Loss of GRB2 Associated Binding Protein 1 in Arteriosclerosis Obliterans Promotes Host Autophagy
Arteriosclerosis obliterans (ASO) is a prevalent peripheral arteriosclerotic vascular disease and a major cause of adult limb loss worldwide. The disease is characterized by the narrowing and hardening of arteries, leading to reduced blood flow and severe complications such as chronic limb ischemia, intermittent claudication, rest pain, and non-healing ischemic ulcers. Despite advancements in therapeutic approaches like bypass surgery and endovascular interventions, high restenosis rates post-treatment remain a significant challenge for long-term recovery. The molecular mechanisms underlying ASO progression are not fully understood, but recent studies have highlighted the role of autophagy in vascular endothelial cells (VECs) as a contributing factor. This study explores the role of GRB2 associated binding protein 1 (GAB1) in regulating VEC autophagy and its implications in ASO progression.
Autophagy is a catabolic process that degrades cytoplasmic components within the lysosome, playing a crucial role in cellular homeostasis and stress responses. In VECs, autophagy has been observed to contribute to the progression of ASO. Dysregulation of autophagy is associated with various human diseases, including neurodegenerative diseases, cancer, and cardiovascular diseases. The study investigates the molecular mechanisms controlling VEC autophagy, focusing on the role of GAB1, a key downstream adaptor protein of insulin growth factor 1 receptor (IGF-1R) signaling.
The study employed both in vivo and in vitro approaches to determine the association between the loss of GAB1 and ASO progression. Histological analysis revealed that GAB1 expression was significantly decreased in the sclerotic vascular intima of ASO patients compared to normal vascular intima. Specifically, the expression level of GAB1 mRNA was reduced by 76% (1.00 vs. 0.24, t = 7.41, P < 0.05), and the protein level was reduced by 71% (0.72 vs. 0.21, t = 5.97, P < 0.05) in the ASO group compared to the control group. Immunofluorescence analysis confirmed that the loss of GAB1 predominantly occurred within the vascular intima of ASO arteries.
The study also examined the role of autophagy in ASO progression. The autophagy repressor p62 was significantly downregulated in ASO intima compared to healthy controls (0.80 vs. 0.20, t = 6.43, P < 0.05). Additionally, the level of LC3II, a component of autophagosomes, was significantly upregulated in the endothelium of ASO intima, indicating increased autophagy in VECs of ASO patients. These findings suggest that the loss of GAB1 within the vascular intima is highly associated with VEC autophagy and ASO progression.
To further validate the role of GAB1 in regulating VEC autophagy, the study conducted gain- and loss-of-function experiments in human umbilical vein endothelial cells (HUVECs). Knockdown of GAB1 led to a remarkable increase in LC3II levels (1.19 vs. 0.68, t = 5.99, P < 0.05), while overexpression of GAB1 significantly decreased LC3II levels (0.41 vs. 0.93, t = 7.12, P < 0.05). These results indicate that GAB1 plays a negative regulatory role in VEC autophagy.
The study also explored the downstream signaling pathways involved in GAB1-mediated autophagy. The phosphorylation levels of JNK and p38 were significantly associated with the gain- and loss-of-function of GAB1 protein. Specifically, the phosphorylation levels of JNK and p38 were increased in ASO intima compared to controls (0.54 vs. 2.67, t = 16.3, P < 0.05). The study found that the JNK inhibitor (SP600215) led to an up-regulation of p62 in normal conditions, HBSS group, and BAF+HBSS group (0.72 vs. 1.01, 0.56 vs. 0.73, and 0.71 vs. 0.82), indicating that JNK can positively activate basal autophagy and autophagic flux. On the other hand, the p38 inhibitor (SB203580) attenuated host autophagy at basal conditions by demonstrating the up-regulation of p62. However, the autophagic flux was not affected by the reduction of p62 in the BAF + HBSS group, suggesting that inactivation of p38 may only play a role in attenuating autophagy under normal conditions (0.70 vs. 1.38, 0.61 vs. 0.58, and 0.94 vs. 0.92).
The findings of this study suggest that the loss of GAB1 promotes VEC autophagy, which is associated with ASO progression. GAB1 and its downstream signaling pathways, particularly JNK and p38, may serve as potential therapeutic targets for ASO treatment. The study provides new insights into the molecular mechanisms underlying ASO and highlights the importance of autophagy regulation in vascular endothelial cells.
In conclusion, this study demonstrates that the loss of GAB1 in ASO patients leads to increased VEC autophagy, contributing to the progression of the disease. The findings suggest that targeting GAB1 and its downstream signaling pathways could offer a novel therapeutic approach for ASO. Further research is needed to explore the detailed mechanisms by which GAB1 regulates autophagy and to develop potential therapeutic strategies based on these findings.
doi.org/10.1097/CM9.0000000000001255
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