Angiotensin 1–7, but not the thrombin-cleaved osteopontin C-terminal fragment, attenuates osteopontin-mediated macrophage-induced endothelial-cell inflammation

Thrombin Cleavage of Osteopontin and the Host Anti-Tumor Immune Response

Osteopontin (OPN) is a multi-functional protein that is involved in various cellular processes such as cell adhesion, migration, and signaling. There is a single conserved thrombin cleavage site in OPN that, when cleaved, yields two fragments with different properties from full-length OPN. In cancer, OPN has tumor-promoting activity and plays a role in tumor growth and metastasis. High levels of OPN expression in cancer cells and tumor tissue are found in various types of cancer, including breast, lung, prostate, ovarian, colorectal, and pancreatic cancer, and are associated with poor prognosis and decreased survival rates. OPN promotes tumor progression and invasion by stimulating cell proliferation and angiogenesis and also facilitates the metastasis of cancer cells to other parts of the body by promoting cell adhesion and migration. Furthermore, OPN contributes to immune evasion by inhibiting the activity of immune cells. Thrombin cleavage of OPN initiates OPN's tumor-promoting activity, and thrombin cleavage fragments of OPN down-regulate the host immune anti-tumor response.

Mechanistic Insights into the Role of OPN in Mediating Brain Damage via Triggering Lysosomal Damage in Microglia/Macrophage

We previously found that osteopontin (OPN) played a role in hypoxia–ischemia (HI) brain damage. However, its underlying mechanism is still unknown. Bioinformatics analysis revealed that the OPN protein was linked to the lysosomal cathepsin B (CTSB) and galectin-3 (GAL-3) proteins after HI exposure. In the present study, we tested the hypothesis that OPN was able to play a critical role in the lysosomal damage of microglia/macrophages following HI insult in neonatal mice. The results showed that OPN expression was enhanced, especially in microglia/macrophages, and colocalized with lysosomal-associated membrane protein 1 (LAMP1) and GAL-3; this was accompanied by increased LAMP1 and GAL-3 expression, CTSB leakage, as well as impairment of autophagic flux in the early stage of the HI process. In addition, the knockdown of OPN expression markedly restored lysosomal function with significant improvements in the autophagic flux after HI insult. Interestingly, cleavage of OPN was observed in the ipsilateral cortex following HI. The wild-type OPN and C-terminal OPN (Leu152-Asn294), rather than N-terminal OPN (Met1-Gly151), interacted with GAL-3 to induce lysosomal damage. Furthermore, the secreted OPN stimulated lysosomal damage by binding to CD44 in microglia in vitro. Collectively, this study demonstrated that upregulated OPN in microglia/macrophages and its cleavage product was able to interact with GAL-3, and secreted OPN combined with CD44, leading to lysosomal damage and exacerbating autophagosome accumulation after HI exposure.

Recombinant osteopontin provides protection for cerebral infarction by inhibiting the NLRP3 inflammasome in microglia

Neuroinflammation is one of the most important secondary pathological events after cerebral infarction. Activation of NLRP3 inflammasome is a pivotal form of neuroinflammation. Osteopontin (OPN) is expressed during the subacute phase after cerebral infarction and has an important chemotactic effect on microglia. The aim of this study was to reveal the effect of recombinant OPN on brain injury after cerebral infarction and the regulation of NLRP3 inflammasome. We used the middle cerebral artery occlusion (MCAO) method-established focal cerebral ischemia model and LPS-induced inflammation model on neonate rat primary microglia. The effects of OPN on cerebral ischemic injury, neural function, microglia inflammation and NLRP3 inflammasome function were studied by immunofluorescence, staining, enzyme-linked immunosorbent assay and Western blot assay. We established MCAO cerebral ischemia and reperfusion injury model, and found that recombinant OPN reduced the volume of cerebral infarction and alleviated the ischemic injury degree of cerebral tissues, neurons, and neurological function. We found that OPN was also involved in the negative regulation of inflammasome and microglia activity in cerebral ischemic injury, and that OPN inhibited the activation of NLRP3 inflammasome and the function of microglia in a LPS-induced inflammatory model. Our findings show that recombinant OPN can reduce the ischemic infarct size and alleviate the cerebral ischemic injury of rats, which may be related to its efficient involvement in the inhibitory regulation of inflammasome and microglia inflammatory activation.

Role of p120 Catenin in Epac1-Induced Chronic Postsurgical Pain in Rats

Chronic postsurgical pain (CPSP) is a chronic pain state that is difficult to be treated clinically. A series of complicated changes have been produced from nociceptive stimulation to the occurrence and development of postsurgical pain. Many mechanisms remain unclear. In order to study the role of intercellular gap junctions in inducing inflammatory microenvironment at the beginning of nociceptor after operation, the model of skin/muscle incision and retraction (SMIR) was established. We observed the changes of the expression of exchange proteins directly activated by cAMP-1 (Epac1) and p120 catenin (p120), the quantities of macrophages and endothelial cells, vascular endothelial permeability, and mechanical withdrawal threshold (MWT). It was found that macrophages and endothelial cells were functionally coupled through Epac1-p120. Adhesive linkage disorder remodeled the chronic, inflammatory, and eutrophic microenvironment at the beginning of nociceptor after operation through macrophages, endothelial cells, and endothelial paracellular pathways. It might be an early event and a key step in peripheral sensitization of CPSP. The expression of p120 in muscle tissue around the incision might become a prognostic marker for the conversion of acute postsurgical pain into CPSP. Targeted intervention of Epac1-p120 might be a clinical strategy for inhibiting the conversion of acute postsurgical pain into CPSP.