Enhanced macrophage uptake of lipoprotein(a) after Ca2+-induced aggregate-formation

Brain metastases-derived extracellular vesicles induce binding and aggregation of low-density lipoprotein

BACKGROUND

Cancer cell-derived extracellular vesicles (EVs) have previously been shown to contribute to pre-metastatic niche formation. Specifically, aggressive tumors secrete pro-metastatic EVs that travel in the circulation to distant organs to modulate the microenvironment for future metastatic spread. Previous studies have focused on the interface between pro-metastatic EVs and epithelial/endothelial cells in the pre-metastatic niche. However, EV interactions with circulating components such as low-density lipoprotein (LDL) have been overlooked.

RESULTS

This study demonstrates that EVs derived from brain metastases cells (Br-EVs) and corresponding regular cancer cells (Reg-EVs) display different interactions with LDL. Specifically, Br-EVs trigger LDL aggregation, and the presence of LDL accelerates Br-EV uptake by monocytes, which are key components in the brain metastatic niche.

CONCLUSIONS

Collectively, these data are the first to demonstrate that pro-metastatic EVs display distinct interactions with LDL, which impacts monocyte internalization of EVs.

Identification and analyses of inhibitors targeting apolipoprotein(a) kringle domains KIV-7, KIV-10, and KV provide insight into kringle domain function

Increased plasma concentrations of lipoprotein(a) (Lp(a)) are associated with an increased risk for cardiovascular disease. Lp(a) is composed of apolipoprotein(a) (apo(a)) covalently bound to apolipoprotein B of low-density lipoprotein (LDL). Many of apo(a)'s potential pathological properties, such as inhibition of plasmin generation, have been attributed to its main structural domains, the kringles, and have been proposed to be mediated by their lysine-binding sites. However, available small-molecule inhibitors, such as lysine analogs, bind unselectively to kringle domains and are therefore unsuitable for functional characterization of specific kringle domains. Here, we discovered small molecules that specifically bind to the apo(a) kringle domains KIV-7, KIV-10, and KV. Chemical synthesis yielded compound AZ-05, which bound to KIV-10 with a K_d of 0.8 μm and exhibited more than 100-fold selectivity for KIV-10, compared with the other kringle domains tested, including plasminogen kringle 1. To better understand and further improve ligand selectivity, we determined the crystal structures of KIV-7, KIV-10, and KV in complex with small-molecule ligands at 1.6-2.1 Å resolutions. Furthermore, we used these small molecules as chemical probes to characterize the roles of the different apo(a) kringle domains in in vitro assays. These assays revealed the assembly of Lp(a) from apo(a) and LDL, as well as potential pathophysiological mechanisms of Lp(a), including (i) binding to fibrin, (ii) stimulation of smooth-muscle cell proliferation, and (iii) stimulation of LDL uptake into differentiated monocytes. Our results indicate that a small-molecule inhibitor targeting the lysine-binding site of KIV-10 can combat the pathophysiological effects of Lp(a).

Morphologic Characteristics of Lamellar Channel Deposits in the Human Eye

OBJECTIVE

To report the histologic characteristics of lamellar channel deposits after polymethyl methacrylate intrastromal corneal ring segments in a human eye.

METHODS

A 34-year-old man previously diagnosed with keratoconus received photorefractive keratectomy in his left eye that exacerbated his corneal ectasia. To delay or possibly prevent corneal transplant, the patient elected to have intrastromal corneal segments implanted in the left eye. One year later the patient underwent corneal transplant. Before transplant, lamellar channel deposits were noted on clinical microscopic examination of the left eye. We performed histologic evaluation to assess changes to the patient's excised corneal tissue and to further characterize the observed lamellar channel deposits.

RESULTS

Lamellar channel deposits in humans are histologically similar to our previous descriptions of deposits in rabbits. These deposits primarily consist of intracellular lipid accumulations that stain positively with oil red O and filipin but not periodic acid Schiff reaction. Immunohistochemistry of cells located in the deposit region stained positively with vimentin, suggesting that these cells were keratocytes. Stains for cytokeratins 3 and 12 and for CD68 were both negative, indicating that epithelial cells and macrophages were not present in the deposit region.

CONCLUSION

Lamellar channel deposits are a common clinical finding after intrastromal corneal implants. This case provides further evidence to support our hypothesis that lamellar channel deposits in humans are a tissue response to corneal implants that consist of intracellular lipid accumulations. We use this case to propose a theoretical construct for the observation of stromal lipid accumulation in response to corneal injury.