Biology subjects

Fransen, M.

Publications and source records attributed to Fransen, M..

4 recordsLinked to original sources

bioRxiv2025

Loss of PREPL alters lipid homeostasis due to mitochondrial defects

Loss of the prolyl endopeptidase-like (PREPL) protein causes congenital myasthenic syndrome-22 (CMS22), a rare neuromuscular and metabolic disorder. PREPL belongs to the serine hydrolase superfamily, but its physiological substrates remain unknown. Based on the predicted lipid binding pocket in its crystal structure and its in vitro esterase activity, we hypothesized that PREPL might act as a lipase in vivo and directly regulate lipid metabolism. To test this, we performed unbiased lipidomics in Prepl knockout (KO) mouse brains and CRISPR-Cas9-generated KO cell lines. Across tissue and cell types, global phospholipid composition was largely unchanged, with only modest, non-significant increases in lysophospholipids, arguing against a direct role of PREPL in (lyso)phospholipid turnover. In contrast, PREPL KO HEK293T cells exhibited a significant accumulation of triacylglycerols (TAGs) and an increased number of lipid droplets, indicating a selective shift toward lipid storage. Given the central role of peroxisomes in lipid metabolism, we assessed PREPL localization and examined peroxisome number, morphology, and levels of key peroxisomal proteins. PREPL did not localize to peroxisomes, and peroxisome number and proteins levels were largely unchanged. However, KO cells displayed elongated peroxisomes, a phenotype possibly linked to mitochondrial dysfunction. Indeed, previous studies have shown that PREPL localizes to mitochondria and is required for respiratory chain activity and oxidative phosphorylation. These mitochondrial defects are predicted to impair fatty acid {beta}-oxidation and disrupt redox balance, thereby promoting TAG synthesis and lipid droplet biogenesis as adaptive responses. Overall, our findings indicate that PREPL does not act as a canonical lipase but indirectly alters lipid homeostasis through its critical role in mitochondrial function. Elevated TAG levels and altered peroxisome morphology likely represent secondary consequences of impaired mitochondrial fatty acid metabolism in PREPL-deficient cells. These results establish a mechanistic link between mitochondrial dysfunction and lipid remodeling in PREPL deficiency, providing novel insights into the metabolic pathology of CMS22.

biochemistry↗

bioRxiv2024

PEX14 acts as the interface linking optineurin to cell type-selective pexophagy

Pexophagy, the selective degradation of peroxisomes, is essential for removing excess or dysfunctional peroxisomes, and its dysregulation is linked to various diseases. Previous research has shown that optineurin (OPTN), an autophagy receptor involved in mitophagy, aggrephagy, and xenophagy, can induce pexophagy in HEK-293 cells. However, the underlying mechanism remains unclear. In this study, we used proximity labeling to identify PEX14, a peroxisomal membrane protein, as a neighboring partner of OPTN. Biochemical analyses revealed that PEX14 and OPTN interact through their respective coiled-coil and ubiquitin-binding domains. Further analyses demonstrated that the C-terminal half of overexpressed OPTN triggers pexophagy, likely by forming oligomers with endogenous OPTN. The co-localization of PEX14-OPTN complexes with LC3, combined with the suppression of OPTN-mediated peroxisome degradation by bafilomycin A1, supports a model in which PEX14 acts as a docking site for OPTN on the peroxisomal membrane, enabling the recruitment of the autophagic machinery for OPTN-mediated pexophagy. SummaryThis study uncovers and defines the peroxisomal membrane protein PEX14 as a key player in optineurin-driven pexophagy, advancing our mechanistic understanding of this cellular process. These findings open new avenues for developing therapeutic strategies targeting diseases associated with defective pexophagy.

cell biology↗

bioRxiv2021

Peroxisome-derived hydrogen peroxide can modulate the sulfenylation profiles of key redox signaling proteins

Ever since the first characterization of peroxisomes, a central theme has been their involvement in cellular hydrogen peroxide (H2O2) metabolism. While the reputation of H2O2 drastically changed from an exclusively toxic molecule to a signaling messenger, the regulatory role of peroxisomes in these signaling events is still largely underappreciated. This is mainly because the number of known protein targets of peroxisome-derived H2O2 is rather limited and testing of specific targets is predominantly based on knowledge previously gathered in related fields of research. To gain a broader and more systematic insight into the role of peroxisomes in redox signaling, an unbiased approach is urgently needed. To accomplish this goal, we have combined a previously developed cell system in which peroxisomal H2O2 production can be modulated with a yeast AP-1-like-based sulfenome mining strategy to inventory protein thiol targets of peroxisome-derived H2O2 in different subcellular compartments. Using this unbiased approach, we were able to identify specific and common targets of peroxisome-derived and exogenous H2O2 in peroxisomes, the cytosol, and mitochondria. We also observed that the sulfenylation kinetics profiles of key targets belonging to different protein families can vary considerably. In addition, we obtained compelling but indirect evidence that peroxisome-derived H2O2 may oxidize at least some of its targets through a redox relay mechanism. In conclusion, given that sulfenic acids function as key intermediates in H2O2 signaling, the findings presented in this study provide initial but critical insight into how peroxisomes may be integrated in the cellular H2O2 signaling network. HighlightsO_LIYAP1C-trapping is a robust tool to assess the peroxisomal H2O2-dependent sulfenome C_LIO_LIExogenous and peroxisome-derived H2O2 have both common and distinct targets C_LIO_LIANXA2, PRDX1, and SKP1 are major targets of peroxisome-derived H2O2 C_LIO_LIThe sulfenylation kinetics profiles of key redox-active proteins vary considerably C_LIO_LIProduction of H2O2 inside peroxisomes directly impacts the mitochondrial sulfenome C_LI

cell biology↗

bioRxiv2020

Mitochondrial fission factor (MFF) is a critical regulator of peroxisome maturation

Peroxisomes are highly dynamic subcellular compartments with important functions in lipid and ROS metabolism. Impaired peroxisomal function can lead to severe metabolic disorders with developmental defects and neurological abnormalities. Recently, a new group of disorders has been identified, characterised by defects in the membrane dynamics and division of peroxisomes rather than by loss of metabolic functions. However, the contribution of impaired peroxisome plasticity to the pathophysiology of those disorders is not well understood. Mitochondrial fission factor (MFF) is a key component of both the peroxisomal and mitochondrial division machinery. Patients with MFF deficiency present with developmental and neurological abnormalities. Peroxisomes (and mitochondria) in patient fibroblasts are highly elongated as a result of impaired organelle division. The majority of studies into MFF-deficiency have focused on mitochondrial dysfunction, but the contribution of peroxisomal alterations to the pathophysiology is largely unknown. Here, we show that MFF deficiency does not cause alterations to overall peroxisomal biochemical function. However, loss of MFF results in reduced import-competency of the peroxisomal compartment and leads to the accumulation of pre-peroxisomal membrane structures. We show that peroxisomes in MFF-deficient cells display alterations in peroxisomal redox state and intra-peroxisomal pH. Removal of elongated peroxisomes through induction of autophagic processes is not impaired. A mathematical model describing key processes involved in peroxisome dynamics sheds further light into the physical processes disturbed in MFF-deficient cells. The consequences of our findings for the pathophysiology of MFF-deficiency and related disorders with impaired peroxisome plasticity are discussed.

cell biology↗