Contribution of Decreased Migration of Monocytes to Impaired Inflammation in Gaucher Disease
Authors: Katz Tamar , Bettman Noam , Rosenbaum Hanna , Avivi Irit 
Published: October 2019

Abstract
Abstract 2162

Background:
Gaucher disease (GD) is an autosomal recessively inherited lysosomal storage disorder caused by an inborn glucocerebrosidase (GBA) deficiency. This leads to the accumulation of glycolipids in macrophages, mainly in the bone marrow, spleen and liver, resulting in organ damage. However, recent studies suggest that clinical presentation of GD is primarily attributed to the impaired inflammatory process induced by “loaded macrophages”, rather than to their physical presence. This impairment could be explained by dysfunction of circulating monocytes, normally capable of migrating into sites of vascular injury and inflammation. The current in vitro study investigated potential changes in migratory capacity of GD-derived monocytes that would contribute to the inflammatory response. Methods: CD14+ monocytes were isolated from peripheral blood mononuclear cells (PBMCs) of untreated GD patients and healthy volunteers, using immunomagnetic bead separation (Miltenyi Biotec). Monocyte migration capacity was assessed with 5μm Polycarbonate Membrane Transwell inserts which contained either stromal cell-derived factor 1 (SDF1; CXCL12) (500 and 1000 ng/ml) or serum (0.25%) at the bottom chamber. Monocytes were allowed to migrate from the upper chamber through the membrane, over 4 hours. Migrating monocytes were collected from the bottom chamber and quantified by FACS. Blockage of the CXCR4 receptor was examined using AMD3100 (10μg/ml) added to the migration assay. Serum SDF-1 levels were evaluated by ELISA (Quntikine® human CXCL12/SDF-1α R&D systems). Results: Upon exposure to SDF-1, migration capacity of GD monocytes (n=7) was significantly lower than that observed in monocytes obtained from healthy volunteers (n=6), approaching 5.7% vs. 14%, p=0.02, for SDF1of 500 ng/ml, and 8.7% vs 21.8%, p=0.013, for SDF1of 1000 ng/ml). Similar results were observed in the presence of autologous serum: migration capacity of GD monocytes (n=7) was lower than demonstrated by healthy monocytes (n=5), (18.6% vs. 45%, p=0.05). Notably, substitution of “GD serum” (n=7) with “healthy serum” (n=7) resulted in significant improvement in migration capacity of GD-derived monocytes (from 18.6% to 33.6%, p=0.038), while a reciprocal substitution of the serum caused a marked reduction in migration of monocytes derived from healthy volunteers (34% instead of 45%). Blockage of the CXCR4 receptor led to a decreased migration capacity of healthy monocytes cultured in autologous serum (from 45.2% to 39.6%) (n=4). Remarkably, this blockage had no impact on migration of both healthy and GD-derived monocytes cultured with GD serum (n=6). However, GD monocytes treated with AMD3100 in the presence of healthy serum, exhibited a reduced migration rate compared to that observed in untreated cells (22.6% vs. 33.6%; p=0.06, n=7).CXCR4 expression on GD-derived monocytes appeared to be lower than that measured on cells derived from healthy donors [64.5% (n=6) vs. 83.6% (n=3)]. Of note, serum levels of SDF-1 were significantly increased in GD subjects compared to healthy ones (2603pg/ml vs 2039 pg/ml; p=0.004, n=10). Conclusions: GD patients exhibit an impaired SDF1-dependent migration of monocytes, despite expressing a significantly increased SDF-1serum level. The impaired migration capacity is partly explained by low levels of CXCR4 on monocyte surface. Additionally, the reduced migration appears to be dependent on as yet undetermined serum-derived factors, as demonstrated by the reversibility of this impairment with substitution of the GD serum for “healthy serum”. The observed reduction in migratory capacity may significantly contribute to the abnormal inflammation accounting for GD-associated vascular and bone complications. Further studies exploring the precise mechanisms involved in this process and their direct impact on GD-related organ damage are warranted.

Disclosures:
No relevant conflicts of interest to declare.