Background and Hypotheses
Lysosomal acid lipase (LAL) plays a key role in intracellular lipid homeostasis by cleaving cholesteryl esters and triglycerides to generate free fatty acids and cholesterol in lysosomes.
Genetic LAL deficiency promotes hepatic steatosis and hypercholesterolemia and results in increased mortality risk. Whether lysosomal cholesterol accumulation due to LAL deficiency affects the function of other organs and systems is unknown.
Previous studies on LAL knock-out (LAL KO) animal models revealed that blockage of cholesteryl ester and triglyceride metabolism leads to a systemic increase of macrophages and neutrophils, causing severe inflammation and pathogenesis in multiple organs. In depth characterization of this animal model showed that LAL is an important regulator of myelopoiesis during hematopoietic development, differentiation, and homeostasis. Moreover, LAL KO mice presented with an abnormal organization of the thymus and spleen, as well as neutral lipid accumulation in these organs, which also led to impaired T cell development and function. This phenotype appears to be the consequence of the key role of LAL in regulating cellular metabolism, both in innate (macrophages) as well as in adaptive immune cells (T lymphocytes). Recent evidence in the most extreme LAL deficiency phenotype (Wolman disease) indicated the presence of bone marrow dysfunction which mimics infant leukemia and a clinical phenotype diagnosed as hemophagocytic lymphohistiocytosis. Of note, patients with mutations in the LIPA gene causing the less severe phenotype (cholesterol ester storage disease, CESD) also showed the accumulation of cholesteryl esters and triglycerides, predominantly in Kupfer cells and macrophages. These findings raise important questions on the immunometabolic consequences of LAL deficiency beyond the liver phenotype. Indeed, the modulation of cellular metabolism is emerging as a key determinant of immune cells functionality and polarization. Interestingly, in vitro screening revealed that cell-intrinsic lysosomal lipolysis is essential for the alternative activation of macrophages as well as for the acquisition of a memory CD8(+) T cells phenotype.
To translate this aspect in humans, the central hypothesis that we will test is whether LAL plays a relevant role in cellular immunometabolism by rewiring intracellular lipid biochemistry, thus regulating human immune cells polarization and function. A deep understanding of this mechanism in the immune context will set the stage for further evaluating the impact of LAL targeting in the context of immune disorders.
The objective of the project is to assess whether genetic and pharmacological LAL inhibition affects human immune cells polarization and function by favoring intracellular cholesterol accumulation (please see the graphical abstract within the attachments). Specific aims are: (i) to immunophenotype ERT-naïve CESD patients, (ii) to address the functionality of immune cells isolated from ERT-naïve CESD patients, and (iii) to unveil the impact of progressive LAL impairment on immune cells function in healthy donors.
Expected outcomes and significance
The results generated within the present project will allow to expand the knowledge on LAL biology by shedding lights in complete new area of research connecting LAL with immune function in humans. Furthermore, the data will the set the stage for exploring application of LAL enzyme replacement therapy in the context of immunometabolic reprogramming of immune cells, thus opening to new applications for the available therapy.
Lysosomal acid lipase (LAL) plays a key role in intracellular lipid homeostasis by cleaving cholesteryl esters and triglycerides to generate free fatty acids and cholesterol in lysosomes.
Genetic LAL deficiency promotes hepatic steatosis and hypercholesterolemia and results in increased mortality risk. Whether lysosomal cholesterol accumulation due to LAL deficiency affects the function of other organs and systems is unknown.
Previous studies on LAL knock-out (LAL KO) animal models revealed that blockage of cholesteryl ester and triglyceride metabolism leads to a systemic increase of macrophages and neutrophils, causing severe inflammation and pathogenesis in multiple organs. In depth characterization of this animal model showed that LAL is an important regulator of myelopoiesis during hematopoietic development, differentiation, and homeostasis. Moreover, LAL KO mice presented with an abnormal organization of the thymus and spleen, as well as neutral lipid accumulation in these organs, which also led to impaired T cell development and function. This phenotype appears to be the consequence of the key role of LAL in regulating cellular metabolism, both in innate (macrophages) as well as in adaptive immune cells (T lymphocytes). Recent evidence in the most extreme LAL deficiency phenotype (Wolman disease) indicated the presence of bone marrow dysfunction which mimics infant leukemia and a clinical phenotype diagnosed as hemophagocytic lymphohistiocytosis. Of note, patients with mutations in the LIPA gene causing the less severe phenotype (cholesterol ester storage disease, CESD) also showed the accumulation of cholesteryl esters and triglycerides, predominantly in Kupfer cells and macrophages. These findings raise important questions on the immunometabolic consequences of LAL deficiency beyond the liver phenotype. Indeed, the modulation of cellular metabolism is emerging as a key determinant of immune cells functionality and polarization. Interestingly, in vitro screening revealed that cell-intrinsic lysosomal lipolysis is essential for the alternative activation of macrophages as well as for the acquisition of a memory CD8(+) T cells phenotype.
To translate this aspect in humans, the central hypothesis that we will test is whether LAL plays a relevant role in cellular immunometabolism by rewiring intracellular lipid biochemistry, thus regulating human immune cells polarization and function. A deep understanding of this mechanism in the immune context will set the stage for further evaluating the impact of LAL targeting in the context of immune disorders.
The objective of the project is to assess whether genetic and pharmacological LAL inhibition affects human immune cells polarization and function by favoring intracellular cholesterol accumulation (please see the graphical abstract within the attachments). Specific aims are: (i) to immunophenotype ERT-naïve CESD patients, (ii) to address the functionality of immune cells isolated from ERT-naïve CESD patients, and (iii) to unveil the impact of progressive LAL impairment on immune cells function in healthy donors.
Expected outcomes and significance
The results generated within the present project will allow to expand the knowledge on LAL biology by shedding lights in complete new area of research connecting LAL with immune function in humans. Furthermore, the data will the set the stage for exploring application of LAL enzyme replacement therapy in the context of immunometabolic reprogramming of immune cells, thus opening to new applications for the available therapy.