Unexpected macrophage-independent dyserythropoiesis in Gaucher disease

Enzyme replacement therapy improves erythropoiesis and iron dysregulation in Gaucher disease

Anemia and hyperferritinemia are frequent findings at diagnosis of Gaucher disease (GD). Macrophage-independent dyserythropoiesis and abnormal iron metabolism have been shown. We evaluated hematological and iron status at diagnosis (T0) and the effect of enzyme replacement therapy (ERT) on erythropoiesis and iron utilization over 5-year follow-up in type 1 GD patients and in an ex vivo model of erythropoiesis from CD34 + peripheral blood cells. At T0, 41% of patients had anemia and 51% hyperferritinemia. Hemoglobin increased from 12.6 (T0) to 13.9 g/dL (T6), GFD15, a marker of ineffective erythropoiesis, decreased from 5401 to 710 pg/ml, and serum ferritin decreased from 614 to 140 mcg/L (p < 0.001). In parallel, transferrin saturation (TSAT) increased. Hepcidin, although in the normal range, decreased from T0 to T6. Ex vivo studies showed that ERT restores the erythroid cells derived from CD34 + impaired ability to differentiate. During ERT, an increase in TFRC expression, consistent with the ability of erythroid precursors to uptake iron, and a reduction in HAMP and concomitant increase in SLC40A1 were observed. This is the largest study with a longitudinal follow-up evaluating erythropoiesis and iron metabolism, combining clinical and ex vivo data in GD. Iron dysregulation likely contributes to anemia, and ERT, by improving iron distribution, improves erythropoiesis.

TFEB-GDF15 axis protects against obesity and insulin resistance as a lysosomal stress response

TFEB, a key regulator of lysosomal biogenesis and autophagy, is induced not only by nutritional deficiency but also by organelle stress. Here, we find that Tfeb and its downstream genes are upregulated together with lipofuscin accumulation in adipose tissue macrophages (ATMs) of obese mice or humans, suggestive of obesity-associated lysosomal dysfunction/stress in ATMs. Macrophage-specific TFEB-overexpressing mice display complete abrogation of diet-induced obesity, adipose tissue inflammation and insulin resistance, which is independent of autophagy, but dependent on TFEB-induced GDF15 expression. Palmitic acid induces Gdf15 expression through lysosomal Ca²⁺-mediated TFEB nuclear translocation in response to lysosomal stress. In contrast, mice fed a high-fat diet with macrophage-specific Tfeb deletion show aggravated adipose tissue inflammation and insulin resistance, accompanied by reduced GDF15 level. Finally, we observe activation of TFEB-GDF15 in ATMs of obese humans as a consequence of lysosomal stress. These findings highlight the importance of the TFEB-GDF15 axis as a lysosomal stress response in obesity or metabolic syndrome and as a promising therapeutic target for treatment of these conditions.

Effects of sphingolipids overload on red blood cell properties in Gaucher disease

Gaucher disease (GD) is a genetic disease with mutations in the GBA gene that encodes glucocerebrosidase causing complications such as anaemia and bone disease. GD is characterized by accumulation of the sphingolipids (SL) glucosylceramide (GL1), glucosylsphingosine (Lyso‐GL1), sphingosine (Sph) and sphingosine‐1‐phosphate (S1P). These SL are increased in the plasma of GD patients and the associated complications have been attributed to the accumulation of lipids in macrophages. Our recent findings indicated that red blood cells (RBCs) and erythroid progenitors may play an important role in GD pathophysiology. RBCs abnormalities and dyserythropoiesis have been observed in GD patients. Moreover, we showed higher SL levels in the plasma and in RBCs from untreated GD patients compared with controls. In this study, we quantified SL in 16 untreated GD patients and 15 patients treated with enzyme replacement therapy. Our results showed that the treatment significantly decreases SL levels in the plasma and RBCs. The increased SL content in RBCs correlates with abnormal RBC properties and with markers of disease activity. Because RBCs lack glucocerebrosidase activity, we investigated how lipid overload could occur in these cells. Our results suggested that SL overload in RBCs occurs both during erythropoiesis and during its circulation in the plasma.

Semaphorin 7A: A novel marker of disease activity in Gaucher disease

Gaucher disease (GD) is a recessively inherited lysosomal storage disorder in which sphingolipids accumulates in the macrophages that transform into Gaucher cells. A growing body of evidence indicates that red blood cells (RBCs) represent important actors in GD pathophysiology. We previously demonstrated that altered RBC properties including increased Lyso-GL1 levels, dyserythropoiesis, and iron metabolism defect in GD patients contribute to anemia and hyperferritinemia. Since RBC defects also correlated well with markers of GD severity and were normalized under enzyme replacement therapy (ERT), the identification of molecules that are deregulated in GD RBCs represents an important issue in the search of pertinent markers of the disease. Here, we found a decreased expression of the GPI-anchored cell surface protein Semaphorin 7A (Sema7A) in RBCs from untreated GD (GD UT) patients, in parallel with increased levels of the soluble form in the plasma. Sema7A plays a role in neural guidance, atherosclerosis, and inflammatory diseases and represents a promigratory cue in physiological and pathological conditions. We showed that the decreased expression of Sema7A in RBCs correlated with their abnormal properties and with markers of GD activity. Interestingly, ERT restored the level of Sema7A to normal values both in RBCs and in plasma from GD patients. We then proposed that SemaA7A represents a simple and pertinent marker of inflammation in GD. Finally, because Sema7A is known to regulate the activity of immune cells, the increased level of soluble Sema7A in GD patients could propagate inflammation in several tissues.

Involvement of hepcidin in iron metabolism dysregulation in Gaucher disease

Gaucher disease (GD) is an inherited deficiency of glucocerebrosidase leading to accumulation of glucosylceramide in tissues such as the spleen, liver, and bone marrow. The resulting lipid-laden macrophages lead to the appearance of “Gaucher cells”. Anemia associated with an unexplained hyperferritinemia is a frequent finding in GD, but whether this pathogenesis is related to an iron metabolism disorder has remained unclear. To investigate this issue, we explored the iron status of a large cohort of 90 type I GD patients, including 66 patients treated with enzyme replacement therapy. Ten of the patients treated with enzyme replacement were followed up before and during treatment. Serum levels of hepcidin, the iron regulatory peptide, remained within the physiological range, while the transferrin saturation was slightly decreased in children. Inflammation-independent hyperferritinemia was found in 65% of the patients, and Perl’s staining of the spleen and marrow smear revealed iron accumulation in Gaucher cells. Treated patients exhibited reduced hyperferritinemia, increased transferrin saturation and transiently increased systemic hepcidin. In addition, the hepcidin and ferritin correlation was markedly improved, and, in most patients, the hemoglobin level was normalized. To further explore eventual iron sequestration in macrophages, we produce a Gaucher cells model by treating the J774 macrophage cell line with a glucocerebrosidase inhibitor and showed induced local hepcidin and membrane retrieval of the iron exporter, ferroportin. These data reveal the involvement of Gaucher cells in abnormal iron sequestration, which may explain the mechanism of hyperferritinemia in GD patients. Local hepcidin-ferroportin interaction was involved in this pathogenesis.