Enhanced Proteostasis in Post-ischemic Stroke Mouse Brains by Ubiquilin-1 Promotes Functional Recovery

Abstract

Stroke is pathologically associated with oxidative stress, protein damage, and neuronal loss. We previously reported that overexpression of a ubiquitin-like protein, ubiquilin-1 (Ubqln), protects neurons against ischemia-caused brain injury, while knockout of the gene exacerbates cerebral ischemia-caused neuronal damage and delays functional recovery. Although these observations indicate that Ubqln is a potential therapeutic target, transgenic manipulation-caused overexpression of Ubqln occurs before the event of ischemic stroke, and it remains unknown whether delayed Ubqln overexpression in post-ischemic brains within a clinically relevant time frame is still beneficial. To address this question, we generated lentiviruses either overexpressing or knocking down mouse Ubqln, and treated post-ischemic stroke mice 6 h following the middle cerebral artery occlusion with the lentiviruses before animal behaviors were evaluated at day 1, 3, 5, and 7. Our data indicate that post-ischemic overexpression of Ubqln significantly promoted functional recovery, whereas post-ischemic downregulation of Ubqln expression delays functional recovery. To further understand the mechanisms underlying how Ubqln functions, we also isolated protein aggregates from the brains of wild-type mice or the mice overexpressing Ubqln following ischemia/reperfusion. Western blot analysis indicates that overexpression of Ubqln significantly reduced the accumulation of protein aggregates. These observations not only suggest that Ubqln is a useful candidate for therapeutic intervention for ischemic stroke but also highlight the significance of proteostasis in functional recovery following stroke.

Overexpression of UBQLN1 reduces neuropathology in the P497S UBQLN2 mouse model of ALS/FTD

“…These improvements are consistent with the role UBQLN1 proteins are known to play in maintaining protein quality control, by facilitating proteasomal degradation, autophagy and ERAD [16,21,25,32,33]. This improvement is also similar to the benefits found upon overexpression of UBQLN1 in other mouse models of neurodegeneration [1,17,18,26].…”

Peripherally expressed misfolded proteins remotely disrupt brain function and aggravate stroke-induced brain injury

“…Isolation of Triton X-100 insoluble protein aggregates from Ntg or CryAB R120G mouse brains were according to previously described methods 10, 45 . Examination of isolated protein aggregates with SEM was performed with the field emission SEM (SIGMA, Zeiss).…”

“…Following cerebral ischemia and reperfusion (I/R), mitochondria dysfunction, glutamate-induced excitotoxicity, and neuroinflammation occurs, leading to oxidative stress, protein damage and aggregation 7, 8 . Proteostasis has been shown to play an important role in neuronal injury and functional recovery following I/R 9, 10 . However, very little is known about the impact of peripherally impaired proteostasis on ischemic stroke-induced brain injury and functional recovery.…”

The Role of Ubiquitin-Proteasome Pathway and Autophagy-Lysosome Pathway in Cerebral Ischemia

“…Ubqln, a ubiquitin-like protein, mediates degradation of damaged proteins. Ubqln overexpression greatly inhibited the accumulation of protein aggregates and conferred neuroprotection against ischemia-induced cerebral injury [17]. Overexpression of Ubqln also protected mice from ischemic stroke and oxidative stress-caused neuronal injury, which was mediated by facilitating removal of misfolded proteins [18] (Figure 1).…”