Rescue of a trafficking defective human pacemaker channel via a novel mechanism: roles of Src, Fyn, and Yes tyrosine kinases

Targeting the tyrosine kinase Src in endothelium attenuates inflammation and atherogenesis induced by disturbed flow

BACKGROUND AND PURPOSE

Previous studies have shown that Src can regulate inflammation and tumour progression. However, the mechanisms by which Src regulates the inflammatory response of vascular endothelium and atherogenesis are currently poorly understood. This study aimed to investigate the role of Src in endothelial inflammation and atherogenesis, as well as the underlying mechanisms.

EXPERIMENTAL APPROACH

Real-time quantitative PCR was used to measure the mRNA levels of inflammatory genes. The phosphorylation and localization of proteins were examined using western blotting and immunofluorescence, respectively. The level of p-Src Y416 in mouse endothelium was directly determined using en face staining. Endothelial-specific knockdown of Src was achieved by tail vein injection of AAV-sgSrc in ApoE-/-; Cas9LSL/LSL; Cdh5-cre mice. Atherosclerosis was induced by partial ligation of the carotid artery.

KEY RESULTS

Oscillatory shear stress (OSS) promotes the phosphorylation of Src at Y416 in endothelial cells, and Piezo1 is required for this regulatory process. Overexpression of constitutively active Src promotes endothelial inflammation, as well as phosphorylation of Stat3 (at Y705) and its nuclear translocation. Endothelial inflammation induced by OSS was abolished by the Src inhibitor dasatinib or si-Src. Dasatinib, when administered orally, reduced endothelial inflammation and plaque formation in ApoE-/- mice induced by partial carotid artery ligation. Additionally, plaque formation was decreased in the ligated left carotid artery of mice with endothelial-specific Src knockdown.

CONCLUSION AND IMPLICATIONS

Disturbed flow promotes endothelial inflammation and atherogenesis through the Piezo1-Src-Stat3 pathway. Therefore, inhibiting Src in endothelial cells could be a promising therapeutic strategy to treat atherogenesis.

Mechanism of Nardostachyos Radix et Rhizoma-Salidroside in the treatment of premature ventricular beats based on network pharmacology and molecular docking

To analyse the mechanism of Nardostachyos Radix et Rhizoma-Salidroside in the treatment of Premature Ventricular Brats by using network pharmacology and molecular docking and to provide the basis for developing the use of experimental and clinical traditional Chinese medicine. The chemical compositions of Nardostachyos Radix et Rhizoma and Salidroside were determined, and their related targets were predicted. The disease-related targets were obtained by searching the common disease databases Genecards, OMIM, Drugbank and DisGeNET, and the intersection between the predicted targets and the disease targets was determined. Then using the STRING database to set up the protein‒protein interactions (PPIs) network between Nardostachyos Radix et Rhizoma-Salidroside and the common targets of PVB. An "herb-ingredient-target" network was constructed and analyzed by Cytoscape3.7.2 software. Using the metascape database to analysis the predicted therapeutic targets based on the GO and KEGG. Finally, molecular docking technology was used toconfirm the capacity of the primary active ingredients of the 2 herbs to bind to central targets using the online CB-Dock2 database. 41 active components of Nardostachyos Radix et Rhizoma-Salidroside were detected, with 420 potential targets of action, with a total of 1688 PVB targets, and the top 10 core targets of herb-disease degree values were AKT1, TNF, GAPDH, SRC, PPARG, EGFR, PTGS2, ESR1, MMP9, and STAT3. KEGG analysis indicated that its mechanism may be related to the calcium signalling pathway, cancer signalling pathway, AGE-RAGE signalling pathway and other pathways. Molecular docking suggested that main of the active ingredients of the Nardostachyos Radix et Rhizoma-Salidroside pairs were well bound to the core targets. Based on novel network pharmacology and molecular docking validation research methods, we revealed for the first time the potential mechanism of Nardostachyos Radix et Rhizoma-Salidroside in PVB therapy.

Regulation of HCN Channels by Protein Interactions

Hyperpolarization-activated, cyclic nucleotide-sensitive (HCN) channels are key regulators of subthreshold membrane potentials in excitable cells. The four mammalian HCN channel isoforms, HCN1-HCN4, are expressed throughout the body, where they contribute to diverse physiological processes including cardiac pacemaking, sleep-wakefulness cycles, memory, and somatic sensation. While all HCN channel isoforms produce currents when expressed by themselves, an emerging list of interacting proteins shape HCN channel excitability to influence the physiologically relevant output. The best studied of these regulatory proteins is the auxiliary subunit, TRIP8b, which binds to multiple sites in the C-terminus of the HCN channels to regulate expression and disrupt cAMP binding to fine-tune neuronal HCN channel excitability. Less is known about the mechanisms of action of other HCN channel interaction partners like filamin A, Src tyrosine kinase, and MinK-related peptides, which have a range of effects on HCN channel gating and expression. More recently, the inositol trisphosphate receptor-associated cGMP-kinase substrates IRAG1 and LRMP (also known as IRAG2), were discovered as specific regulators of the HCN4 isoform. This review summarizes the known protein interaction partners of HCN channels and their mechanisms of action and identifies gaps in our knowledge.

