Activation of SK2 channels preserves ER Ca²⁺ homeostasis and protects against ER stress-induced cell death

Alteration of endoplasmic reticulum (ER) Ca(2+) homeostasis leads to excessive cytosolic Ca(2+) accumulation and delayed neuronal cell death in acute and chronic neurodegenerative disorders. While our recent studies established a protective role for SK channels against excessive intracellular Ca(2+) accumulation, their functional role in the ER has not been elucidated yet. We show here that SK2 channels are present in ER membranes of neuronal HT-22 cells, and that positive pharmacological modulation of SK2 channels with CyPPA protects against cell death induced by the ER stressors brefeldin A and tunicamycin. Calcium imaging of HT-22 neurons revealed that elevated cytosolic Ca(2+) levels and decreased ER Ca(2+) load during sustained ER stress could be largely prevented by SK2 channel activation. Interestingly, SK2 channel activation reduced the amount of the unfolded protein response transcription factor ATF4, but further enhanced the induction of CHOP. Using siRNA approaches we confirmed a detrimental role for ATF4 in ER stress, whereas CHOP regulation was dispensable for both, brefeldin A toxicity and CyPPA-mediated protection. Cell death induced by blocking Ca(2+) influx into the ER with the SERCA inhibitor thapsigargin was not prevented by CyPPA. Blocking the K(+) efflux via K(+)/H(+) exchangers with quinine inhibited CyPPA-mediated neuroprotection, suggesting an essential role of proton uptake and K(+) release in the SK channel-mediated neuroprotection. Our data demonstrate that ER SK2 channel activation preserves ER Ca(2+) uptake and retention which determines cell survival in conditions where sustained ER stress contributes to progressive neuronal death.

Progression of liver fibrosis in HIV/HCV genotype 1 co-infected patients is related to the T allele of the rs12979860 polymorphism of the IL28B gene

OBJECTIVE

HIV/HCV co-infection is characterised by accelerated progression of liver disease. Recently, the rs12979860 C/T polymorphism in the IL28B gene has been linked to progression towards cirrhosis in HCV mono-infected patients and to treatment response of HCV-infection in HIV/HCV co-infected patients. Our aim was to clarify by non-invasive techniques if this polymorphism affects fibrosis progression in HIV/HCV co-infection.

METHODS

In a cross-sectional design, liver stiffness (transient elastography), surrogate markers of liver fibrosis (APRI and FIB-4 scores) and rs12979860 genotypes were analysed in 84 HCV/HIV co-infected patients. IL28B genotypes were determined by real-time PCR using a light cycler. In 56 HIV/HCV co-infected patients we also studied progression of fibrosis in relation to rs12979860 C/T genotypes over two years.

RESULTS

82% of the patients were on HAART (74% without detectable HI viremia) and 67% were haemophiliacs, respectively. HCV genotype 1 was present in 62%. Cross-sectional median liver stiffness was 7.4 kPa and correlated with APRI and FIB-4 scores (r = 0.6 each, p < 0.001). Frequencies of IL28B genotypes were: CC 50%, CT 43% and TT 7%. In the cross-sectional analysis liver stiffness values were not different between the various IL28B-genotypes. Upon follow-up under HAART carriers of a C allele did not show further progression, while liver stiffness significantly increased in HIV/HCV co-infected patients with the T allele (p = 0.047).

CONCLUSION

Although progression of liver fibrosis was low under HAART in our cohort, progression was more pronounced in HIV/HCV genotype 1 co-infected patients with the T allele.

Transient elastography discloses identical distribution of liver fibrosis in chronic hepatitis C between HIV-negative and HIV-positive patients on HAART

Objective

Progressive immunodeficiency associated with HIV-infection leads to a progressive course of liver disease in HIV/HCV-co-infected patients. Highly active antiretroviral therapy (HAART) efficiently restores and preserves immune functions and has recently been demonstrated to also result in reduced liver-related mortality in HIV/HCV-co-infected patients.

Methods

To analyse differences in current liver fibrosis as a possible effect of HAART on fibrosis progression we assessed hepatic fibrosis by transient elastography in a cross-sectional comparison between HCV-mono-infected and HIV/HCV-co-infected patients presenting at our outpatient department in 2007.

Results

Overall, we did not find any difference in the distribution of liver stiffness between mono- (n = 84) and double-infected (n = 57) patients (14.4 kPa (10.8 - 18.2) versus 12.4 kPa (9.1 - 16.1), mean (95%-CI)). However, in the 8 HIV+ patients with CD4 counts < 200/μl liver stiffness was markedly greater (18.4 kPa (0.8 - 36.0)) than in HIV+ patients with preserved immunity (11.5 kPa (8.4 - 15.0)).

Conclusions

These findings are in line with other data that show an improved prognosis of chronic hepatitis C in HIV+ patients under effective HAART, and may be a hint that fibrosis progression in well-treated HIV+ patients will no longer be different from that in HCV-mono-infected patients.