Elevated granulocyte-colony stimulating factor and hematopoietic stem cell mobilization in Niemann-Pick type C1 disease.

Niemann-Pick type C1 (NPC1) disease is a progressive lysosomal storage disorder caused by mutations of the NPC1 gene. While neurodegeneration is the most severe symptom, a large proportion of NPC1 patients also present with splenomegaly, which has been attributed to cholesterol and glycosphingolipid accumulation in late endosomes and lysosomes. However, recent data also reveal an increase in the inflammatory monocyte subset in the Npc1nih mouse model expressing an Npc1 null allele. We evaluated the contribution of hematopoietic cells to splenomegaly in NPC1 disease under conditions of hypercholesterolemia. We transplanted Npc1nih (Npc1 null mutation) or Npc1wt bone marrow (BM) into Ldlr-/- mice and fed these mice a cholesterol-rich Western-type diet. At 9 weeks after BM transplant, on a chow diet, the Npc1 null mutation increased plasma granulocyte-colony stimulating factor (G-CSF) by 2-fold and caused mild neutrophilia. At 18 weeks after BM transplant, including 9 weeks of Western-type diet feeding, the Npc1 mutation increased G-csf mRNA levels by ∼5-fold in splenic monocytes/macrophages accompanied by a ∼4-fold increase in splenic neutrophils compared with controls. We also observed ∼5-fold increased long-term and short-term hematopoietic stem cells (HSCs) in the spleen, and a ∼30-75% decrease of these populations in BM, reflecting HSC mobilization, presumably downstream of elevated G-CSF. In line with these data, four patients with NPC1 disease showed higher plasma G-CSF compared with age-matched and gender-matched healthy controls. In conclusion, we show elevated G-CSF levels and HSC mobilization in the setting of an Npc1 null mutation and propose that this contributes to splenomegaly in patients with NPC1 disease.

Myeloid cells regulate plasma LDL-cholesterol levels.

PURPOSE OF REVIEW: Leukocytosis, elevated blood leukocyte levels, is associated with enhanced cardiovascular risk in humans. Hematopoietic stem and progenitor cells (HSPCs) drive leukocyte production in a process called hematopoiesis, which mainly occurs in the bone marrow, and under certain conditions also in other organs such as the spleen. Cholesterol accumulation in HSPCs enhances hematopoiesis, increasing levels of blood monocytes that infiltrate into atherosclerotic plaques. Although HSPC proliferation and monocytosis enhance atherogenesis in several studies, concomitant decreases in LDL-cholesterol levels have also been reported, associated with anti-atherogenic effects. This review focuses on the link between HSPC proliferation, leukocytosis, plasma LDL-cholesterol levels, and atherogenesis. RECENT FINDINGS: Recent studies have shown that an acute infection enhances cholesterol accumulation in HSPCs, driving HSPC proliferation, and leading to the expansion of myeloid cells (monocytes, neutrophils, and macrophages). Enhanced hematopoiesis is associated with low plasma LDL-cholesterol levels in animal models and humans, probably because of the increased number of myeloid cells that take up LDL-cholesterol. Despite low-plasma LDL-cholesterol levels, specific patient populations with enhanced hematopoiesis show increased cardiovascular risk. SUMMARY: Enhanced hematopoiesis and monocytosis may accelerate atherogenesis. Studies on these processes may lead to the identification of new therapeutic targets for cardiovascular diseases.

Increased atherosclerosis in a mouse model of glycogen storage disease type 1a.

Glycogen storage disease type 1a (GSD Ia) is an inborn error of carbohydrate metabolism. Despite severe hyperlipidemia, GSD Ia patients show limited atherogenesis compared to age-and-gender matched controls. Employing a GSD Ia mouse model that resembles the severe hyperlipidemia in patients, we here found increased atherogenesis in GSD Ia. These data provide a rationale for investigating atherogenesis in GSD Ia in a larger patient cohort.

T cell cholesterol efflux suppresses apoptosis and senescence and increases atherosclerosis in middle aged mice.

Atherosclerosis is a chronic inflammatory disease driven by hypercholesterolemia. During aging, T cells accumulate cholesterol, potentially affecting inflammation. However, the effect of cholesterol efflux pathways mediated by ATP-binding cassette A1 and G1 (ABCA1/ABCG1) on T cell-dependent age-related inflammation and atherosclerosis remains poorly understood. In this study, we generate mice with T cell-specific Abca1/Abcg1-deficiency on the low-density-lipoprotein-receptor deficient (Ldlr-/-) background. T cell Abca1/Abcg1-deficiency decreases blood, lymph node, and splenic T cells, and increases T cell activation and apoptosis. T cell Abca1/Abcg1-deficiency induces a premature T cell aging phenotype in middle-aged (12-13 months) Ldlr-/- mice, reflected by upregulation of senescence markers. Despite T cell senescence and enhanced T cell activation, T cell Abca1/Abcg1-deficiency decreases atherosclerosis and aortic inflammation in middle-aged Ldlr-/- mice, accompanied by decreased T cells in atherosclerotic plaques. We attribute these effects to T cell apoptosis downstream of T cell activation, compromising T cell functionality. Collectively, we show that T cell cholesterol efflux pathways suppress T cell apoptosis and senescence, and induce atherosclerosis in middle-aged Ldlr-/- mice.

