Cholera toxin treatment of vascular smooth muscle cells decreases smooth muscle alpha-actin content and abolishes the platelet-derived growth factor-BB-stimulated DNA synthesis

Uptake of severe acute respiratory syndrome coronavirus 2 spike protein mediated by angiotensin converting enzyme 2 and ganglioside in human cerebrovascular cells

Introduction

There is clinical evidence of neurological manifestations in coronavirus disease-19 (COVID-19). However, it is unclear whether differences in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)/spike protein (SP) uptake by cells of the cerebrovasculature contribute to significant viral uptake to cause these symptoms.

Methods

Since the initial step in viral invasion is binding/uptake, we used fluorescently labeled wild type and mutant SARS-CoV-2/SP to study this process. Three cerebrovascular cell types were used (endothelial cells, pericytes, and vascular smooth muscle cells), in vitro.

Results

There was differential SARS-CoV-2/SP uptake by these cell types. Endothelial cells had the least uptake, which may limit SARS-CoV-2 uptake into brain from blood. Uptake was time and concentration dependent, and mediated by angiotensin converting enzyme 2 receptor (ACE2), and ganglioside (mono-sialotetrahexasylganglioside, GM1) that is predominantly expressed in the central nervous system and the cerebrovasculature. SARS-CoV-2/SPs with mutation sites, N501Y, E484K, and D614G, as seen in variants of interest, were also differentially taken up by these cell types. There was greater uptake compared to that of the wild type SARS-CoV-2/SP, but neutralization with anti-ACE2 or anti-GM1 antibodies was less effective.

Conclusion

The data suggested that in addition to ACE2, gangliosides are also an important entry point of SARS-CoV-2/SP into these cells. Since SARS-CoV-2/SP binding/uptake is the initial step in the viral penetration into cells, a longer exposure and higher titer are required for significant uptake into the normal brain. Gangliosides, including GM1, could be an additional potential SARS-CoV-2 and therapeutic target at the cerebrovasculature.

Cyclic AMP acts through Rap1 and JNK signaling to increase expression of cutaneous smooth muscle alpha2C-adrenoceptors

Cold increases cutaneous vasoconstriction by unmasking the contractile activity of alpha(2C)-adrenoceptors (alpha(2C)-ARs) in vascular smooth muscle cells (VSMCs), which is mediated by the cold-induced mobilization of alpha(2C)-ARs from the transGolgi to the cell surface. The expression of alpha(2C)-ARs in human cutaneous VSMCs is under dual regulation by cyclic AMP: gene transcription is inhibited by cyclic AMP acting through protein kinase A but is increased by cyclic AMP acting through the exchange protein directly activated by cyclic AMP (EPAC) and the GTP-binding protein Rap1. Experiments were performed to further characterize the Rap1 signaling pathway. Forskolin (10 muM), the selective EPAC activator, 8-pCPT-2'-O-Me-cyclic AMP (CMC; 100 microM), or a constitutively active mutant of Rap1 (Rap1CA) increased the activity of c-Jun NH(2)-terminal kinase (JNK) in human cutaneous VSMCs. This was associated with the increased phosphorylation of c-Jun and activation of an activator protein (AP)-1 reporter construct, which were inhibited by the JNK inhibitor SP600125 (3 microM). Rap1CA increased the activity of an alpha(2C)-AR promoter-reporter construct, which was inhibited by SP600125 (3 microM) or by the mutation of an AP-1 binding site in the alpha(2C)-AR promoter. Furthermore, forskolin (10 microM) or CMC (100 microM) increased the expression of the alpha(2C)-AR protein, and these effects were inhibited by SP600125 (3 microM). Therefore, cyclic AMP increases the expression of alpha(2C)-ARs in cutaneous VSMCs by activating a novel Rap1 signaling pathway, mediated by the activation of JNK, AP-1, and the subsequent transcriptional activation of the alpha(2C)-AR gene. By increasing the expression of cold-responsive alpha(2C)-ARs, this pathway may contribute to enhanced cold-induced vasoconstriction in the cutaneous circulation, including Raynaud's phenomenon.

