Regulation of cardiomyocyte autophagy by calcium

The role of autophagy in the progression of HIV infected cardiomyopathy

Although highly active antiretroviral therapy (HAART) has changed infection with human immunodeficiency virus (HIV) from a diagnosis with imminent mortality to a chronic illness, HIV positive patients who do not develop acquired immunodeficiency syndrome (AIDs) still suffer from a high rate of cardiac dysfunction and fibrosis. Regardless of viral load and CD count, HIV-associated cardiomyopathy (HIVAC) still causes a high rate of mortality and morbidity amongst HIV patients. While this is a well characterized clinical phenomena, the molecular mechanism of HIVAC is not well understood. In this review, we consolidate, analyze, and discuss current research on the intersection between autophagy and HIVAC. Multiple studies have linked dysregulation in various regulators and functional components of autophagy to HIV infection regardless of mode of viral entry, i.e., coronary, cardiac chamber, or pericardial space. HIV proteins, including negative regulatory factor (Nef), glycoprotein 120 (gp120), and transactivator (Tat), have been shown to interact with type II microtubule-associated protein-1 β light chain (LC3-II), Rubiquitin, SQSTM1/p62, Rab7, autophagy-specific gene 7 (ATG7), and lysosomal-associated membrane protein 1 (LAMP1), all molecules critical to normal autophagy. HIV infection can also induce dysregulation of mitochondrial bioenergetics by altering production and equilibrium of adenosine triphosphate (ATP), mitochondrial reactive oxygen species (ROS), and calcium. These changes alter mitochondrial mass and morphology, which normally trigger autophagy to clear away dysfunctional organelles. However, with HIV infection also triggering autophagy dysfunction, these abnormal mitochondria accumulate and contribute to myocardial dysfunction. Likewise, use of HAART, azidothymidine and Abacavir, have been shown to induce cardiac dysfunction and fibrosis by inducing abnormal autophagy during antiretroviral therapy. Conversely, studies have shown that increasing autophagy can reduce the accumulation of dysfunctional mitochondria and restore cardiomyocyte function. Interestingly, Rapamycin, a mammalian target of rapamycin (mTOR) inhibitor, has also been shown to reduce HIV-induced cytotoxicity by regulating autophagy-related proteins, making it a non-antiviral agent with the potential to treat HIVAC. In this review, we synthesize these findings to provide a better understanding of the role autophagy plays in HIVAC and discuss the potential pharmacologic targets unveiled by this research.

Hallmarks of cardiovascular ageing

Normal circulatory function is a key determinant of disease-free life expectancy (healthspan). Indeed, pathologies affecting the cardiovascular system, which are growing in prevalence, are the leading cause of global morbidity, disability and mortality, whereas the maintenance of cardiovascular health is necessary to promote both organismal healthspan and lifespan. Therefore, cardiovascular ageing might precede or even underlie body-wide, age-related health deterioration. In this Review, we posit that eight molecular hallmarks are common denominators in cardiovascular ageing, namely disabled macroautophagy, loss of proteostasis, genomic instability (in particular, clonal haematopoiesis of indeterminate potential), epigenetic alterations, mitochondrial dysfunction, cell senescence, dysregulated neurohormonal signalling and inflammation. We also propose a hierarchical order that distinguishes primary (upstream) from antagonistic and integrative (downstream) hallmarks of cardiovascular ageing. Finally, we discuss how targeting each of the eight hallmarks might be therapeutically exploited to attenuate residual cardiovascular risk in older individuals.

