Ecytonucleospora hepatopenaei causes lipid droplet depletion and imbalanced lipid metabolism in Penaeus vannamei.

Ecytonucleospora hepatopenaei (EHP) infection in Penaeus vannamei causes significant economic losses in shrimp aquaculture due to growth retardation. Unable to generate ATP, EHP obligately relies on host energy production to survive. We hypothesize that EHP may potentially disrupt its host's lipid metabolism as lipid is the most energy-dense resource. To this end, the effects of EHP infection on lipid metabolism were investigated by evaluating activities and expressions of digestive enzymes, accumulation of lipid droplets, and expression of genes involved in lipid breakdown and synthesis. Results revealed that EHP infection progressively diminished digestive enzyme activities, leading to reduced nutrient availability. A persistent reduction of lipid droplet accumulation was detected from the onset of EHP infection. The marked decrease in the early stages was attributable to increased lipid droplet breakdown outpacing lipid synthesis. In the later stage, a partial recovery of lipid synthesis gene expression was observed; however, this was insufficient to counteract increased lipid breakdown, as genes in this pathway were upregulated. Ultimately, this imbalance resulted in a marked depletion of lipid droplets. These findings highlight how EHP infection chronically impairs digestion, drains lipid reservoir of its host and, eventually, retards growth. In terms of a potential practical solution, this study implies that dietary lipid supplementation might alleviate the metabolic disruption of EHP and, thereby, lessen the extent of growth retardation in infected population.