Localization and Expression of Sirtuins 1, 2, 6 and Plasticity-Related Proteins in the Recovery Period after a Photothrombotic Stroke in Mice

Abstract

Sirtuins, class III histone deacetylases, are involved in the regulation of tissue repair processes and brain functions after a stroke. The ability of some isoforms of sirtuins to circulate between the nucleus and cytoplasm may have various pathophysiological effects on the cells. In present work, we focused on the role of non-mitochondrial sirtuins SIRT1, SIRT2, and SIRT6 in the restoration of brain cells following ischemic stroke. Here, using a photothrombotic stroke (PTS) model in mice, we studied whether local stroke affects the level and intracellular localization of SIRT1, SIRT2, and SIRT6 in neurons and astrocytes of the intact cerebral cortex adjacent to the ischemic ipsilateral hemisphere and in the analogous region of the contralateral hemisphere at different time points during the recovery period after a stroke. We evaluated the co-localization of sirtuins with growth-associated protein-43 (GAP-43), the presynaptic marker synaptophysin (SYN) and acetylated α-tubulin (Ac-α-Tub), that are associated with brain plasticity and are known to be involved in brain repair after a stroke. The results show that during the recovery period, an increase in SIRT1 and SIRT2 levels occurred. The increase of SIRT1 level was associated with an increase in synaptic plasticity proteins, whereas the increase of SIRT2 level was associated with an acetylated of α-tubulin, that can reduce the mobility of neurites. SIRT6 co-localized with GAP-43, but not with SYN. Moreover, we showed that SIRT1, SIRT2, and SIRT6 are not involved in the PTS-induced apoptosis of penumbra cells. Taken together, our results suggest that sirtuins functions differ depending on cell type, intracellular localization, specificity of sirtuins isoforms to different substrates and nature of post-translational modifications of enzymes.

Histone Deacetylases and Their Isoform-Specific Inhibitors in Ischemic Stroke

“…Whether SIRT6 functions as a part of the multiprotein complex in the postsynaptic membranes [102], or it regulates the neurite growth during the post-stroke recovery phase should be further studied. SIRT6 immunofluorescence was not observed in apoptotic cells in the PTS-induced penumbra [89]. On the other hand, its overexpression in cultured neurons under oxygen and glucose deprivation was associated with necrosis of cortical cells [103].…”

“…Nevertheless, the translocation of SIRT1 into the cytoplasm was not associated with cell apoptosis in the peri-infarct area at 7 days after photothrombotic stroke in the mouse cerebral cortex. In this case, the cytoplasmic localization of SIRT1 was associated with the upregulation of synaptophysin and GAP-43 that mediate the axon outgrowth and restoration of synaptic connections [89]. The cytoplasmic SIRT1 was shown to enhance the neurite outgrowth that was induced by nerve growth factor NGF.…”

“…It was not found in astrocytes, microglia, or neurons [91]. However, other authors reported the presence of SIRT2 in the cytoplasm of neurons, but not astrocytes in the mouse cerebral cortex [89,92]. In the cytoplasm, SIRT2 such as HDAC6 regulates the microtubule dynamics through deacetylation of α-tubulin [93].…”

“…SIRT6 was found in both: cerebral neurons and astrocytes [89,98]. It deacetylates mainly the lysine residues 9 and 56 in histone H3 that possibly represses genes associated with aging [99].…”

“…On one hand, SIRT6 protected the brain from postischemic reperfusion injury due to stimulation of transcription factor Nrf2 (nuclear factor-like (erythroid 2)-like 2), which regulates the expression of antioxidant proteins and suppresses oxidative stress [100,101]. SIRT6 was co-expressed with GAP-43, a marker of axon growth and synapse formation, at 14 days after photothrombotic stroke in the mouse cerebral cortex [89]. Whether SIRT6 functions as a part of the multiprotein complex in the postsynaptic membranes [102], or it regulates the neurite growth during the post-stroke recovery phase should be further studied.…”