Very-long-chain fatty acids activate lysosomal hydrolases in neonatal human skin tissue

Peroxisomal defects in microglial cells induce a disease-associated microglial signature

Microglial cells ensure essential roles in brain homeostasis. In pathological condition, microglia adopt a common signature, called disease-associated microglial (DAM) signature, characterized by the loss of homeostatic genes and the induction of disease-associated genes. In X-linked adrenoleukodystrophy (X-ALD), the most common peroxisomal disease, microglial defect has been shown to precede myelin degradation and may actively contribute to the neurodegenerative process. We previously established BV-2 microglial cell models bearing mutations in peroxisomal genes that recapitulate some of the hallmarks of the peroxisomal β-oxidation defects such as very long-chain fatty acid (VLCFA) accumulation. In these cell lines, we used RNA-sequencing and identified large-scale reprogramming for genes involved in lipid metabolism, immune response, cell signaling, lysosome and autophagy, as well as a DAM-like signature. We highlighted cholesterol accumulation in plasma membranes and observed autophagy patterns in the cell mutants. We confirmed the upregulation or downregulation at the protein level for a few selected genes that mostly corroborated our observations and clearly demonstrated increased expression and secretion of DAM proteins in the BV-2 mutant cells. In conclusion, the peroxisomal defects in microglial cells not only impact on VLCFA metabolism but also force microglial cells to adopt a pathological phenotype likely representing a key contributor to the pathogenesis of peroxisomal disorders.

Endothelial peroxisomal dysfunction and impaired pexophagy promotes oxidative damage in lipopolysaccharide-induced acute kidney injury

AIMS

We examined that (a) how the endotoxic stress affects peroxisomal function and autophagic degradation of peroxisomes-pexophagy, (b) how a superimposed dysfunction of lysosomes and pexophagy modifies responses to lipopolysaccharide (LPS), and (c) the mechanisms of peroxisomal contribution to renal injury. To accomplish this, we used lysosome-defective Lyst-mice in vivo and primary endothelial cells in vitro, and compared the responses with wild-type (WT) littermates.

RESULTS

LPS induced pexophagic degradation, followed by proliferation of peroxisomes in WT mice, which was abolished in Lyst-mice. Lyst-mice exhibited impaired activation of catalase, which together with preserved hydrogen peroxide-generating β-oxidation resulted in redox disequilibrium. LPS treatment induced a heightened inflammatory response, increased oxidative damage, and aggravated renal injury in Lyst-mice. Similarly, as in vivo, LPS-activated lysosomal (LYS) pexophagy and transiently repressed peroxisomes in vitro, supported by reduced peroxisomal density in the vicinity of lysosomes. Peroxisomal dynamics was also abolished in lysosome-defective cells, which accumulated peroxisomes with compromised functions and intraorganellar redox imbalance.

INNOVATION

We demonstrated that pexophagy is a default response to endotoxic injury. However, when LYS dysfunction (a frequent companion of chronic diseases) is superimposed, recycling and functioning of peroxisomes are impaired, and an imbalance between hydrogen peroxide-generating β-oxidation and hydrogen peroxide-detoxifying catalase ensues, which ultimately results in peroxisomal burnout.

CONCLUSION

Our data strongly suggest that pexophagy, a cellular mechanism per se, is essential in functional maintenance of peroxisomes during LPS exposure. Inhibition of pexophagy results in accumulation of impaired peroxisomes, redox disequilibrium, and aggravated renal damage.