Insights into the intramembrane protease SPPL2b and its substrates: Functions and disease implications

Abstract

Specialized intramembrane proteases, known as iCLiPs, regulate the processing of transmembrane proteins by releasing intracellular domains, which can function as transcriptional regulators. The signal peptide peptidase–like (SPPL) family of iCLiPs, particularly SPPL2b, has roles in immune regulation, neuronal function, and disease pathogenesis. In the brain, SPPL2b localizes mainly in the plasma membrane of neurons and microglia and is abundant in the cortex and hippocampus. Its known substrates regulate neuronal growth, inflammation, and synaptic function, and increased amounts of SPPL2b have been found in postmortem brain tissue from patients with Alzheimer’s disease. In this review, we discuss the currently known roles of SPPL2b, its substrates, and its disease implications. Understanding the downstream effects of SPPL2b-cleaved substrates will provide clearer insights into the impact of SPPL2b on cellular homeostasis and disease, potentially leading to new therapeutic strategies.