An overview of combined D-2-and L-2-hydroxyglutaric aciduria: functional analysis of CIC variants
JOURNAL OF INHERITED METABOLIC DISEASE
Authors: Pop, Ana; Williams, Monique; Struys, Eduard A.; Monne, Magnus; Jansen, Erwin E. W.; De Grassi, Anna; Kanhai, Warsha A.; Scarcia, Pasquale; Ojed, Matilde R. Fernandez; Porcelli, Vito; van Dooren, Silvy J. M.; Lennertz, Pascal; Nota, Benjamin; Abdenur, Jose E.; Coman, David; Das, Anibh Martin; El-Gharbawy, Areeg; Nuoffer, Jean-Marc; Polic, Branka; Santer, Rene; Weinhold, Natalie; Zuccarelli, Britton; Palmieri, Ferdinando; Palmieri, Luigi; Salomons, Gajja S.
Abstract
Combined D-2- and L-2-hydroxyglutaric aciduria (D/L-2-HGA) is a devastating neurometabolic disorder, usually lethal in the first years of life. Autosomal recessive mutations in the SLC25A1 gene, which encodes the mitochondrial citrate carrier (CIC), were previously detected in patients affected with combined D/L-2-HGA. We showed that transfection of deficient fibroblasts with wild-type SLC25A1 restored citrate efflux and decreased intracellular 2-hydroxyglutarate levels, confirming that deficient CIC is the cause of D/L-2-HGA. We developed and implemented a functional assay and applied it to all 17 missense variants detected in a total of 26 CIC-deficient patients, including eight novel cases, showing reduced activities of varying degrees. In addition, we analyzed the importance of residues affected by these missense variants using our existing scoring system. This allowed not only a clinical and biochemical overview of the D/L-2-HGA patients but also phenotype-genotype correlation studies.
A Network of SLC and ABC Transporter and DME Genes Involved in Remote Sensing and Signaling in the Gut-Liver-Kidney Axis
SCIENTIFIC REPORTS
Authors: Rosenthal, Sara Brin; Bush, Kevin T.; Nigam, Sanjay K.
Abstract
Genes central to drug absorption, distribution, metabolism and elimination (ADME) also regulate numerous endogenous molecules. The Remote Sensing and Signaling Hypothesis argues that an ADME gene-centered network-including SLC and ABC "drug" transporters, "drug" metabolizing enzymes (DMEs), and regulatory genes-is essential for inter-organ communication via metabolites, signaling molecules, antioxidants, gut microbiome products, uremic solutes, and uremic toxins. By cross-tissue co-expression network analysis, the gut, liver, and kidney (GLK) formed highly connected tissue-specific clusters of SLC transporters, ABC transporters, and DMEs. SLC22, SLC25 and SLC35 families were network hubs, having more inter-organ and intra-organ connections than other families. Analysis of the GLK network revealed key physiological pathways (e.g., involving bile acids and uric acid). A search for additional genes interacting with the network identified HNF4 alpha, HNF1 alpha, and PXR. Knockout gene expression data confirmed similar to 60-70% of predictions of ADME gene regulation by these transcription factors. Using the GLK network and known ADME genes, we built a tentative gut-liver-kidney "remote sensing and signaling network" consisting of SLC and ABC transporters, as well as DMEs and regulatory proteins. Together with protein-protein interactions to prioritize likely functional connections, this network suggests how multi-specificity combines with oligo-specificity and mono-specificity to regulate homeostasis of numerous endogenous small molecules.