Growth-promoting effect of platelet-derived growth factor on rat cardiac myocytes

Platelet-derived growth factor (PDGF) is a dimeric molecule consisting of disulfide-bonded A- and B-polypeptide chains. Homodimeric (PDGF-AA, PDGF-BB) as well as heterodimeric (PDGF-AB) isoforms exert their effects on target cells by binding with different specificities to two structurally related protein tyrosine kinase receptors, denoted alpha- and beta-receptors. PDGF stimulates growth in various cell types, but little is known about its effect on mammalian cardiomyocytes. Therefore, growth-promoting effect of PDGF on rat cardiomyocytes was investigated. Primary culture of neonatal rat ventricular myocytes was prepared and cellular growth was estimated by [3H]-leucine incorporation assay. Tyrosine-phosphorylated PDGF-beta receptor of cardiomyocytes was determined by immunoblotting analysis after immunoprecipitation. PDGF-beta receptor, extracellular signal-regulated kinase (ERK) 1/2 and phosphorylated ERK1/2 of cardiomyocytes were measured by immunoblotting analysis. [3H]-leucine incorporation into the cultured myocytes was increased in a time- and dose-dependent manner after PDGF-BB stimulation. Phosphorylation of PDGF-beta receptor and ERK1/2 in cardiomyocytes was increased after short-term stimulation of PDGF-BB. Protein expression of PDGF-beta receptor and ERK1/2 was increased after long-term stimulation of PDGF-BB. [(3)H]-leucine incorporation into the cultured myocytes induced by PDGF-BB was partly blocked by mitogen-activated ERK-activating kinase (MEK) inhibitor PD98059, phospholipase C (PLC) inhibitor U73122, and protein kinase C (PKC) inhibitor staurosporin aglycone, respectively. Therefore, PDGF beta receptor, ERK1/2, PLC and PKC are involved in the signal transduction of PDGF-induced growth response of rat cardiac myocytes.

Mode of action of a potentially important excretory–secretory product fromGiardia lambliain mice enterocytes

Giardia, a common enteric protozoan parasite is a well-recognized cause of diarrhoeal illness. The detailed mechanism of diarrhoea due to this infection is not well understood. A 58 kDa enterotoxin (ESP) was purified from the excretory–secretory product of the parasite. The present study was designed to investigate the mode of action of this enterotoxin ofG. lambliain mice enterocytes. An increase in cyclic adenosine monophosphate level, as well as intracellular Ca2+concentration, was observed in the ESP-triggered enterocytes. The levels of phospholipase Cγ1and inositol triphosphate were found to be upregulated. The activity of protein kinase C (PKC) in the enterocytes was also enhanced following stimulation with the ESP. An increase in the level of reactive oxygen species in ESP-stimulated cells correlated well with the decline in the activity of antioxidant enzymes (superoxide dismutase and catalase). The significantly high levels of nitrite and citrulline indicated the generation of reactive nitrogen intermediates in the ESP-triggered enterocytes. Thus, ESP could induce cross-talk among the different signal transduction pathways in the enterocytes, which could together bring about a common secretory response.

Gangliosides GM1 and GM2 induce vascular smooth muscle cell proliferation via extracellular signal-regulated kinase 1/2 pathway

Gangliosides, sialic acid-containing glycophospholipids, accumulate in atherosclerotic vessels and appear to regulate the proliferation of various cell types. Furthermore, vascular smooth muscle cell (VSMC) proliferation is associated with the development and progression of cardiovascular diseases. To demonstrate whether gangliosides are able to modulate the VSMC growth, the effect of gangliosides GM1, GM2, and GM3 on cell DNA synthesis and cell number has been examined. Moreover, we investigated possible intracellular mechanisms by which GM1 and GM2 elicit their mitogenic effects. Stimulation of VSMCs with GM1 and GM2 resulted in a dose-dependent increase in DNA synthesis and cell number, whereas GM3 caused a decrease in DNA synthesis. GM1 and GM2 (50 micromol/L) stimulate phosphorylation of extracellular signal-regulated kinases (ERKs) 1 and 2 and phosphorylation of the c-Jun N-terminal kinase (JNK), with a maximum at 15 minutes, but they do not have an effect on the phosphorylation of p38 mitogen-activated protein kinase (MAPK). GM3 (50 micromol/L), on the other hand, does not stimulate any of the 3 aforementioned MAPKs. Pretreatment of the cells with 20 micromol/L PD 098,059 caused a complete inhibition of ERK1/2 and JNK MAPK, whereas pretreatment with a Ras (farnesyl transferase) inhibitor did not abrogate the GM1- and GM2-induced ERK1/2 phosphorylation. Furthermore, GM1 and GM2 did not activate Raf-1 kinase. Interestingly, pretreatment of VSMCs with 100 nmol/L pertussis toxin resulted in a complete inhibition of the ERK1/2 phosphorylation. Finally, the GM1- and GM2-induced increase in cell number was significantly inhibited by PD 098,059. We may conclude that GM1 and GM2 stimulate ERK1/2 via a pertussis toxin-sensitive G(i)-coupled receptor through a Raf-1 kinase-independent pathway. Moreover, the GM1- and GM2-induced VSMC growth is ERK1/2 dependent.