Neurohormonal activation induces intracellular iron deficiency and mitochondrial dysfunction in cardiac cells

Background

Iron deficiency (ID) is common in patients with heart failure (HF) and is associated with poor outcomes, yet its role in the pathophysiology of HF is not well-defined. We sought to determine the consequences of HF neurohormonal activation in iron homeostasis and mitochondrial function in cardiac cells.

Methods

HF was induced in C57BL/6 mice by using isoproterenol osmotic pumps and embryonic rat heart-derived H9c2 cells were subsequently challenged with Angiotensin II and/or Norepinephrine. The expression of several genes and proteins related to intracellular iron metabolism were assessed by Real time-PCR and immunoblotting, respectively. The intracellular iron levels were also determined. Mitochondrial function was analyzed by studying the mitochondrial membrane potential, the accumulation of radical oxygen species (ROS) and the adenosine triphosphate (ATP) production.

Results

Hearts from isoproterenol-stimulated mice showed a decreased in both mRNA and protein levels of iron regulatory proteins, transferrin receptor 1, ferroportin 1 and hepcidin compared to control mice. Furthermore, mitoferrin 2 and mitochondrial ferritin were also downregulated in the hearts from HF mice. Similar data regarding these key iron regulatory molecules were found in the H9c2 cells challenged with neurohormonal stimuli. Accordingly, a depletion of intracellular iron levels was found in the stimulated cells compared to non-stimulated cells, as well as in the hearts from the isoproterenol-induced HF mice. Finally, neurohormonal activation impaired mitochondrial function as indicated by the accumulation of ROS, the impaired mitochondrial membrane potential and the decrease in the ATP levels in the cardiac cells.

Conclusions

HF characteristic neurohormonal activation induced changes in the regulation of key molecules involved in iron homeostasis, reduced intracellular iron levels and impaired mitochondrial function. The current results suggest that iron could be involved in the pathophysiology of HF.

The pathophysiology of triose phosphate isomerase dysfunction in Alzheimer's disease

Alzheimer's disease (AD), the most prevalent neurodegenerative disease worldwide, has two main hallmarks: extracellular deposits of amyloid β-peptide (Aβ) and intracellular neurofibrillary tangles composed by tau protein. Most AD cases are sporadic and are not dependent on known genetic causes; aging is the major risk factor for AD. Therefore, the oxidative stress has been proposed to initiate the uncontrolled increase in Aβ production and also to mediate the Aβ's deleterious effects on brain cells, especially on neurons from the cortex and hippocampus. The production of free radicals in the presence of nitric oxide (NO) yields to the peroxynitrite generation, a very reactive agent that nitrotyrosinates the proteins irreversibly. The nitrotyrosination produces a loss of protein physiological functions, contributing to accelerate AD progression. One of the most nitrotyrosinated proteins in AD is the enzyme triosephosphate isomerase (TPI) that isomerises trioses, regulating glucose consumption by both phosphate pentose and glycolytic pathways and thereby pyruvate production. Hence, any disturbance in the glucose supply could affect the proper brain function, considering that the brain has a high rate of glucose consumption. Besides this directly affecting to the energetic metabolism of the neurons, TPI modifications, such as mutation or nitrotyrosination, increase methylglyoxal production, a toxic precursor of advanced glycated end-products (AGEs) and responsible for protein glycation. Moreover, nitro-TPI aggregates interact with tau protein inducing the intraneuronal aggregation of tau. Here we review the relationship between modified TPI and AD, highlighting the relevance of this protein in AD pathology and the consequences of protein nitro-oxidative modifications.

[Effects of melatonin in the brain of the senescence-accelerated mice-prone 8 (SAMP8) model]

Senescence-accelerated mice (SAM) represent an aging model establish by selective inbreeding of the AKR/J strain. SAMP8 is a suitable model to study the genetics or proteics fundamental mechanisms of aging, in physiological or pathological conditions, because SAMP8 develop neuropathological markers also found in neurodegenerative diseases like Alzheimer. Melatonin is known as sleep hormone because its action controlling the sleep/awake circadian rhythm. Moreover, melatonin has antioxidant properties and may have an important anti-aging role. The chronic treatment with melatonin in the SAMP8 model was able to reduce oxidative stress and the neurodegenerative calpain/Cdk5 pathway and primed phosphorylation of GSK3beta and tau hiperphosphorylation markers of cerebral aging and neurodegeneration in SAMP8 brains, indicating the neuroprotective and anti-aging effect of melatonin.

