Structural determinants of the integrin transmembrane domain required for bidirectional signal transmission across the cell membrane

Intrinsic self-organization of integrin nanoclusters within focal adhesions is required for cellular mechanotransduction

Upon interaction with the extracellular matrix, the integrin receptors form nanoclusters as a first biochemical response to ligand binding. Here, we uncover a critical biodesign principle where these nanoclusters are spatially self-organized, facilitating effective mechanotransduction. Mouse Embryonic Fibroblasts (MEFs) with integrin β3 nanoclusters organized themselves with an intercluster distance of ∼550 nm on uniformly coated fibronectin substrates, leading to larger focal adhesions. We determined that this spatial organization was driven by cell-intrinsic factors since there was no pre-existing pattern on the substrates. Altering this spatial organization using cyclo-RGD functionalized Titanium nanodiscs (of 100 nm, corroborating to the integrin nanocluster size) spaced at intervals of 300 nm (almost half), 600 nm (normal) or 1000 nm (almost double) resulted in abrogation in mechanotransduction, indicating that a new parameter i.e., an optimal intercluster distance is necessary for downstream function. Overexpression of α-actinin, which induces a kink in the integrin tail, disrupted the establishment of the optimal intercluster distance, while simultaneous co-overexpression of talin head with α-actinin rescued it, indicating a concentration-dependent competition, and that cytoplasmic activation of integrin by talin head is required for the optimal intercluster organization. Additionally, talin head-mediated recruitment of FHOD1 that facilitates local actin polymerization at nanoclusters, and actomyosin contractility were also crucial for establishing the optimal intercluster distance and a robust mechanotransduction response. These findings demonstrate that cell-intrinsic machinery plays a vital role in organizing integrin receptor nanoclusters within focal adhesions, encoding essential information for downstream mechanotransduction signalling.

LncRNA MSTRG.22719.16 mediates the reduction of enoxaparin sodium high-viscosity bone cement-induced thrombosis by targeting the ocu-miR-326-5p/CD40 axis

OBJECTIVE

Polymethylmethacrylate (PMMA) bone cement promotes the development of local thrombi. Our study found that a novel material, ES-PMMA bone cement, can reduce local thrombosis. We used a simple and reproducible animal model to confirm the reduction in local thrombosis and explored the associated molecular mechanism.

METHODS

New Zealand rabbits, which were used to model thrombosis using extracorporeal carotid artery shunts, were divided into the following two groups, with 3 rabbits in each group: the PMMA bone cement group and the ES-PMMA bone cement group. Four hours after modelling, experimental samples, including thrombotic and vascular tissues, were collected. Thrombotic samples from the PMMA group and ES-PMMA group were subjected to lncRNA sequencing, and a lncRNA microarray was used to screen the differentially expressed lncRNAs. The expression of thrombomodulin in endothelial cells was quantified in vascular tissue samples. Differences in the lncRNA expression profiles between the thrombotic samples of the PMMA group and ES-PMMA group were assessed by base-to-base alignment in the intergenic regions of genomes. The lncRNA-miRNA-mRNA competitive endogenous RNA (ceRNA) network was established in light of ceRNA theory. Thrombosis was observed in the PMMA group and ES-PMMA group.

RESULTS

The thrombotic weight was 0.00706 ± 0.00136 g/cm in the PMMA group and 0.00551 ± 0.00115 g/cm in the ES-PMMA group. Quantitative real-time polymerase chain reaction (RT-q-CR) and Western blotting revealed that the expression of CD40, which can regulate thrombosis in vascular endothelial cells, was significantly lower in the ES-PMMA group than in the PMMA group. High-throughput sequencing was used to identify 111 lncRNAs with lower expression in the ES-PMMA group than in the PMMA group. Through bioinformatics investigation, lncRNA MSTRG22719.16/ocu-miR-326-5p/CD40 binding sites were selected. Fluorescent in situ RNA hybridization (FISH) was performed to verify the lower expression of lncRNA MSTRG.22719.16 in vascular tissues from the ES-PMMA group. A dual-luciferase reporter gene assay was applied to verify that ocu-miR-326-5p binds the CD40 3'-UTR and targets lncRNA MSTRG.22719.16.

CONCLUSION

Compared with PMMA bone cement, ES-PMMA bone cement can reduce thrombosis through the lncRNA MSTRG.22719.16/ocu-miR-326-5p/CD40 axis.

Molecular Modeling Insights into the Structure and Behavior of Integrins: A Review

Integrins are heterodimeric glycoproteins crucial to the physiology and pathology of many biological functions. As adhesion molecules, they mediate immune cell trafficking, migration, and immunological synapse formation during inflammation and cancer. The recognition of the vital roles of integrins in various diseases revealed their therapeutic potential. Despite the great effort in the last thirty years, up to now, only seven integrin-based drugs have entered the market. Recent progress in deciphering integrin functions, signaling, and interactions with ligands, along with advancement in rational drug design strategies, provide an opportunity to exploit their therapeutic potential and discover novel agents. This review will discuss the molecular modeling methods used in determining integrins' dynamic properties and in providing information toward understanding their properties and function at the atomic level. Then, we will survey the relevant contributions and the current understanding of integrin structure, activation, the binding of essential ligands, and the role of molecular modeling methods in the rational design of antagonists. We will emphasize the role played by molecular modeling methods in progress in these areas and the designing of integrin antagonists.

Analysis of Integrin αIIb Subunit Dynamics Reveals Long-Range Effects of Missense Mutations on Calf Domains

Integrin α_IIbβ₃, a glycoprotein complex expressed at the platelet surface, is involved in platelet aggregation and contributes to primary haemostasis. Several integrin α_IIbβ₃ polymorphisms prevent the aggregation that causes haemorrhagic syndromes, such as Glanzmann thrombasthenia (GT). Access to 3D structure allows understanding the structural effects of polymorphisms related to GT. In a previous analysis using Molecular Dynamics (MD) simulations of α_IIbCalf-1 domain structure, it was observed that GT associated with single amino acid variation affects distant loops, but not the mutated position. In this study, experiments are extended to Calf-1, Thigh, and Calf-2 domains. Two loops in Calf-2 are unstructured and therefore are modelled expertly using biophysical restraints. Surprisingly, MD revealed the presence of rigid zones in these loops. Detailed analysis with structural alphabet, the Proteins Blocks (PBs), allowed observing local changes in highly flexible regions. The variant P741R located at C-terminal of Calf-1 revealed that the Calf-2 presence did not affect the results obtained with isolated Calf-1 domain. Simulations for Calf-1 + Calf-2, and Thigh + Calf-1 variant systems are designed to comprehend the impact of five single amino acid variations in these domains. Distant conformational changes are observed, thus highlighting the potential role of allostery in the structural basis of GT.