Characterization of the visceral and neuronal phenotype of 4L/PS-NA mice modeling Gaucher disease

Abstract

Gaucher disease is caused by a deficiency in glucocerebrosidase that can result in non-neuronal as well as neuronal symptoms. Common visceral symptoms are an increased organ size, specifically of the spleen, and glucosylceramide as well as glucosylsphingosine substrate accumulations as a direct result of the glucocerebrosidase deficiency. Neuronal symptoms include motor deficits and strong alterations in the cerebellum. To evaluate the effect of new compounds for the treatment of this devastating disease, animal models are needed that closely mimic the human phenotype. The 4L/PS-NA mouse as model of Gaucher disease is shown to present reduced glucocerebrosidase activity similar to human cases but an in-depth characterization of the model was still not performed. We therefore analyzed 4L/PS-NA mice for visceral alterations, motor deficits and also neuronal changes like glucocerebrosidase activity, substrate levels and neuroinflammation. A special focus was set at pathological changes of the cerebellum. Our results show that 4L/PS-NA mice have strongly enlarged visceral organs that are infiltrated by enlarged leukocytes and macrophages. Furthermore, animals present strong motor deficits that are accompanied by increased glucosylceramide and glucosylsphingosine levels in the brain, astrocytosis and activated microglia in the cortex and hippocampus as well as reduced calbindin levels in the cerebellum. The latter was directly related to a strong Purkinje cell loss. Our results thus provide a detailed characterization of the 4L/PS-NA mouse model over age showing the translational value of the model and validating its usefulness for preclinical efficiency studies to evaluate new compounds against Gaucher disease.

Treatment of a genetic brain disease by CNS-wide microglia replacement

“…To assess the proof of concept that microglia replacement with CDMCs has therapeutic activity in the brain, we chose a genetic mouse model of a progressive neurodegenerative condition. The model contains three different genetic elements ( 43 , 44 ): (i) a homozygous D409H mutation in the Gba1 gene ( Gba1 D409H ) encoding a lysosomal enzyme glucocerebrosidase (GCase); (ii) a homozygous knockout of Prosaposin ( Psap ), which is a known cofactor of GCase; and (iii) a Psap transgene (termed PS-NA), which renders overall PSAP protein quantity below 50%. Among other potential mechanisms, the mutant Gba1 D409H and reduced PSAP protein in this mouse model cause reduced activity of GCase and accumulations of GCase substrates in tissues, and show a progressive neurodegenerative phenotype with loss of cerebellar Purkinje cells, astrogliosis, and behavioral cerebellar symptoms including progressive ataxia, waddle gait, and decreased life span ( 43 ).…”

“…In this study, we show the proof of concept that a highly efficient microglia cell replacement with CDMCs provides therapeutic benefit in mice with a progressive neurodegenerative condition. This model combines mutant Gba1 D409H and genetically reduced PSAP protein, which cause reduced GCase activity and GCase substrate accumulation and lead to pronounced CNS pathology ( 43 , 44 ). Because homozygous Gba1 D409H - mutant mice show only mild disease and the full Psap knockout is lethal, the primary genetic driver of the disease symptoms is the reduction of PSAP in this model ( 43 ).…”

Neurofilament-Light Chain as Biomarker of Neurodegenerative and Rare Diseases With High Translational Value

“…Recent results show a strong Purkinje cell loss in the cerebellar network of 4L/PS-NA mice (Schiffer et al, 2020) and thus validating previous findings that link Purkinje cell loss to saposin D deficiency (Matsuda et al, 2004) as it is caused by reduced prosapsin expression in 4L/PS-NA mice (Sun et al, 2005). Future studies will have to show, if the observed increase in plasma and CSF NF-L levels in 4L/PS-NA mice is solely initiated by the cerebellar neuronal loss or if also other brain regions are affected.…”

Targeting neuronal lysosomal dysfunction caused by β-glucocerebrosidase deficiency with an enzyme-based brain shuttle construct

“…The mice exhibit neuronal phenotypes that are similar to those in GD2 or GD3 patients, eg . decreased GCase activity and a strong accumulation of GlcCer and GlcSph in the lysosomal compartment 43 , 44 . Assuming that the pharmacokinetics in the brain in these mice also run in parallel to the blood profile, the rationale for the dosing regime was to generate high enough brain exposures to allow target engagement and so induce a clear pharmacodynamic effect on relevant markers.…”