The Role of Impaired Receptor Trafficking in Mediating the Pathological Effects of APOE4 in Alzheimer's Disease

BACKGROUND

Apolipoprotein E4 (APOE4) is the most prevalent genetic risk factor of Alzheimer's disease. Several studies suggest that APOE4 binding to its receptors is associated with their internalization and accumulation in intracellular compartments. Importantly, this phenomenon also occurs with other, non-ApoE receptors. Based on these observations, we hypothesized that APOE4 pathological effects are mediated by impairment in the life cycle of distinct receptors (APOER2, LRP1, IR, VEGFR).

OBJECTIVE

To examine the effects of APOE genotype on receptors protein levels and compartmentalization.

METHODS

Primary mouse neurons were prepared from APOE3 or APOE4 targeted replacement mice, or APOE-KO mice. Specific receptors protein levels were evaluated in these neurons, utilizing immunofluorescent staining. Additionally, surface membrane protein levels of those receptors were assessed by cell surface biotinylation assay and ELISA. Receptors' colocalization with intracellular compartments was assessed by double staining and confocal microscopy, followed by colocalization analysis. Finally, LRP1 or APOER2 were knocked-down with CRISPR/Cas9 system to examine their role in mediating APOE4 effects on the receptors.

RESULTS

Our results revealed lower receptors' levels in APOE4, specifically on the membrane surface. Additionally, APOE4 affects the compartmentation of these receptors in two patterns: the first was observed with LRP1 and was associated with decreased receptor levels in numerous intracellular compartments. The second was obtained with the other receptors and was associated with their accumulation in early endosomes and their decrease in the late endosomes.

CONCLUSIONS

These results provide a unifying mechanism, in which APOE4 drives the down regulation of various receptors, which plays important roles in distinct APOE4 related pathological processes.

Tocilizumab (TCZ) Decreases Angiogenesis in Rheumatoid Arthritis Through Its Regulatory Effect on miR-146a-5p and EMMPRIN/CD147

Background

Angiogenesis is a major contributor to the development of inflammation during Rheumatoid arthritis (RA), as the vascularization of the pannus provides nutrients and oxygen for the infiltrating immune cells and proliferating synoviocytes. Tocilizumab (TCZ) is an anti-IL-6 receptor antibody that is used in the treatment of RA patients, and has been shown to exert anti-inflammatory effects. However, its effects on angiogenesis are not fully elucidated, and the molecular mechanisms regulating this effect are unknown.

Methods

We evaluated the concentrations of several pro- and anti-angiogenic factors and the expression levels of several microRNA molecules that are associated with RA and angiogenesis in serum samples obtained from 40 RA patients, before and 4 months after the initiation of TCZ treatment. Additionally, we used an in vitro co-culture system of fibroblasts (the HT1080 cell line) and monocytes (the U937 cell line) to explore the mechanisms of TCZ action.

Results

Serum samples from RA patients treated with TCZ exhibited reduced circulating levels of EMMPRIN/CD147, enhanced expression of circulating miR-146a-5p and miR-150-5p, and reduced the angiogenic potential as was manifested by the lower number of tube-like structures that were formed by EaHy926 endothelial cell line. In vitro, the accumulation in the supernatants of the pro-angiogenic factors EMMPRIN, VEGF and MMP-9 was increased by co-culturing the HT1080 fibroblasts and the U937 monocytes, while the accumulation of the anti-angiogenic factor thrombospondin-1 (Tsp-1) and the expression levels of miR-146a-5p were reduced. Transfection of HT1080 cells with the miR-146a-5p mimic, decreased the accumulation of EMMPRIN, VEGF and MMP-9. When we neutralized EMMPRIN with a blocking antibody, the supernatants derived from these co-cultures displayed reduced migration, proliferation and tube formation in the functional assays.

Conclusions

Our findings implicate miR-146a-5p in the regulation of EMMPRIN and propose that TCZ affects angiogenesis through its effects on EMMPRIN and miR-146a-5p.

POS0613 TOCILIZUMAB DECREASES ANGIOGENESIS IN RHEUMATOID ARTHRITIS THROUGH ITS REGULATORY EFFECT ON EMMPRIN/CD147

Background:

Angiogenesis is an important contributor to the development of Rheumatoid arthritis (RA). Tocilizumab (TCZ), an anti-IL-6 receptor antibody, is an immunosuppressant used in the treatment of RA patients, but its effects on angiogenesis and the molecular mechanisms regulating new blood vessel formation are not fully elucidated.

