mTOR Inhibition and Cardiovascular Diseases: Cardiac Hypertrophy

Emerging roles of senolytics/senomorphics in HIV-related co-morbidities

Human immunodeficiency virus (HIV) is known to cause cellular senescence and inflammation among infected individuals. While the traditional antiretroviral therapies (ART) have allowed the once fatal infection to be managed effectively, the quality of life of HIV patients on prolonged ART use is still inferior. Most of these individuals suffer from life-threatening comorbidities like chronic obstructive pulmonary disease (COPD), pulmonary arterial hypertension (PAH), and diabetes, to name a few. Interestingly, cellular senescence is known to play a critical role in the pathophysiology of these comorbidities as well. It is therefore important to understand the role of cellular senescence in the disease progression and co-morbidity development in HIV-infected individuals. In this respect, use of senolytic/senomorphic drugs as combination therapy with ART would be beneficial for HIV patients. This review provides a critical analysis of the current literature to determine the potential and efficacy of using senolytics/senotherapeutics in managing HIV infection, latency, and associated co-morbidities in humans. The various classes of senolytics have been studied in detail to focus on their potential to combat against HIV infections and associated pathologies with advancing age.

The history of cardiac xenotransplantation: early attempts, major advances, and current progress

In light of ongoing shortage of donor organs for transplantation, alternative sources for donor organ sources have been examined to address this supply-demand mismatch. Of these, xenotransplantation, or the transplantation of organs across species, has been considered, with early applications dating back to the 1600s. The purpose of this review is to summarize the early experiences of xenotransplantation, with special focus on heart xenotransplantation. It aims to highlight the important ethical concerns of animal-to-human heart xenotransplantation, identify the key immunological barriers to successful long-term xenograft survival, as well as summarize the progress made in terms of development of pharmacological and genetic engineering strategies to address these barriers. Lastly, we discuss more recent attempts of porcine-to-human heart xenotransplantation, as well as provide some commentary on the current concerns and possible applications for future clinical heart xenotransplantation.

Therapeutic potential of natural compounds from herbs and nutraceuticals in spinal cord injury: Regulation of the mTOR signaling pathway

Spinal cord injury (SCI) is a disease in which the spinal cord is subjected to various external forces that cause it to burst, shift, or, in severe cases, injure the spinal tissue, resulting in nerve injury. SCI includes not only acute primary injury but also delayed and persistent spinal tissue injury (i.e., secondary injury). The pathological changes post-SCI are complex, and effective clinical treatment strategies are lacking. The mammalian target of rapamycin (mTOR) coordinates the growth and metabolism of eukaryotic cells in response to various nutrients and growth factors. The mTOR signaling pathway has multiple roles in the pathogenesis of SCI. There is evidence for the beneficial effects of natural compounds and nutraceuticals that regulate the mTOR signaling pathways in a variety of diseases. Therefore, the effects of natural compounds on the pathogenesis of SCI were evaluated by a comprehensive review using electronic databases, such as PubMed, Web of Science, Scopus, and Medline, combined with our expertise in neuropathology. In particular, we reviewed the pathogenesis of SCI, including the importance of secondary nerve injury after the primary mechanical injury, the roles of the mTOR signaling pathways, and the beneficial effects and mechanisms of natural compounds that regulate the mTOR signaling pathway on pathological changes post-SCI, including effects on inflammation, neuronal apoptosis, autophagy, nerve regeneration, and other pathways. This recent research highlights the value of natural compounds in regulating the mTOR pathway, providing a basis for developing novel therapeutic strategies for SCI.

Cardiovascular Outcomes in De Novo Kidney Transplant Recipients Receiving Everolimus and Reduced Calcineurin Inhibitor or Standard Triple Therapy: 24-month Post Hoc Analysis From TRANSFORM Study

BACKGROUND

The comparative impact of everolimus (EVR)-based regimens versus standard of care (mycophenolic acid+standard calcineurin inhibitor [MPA+sCNI]) on cardiovascular outcomes in de novo kidney transplant recipients (KTRs) is poorly understood. The incidence of major adverse cardiac events (MACEs) in KTRs receiving EVR+reduced CNI (rCNI) or MPA+sCNI from the TRANSplant eFficacy and safety Outcomes with an eveRolimus-based regiMen study was evaluated.

METHODS

The incidence of MACE was determined for all randomized patients receiving at least 1 dose of the study drug. Factors associated with MACEs were determined by logistic regression. Risk of MACE out to 3 y post-study was calculated using the Patient Outcome in Renal Transplantation equation.

