Nonalcoholic Steatohepatitis Modulates Membrane Protein Retrieval and Insertion Processes

Area of Science:

• Hepatology
• Cell Biology
• Pharmacology

Background:

• Interindividual variability in drug response is a challenge in nonalcoholic steatohepatitis (NASH).
• Mislocalization of the drug transporter multidrug resistance-associated protein 2 (MRP2) from the canalicular membrane contributes to altered drug transport in NASH.
• The precise mechanisms driving MRP2 mislocalization remain unclear, but enhanced membrane retrieval processes are suspected.

Purpose of the Study:

• To investigate the activation status of mediators involved in membrane protein retrieval and insertion in a rodent model of NASH.
• To identify specific cellular processes contributing to the mislocalization of membrane proteins, such as MRP2, in NASH pathogenesis.

Main Methods:

• Rodent methionine and choline-deficient (MCD) diet-induced NASH model was utilized.
• Expression, phosphorylation, and membrane translocation of key mediators (protein kinases PKA, PKCα, PKCδ, PKCε; substrates radixin, myristoylated alanine-rich C-kinase substrate, Rab11) were measured.
• Comparisons were made between control and NASH rat groups.

Main Results:

• Several mediators showed altered activation in NASH rats compared to controls.
• NASH rats displayed decreased radixin phosphorylation and increased membrane localization of PKCδ and PKCε, suggesting enhanced membrane retrieval.
• Altered activation of PKCδ, PKA, and PKCα was observed, potentially impairing Rab11-mediated Mrp2 insertion.

Conclusions:

• Nonalcoholic steatohepatitis is associated with altered activation of mediators regulating membrane protein dynamics.
• Changes in membrane retrieval and insertion processes likely contribute to the mislocalization of membrane proteins, including drug transporters, in NASH.
• These findings provide insights into the mechanisms underlying drug response variability in NASH.