Neuroprotective role of intermittent fasting in senescence-accelerated mice P8 (SAMP8)

Dietary interventions have been proposed as a way to increase lifespan and improve health. The senescence-accelerated prone 8 (SAMP8) mice have a shorter lifespan and show alterations in the central nervous system. Moreover, this mouse strain shows decreased sirtuin 1 protein expression and elevated expression of the acetylated targets NFkappaB and FoxO1, which are implicated in transcriptional control of key genes in cell proliferation and cell survival, in reference to control strain, SAMR1. After eight weeks of intermittent fasting, sirtuin 1 protein expression was recovered in SAMP8. This recovery was accompanied by a reduction in the two acetylated targets. Furthermore, SAMP8 showed a lower protein expression of BDNF and HSP70 while intermittent fasting re-established normal values. The activation of JNK and FoxO1 was also reduced in SAMP8 mice subjected to an IF regimen, compared with control SAMP8. Our findings provide new insights into the participation of sirtuin 1 in ageing and point to a potential novel application of this enzyme to prevent frailty due to ageing processes in the brain.

Anti-aging properties of melatonin in an in vitro murine senescence model: involvement of the sirtuin 1 pathway

Sirtuin 1 is a member of the sirtuin family of protein deacetylases, which have attracted considerable attention as mediators of lifespan extension in several model organisms. Induction of sirtuin 1 expression also attenuates neuronal degeneration and death in animal models of Alzheimer's disease and Huntington's disease. In this study, an in vitro model of neuronal aging was used to test in several ways whether melatonin acts as a sirtuin 1 inducer and if this effect could be neuroprotective. It is shown that melatonin is able to increase the level of this deacetylase in young primary neurons, as well as in aged neurons. We also observed an increase in the deacetylation of several substrates of sirtuin 1, such as p53, PGC-1alpha, FoxO1, ADAM10 and NFkappaB. In addition, there was a reduction in its nuclear translocation and, subsequently, an improvement in transcriptional activity. Sirtinol, a sirtuin 1 inhibitor, was used to correlate these effects with sirtuin. It is shown that sirtinol reduces sirtuin 1 expression and impairs the beneficial action of melatonin on cell viability and apoptosis prevention. Moreover, some of the sirtuin 1 substrates studied also reversed the melatonin effect when sirtinol is added to the cells, mainly p53. Globally, these results add weight to the findings of previous reports, indicating a new role for melatonin in improving cell function gated to an increased neuroprotective role for the sirtuin 1 pathway.

Inhibition of cyclin-dependent kinases is neuroprotective in 1-methyl-4-phenylpyridinium-induced apoptosis in neurons

The biochemical pathways involved in neuronal cell death in Parkinson's disease are not completely characterized. Mitochondrial dysfunction, specifically alteration of the mitochondrial complex I, is the primary target of the parkinsonian neurotoxin 1-methyl-4-phenylpyridinium (MPP+) induced apoptosis in neurons. In the present study, we examine the role of caspase-dependent and -independent routes in MPP+-induced apoptosis in rat cerebellar granule neurons (CGNs). We show a distinct increase in the expression of the cell cycle proteins cyclin D, cyclin E, cdk2, cdk4 and the transcription factor E2F-1 following a MPP+ treatment of CGNs. Flavopiridol (FLAV), a broad inhibitor of cyclin-dependent kinases (CDKs), attenuated the neurotoxic effects of MPP+ and significantly attenuates apoptosis mediated by MPP+ 200 microM. Likewise, the antioxidant vitamin E (vit E) increases neuronal cell viability and attenuates apoptosis induced by MPP+. Moreover, the expression levels of cyclin D and E2F-1 induced by this parkinsonian neurotoxin were also attenuated by vit E. Since, the broad-spectrum caspase inhibitor zVAD-fmk did not attenuate MPP+-induced apoptosis in CGNs, our data provide a caspase-independent mechanism mediated by neuronal reentry in the cell cycle and increased expression of the pro-apoptotic transcription factor E2F-1. Our results also suggest a potential role of oxidative stress in neuronal reentry in the cell cycle mediated by MPP+. Finally, our data further support the therapeutic potential of flavopiridol, for the treatment of Parkinson's disease.

Evaluation of acute antiapoptotic effects of Li+ in neuronal cell cultures

Li(+) exerts protective effect against several neurotoxins in neuronal cell preparations. Here we examined the antiapoptotic effects of GSK3beta in cerebellar granule neurons (CGNs) in the presence of several neurotoxins. Acute treatment with Li(+) protected neurons against nocodazole and serum/potassium (S/K) deprivation, but were ineffective against kainic acid and MPP(+). Li(+) 5 mM also decreased caspase-3 activation induced by nocodazole and S/K deprivation as measured by Ac-DEVD-p-nitroaniline and the breakdown of alpha-spectrin. All the neurotoxins used in the present study activated GSK3beta, evaluated with a specific antibody phospho-GSK-3beta (Ser9) by Western-blot and immunocytochemistry and were always inhibited by Li(+) 5 mM. Our results implicate Li(+) in the regulation of apoptosis mediated by caspase activation (Type I). Furthermore inhibition of GSK3beta by acute treatment with Li(+) 5 mM is not an indicator of neuroprotection. The acute antiapoptotic function of Li(+) is discussed in terms of its inhibition of Type I pathway, the intrinsic (mitochondrial) apoptotic pathway in cerebellar granule cells.