Muscle Dysfunction in Androgen Deprivation: Role of Ryanodine Receptor

Introduction: Approximately 50% of men diagnosed with prostate cancer will be exposed to androgen deprivation therapy (ADT) at some stage. The role of ADT in the management of metastatic disease has long been recognised, and its place in the management of localised and locally advanced disease has become clearer in the past few years. Nevertheless, concerns remain that some men might not benefit from ADT in earlier-stage disease. The purpose of the current article is to provide a brief narrative review of the role of ADT as part of a strategy of treatment with curative intent, concentrating mainly on key recent developments in the area. Methods: Narrative literature review of key publications in the English language relating to ADT in the management of localised and locally advanced prostate cancer. Results: In locally advanced and high-risk localised prostate cancer, the use of ADT in combination with radiotherapy improves disease-specific and overall survival. There is no evidence to support the use of ADT in the treatment of low-risk localised prostate cancer. There appears to be an increased risk of cardiovascular morbidity and mortality associated with luteinizing hormone-releasing hormone agonists, particularly in men with pre-existing cardiovascular disease, but the relevance of this in the adjuvant/neoadjuvant setting is currently unclear. Conclusions: Future studies should focus on identification of men who are at risk from cardiovascular complications associated with ADT and on the comparison of radiotherapy with ADT versus surgery in the management of localised and locally advanced prostate cancer, particularly with regards to men with pre-existing comorbidities.

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Abstract 11423: Mitochondrial Calcium Flux Modulates Pacemaker Activity in Mouse Stem Cell Derived Cardiomyocytes

Circulation ◽

10.1161/circ.130.suppl_2.11423 ◽

2014 ◽

Vol 130 (suppl_2) ◽

Author(s):

An Xie ◽

Anyu Zhou ◽

Hong Liu ◽

Guangbin Shi ◽

Kenneth R Boheler ◽

...

Keyword(s):

Ryanodine Receptor ◽

Mrna Level ◽

Embryonic Stem ◽

Calcium Flux ◽

Pacemaker Activity ◽

Receptor Subtypes ◽

Ip3 Receptors ◽

Cell Current ◽

Beating Rate

INTRODUCTION: Ca2+ release from sarcoplasmic reticulum (SR) is known to contribute to the pacemaker activity in embryonic stem cells (ESC) derived cardiomyocytes (CMs). Mitochondria are known to participate in Ca2+ cycling. Nevertheless, the role of mitochondria in pacemaker activity is unclear. We studied the role of mitochondrial Ca2+ flux in spontaneously activity of ESC derived CMs. METHODS: CMs were derived from Wt and ryanodine receptor type 2 knockout (RYR2-/-) mouse ESC. Action potentials (APs) were recorded by perforated whole-cell current-clamp. Cytoplasmic and mitochondrial Ca2+ transients were determined by Fluo-4 and Rhod-2 respectively. Mitochondrial Ca2+ uniporter (MCU) siRNA was used. The mRNA level was evaluated by qPCR. RESULTS: As predicted, SR Ca2+ handling inhibitors, 10 μM ryanodine and 2 μM 2-APB, reduced spontaneous beating rate to 56% and 73% respectively in Wt CMs. Inhibition of mitochondrial Ca2+ flux by 10 μM Ru360 showed a similar inhibition effect on the pacemaker activity as 2 μM 2-APB in Wt CMs. To isolate the mitochondrial component, we used RYR2-/- CMs. In these cells, MCU inhibition by pharmacological or molecular biological means reduced beating rate. The MCU mRNA decreased by 96% after MCU siRNA silence 72 hrs (p<0.01). AP and mitochondrial Ca2+ transient synchronous recording revealed that the reduction of spontaneous beating rate accompanied with the depressed mitochondrial Ca2+ uptaking and releasing. In RyR2-/- CMs, 2 μM 2-APB could significantly lower the spontaneous beating rate. While 2 μM 2-APB was applied to MCU silenced RyR2-/- CMs, the beating rate couldn’t be slowed down further. This indicated IP3 receptors reduced spontaneous beating rate via MCU. Thapsigargin could substantially slow down beating rate like 2-APB. Caffeine depletion experiments showed other ryanodine receptor subtypes didn’t contribute Ca2+ release in RyR2-/- CMs. A L-type Ca2+ channel block, 10 μM nifedipine, couldn’t reduce beating frequency. This indicated spontaneous beating rate is Ca2+ influx independent in RyR2-/- CMs. CONCLUSIONS: Mitochondrial Ca2+ handling plays an important role in decreasing spontaneous beating rate. IP3R reduced spontaneous beating rate through MCU.

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