Functional assessment of homozygous ALDH18A1 variants reveals alterations in amino acid and antioxidant metabolism

Abstract

Mono- and biallelic variants in ALDH18A1 cause a spectrum of human disorders associated with cutaneous and neurological findings that overlap with both cutis laxa and spastic paraplegia. ALDH18A1 encodes the bifunctional enzyme pyrroline-5-carboxylate synthetase (P5CS) that plays a role in the de novo biosynthesis of proline and ornithine. Here we characterize a previously unreported homozygous ALDH18A1 variant (p.Thr331Pro) in four affected probands from two unrelated families, and demonstrate broad-based alterations in amino acid and antioxidant metabolism. These four patients exhibit variable developmental delay, neurological deficits, and loose skin. Functional characterization of the p.Thr331Pro variant demonstrated a lack of any impact on the steady-state level of the P5CS monomer or mitochondrial localization of the enzyme, but reduced incorporation of the monomer into P5CS oligomers. Using an unlabeled NMR-based metabolomics approach in patient fibroblasts and ALDH18A1-null human embryonic kidney cells expressing the variant P5CS, we identified reduced abundance of glutamate and several metabolites derived from glutamate, including proline and glutathione. Biosynthesis of the polyamine putrescine, derived from ornithine, was also decreased in patient fibroblasts, highlighting the functional consequence on another metabolic pathway involved in antioxidant responses in the cell. RNA sequencing of patient fibroblasts revealed transcript abundance changes in several metabolic and ECM-related genes, adding further insight into pathogenic processes associated with impaired P5CS function. Together these findings shed new light on amino acid and antioxidant pathways associated with ALDH18A1-related disorders, and underscore the value of metabolomic and transcriptomic profiling to discover new pathways that impact disease pathogenesis.

Translation Fidelity and Respiration Deficits in CLPP-Deficient Tissues: Mechanistic Insights from Mitochondrial Complexome Profiling

“…As expected, as a consequence of the gain-of-function of CLPX and PLP, their established target ALAS2 as a rate-limiting enzyme of porphyrin/heme biosynthesis in most tissues showed massive accumulation. Strong accumulation, dispersion, and co-migration with CLPX were also apparent for the PLPdependent enzyme OAT, and similar accumulation also concerned the enzyme ALDH18A1, as previously reported in global proteome profiles [56,96]. Both factors have connected pathway functions in the interconversion of amino acids such as proline, glutamate, and arginine.…”

Translation fidelity and respiration deficits in CLPP-deficient tissues: Mechanistic insights from mitochondrial complexome

“…As expected consequence of the gain-of-function of CLPX and the PLP, their established target ALAS2 as ratelimiting enzyme of porphyrin/heme biosynthesis in most tissues showed massive accumulation. Strong accumulation, dispersion and comigration with CLPX was apparent also for the PLP-dependent enzyme OAT, and similar accumulation concerned also the enzyme ALDH18A1, as previously reported in global proteome profiles [56,104]. Both factors play connected pathway functions in the interconversion of amino acids such as proline, glutamate and arginine.…”

Carnosol ameliorated cancer cachexia-associated myotube atrophy by targeting P5CS and its downstream pathways

“…The most important roles it plays are catalyzing the reduction conversion and coupled phosphorylation and synthesizing proline from glutamate (Guo et al, 2020;Kalmar et al, 2021;Pickwick et al, 2022). Furthermore, a recent study conducting a functional assessment of homozygous P5CS variants revealed alterations in amino acid and antioxidant metabolism (Colonna et al, 2023), which further supported the important role of P5CS in regulating the antioxidant system. Interestingly, derangements of amino acids in cachectic skeletal muscle such as significantly reduced quantities of glutamate were observed in both cancer cachexia animals as well as human cancer cachexia patients (Kunzke et al, 2020).…”

“…P5CS (Aldh18a1) is linked to antioxidant function and amino acid metabolism. The P5CS (Aldh18a1) regulates glutamate replenishment, which affects the metabolism of glutamine and glutathione (Colonna et al, 2023). When glutamate-cysteine ligase is overused, it can result in a glutamate shortage, which interference the synthesis of amino acids, including ornithine and proline.…”