Molecular Mechanisms and Epigenetic Regulation in Diabetic Cardiomyopathy

Diabetes mellitus (DM) is an important lifestyle disease. Type 2 diabetes is one of the prime contributors to cardiovascular diseases (CVD) and diabetic cardiomyopathy (DbCM) and leads to increased morbidity and mortality in patients with DM. DbCM is a typical cardiac disease, characterized by cardiac remodeling in the presence of DM and in the absence of other comorbidities such as hypertension, valvular diseases, and coronary artery disease. DbCM is associated with defective cardiac metabolism, altered mitochondrial structure and function, and other physiological and pathophysiological signaling mechanisms such as oxidative stress, inflammation, myocardial apoptosis, and autophagy. Epigenetic modifiers are crucial players in the pathogenesis of DbCM. Thus, it is important to explore the role of epigenetic modifiers or modifications in regulating molecular pathways associated with DbCM. In this review, we have discussed the role of various epigenetic mechanisms such as histone modifications (acetylation and methylation), DNA methylation and non-coding RNAs in modulating molecular pathways involved in the pathophysiology of the DbCM.

Calcium Ions Aggravate Alzheimer's Disease Through the Aberrant Activation of Neuronal Networks, Leading to Synaptic and Cognitive Deficits

Alzheimer’s disease (AD) is a neurodegenerative disease that is characterized by the production and deposition of β-amyloid protein (Aβ) and hyperphosphorylated tau, leading to the formation of β-amyloid plaques (APs) and neurofibrillary tangles (NFTs). Although calcium ions (Ca²⁺) promote the formation of APs and NFTs, no systematic review of the mechanisms by which Ca²⁺ affects the development and progression of AD has been published. Therefore, the current review aimed to fill the gaps between elevated Ca²⁺ levels and the pathogenesis of AD. Specifically, we mainly focus on the molecular mechanisms by which Ca²⁺ affects the neuronal networks of neuroinflammation, neuronal injury, neurogenesis, neurotoxicity, neuroprotection, and autophagy. Furthermore, the roles of Ca²⁺ transporters located in the cell membrane, endoplasmic reticulum (ER), mitochondria and lysosome in mediating the effects of Ca²⁺ on activating neuronal networks that ultimately contribute to the development and progression of AD are discussed. Finally, the drug candidates derived from herbs used as food or seasoning in Chinese daily life are summarized to provide a theoretical basis for improving the clinical treatment of AD.

Bafilomycin-A1 and ML9 Exert Different Lysosomal Actions to Induce Cell Death

OBJECTIVE

Bafilomycin-A1 and ML9 are lysosomotropic agents, irrespective of cell types. However, the mechanisms of lysosome targeting either bafilomycin-A1 or ML9 are unclear.

METHODS

The present research has been carried out by different molecular and biochemical analyses like western blot, confocal imaging and FACS studies, as well as molecular docking.

RESULTS

Our data shows that pre-incubation of neonatal cardiomyocytes with ML9 for 4h induced cell death, whereas a longer period of time (24h) with bafilomycin-A1 was required to induce an equivalent effect. Neither changes in ROS nor ATP production is associated with such death mechanisms. Flow cytometry, LC3-II expression levels, and LC3-GFP puncta formation revealed a similar lysosomotropic effect for both compounds. We used a molecular docking approach, that predicts a stronger inhibitory activity against V-ATPase-C1 and C2 domains for bafilomycin-A1 in comparison to ML9.

CONCLUSION

Bafilomycin-A1 and ML9 are lysosomotropic agents, involved in cell death events. But such death events are not associated with ATP and ROS production. Furthermore, both the drugs target lysosomes through different mechanisms. For the latter, cell death is likely due to lysosomal membrane permeabilization and release of lysosomal proteases into the cytosol.

Autophagy in Cardiovascular Aging

Cardiovascular diseases are the most prominent maladies in aging societies. Indeed, aging promotes the structural and functional declines of both the heart and the blood circulation system. In this review, we revise the contribution of known longevity pathways to cardiovascular health and delineate the possibilities to interfere with them. In particular, we evaluate autophagy, the intracellular catabolic recycling system associated with life- and health-span extension. We present genetic models, pharmacological interventions, and dietary strategies that block, reduce, or enhance autophagy upon age-related cardiovascular deterioration. Caloric restriction or caloric restriction mimetics like metformin, spermidine, and rapamycin (all of which trigger autophagy) are among the most promising cardioprotective interventions during aging. We conclude that autophagy is a fundamental process to ensure cardiac and vascular health during aging and outline its putative therapeutic importance.

