HSP110, caspase-3 and -9 expression in physiological apoptosis and apoptosis induced by in vivo embryonic exposition to all-trans retinoic acid or irradiation during early mouse eye development

Ginsenoside Rk1 protects human melanocytes from H2O2‑induced oxidative injury via regulation of the PI3K/AKT/Nrf2/HO‑1 pathway

Vitiligo is a cutaneous depigmentation disorder caused by melanocyte injury or aberrant functioning. Oxidative stress (OS) is considered to be a major cause of the onset and progression of vitiligo. Ginsenoside Rk1 (RK1), a major compound isolated from ginseng, has antioxidant activity. However, whether RK1 can protect melanocytes against oxidative injury remains unknown. The aim of the present study was to investigate the potential protective effect of RK1 against OS in the human PIG1 melanocyte cell line induced with hydrogen peroxide (H₂O₂), and to explore its underlying mechanism. PIG1 cells were pretreated with RK1 (0, 0.1, 0.2 and 0.4 mM) for 2 h followed by exposure to 1.0 mM H₂O₂ for 24 h. Cell viability and apoptosis were determined with Cell Counting Kit‑8 and flow cytometry assays, respectively. The activity levels of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH‑Px) were analyzed using ELISA kits. Protein expression levels, including Bax, caspase‑3, Bcl‑2, phosphorylated‑AKT, AKT, nuclear factor erythroid 2‑related factor 2 (Nrf2), heme oxygenase‑1 (HO‑1), cytosolic Nrf2 and nuclear Nrf2, were analyzed using western blot analysis. In addition, the expression and localization of Nrf2 were detected by immunofluorescence. RK1 treatment significantly improved cell viability, reduced the apoptotic rate and increased the activity levels of SOD, CAT and GSH‑Px in the PIG1 cell line exposed to H₂O₂. In addition, RK1 treatment notably induced Nrf2 nuclear translocation, increased the protein expression levels of Nrf2 and HO‑1, and the ratio of phosphorylated‑AKT to AKT in the PIG1 cells exposed to H₂O₂. Furthermore, LY294002 could reverse the protective effect of RK1 in melanocytes against oxidative injury. These data demonstrated that RK1 protected melanocytes from H₂O₂‑induced OS by regulating Nrf2/HO‑1 protein expression, which may provide evidence for the application of RK1 for the treatment of vitiligo.

Loss of Hsp110 leads to age-dependent tau hyperphosphorylation and early accumulation of insoluble amyloid beta

Accumulation of tau into neurofibrillary tangles is a pathological consequence of Alzheimer's disease and other tauopathies. Failures of the quality control mechanisms by the heat shock proteins (Hsps) positively correlate with the appearance of such neurodegenerative diseases. However, in vivo genetic evidence for the roles of Hsps in neurodegeneration remains elusive. Hsp110 is a nucleotide exchange factor for Hsp70, and direct substrate binding to Hsp110 may facilitate substrate folding. Hsp70 complexes have been implicated in tau phosphorylation state and amyloid precursor protein (APP) processing. To provide evidence for a role for Hsp110 in central nervous system homeostasis, we have generated hsp110(-)(/)(-) mice. Our results show that hsp110(-)(/)(-) mice exhibit accumulation of hyperphosphorylated-tau (p-tau) and neurodegeneration. We also demonstrate that Hsp110 is in complexes with tau, other molecular chaperones, and protein phosphatase 2A (PP2A). Surprisingly, high levels of PP2A remain bound to tau but with significantly reduced activity in brain extracts from aged hsp110(-)(/)(-) mice compared to brain extracts from wild-type mice. Mice deficient in the Hsp110 partner (Hsp70) also exhibit a phenotype comparable to that of hsp110(-)(/)(-) mice, confirming a critical role for Hsp110-Hsp70 in maintaining tau in its unphosphorylated form during aging. In addition, crossing hsp110(-)(/)(-) mice with mice overexpressing mutant APP (APPβsw) leads to selective appearance of insoluble amyloid β42 (Aβ42), suggesting an essential role for Hsp110 in APP processing and Aβ generation. Thus, our findings provide in vivo evidence that Hsp110 plays a critical function in tau phosphorylation state through maintenance of efficient PP2A activity, confirming its role in pathogenesis of Alzheimer's disease and other tauopathies.

Role of the immune modulator programmed cell death-1 during development and apoptosis of mouse retinal ganglion cells

PURPOSE

Mammalian programmed cell death (PD)-1 is a membrane-associated receptor regulating the balance between T-cell activation, tolerance, and immunopathology; however, its role in neurons has not yet been defined. The hypothesis that PD-1 signaling actively promotes retinal ganglion cell (RGC) death within the developing mouse retina was investigated.

METHODS

Mature retinal cell types expressing PD-1 were identified by immunofluorescence staining of vertical retina sections; developmental expression was localized by immunostaining and quantified by Western blot analysis. PD-1 involvement in developmental RGC survival was assessed in vitro using retinal explants and in vivo using PD-1 knockout mice. PD-1 ligand gene expression was detected by RT-PCR.

RESULTS

PD-1 is expressed in most adult RGCs and undergoes dynamic upregulation during the early postnatal window of retinal cell maturation and physiological programmed cell death (PCD). In vitro blockade of PD-1 signaling during this time selectively increases the survival of RGCs. Furthermore, PD-1-deficient mice show a selective increase in RGC number in the neonatal retina at the peak of developmental RGC death. Lastly, gene expression of the immune PD-1 ligand genes Pdcd1lg1 and Pdcd1lg2 was found throughout postnatal retina maturation.

CONCLUSIONS

These findings collectively support a novel role for a PD-1-mediated signaling pathway in developmental PCD during postnatal RGC maturation.

HSP105 interacts with GRP78 and GSK3 and promotes ER stress-induced caspase-3 activation

Stress of the endoplasmic reticulum (ER stress) is caused by the accumulation of misfolded proteins, which occurs in many neurodegenerative diseases. ER stress can lead to adaptive responses or apoptosis, both of which follow activation of the unfolded protein response (UPR). Heat shock proteins (HSP) support the folding and function of many proteins, and are important components of the ER stress response, but little is known about the role of one of the major large HSPs, HSP105. We identified several new partners of HSP105, including glycogen synthase kinase-3 (GSK3), a promoter of ER stress-induced apoptosis, and GRP78, a key component of the UPR. Knockdown of HSP105 did not alter UPR signaling after ER stress, but blocked caspase-3 activation after ER stress. In contrast, caspase-3 activation induced by genotoxic stress was unaffected by knockdown of HSP105, suggesting ER stress-specificity in the apoptotic action of HSP105. However, knockdown of HSP105 did not alter cell survival after ER stress, but instead diverted signaling to a caspase-3-independent cell death pathway, indicating that HSP105 is necessary for apoptotic signaling after UPR activation by ER stress. Thus, HSP105 appears to chaperone the responses to ER stress through its interactions with GRP78 and GSK3, and without HSP105 cell death following ER stress proceeds by a non-caspase-3-dependent process.