Mitochondrial fatty acid oxidation dysfunction impairs autophagic flux through ATP deficiency-caused lysosomal pH abnormity

Autophagy, a pivotal lysosomal degradation process, plays crucial roles in cellular homeostasis and energy metabolism. Mitochondrial fatty acid oxidation (FAO), a key mitochondrial function, is crucial for energy production. Generally, mitochondrial dysfunction exerts negative effects on autophagy, but the regulatory role of mitochondrial FAO dysfunction on the autophagic process remains unclear. The present study aimed to elucidate the role and mechanism of mitochondrial FAO in regulating autophagy process. We used Nile tilapia (Oreochromis niloticus) as a model and inhibited mitochondrial FAO by dietary mildronate feeding or knocking down carnitine palmitoyl transferase 1a. We found that mitochondrial FAO inhibition enhanced autophagy initiation and lysosomal proliferation accompanied by decreased autophagy degradation activity due to lysosomal acidification abnormity. Moreover, mitochondrial FAO inhibition decreased adenosine triphosphate (ATP) production and elevated adenosine monophosphate (AMP)/ATP promoted autophagy initiation via the AMP-activated protein kinase‑serine/threonine kinase 1 pathway. Furthermore, mitochondrial FAO inhibition upregulated peroxisome proliferator-activated receptor alpha and retinoid X receptor alpha protein expression, which promoted transcription factor EB mRNA and its protein expression. Meanwhile, mitochondrial FAO inhibition led to lysosomal alkalinization, which is due to a pH increase caused by v-ATPase V1/V0 imbalance and ATP deficiency from mitochondrial dysfunction. Collectively, our results highlight the role of mitochondrial FAO in maintaining lysosomal homeostasis and autophagic flux through stabilizing lysosomal acidification.