Systematic Review and Meta-Analyses of Aminopeptidases as Prognostic Biomarkers in Amyotrophic Lateral Sclerosis

Abstract

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive loss of motor neurons in the spinal cord, brain stem, and cerebral cortex. Biomarkers for ALS are essential for disease detection and to provide information on potential therapeutic targets. Aminopeptidases catalyze the cleavage of amino acids from the amino terminus of protein or substrates such as neuropeptides. Since certain aminopeptidases are known to increase the risk of neurodegeneration, such mechanisms may reveal new targets to determine their association with ALS risk and their interest as a diagnostic biomarker. The authors performed a systematic review and meta-analyses of genome-wide association studies (GWASs) to identify reported aminopeptidases genetic loci associated with the risk of ALS. PubMed, Scopus, CINAHL, ISI Web of Science, ProQuest, LILACS, and Cochrane databases were searched to retrieve eligible studies in English or Spanish, published up to 27 January 2023. A total of 16 studies were included in this systematic review, where a series of aminopeptidases could be related to ALS and could be promising biomarkers (DPP1, DPP2, DPP4, LeuAP, pGluAP, and PSA/NPEPPS). The literature reported the association of single-nucleotide polymorphisms (SNPs: rs10260404 and rs17174381) with the risk of ALS. The genetic variation rs10260404 in the DPP6 gene was identified to be highly associated with ALS susceptibility, but meta-analyses of genotypes in five studies in a matched cohort of different ancestry (1873 cases and 1861 control subjects) showed no ALS risk association. Meta-analyses of eight studies for minor allele frequency (MAF) also found no ALS association for the "C" allele. The systematic review identified aminopeptidases as possible biomarkers. However, the meta-analyses for rs1060404 of DPP6 do not show a risk associated with ALS.

Keywords: aminopeptidase; amyotrophic lateral sclerosis; biomarker.

Figure 1

Flow chart of study selection for meta-analyses.

Figure 2

Forest plots reported no significant associations between single-nucleotide polymorphisms (SNP rs10260404) and risk of genotype for sporadic amyotrophic lateral sclerosis (SALS) from meta-analyses. The square size indicates the weight of each study and pooled data, together odds ratio and 95% confidence interval for the difference between control and cases with CC (A), CT (B), and TT genotype (C) between the SALS group and control group [38,41,46,47,48].

Figure 3

Forest plots reported no significant associations between single-nucleotide polymorphisms (SNP rs10260404) and risk of allele (C > T) of sporadic amyotrophic lateral sclerosis (SALS) from meta-analyses. Despite not being significant, the C allele points to a marked ALS risk (A) compared to the T allele (B). The square size indicates the weight of each study and pooled data, together with odds ratio and 95% confidence interval Odds ratio meta-analyses for the difference between alleles from control and SALS cases [21,29,30,38,41,46,47,48].

Figure 4

Schematic diagram summarizing (A) the most representative results of aminopeptidases found in studies of patients with early and advanced stage amyotrophic lateral sclerosis. The need to use aminopeptidases as pre-diagnosis markers hypothesize the early possibility of detecting the disease before manifesting neurodegenerative motor symptoms (result forecast). The aminopeptidase DPP6 (B) binds to voltage-gated potassium channels (Kv4.2), but variations in the expression of the DPP6 gene alter the biological functions of the potassium channel, causing motor neuron hyperexcitability. Schematic representation (C) of the deregulation of aminopeptidases that manifest in neurodegenerative diseases (amyotrophic lateral sclerosis, Alzheimer’s disease, Parkinson’s, Huntington’s) with common metabolic processes. The similarity in these processes can become an advantage, and aminopeptidases can be used as a diagnostic tool for the detection of multiple neurodegenerative pathologies. DPP4 is involved in collagen remodeling, but it is also involved in amyloid beta plaque degradation along with IRAP, leading to memory problems (green arrows). The overactivation of the renin-angiotensin system (red curved arrow) contributes to a high production of Ang-II, leading to neurodegeneration due to the release of glutamate and causing ROS by oxidative stress (orange dotted arrow); all of them are factors associated with metabolic syndrome. APA allows the conversion of Ang-II to Ang-III. In ALS patients, the neuroprotective enzyme PSA/NPEPPS is reduced, known to hydrolyze misfolded and aggregated proteins (such as mutated SOD1 and hyperphosphorylated tau) that cause mitochondrial, Golgi apparatus, and nuclear damage. Genetic variants of the DPP6 gene (SNP rs10260404) reduce potassium leakage in Kv4.2 potassium channels (red dotted arrow). ADA: adenosine deaminase; ALS: amyotrophic lateral sclerosis; APA: aminopeptidase A; Ang-II: angiotensin II; Ang-III: angiotensin III; Aβ or β: amyloid-β plaques; DPP2: dipeptidyl peptidase II; DPP4: dipeptidyl peptidase IV; DPP6: dipeptidyl peptidase VI; GluAP: glutamyl aminopeptidase; IRAP: insulin-regulated aminopeptidase activity; LeuAP: leucine aminopeptidase; K⁺: potassium ion; KChIPs: potassium channel-interacting proteins; N.d.: Not determined; NFTs: neurofibrillary tangle; pGluAP: pyroglutamyl-aminopeptidase; PSA/NPEPPS: puromycin-sensitive aminopeptidase; ROS: reactive oxygen species; SNP: single-nucleotide polymorphisms; SOD1: superoxide dismutase 1. The symbol of the scissors represents the hydrolytic activity of aminopeptidase, which cleaves amino acids from the amino terminals (NH₂).