regulate signaling pathways. Mechanotransduction and epigenetic changes could be potential markers and therapeutic targets in clinical practice.

Effects of RhoA on depression-like behavior in prenatally stressed offspring rats

Depression is a common mental disease that can lead to suicide when severe. Exposure to prenatal stress (PS) can lead to depression-like behavior in offspring, but the mechanism is unclear. RhoA (Ras homology family member A) plays an important role in stress-induced changes in synaptic plasticity, participating in the development of depression by activating the downstream effector ROCK (Rho-associated protein kinase). This study explored the influence in the expression of RhoA and downstream molecules ROCK1/2 in prenatally stressed rats, and the effect of RhoA inhibitor simvastatin on depression-like behavior induced by PS. Depression-like behavior in offspring was detected by sucrose preference test, forced swimming test, and open-field test. The mRNA and protein expression of RhoA and ROCK1/2 in the hippocampus and prefrontal cortex of offspring rats were detected by qRT-PCR and western blotting, respectively. Our results showed that PS causes depression-like behavior in offspring rats, associated with elevated expression of RhoA, ROCK1/2 in the hippocampus and prefrontal cortex. After administration of simvastatin to PS rats, the expression of RhoA and ROCK2 was significantly reduced, alleviating depression-like behavior. Our study demonstrated that RhoA participates in the depression-like behavior in prenatally stressed offspring rats, which may be a potential target for antidepressant therapy.

Expression of a RhoA-Specific Guanine Nucleotide Exchange Factor, p190RhoGEF, in Mouse Macrophages Negatively Affects M1 Polarization and Inflammatory Responses

A RhoA-specific guanine nucleotide exchange factor, p190RhoGEF, was first cloned and identified in neuronal cells. In immune cells, we first reported the role of p190RhoGEF in B cells: expression of p190RhoGEF increased after CD40 stimulation and was required for CD40-mediated B cell activation and differentiation. We also showed that over-expression of p190RhoGEF negatively affected dendritic cell function in response to bacterial lipopolysaccharide (LPS). In this study, we examined the role of p190RhoGEF in macrophages using p190RhoGEF over-expressing transgenic (TG) mice. We found macrophages from TG mice to be more round than those from control mice, with enriched polymerized actin at the edge attached to the glass. TG macrophages also responded less to LPS: production of reactive oxygen species, phagocytosis, chemokine-dependent migration, and pro-inflammatory cytokine secretion were all reduced compared with the responses of macrophages from littermate (LTM) control mice. Furthermore, the classical M1 subset population was observed less in the peritoneal macrophages of TG mice than the LTM control mice during LPS-elicited peritoneal inflammation. When the activity of RhoA was inhibited in TG macrophages, their morphology and LPS responses became similar to those of the LTM macrophages. These results suggest that over-expression of p190RhoGEF in macrophages could reduce M1 polarization and inflammatory responses by regulating the actin cytoskeleton.