MicroRNAs, small noncoding RNAs, not only regulate gene expression at the post-transcriptional level in a variety of physiological processes but also accompany the initiation and progression of a vast number of diseases, including dementia. While miR-125b has been shown to be aberrantly expressed in some dementia patients, its role in the pathological process remains ambiguous. Presenilin-1/2 conditional double knockout mice exhibit a range of symptoms, including impaired cognition and memory, increased tau phosphorylation, neuroinflammation, and apoptosis, and are therefore regarded as a useful dementia model. In the prefrontal cortices of double knockout mice, miR-125b was found to be abnormally increased in an age-dependent manner. We further verified the neural cell adhesion molecule (NCAM) as an miR-125b target using the dual luciferase reporter assay. The NCAM protein level was decreased when miR-125b was overexpressed (OE) in neuronal growth factor-induced differentiated PC12 cells, which further inhibited the neuronal growth factor-induced phosphorylation of glycogen synthase kinase 3 beta (GSK beta) at the Ser9 site and ultimately increased the GSK3 beta activity and tau phosphorylation. Moreover, on serum deprivation, high GSK3 beta activity in differentiated miR-125b-OE PC12 cells induced increased caspase-3 activation. Finally, adeno-associated virus-mediated miR-125b overexpression in the prefrontal cortexes of wild-type C57B/L6 mice resulted in decreased dendritic spine density. In addition, similar to the in vitro data, elevated GSK3 beta activity and hyperphosphorylation of the tau protein were confirmed. Taken together, our findings reveal a direct regulation of miR-125b on NCAM, which leads to further effects on downstream GSK3 beta activity and tau phosphorylation and may contribute to the generation of neurofibrillary tangles in neuropathological progression. (C) 2018 Elsevier Inc. All rights reserved.

GSK3β regulates some functions of the brain, but the mechanisms involved in the maintenance of GSK3β protein stability remain ambiguous. REGγ, an important proteasome activator for ubiquitin-independent protein degradation, has been shown to degrade certain intact proteins and is involved in the regulation of important biological processes. Here we demonstrate that REGγ promotes the degradation of GSK3β protein in vitro and in vivo. With increased GSK3β activity, REGγ knockout (REGγ−/−) mice exhibit late-onset sensorimotor gating and cognitive deficiencies including decreased working memory, hyperlocomotion, increased stereotype, defective prepulse inhibition (PPI), and disability in nest building, at the age of 8 months or older. Inhibition of GSK3β rescued the compromised PPI phenotypes and working memory deficiency in the knockout mice. Also, we found an age-dependent decrease in the trypsin-like proteasomal activity in REGγ−/− mice brains, which may be reflective of a lack of degradation of GSK3β. Collectively, our findings reveal a novel regulatory pathway in which the REGγ-proteasome controls the steady-state level of GSK3β protein. Dysfunction in this non-canonical proteasome degradation pathway may contribute to the sensorimotor gating deficiency and cognitive disorders in aging mice.

GSK3 β regulates some functions of the brain, but the mechanisms involved in the maintenance of GSK3 β protein stability remain ambiguous. REG γ , an important proteasome activator for ubiquitin-independent protein degradation, has been shown to degrade certain intact proteins and is involved in the regulation of important biological processes. Here we demonstrate that REG γ promotes the degradation of GSK3 β protein in vitro and in vivo . With increased GSK3 β activity, REG γ knockout (REG γ −/−) mice exhibit late-onset sensorimotor gating and cognitive deficiencies including decreased working memory, hyperlocomotion, increased stereotype, defective prepulse inhibition (PPI), and disability in nest building, at the age of 8 months or older. Inhibition of GSK3 β rescued the compromised PPI phenotypes and working memory deficiency in the knockout mice. Also, we found an age-dependent decrease in the trypsin-like proteasomal activity in REG γ −/− mice brains, which may be reflective of a lack of degradation of GSK3 β . Collectively, our findings reveal a novel regulatory pathway in which the REG γ -proteasome controls the steady-state level of GSK3 β protein. Dysfunction in this non-canonical proteasome degradation pathway may contribute to the sensorimotor gating deficiency and cognitive disorders in aging mice.