Aging-associated REGγ proteasome decline predisposes to tauopathy.

The REGγ-20S proteasome is an ubiquitin- and ATP-independent degradation system, targeting selective substrates, possibly helping to regulate aging. The studies we report here demonstrate that aging-associated REGγ decline predisposes to decreasing tau turnover, as in a tauopathy. The REGγ proteasome promotes degradation of human and mouse tau, notably phosphorylated tau and toxic tau oligomers that shuttle between the cytoplasm and nuclei. REGγ-mediated proteasomal degradation of tau was validated in 3- to 12-month-old REGγ KO mice, REGγ KO;PS19 mice, and PS19 mice with forebrain conditional neuron-specific overexpression of REGγ (REGγ OE) and behavioral abnormalities. Coupled with tau accumulation, we found with REGγ-deficiency, neuron loss, dendrite reduction, tau filament accumulation, and microglial activation are much more prominent in the REGγ KO;PS19 than the PS19 model. Moreover, we observed that the degenerative neuronal lesions and aberrant behaviors were alleviated in REGγ OE;PS19 mice. Memory and other behavior analysis substantiate the role of REGγ in prevention of tauopathy-like symptoms. In addition, we investigated the potential mechanism underlying aging-related REGγ decline. This study provides valuable insights into the novel regulatory mechanisms and potential therapeutic targets for tau-related neurodegenerative diseases.

Reciprocal REGγ-Nrf2 Regulation Promotes Long Period ROS Scavenging in Oxidative Stress-Induced Cell Aging.

Increased accumulation of reactive oxygen species (ROS) and decline of adaptive response of antioxidants to oxidative stimuli has been implicated in the aging process. Nuclear factor erythroid 2-related factor 2 (Nrf2) activation is a core event in attenuating oxidative stress-associated aging. The activity is modulated by a more complex regulatory network. In this study, we demonstrate the proteasome activator REGγ function as a new regulator of Nrf2 activity upon oxidative stress in cell aging model induced by hydrogen peroxide (H2O2). REGγ deficiency promotes cell senescence in primary MEF cells after H2O2 treatment. Accordingly, ROS scavenging is accelerated in WT cells but blunted in REGγ lacking cells during 12-hour recovery from a 1-hour H2O2 treatment, indicating long-lasting antioxidant buffering capacity of REGγ. Mechanistically, through GSK-3ß inhibition, REGγ enhances the nuclear distribution and transcriptional activity of Nrf2, which is surveyed by induction of phase II enzymes including Ho1 and Nqo1. Meanwhile, Nrf2 mediates the transcriptional activation of REGγ upon H2O2 stimulation. More interestingly, short-term exposure to H2O2 leads to transiently upregulation and gradually descent of REGγ transcription, however sustained higher REGγ protein level even in the absence of H2O2 for 24 hours. Thus, our results establish a positive feedback loop between REGγ and Nrf2 and a new layer of adaptive response after oxidative stimulation that is the REGγ-GSK-3ß-Nrf2 pathway.