Insulin-Like Growth Factor 1 in the Cardiovascular System

Non-communicable diseases, such as cardiovascular diseases, are the leading cause of mortality worldwide. For this reason, a tremendous effort is being made worldwide to effectively circumvent these afflictions, where insulin-like growth factor 1 (IGF1) is being proposed both as a marker and as a central cornerstone in these diseases, making it an interesting molecule to focus on. Firstly, at the initiation of metabolic deregulation by overfeeding, IGF1 is decreased/inhibited. Secondly, such deficiency seems to be intimately related to the onset of MetS and establishment of vascular derangements leading to atherosclerosis and finally playing a definitive part in cerebrovascular and myocardial accidents, where IGF1 deficiency seems to render these organs vulnerable to oxidative and apoptotic/necrotic damage. Several human cohort correlations together with basic/translational experimental data seem to confirm deep IGF1 implication, albeit with controversy, which might, in part, be given by experimental design leading to blurred result interpretation.

Increased store-operated Ca2+ entry mediated by GNB5 and STIM1

Recent human genetic studies have shown that Gβ5 is related to various clinical symptoms, such as sinus bradycardia, cognitive disability, and attention deficit hyperactivity disorder. Although the calcium signaling cascade is closely associated with a heterotrimeric G-protein, the function of Gβ5 in calcium signaling and its relevance to clinical symptoms remain unknown. In this study, we investigated the in vitro changes of store-operated calcium entry (SOCE) with exogenous expression of Gβ5. The cells expressing Gβ5 had enhanced SOCE after depletion of calcium ion inside the endoplasmic reticulum. Gβ5 also augmented Stim1- and Orai1-dependent SOCE. An ORAI1 loss-of-function mutant did not show inhibition of Gβ5-induced SOCE, and a STIM1-ERM truncation mutant showed no enhancement of SOCE. These results suggested a novel role of GNB5 and Stim1, and provided insight into the regulatory mechanism of SOCE.

Natural autophagy blockers, dauricine (DAC) and daurisoline (DAS), sensitize cancer cells to camptothecin-induced toxicity

Autophagy is a cellular bulk degradation pathway implicated in various diseases. Inhibition of autophagy has been regarded as a new therapeutic strategy for cancer treatment, especially in combination with chemotherapy. In our study, we identified two natural compounds, dauricine (DAC) and daurisoline (DAS), as two potent autophagy blockers through a high-content screening. DAC and DAS are alkaloids isolated from traditional Chinese medicine Rhizoma Menispermi. We systematically examined the effects of DAC and DAS on autophagy function in HeLa cells and found that DAC and DAS induced massive formation of autophagic vacuoles and lipidation of LC3. The accumulation of autophagic vacuoles and LC3 lipidation are due to blockage of autophagosome maturation as evidenced by interrupted colocalization of autophagsosome and lysosome, increased GFP-LC3/RFP-LC3 ratio and accumulation of autophagic substrate p62. Moreover, DAC and DAS impaired lysosomal function, as indicated by reduced lysosomal protease activity and increased lysosomal pH values. Importantly, we showed that DAC and DAS strongly inhibited the lysosome V-type ATPase activity. For the therapeutic potential, we found that DAC and DAS blocked the campothecin (CPT)-induced protective autophagy in HeLa cells, and dramatically sensitized the multiple cancer cells to CPT-induced cell death. In conclusion, our result shows that DAC and DAS are autophagy inhibitors which inhibit the lysosomal degradation of auophagic vacuoles, and sensitize the CPT-induced cancer cell death. The study implies the therapeutic potential of DAC and DAS in the treatment of cancers in combination of chemotherapy by inhibiting autophagy.