Hepatocyte-specific glucose-6-phosphatase deficiency disturbs platelet aggregation and decreases blood monocytes upon fasting-induced hypoglycemia.

OBJECTIVE: Glycogen storage disease type 1a (GSD Ia) is a rare inherited metabolic disorder caused by mutations in the glucose-6-phosphatase (G6PC1) gene. When untreated, GSD Ia leads to severe fasting-induced hypoglycemia. Although current intensive dietary management aims to prevent hypoglycemia, patients still experience hypoglycemic events. Poor glycemic control in GSD Ia is associated with hypertriglyceridemia, hepatocellular adenoma and carcinoma, and also with an increased bleeding tendency of unknown origin. METHODS: To evaluate the effect of glycemic control on leukocyte levels and coagulation in GSD Ia, we employed hepatocyte-specific G6pc1 deficient (L-G6pc-/-) mice under fed or fasted conditions, to match good or poor glycemic control in GSD Ia, respectively. RESULTS: We found that fasting-induced hypoglycemia in L-G6pc-/- mice decreased blood leukocytes, specifically proinflammatory Ly6Chi monocytes, compared to controls. Refeeding reversed this decrease. The decrease in Ly6Chi monocytes was accompanied by an increase in plasma corticosterone levels and was prevented by the glucocorticoid receptor antagonist mifepristone. Further, fasting-induced hypoglycemia in L-G6pc-/- mice prolonged bleeding time in the tail vein bleeding assay, with reversal by refeeding. This could not be explained by changes in coagulation factors V, VII, or VIII, or von Willebrand factor. While the prothrombin and activated partial thromboplastin time as well as total platelet counts were not affected by fasting-induced hypoglycemia in L-G6pc-/- mice, ADP-induced platelet aggregation was disturbed. CONCLUSIONS: These studies reveal a relationship between fasting-induced hypoglycemia, decreased blood monocytes, and disturbed platelet aggregation in L-G6pc-/- mice. While disturbed platelet aggregation likely accounts for the bleeding phenotype in GSD Ia, elevated plasma corticosterone decreases the levels of proinflammatory monocytes. These studies highlight the necessity of maintaining good glycemic control in GSD Ia.

Cholangiopathy and Biliary Fibrosis in Cyp2c70-Deficient Mice Are Fully Reversed by Ursodeoxycholic Acid.

BACKGROUND AND AIMS: Bile acids (BAs) aid intestinal fat absorption and exert systemic actions by receptor-mediated signaling. BA receptors have been identified as drug targets for liver diseases. Yet, differences in BA metabolism between humans and mice hamper translation of pre-clinical outcomes. Cyp2c70-ablation in mice prevents synthesis of mouse/rat-specific muricholic acids (MCAs), but potential (patho)physiological consequences of their absence are unknown. We therefore assessed age- and gender-dependent effects of Cyp2c70-deficiency in mice. METHODS: The consequences of Cyp2c70-deficiency were assessed in male and female mice at different ages. RESULTS: Cyp2c70-/- mice were devoid of MCAs and showed high abundances of chenodeoxycholic and lithocholic acids. Cyp2c70-deficiency profoundly impacted microbiome composition. Bile flow and biliary BA secretion were normal in Cyp2c70-/- mice of both sexes. Yet, the pathophysiological consequences of Cyp2c70-deficiency differed considerably between sexes. Three-week old male Cyp2c70-/- mice showed high plasma BAs and transaminases, which spontaneously decreased thereafter to near-normal levels. Only mild ductular reactions were observed in male Cyp2c70-/- mice up to 8 months of age. In female Cyp2c70-/- mice, plasma BAs and transaminases remained substantially elevated with age, gut barrier function was impaired and bridging fibrosis was observed at advanced age. Addition of 0.1% ursodeoxycholic acid to the diet fully normalized hepatic and intestinal functions in female Cyp2c70-/- mice. CONCLUSION: Cyp2c70-/- mice show transient neonatal cholestasis and develop cholangiopathic features that progress to bridging fibrosis in females only. These consequences of Cyp2c70-deficiency are restored by treatment with UDCA, indicating a role of BA hydrophobicity in disease development.