Department of Biochemistry and Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, QC, H3G 0B1, Canada.
Published: April 2018
AI Article Synopsis
Article Abstract
Acid ceramidase (aCDase, ASAH1) hydrolyzes lysosomal membrane ceramide into sphingosine, the backbone of all sphingolipids, to regulate many cellular processes. Abnormal function of aCDase leads to Farber disease, spinal muscular atrophy with progressive myoclonic epilepsy, and is associated with Alzheimer's, diabetes, and cancer. Here, we present crystal structures of mammalian aCDases in both proenzyme and autocleaved forms. In the proenzyme, the catalytic center is buried and protected from solvent. Autocleavage triggers a conformational change exposing a hydrophobic channel leading to the active site. Substrate modeling suggests distinct catalytic mechanisms for substrate hydrolysis versus autocleavage. A hydrophobic surface surrounding the substrate binding channel appears to be a site of membrane attachment where the enzyme accepts substrates facilitated by the accessory protein, saposin-D. Structural mapping of disease mutations reveals that most would destabilize the protein fold. These results will inform the rational design of aCDase inhibitors and recombinant aCDase for disease therapeutics.
Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of chronic liver conditions, ranging from simple steatosis to nonalcoholic steatohepatitis, which may progress to fibrosis/cirrhosis. Here, the GSE163211 data set was analyzed, and Asah1 (encoding acid ceramidase) was identified as a crucial lysosomal gene that positively correlated with NAFLD stages in obese patients. To evaluate the role of Asah1 in the progression of NAFLD, Asah1/Alb mice (hepatocyte-specific deletion of Asah1) and Asah1 floxed (Asah1/wild-type) mice were fed with either a normal diet or a high-fat, high-cholesterol paigen diet (PD) for 20 weeks.
Farber disease (FD) is an ultra-rare, autosomal-recessive, lysosomal storage disorder attributed to ASAH1 gene mutations. FD is characterized by acid ceramidase (ACDase) deficiency and the accumulation of ceramide in various tissues. Classical FD patients typically manifest symptoms including lipogranulomatosis, respiratory complications, and neurological deficits, often leading to mortality during infancy.
Sphingolipids like ceramides play a significant role in high-fat diets and can influence fatty acid oxidation and intestinal stem cell (ISC) proliferation, potentially leading to cancer risk.
The study manipulated the ceramide synthesis pathway in midgut intestinal cells to observe how changes in enzyme activities impacted cell behavior, revealing significant alterations in ISC proliferation and cell characteristics.
Findings suggest that increased levels of saturated sphingolipids trigger inflammation in the gut, which in turn stimulates ISC proliferation through specific pro-inflammatory signals.
Multiple myeloma (MM) patients are often refractory to targeted therapies including proteasome inhibitors (PIs). Here, analysis of RNA sequencing data derived from 672 patients with newly diagnosed or relapsed/refractory disease identified the acid ceramidase, ASAH1, as a key regulator of PI resistance. Genetic or pharmacological blockade of ASAH1 remarkably restored PI sensitivity and protected mice from resistant MM progression in vivo.