Contribution of HCN1 variant to sinus bradycardia: A case report

BACKGROUND

Missense mutations in the hyperpolarization-activated cyclic nucleotide-modulated (HCN) channel 4 (HCN4) are one of the genetic causes of cardiac sinus bradycardia.

OBJECTIVE

To investigate possible HCN4 channel mutation in a young patient with profound sinus bradycardia.

METHODS

Direct sequencing of HCN4 and whole-exome sequencing were performed on DNA samples from the indexed patient (P), the patient's son (PS), and a family unrelated healthy long-distance running volunteer (V). Resting heart rate was 31 bpm for P, 67 bpm for PS, and 50 bpm for V. Immunoblots, flow cytometry, and immunocytofluorescence confocal imaging were used to study cellular distribution of channel variants. Patch-clamp electrophysiology was used to investigate the properties of mutant HCN1 channels.

RESULTS

In P no missense mutations were found in the HCN4 gene; instead, we found two heterozygous variants in the HCN1 gene: deletion of an N-terminal glycine triplet (72GGG74, "N-del") and a novel missense variant, P851A, in the C-terminal region. N-del variant was found before and shared by PS. These two variations were not found in V. Compared to wild type, N-del and P851A reduced cell surface expression and negatively shifted voltage-activation with slower activation kinetics.

CONCLUSION

Decreased channel activity HCN1 mutant channel makes it unable to contribute to early depolarization of sinus node action potential, thus likely a main cause of the profound sinus bradycardia in this patient.

Src-family Protein Tyrosine Kinases: A promising target for treating Cardiovascular Diseases

The Src-family protein tyrosine kinases (SFKs), a subfamily of non-receptor tyrosine kinases, are ubiquitously expressed in various cell types. Numerous studies have suggested that SFKs are related to signal transduction in major cardiac physiological and pathological processes, it is the activity of SFKs that is connected with the maintenance of cardiovascular homeostasis. Upon stimulation of various injury factors or stress, the phosphorylation state of SFKs is changed, which has been found to modulate different cardiac pathological conditions, such as hypertension, coronary heart disease, ischemic heart disease, myocardial ischemia-reperfusion injury, arrhythmia and cardiomyopathy via regulating cell growth, differentiation, movement and function, electrophysiologic signals. This review summarizes the basic information about SFKs, updates its role in the different processes underlying the development of multiple cardiovascular diseases (CVDs), and highlights their potential role as disease biomarkers and therapeutic targets, which would help understand the pathophysiology of CVDs and promote the further potential clinical adhibition.

Identification of phosphorylation sites and binding pockets for modulation of NaV 1.5 channel by Fyn tyrosine kinase

Cardiac sodium channel Na_V 1.5 is the predominant form of sodium channels in cardiomyocytes, which exists as a macromolecular complex and interacts with multiple protein partners. Fyn kinase is one of the interacting proteins which colocalize, phosphorylate and modulate the Na_V 1.5 channel. To elaborate this interaction we created expression vectors for the N-terminal, intracellular loop, and C-terminal regions of the Na_V 1.5 channel, to express in HEK-293 cells. By co-immunoprecipitation and anti-phosphotyrosine blotting, we identified proline-rich binding sites for Fyn kinase in the N-terminal, IC-loop_i-ii and C-terminal. After binding, Fyn kinase phosphorylates tyrosine residues present in the N- and C-terminal, which produce a depolarizing shift of 7 mV in fast inactivation. The functional relevance of these binding and phosphorylation sites was further underpinned by creating full length mutants masking these sites sequentially. An activation and inactivation curves were recorded with or without co-expressed Fyn kinase which indicates that phosphorylation of tyrosine residues at positions 68, 87, 112 in the N-terminal and at positions 1811 and 1889 in the C-terminal creates a depolarizing shift in fast inactivation of Na_V 1.5 channel.

