UBQLN2 regulation of α- synuclein in synucleinopathies

Abstract

BackgroundThe protein quality control protein ubiquilin- 2 (UBQLN2) is implicated in synucleinopathies due to its accumulation in Lewy body diseases. However, little is known about how it may interact with and clear α- synuclein (α- syn). This study aimed to define the role of UBQLN2 in handling α- syn.MethodTo evaluate whether UBQLN2 regulates α- syn, we measured levels of α- synuclein in HEK- 293 cells transiently expressing or deleted of UBQLN2. To evaluate whether UBQLN2 regulates α- syn clearance in the nervous system in vivo, we used western blot to measure total α- syn or phosphorylated human α- syn (pS129) levels in multiple transgenic mouse lines including: UBQLN2 overexpressing mice (Ub2- hi), UBQLN2 knock- out mice (Ub2- KO), and A53T α- syn mice crossed to either Ub2- hi or Ub2- KO mice. To assess changes in UBQLN2 solubility in synucleinopathies we measured levels of UBQLN2 by Western blot in PBS- soluble versus sarkosyl- soluble brain lysates from PD and LBD human brains and from A53T mouse brains.ResultIn vitro, UBQLN2 significantly decreased levels of soluble α- syn. In vivo, endogenous insoluble α- syn levels are decreased in Ub2- hi mice, while total endogenous α- syn levels are significantly increased in Ub2- KO mice. Total α- syn and pS129 levels were unchanged in A53TxUb2- hi mice versus A53T controls, but were significantly increased in A53TxUb2- KO mice. Solubility studies revealed increased insoluble UBQLN2 levels in human LBD and mouse A53T brains.ConclusionWhile UBQLN2 is known to colocalize with a- syn in disease, our results support a functional role for UBQLN2 in regulating α- syn levels. Further, we show that UBQLN2 solubility is altered in synucleinopathies. In disease, a change in UBQLN2 solubility may indicate a loss of its ability to handle a- syn, contributing to a- syn toxicity. Ongoing studies seek to elucidate the mechanism by which UBQLN2 handles, and potentially clears, α- syn.