Physiopathological Bases of the Disease Caused by HACE1 Mutations: Alterations in Autophagy, Mitophagy and Oxidative Stress Response.

Olatz Ugarteburu,Olatz Ugarteburu,Olatz Ugarteburu,Frederic Tort,Judit García-Villoria,Julio Ramos,Judit García-Villoria,Judit García-Villoria,Antonia Ribes,Marta Sánchez-Vilés,Tamara Barcos-Rodríguez,Frederic Tort,Frederic Tort,Marta Sánchez-Vilés,Tamara Barcos-Rodríguez,Gloria Garrabou,Marta Sánchez-Vilés

doi:10.3390/jcm9040913

Abstract

Recessive HACE1 mutations are associated with a severe neurodevelopmental disorder (OMIM: 616756). However, the physiopathologycal bases of the disease are yet to be completely clarified. Whole-exome sequencing identified homozygous HACE1 mutations (c.240C>A, p.Cys80Ter) in a patient with brain atrophy, psychomotor retardation and 3-methylglutaconic aciduria, a biomarker of mitochondrial dysfunction. To elucidate the pathomechanisms underlying HACE1 deficiency, a comprehensive molecular analysis was performed in patient fibroblasts. Western Blot demonstrated the deleterious effect of the mutation, as the complete absence of HACE1 protein was observed. Immunofluorescence studies showed an increased number of LC3 puncta together with the normal initiation of the autophagic cascade, indicating a reduction in the autophagic flux. Oxidative stress response was also impaired in HACE1 fibroblasts, as shown by the reduced NQO1 and Hmox1 mRNA levels observed in H2O2-treated cells. High levels of lipid peroxidation, consistent with accumulated oxidative damage, were also detected. Although the patient phenotype could resemble a mitochondrial defect, the analysis of the mitochondrial function showed no major abnormalities. However, an important increase in mitochondrial oxidative stress markers and a strong reduction in the mitophagic flux were observed, suggesting that the recycling of damaged mitochondria might be targeted in HACE1 cells. In summary, we demonstrate for the first time that the impairment of autophagy, mitophagy and oxidative damage response might be involved in the pathogenesis of HACE1 deficiency.

Highlights

HACE1 (MIM#610876) encodes for a HECT domain and ankyrin repeat-containing ubiquitin ligase which is reported to be involved in tagging specific target proteins for subcellular localization or for degradation [1]
This research showed that elevated levels of the Ras-related C3 botulinum toxin substrate 1 protein (RAC1), a well-known target of HACE1, were found in HACE1-knockout mice as well as in patient cells, hypothesizing that altered RAC1 signalling might contribute to the pathogenesis of the disorder [13,14]
We report a patient carrying HACE1 mutations presenting with psychomotor retardation, brain atrophy and high urinary excretion of 3-methylglutaconic acid (3-MGA), a well-established biomarker of mitochondrial dysfunction [19]

Summary

Introduction

HACE1 (MIM#610876) encodes for a HECT domain and ankyrin repeat-containing ubiquitin ligase which is reported to be involved in tagging specific target proteins for subcellular localization or for degradation [1]. This protein is a potential tumor suppressor, as it has been shown to be downregulated in many human tumors [2,3]. The role of RAC1 in the physiopathology of HACE1 deficiency is supported by the fact that this protein is involved in brain development and in the regulation of reactive oxygen species (ROS) levels [6,15,16,17]. The fact that HACE1 has multiple substrates which participate in different fundamental biological processes suggest that mechanisms other than RAC1 upregulation may be to blame for this disorder [18]

Results

Discussion

Conclusion