Objectives:

To evaluate the concentrations of pro- and anti-angiogenic factors in serum samples of RA patients, before and after the initiation of TCZ treatment and to explore in an in vitro co-culture system the mechanisms of TCZ action.

Methods:

We evaluated the concentrations of EMMPRIN, VEGF, MMP-9, IL-6, NGAL, endostatin and thrombospondin-1 (Tsp-1) using commercial ELISA kits from 40 RA patients, before and 4 months after the initiation of TCZ treatment. The levels of secreted EMMPRIN, VEGF MMP-9 and Tsp-1 were measured in an in vitro co-culture system of HT1080 fibroblasts and U937 monocytes with and without addition of anti-EMMPRIN blocking antibody. In the tube formation assay serum samples and supernatnats from the co-cultures were added to endothelial layer. Images were obtained after 6 hours of incubation and the number of closed lumens were counted in two separate fields. In the wound assay, supernatants from the co-cultures, with or without the addition of the anti-EMMPRIN antibody were added to the endothelial layer after scratching. The scratch site area was measured immediately and compared to the area after 24 hours of incubation to assess the distance of cell migration.

Results:

Study population included 40 RA patients, 33 (82.5%) females, mean age of 57.5±11.1 years, disease duration of 7.7±5.6 years, and 53.9% positive for rheumatoid factor initiating treatment with TCZ. In this patient cohort, 25/40 (62.5%) patients were classified as “responders” according to EULAR criteria.

Following 4 mounts of treatment, statistically significant reductions in the levels of EMMPRIN/CD147 (p=0.035), without significant changes in serum levels of MMP-9, VEGF, MMP-3 and MMP-7 and of the anti-angiogenetic factors Tsp-1 and endostatin were found. A statistically significant decrease in the ratio between the pro-angiogenic factor EMMPRIN and the anti-angiogenic factor Tsp-1 that was calculated for each patient 4 months after initiating TCZ was found(p=0.031). The decrease in angiogenesis was manifested by the reduced number of closed lumen tube-like structures formed by EaHy926 endothelial cell line after incubation with serum samples 4 months after initiation of TCZ, relative to the number of closed lumens formed prior to TCZ initiation (p=0.007). The ratio between EMMPRIN and Tsp-1 was significantly reduced in the responding patients versus non-responders (p=0.033), while the levels of VEGF, MMP-9, Tsp-1, and EMMPRIN were unchanged.

In vitro, the accumulation of the pro-angiogenic factors EMMRPIN, VEGF and MMP-9 in the supernatants was increased in the co-culture, while the accumulation of the anti-angiogenic factor Tsp-1 was decreased. When EMMPRIN was neutralized with a blocking antibody, supernatants derived from these co-cultures exhibited reduced migration, proliferation, and tube-like structure formation in functional assays.

Conclusion:

Our findings suggest an important role for EMMPRIN in mediating pro-angiogenic signals in RA patients, with EMMPRIN/Tsp-1 ratio serving as a marker of angiogenesis in RA. When administered to RA patients, TCZ in turn, exerts an anti-angiogenic effect through its regulation of EMMRPIN/CD147 levels.

Disclosure of Interests:

None declared

The role of EMMPRIN/CD147 in regulating angiogenesis in patients with psoriatic arthritis

BACKGROUND

Angiogenesis plays a central role in the pathophysiology of rheumatic diseases. Patients with psoriatic arthritis (PsA) demonstrate increased vascularity over patients with rheumatoid arthritis (RA), with unknown mechanisms.

METHODS

We evaluated the serum levels of several pro- and anti-angiogenic factors in 62 PsA patients with active disease, 39 PsA patients in remission, 33 active RA patients, and 33 healthy controls (HC). Additionally, we used an in vitro co-culture system of fibroblast (HT1080) and monocytic-like (MM6) cell lines, to evaluate how their interactions affect the secretion of angiogenic factors and angiogenesis promoting abilities using scratch and tube formation assays.

RESULTS

PsA patients, regardless of disease activity, exhibited higher levels of EMMPRIN/CD147, IL-17, and TNF-α relative to RA patients or HC. Factors, such as IL-6, and the ratio between CD147 and thrombospondin-1, exhibited elevated levels in active PsA patients relative to PsA patients in remission. Secretion of CD147, VEGF, and MMP-9 was increased in vitro. CD147 neutralization with an antibody reduced these levels and the ability of endothelial cells to form tube-like structures or participate in wound healing.

CONCLUSIONS

CD147 plays a role in mediating angiogenesis in PsA, and the therapeutic possibilities of neutralizing it merit further investigation.