RESULTS

MACE occurred in 81 of 1014 (8.0%; EVR+rCNI) versus 89 of 1012 (8.8%; MPA+sCNI) KTRs (risk ratio, 0.91 [95% confidence interval [CI], 0.68-1.21]). The incidence of circulatory death, myocardial infarction, revascularization, or angina was similar between the arms. Incidence of MACE was similar between EVR+rCNI and MPA+sCNI arms with a higher incidence in prespecified risk groups: older age, pretransplant diabetes (15.1% versus 15.9%), statin use (8.5% versus 10.8%), and low estimated glomerular filtration rate (Month 2 estimated glomerular filtration rate <30 versus >60 mL/min/1.73 m 2 ; odds ratio, 2.23 [95% CI, 1.02-4.86]; P = 0.044), respectively. Predicted risk of MACE within 3 y of follow-up did not differ between the treatment arms.

CONCLUSIONS

Cardiovascular morbidity and mortality were similar between de novo KTRs receiving EVR+rCNI and MPA+sCNI. EVR+rCNI is a viable alternative to the current standard of care in KTRs.

Cardiovascular effects of immunosuppression agents

Immunosuppressive medications are widely used to treat patients with neoplasms, autoimmune conditions and solid organ transplants. Key drug classes, namely calcineurin inhibitors, mammalian target of rapamycin (mTOR) inhibitors, and purine synthesis inhibitors, have direct effects on the structure and function of the heart and vascular system. In the heart, immunosuppressive agents modulate cardiac hypertrophy, mitochondrial function, and arrhythmia risk, while in vasculature, they influence vessel remodeling, circulating lipids, and blood pressure. The aim of this review is to present the preclinical and clinical literature examining the cardiovascular effects of immunosuppressive agents, with a specific focus on cyclosporine, tacrolimus, sirolimus, everolimus, mycophenolate, and azathioprine.

Hyperactivation of mTOR and AKT in a cardiac hypertrophy animal model of Friedreich ataxia

Cardiomyopathy is a primary cause of death in Friedreich ataxia (FRDA) patients with defective iron-sulfur cluster (ISC) biogenesis due to loss of functional frataxin and in rare patients with functional loss of other ISC biogenesis factors. The mechanistic target of rapamycin (mTOR) and AKT signaling cascades that coordinate eukaryotic cell growth and metabolism with environmental inputs, including nutrients and growth factors, are crucial regulators of cardiovascular growth and homeostasis. We observed increased phosphorylation of AKT and dysregulation of multiple downstream effectors of mTORC1, including S6K1, S6, ULK1 and 4EBP1, in a cardiac/skeletal muscle specific FRDA conditional knockout (cKO) mouse model and in human cell lines depleted of ISC biogenesis factors. Knockdown of several mitochondrial metabolic proteins that are downstream targets of ISC biogenesis, including lipoyl synthase and subunit B of succinate dehydrogenase, also resulted in activation of mTOR and AKT signaling, suggesting that mTOR and AKT hyperactivations are part of the metabolic stress response to ISC deficiencies. Administration of rapamycin, a specific inhibitor of mTOR signaling, enhanced the survival of the Fxn cKO mice, providing proof of concept for the potential of mTOR inhibition to ameliorate cardiac disease in patients with defective ISC biogenesis. However, AKT phosphorylation remained high in rapamycin-treated Fxn cKO hearts, suggesting that parallel mTOR and AKT inhibition might be necessary to further improve the lifespan and healthspan of ISC deficient individuals.

Camellia (Camellia oleifera bel.) seed oil reprograms gut microbiota and alleviates lipid accumulation in high fat-fed mice through the mTOR pathway

Camellia (Camellia oleifera bel.) seed oil (CO) is extensively used as an edible oil in China and Asian countries owing to its high nutritional and medicinal values. It has been shown that a high-fat diet enhances lipid accumulation and induces intestinal microbiota imbalance in mice. However, it is still to be learned whether CO prevents dyslipidemia through gut microbiota. Here, using 16S rRNA gene sequencing analysis of the gut microbiota, we found that oral CO relieved lipid accumulation and reversed gut microbiota dysbiosis. Compared to mice (C57BL/6J male mice) fed a high-fat diet, treatment with CO regulated the composition and functional profiling communities related to the lipid metabolism of gut microbiota. The abundances of Dubosiella, Lactobacillus, and Alistipes were markedly increased in CO supplementation mice. In addition, the colon levels of isobutyric acid, pentanoic acid, and isovaleric acid were similar between the control and CO supplementation mice. Besides, the results indicated that CO supplementation in mice alleviated lipid droplet accumulation in the hepatocytes and subcutaneous adipose tissue, although the liver index did not show a difference. Notably, CO supplementation for 6 weeks significantly reduced the levels of LDL, TC, and TG, while enhancing the level of HDL in serum and liver. Meanwhile, we also identified that CO supplementation suppressed the mammalian target of rapamycin (mTOR) signaling pathway in high fat-fed (HF-fed) mice. Taken together, our results suggest that CO improved dyslipidemia and alleviated lipid accumulation in HF-fed mice, the molecular mechanisms possibly associated with the reorganization of gut microbiota, in particular, Alistipes and Dubosiella, mediated the inhibition of the mTOR pathway.

