G protein subunit alpha i2's pivotal role in angiogenesis

Here we explored the potential role of Gαi2 (G protein subunit alpha i2) in endothelial cell function and angiogenesis. Methods: Genetic methodologies such as shRNA, CRISPR/Cas9, dominant negative mutation, and overexpression were utilized to modify Gαi2 expression or regulate its function. Their effects on endothelial cell functions were assessed in vitro. In vivo, the endothelial-specific Gαi2 shRNA adeno-associated virus (AAV) was utilized to silence Gαi2 expression. The impact of this suppression on retinal angiogenesis in control mice and streptozotocin (STZ)-induced diabetic retinopathy (DR) mice was analyzed. Results: Analysis of single-cell RNA sequencing data revealed Gαi2 (GNAI2) was predominantly expressed in retinal endothelial cells and expression was increased in retinal endothelial cells following oxygen-induced retinopathy (OIR) in mice. Moreover, transcriptome analysis linking Gαi2 to angiogenesis-related processes/pathways, supported by increased Gαi2 expression in experimental OIR mouse retinas, highlighted its possible role in angiogenesis. In various endothelial cell types, shRNA-induced silencing and CRISPR/Cas9-mediated knockout (KO) of Gαi2 resulted in substantial reductions in cell proliferation, migration, invasion, and capillary tube formation. Conversely, Gαi2 over-expression in endothelial cells induced pro-angiogenic activities, enhancing cell proliferation, migration, invasion, and capillary tube formation. Furthermore, our investigation revealed a crucial role of Gαi2 in NFAT (nuclear factor of activated T cells) activation, as evidenced by the down-regulation of NFAT-luciferase reporter activity and pro-angiogenesis NFAT-targeted genes (Egr3, CXCR7, and RND1) in Gαi2-silenced or -KO HUVECs, which were up-regulated in Gαi2-overexpressing endothelial cells. Expression of a dominant negative Gαi2 mutation (S48C) also down-regulated NFAT-targeted genes, slowing proliferation, migration, invasion, and capillary tube formation in HUVECs. Importantly, in vivo experiments revealed that endothelial Gαi2 knockdown inhibited retinal angiogenesis in mice, with a concomitant down-regulation of NFAT-targeted genes in mouse retinal tissue. In contrast, Gαi2 over-expression in endothelial cells enhanced retinal angiogenesis in mice. Single-cell RNA sequencing data confirmed increased levels of Gαi2 specifically in retinal endothelial cells of mice with streptozotocin (STZ)-induced diabetic retinopathy (DR). Importantly, endothelial Gαi2 silencing ameliorated retinal pathological angiogenesis in DR mice. Conclusion: Our study highlights a critical role for Gαi2 in NFAT activation, endothelial cell activation and angiogenesis, offering valuable insights into potential therapeutic strategies for modulating these processes.

Inhibition of Basic Secretagogue-Induced Signaling in Mast Cells by Cell Permeable Gαi-Derived Peptides

BACKGROUND

Basic secretagogues of connective tissue mast cells act as receptor mimetic agents that trigger mast cells by activating G proteins. This leads to simultaneous propagation of two signaling pathways: one that culminates in exocytosis, while the other involves protein tyrosine phosphorylation and leads to release of arachidonic acid metabolites. We have previously shown that introduction of a peptide that comprises the C-terminal end of G alpha i3 into permeabilized mast cells inhibits basic secretagogue-induced exocytosis [Aridor et al., Science 1993;262:1569-1572]. We investigated whether cell-permeable peptides, composed of the C-terminus of G alpha i3 fused with importation sequences, affect mast cell function.

METHODS

Following preincubation with the fused peptides, rat peritoneal mast cells were activated by compound 48/80 and analyzed for histamine and prostaglandin D2 release and protein tyrosine phosphorylations.

RESULTS

We demonstrate that out of three importation sequences tested only G alpha i3 peptide fused with the Kaposi fibroblast growth factor importation sequence (ALL1) inhibited release of histamine. ALL1 as well as a cell-permeable peptide that corresponds to G alpha i2 also blocked compound 48/80-stimulated protein tyrosine phosphorylation, though the latter did not block histamine release. ALL1 effect was G protein-specific, as it was incapable of blocking protein tyrosine phosphorylation stimulated by pervanadate.

CONCLUSION

ALL1, a transducible G alpha i3-corresponding peptide, blocks the two signaling pathways in mast cells: histamine release and protein tyrosine phosphorylation. Cell permeable peptides that block these two signaling cascades may constitute a novel approach for preventing the onset of the allergic reaction.

Molecular mechanisms of modified sensitivity of the adenylate cyclase signaling system to biogenic amines during streptozotocin-induced diabetes

We demonstrated changes in the sensitivity of the adenylate cyclase signaling system to biogenic amines (adrenoceptor agonists and serotonin) underwent a change in skeletal muscles of rats with 30-day streptozotocin-induced diabetes. Isoproterenol had a less significant stimulatory effect on adenylate cyclase in diabetic rats. Hormonal signals via Gi proteins were suppressed in animals with diabetes, which determined a greater stimulatory effect of norepinephrine and serotonin on adenylate cyclase. Hormones less significantly increased guanosine triphosphate-binding activity of G proteins in diabetic rats, which reflects the impairment of their functional coupling with receptors.