Effects of Yiqi Tongyang on HCN4 Protein Phosphorylation in Damaged Rabbit Sinoatrial Node Cells

The hyperpolarization-activated cyclic nucleotide-gated cation channel (I_f) is closely associated with sinoatrial node pacing function. The present study aimed to investigate the molecular mechanisms involved in pacing function improvements of damaged sinoatrial node cells and the consequent treatment effects on sick sinus syndrome (SSS) after the use of Yiqi Tongyang. HCN4 channel protein expression and phosphorylation were measured by immunoblotting and fluorescent quantitation. After ischemia-reperfusion injury (model group), the HCN4 protein and the optical density (OD) of the phosphorylated HCN4 protein as well as intracellular PKA activity in the sinoatrial node cells decreased significantly. However, the OD values and PKA activity increased to different degrees after treatment with serum containing different doses of Yiqi Tongyang; in contrast, no significant improvement was seen in the control group compared to the model group. These findings demonstrated that the use of the traditional Chinese medicine Yiqi Tongyang could increase HCN4 protein expression and phosphorylation as well as PKA activity within sinoatrial node cells damaged by ischemia-reperfusion. The HCN4 protein is involved in the I_f-related ion channel. Here, we speculated that these effects could be associated with upregulation of HCN4 protein phosphorylation, which consequently improved cell automaticity, increased heart rate, and had treatment effects on SSS.

PP2 prevents β-adrenergic stimulation of cardiac pacemaker activity

One of the main strategies for cancer therapy is to use tyrosine kinase inhibitors for inhibiting tumor proliferation. Increasing evidence has demonstrated the potential risks of cardiac arrhythmias (such as prolonged QT interval) of these drugs. We report here that a widely used selective inhibitor of Src tyrosine kinases, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), can inhibit and prevent β-adrenergic stimulation of cardiac pacemaker activity. First, in dissected rat sinus node, PP2 inhibited and prevented the isoproterenol-induced increase of spontaneous beating rate. Second, in isolated rat sinus node myocytes, PP2 suppressed the hyperpolarization-activated "funny" current (traditionally called cardiac pacemaker current, I(f)) by negatively shifting the activation curve and decelerating activation kinetics. Third, in isolated rat sinus node myocytes, PP2 decreased the Src kinase activity, the cell surface expression, and tyrosine phosphorylation of hyperpolarization-activated, cyclic nucleotide-modulated channel 4 (HCN4) channel proteins. Finally, in human embryonic kidney 293 cells overexpressing recombinant human HCN4 channels, PP2 reversed the enhancement of HCN4 channels by isoproterenol and inhibited 573x, a cyclic adenosine momophosphate-insensitive human HCN4 mutant. These results demonstrated that inhibition of Src kinase activity in heart by PP2 decreased and prevented β-adrenergic stimulation of cardiac pacemaker activity. These effects are mediated, at least partially, by a cAMP-independent attenuation of channel activity and cell surface expression of HCN4, the main channel protein that controls the heart rate.

Neurobiology: Reelin mediates form and function

Reelin choreographs neuronal migration to establish laminar structures during brain formation. A recent paper uncovers a new function for Reelin signaling in specifying dendritic compartmentalization. Reelin-induced tyrosine phosphorylation is responsible for enrichment of ion channels in dendritic tufts.

Reelin signaling specifies the molecular identity of the pyramidal neuron distal dendritic compartment

The apical dendrites of many neurons contain proximal and distal compartments that receive synaptic inputs from different brain regions. These compartments also contain distinct complements of ion channels that enable the differential processing of their respective synaptic inputs, making them functionally distinct. At present, the molecular mechanisms that specify dendritic compartments are not well understood. Here, we report that the extracellular matrix protein Reelin, acting through its downstream, intracellular Dab1 and Src family tyrosine kinase signaling cascade, is essential for establishing and maintaining the molecular identity of the distal dendritic compartment of cortical pyramidal neurons. We find that Reelin signaling is required for the striking enrichment of HCN1 and GIRK1 channels in the distal tuft dendrites of both hippocampal CA1 and neocortical layer 5 pyramidal neurons, where the channels actively filter inputs targeted to these dendritic domains.

Src regulates membrane trafficking of the Kv3.1b channel

The Kv3.1 channel plays a crucial role in regulating the high-frequency firing properties of neurons. Here, we determined whether Src regulates the subcellular distributions of the Kv3.1b channel. Co-expression of active Src induced a dramatic redistribution of Kv3.1b to the endoplasmic reticulum. Furthermore, co-expression of the Kv3.1b channel with active Src induced a remarkable decrease in the pool of Kv3.1b at the cell surface. Moreover, the co-expression of active Src results in a significant decrease in the peak current densities of the Kv3.1b channel, and a substantial alteration in the voltage dependence of its steady-state inactivation. Taken together, these results indicate that Src kinase may play an important role in regulating membrane trafficking of Kv3.1b channels.