Ginger: A complementary approach for management of cardiovascular diseases

Cardiovascular disease (CVD) is a leading cause of morbidity and mortality worldwide. Inflammation and oxidative stress play critical roles in progression of various types of CVD. Broad pharmacological properties of ginger (the rhizome of Zingiber officinale) and its bioactive components have been reported, suggesting that they can be a therapeutic choice for clinical use. Consistent with its rich phenolic content, the anti-inflammatory and antioxidant properties of ginger have been confirmed in many studies. Ginger modifies many cellular processes and in particular was shown to have potent inhibitory effects against nuclear factor kappa B (NF-κB); signal transducer and activator of transcription; NOD-, LRR-, and pyrin domain-containing proteins; toll-like receptors; mitogen-activated protein kinase; and mammalian target of rapamycin signaling pathways. Ginger also blocks pro-inflammatory cytokines and the activation of the immune system. Ginger suppresses the activity of oxidative molecules such as reactive oxygen species, inducible nitric oxide synthase, superoxide dismutase, glutathione, heme oxygenase, and GSH-Px. In this report, we summarize the biochemical pathologies underpinning a variety of CVDs and the effects of ginger and its bioactive components, including 6-shogaol, 6-gingerol, and 10-dehydrogingerdione. The properties of ginger and its phenolic components, mechanism of action, biological functions, side effects, and methods for enhanced cell delivery are also discussed. Together with preclinical and clinical studies, the positive biological effects of ginger and its bioactive components in CVD support the undertaking of further in vivo and especially clinical studies.

PEX5 prevents cardiomyocyte hypertrophy via suppressing the redox-sensitive signaling pathways MAPKs and STAT3

Peroxisomal biogenesis factor 5 (PEX5) is a member of peroxisome biogenesis protein family which serves as a shuttle receptor for the import of peroxisome matrix protein. The function of PEX5 on cardiomyocyte hypertrophy remained to be elucidated. Our study demonstrated that the protein expression level of PEX5 was declined in primary neonatal rat cardiomyocytes treated with phenylephrine (PE) and hearts from cardiac hypertrophic rats induced by abdominal aortic constriction (AAC). Overexpression of PEX5 alleviated cardiomyocyte hypertrophy induced by PE, while silencing of PEX5 exacerbated cardiomyocyte hypertrophy. PEX5 improved redox imbalance by decreasing cellular reactive oxygen species level and preserving peroxisomal catalase. Moreover, PEX5 knockdown aggravated PE-induced activation of redox-sensitive signaling pathways, including mitogen-activated protein kinase (MAPK) pathway and signal transducer and activator of transcription 3 (STAT3); whereas PEX5 overexpression suppressed activation of MAPK and STAT3. But PEX5 did not affect PE-induced phosphorylation of mammalian target of rapamycin (mTOR). In conclusion, the present study suggests that PEX5 protects cardiomyocyte against hypertrophy via regulating redox homeostasis and inhibiting redox-sensitive signaling pathways MAPK and STAT3.

Clinical trials in cardiac xenotransplantation: Are we ready to overcome barriers?

Heart allotransplantation has become one of the methods of choice in the treatment of severe heart failure. In the face of its difficulties, such as the unmet balance between organ supply and demand, the use of xenotransplantation (XTx) might be an attractive option shortly, even more with the ongoing progress achieved regarding the avoidance of hyperacute rejection and primary organ disfunction, maintenance of xenograft function and control of xenograft growth. To make possible this translational challenge, some points must be taken into account indeed, and they are the equipoise of human benefit and animal suffering, the risk of unknown infections, a well prepared informed consent, ethical and religious beliefs, and the role of cardiac XTx in a ventricular assistance device era.

mTOR pathway in human cardiac hypertrophy caused by LEOPARD syndrome: a different role compared with animal models?

Background

Animal studies suggested that blocking the activation of the mammalian target of rapamycin (mTOR) pathway might be effective to treat cardiac hypertrophy in LEOPARD syndrome (LS) caused by PTPN11 mutations.

Results

In the present study, mTOR pathway activity was examined in human myocardial samples from two patients with LS, four patients with hypertrophic cardiomyopathy (HCM), and four normal controls. The two patients with LS had p.Y279C and p.T468 M mutations of the PTPN11 gene, respectively. Although PTPN11 mutation showed initially positive regulation on phosphoinositide 3-kinase, overall the mTOR complex 1 pathway showed widely attenuated activity in LS. This included mildly hypophosphorylated mTOR and ribosomal protein S6 kinase and significantly hypophosphorylated Akt³⁰⁸ and ribosomal protein S6, which is similar to HCM. Akt⁴⁷³ is a basal molecule of the mTOR complex 2 pathway. Akt⁴⁷³ was less affected and showed hyperactivity in LS compared with HCM and normal controls. Additionally, MAPK/ERK kinase and ERK1/2 were significantly more phosphorylated in both HCM and LS than normal controls.

Conclusions

In LS, the mTOR signaling pathway shows similar activity to HCM and is attenuated compared with normal controls. Thus, caution should be applied when using rapamycin to treat heart hypertrophy in LS.

Cardiovascular risk in renal transplant recipients

Successful kidney transplantation offers patients with end-stage renal disease the greatest likelihood of survival. However, cardiovascular disease poses a major threat to both graft and patient survival in this cohort. Transplant recipients are unique in their accumulation of a wide range of traditional and non-traditional cardiovascular risk factors. Hypertension, diabetes, dyslipidaemia and obesity are highly prevalent in patients with end-stage renal disease. These risk factors persist following transplantation and are often exacerbated by the drugs used for immunosuppression in organ transplantation. Additional transplant-specific factors such as poor graft function and proteinuria are also associated with increased cardiovascular risk. However, these transplant-related factors remain unaccounted for in current cardiovascular risk prediction models, making it challenging to identify transplant recipients with highest risk. With few interventional trials in this area specific to transplant recipients, strategies to reduce cardiovascular risk are largely extrapolated from other populations. Aggressive management of traditional cardiovascular risk factors remains the cornerstone of prevention, though there is also a potential role for selecting immunosuppression regimens to minimise additional cardiovascular injury.

FKBP12.6 protects heart from AngII-induced hypertrophy through inhibiting Ca2+ /calmodulin-mediated signalling pathways in vivo and in vitro

We previously observed that disruption of FK506‐binding protein 12.6 (FKBP12.6) gene resulted in cardiac hypertrophy in male mice. Studies showed that overexpression of FKBP12.6 attenuated thoracic aortic constriction (TAC)‐induced cardiac hypertrophy in mice, whereas the adenovirus‐mediated overexpression of FKBP12.6 induced hypertrophy and apoptosis in cultured neonatal cardiomyocytes, indicating that the role of FKBP12.6 in cardiac hypertrophy is still controversial. In this study, we aimed to investigate the roles and mechanisms of FKBP12.6 in angiotensin II (AngII)‐induced cardiac hypertrophy using various transgenic mouse models in vivo and in vitro. FKBP12.6 knockout (FKBP12.6^−/−) mice and cardiac‐specific FKBP12.6 overexpressing (FKBP12.6 TG) mice were infused with AngII (1500 ng/kg/min) for 14 days subcutaneously by implantation of an osmotic mini‐pump. The results showed that FKBP12.6 deficiency aggravated AngII‐induced cardiac hypertrophy, while cardiac‐specific overexpression of FKBP12.6 prevented hearts from the hypertrophic response to AngII stimulation in mice. Consistent with the results in vivo, overexpression of FKBP12.6 in H9c2 cells significantly repressed the AngII‐induced cardiomyocyte hypertrophy, seen as reductions in the cell sizes and the expressions of hypertrophic genes. Furthermore, we demonstrated that the protection of FKBP12.6 on AngII‐induced cardiac hypertrophy was involved in reducing the concentration of intracellular Ca²⁺ ([Ca²⁺]i), in which the protein significantly inhibited the key Ca²⁺/calmodulin‐dependent signalling pathways such as calcineurin/cardiac form of nuclear factor of activated T cells 4 (NFATc4), calmodulin kinaseII (CaMKII)/MEF‐2, AKT/Glycogen synthase kinase 3β (GSK3β)/NFATc4 and AKT/mTOR signalling pathways. Our study demonstrated that FKBP12.6 protects heart from AngII‐induced cardiac hypertrophy through inhibiting Ca²⁺/calmodulin‐mediated signalling pathways.