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EGCG preconditioned adipose derived stem cell confers enhanced neuroprotection in aged Wistar rats.
Adipose derived mesenchymal stem cells (ADSCs) co-cultured with Epigallocatechin gallate were injected into 20 month aged Wistar rats. Haematoxylin and eosin staining of the cerebral cortex revealed noticeable neurogenic activity and visible improvements in the integrity of the pre frontal cortex tissue compared to ADSC treatment alone. Western blot tests confirmed that ADSCs co-cultured with EGCG enhances cell survival via the p-AKTs473 pathway and improves mitochondrial biogenesis via the SIRT1 pathway while increasing available Brain-derived neurotrophic factor compared to the ADSC group. Furthermore, western blotting shows that EGCG improves the antioxidant activity of the ADSCs in the cortex tissues via the Nrf-2 and HO-1 pathway. However, when miRNA-3575 mimic or inhibitor co-cultured with ADSC was administered, no marked improvements over ADSC alone were detected. Based on these findings, we propose that this variation in EGCG administration combined with stem cell treatment may facilitate functional recovery and enhanced neuroprotection in the aged brain.
The disease of aging is one of mankind’s most aggressive battles. Until modern times, humans have had to focus on developing cures and vaccines for ever present immediate dangers. Such dangers and diseases were usually environmental in origin and many had a strong chance of mortally affecting humans during youth and middle age. As medical technology and sanitary conditions were introduced and developed, so has our ability to gain a deeper understanding of the human body and live longer and fuller lives.
Living longer has always been the goal, and as mankind slowly succeeded in managing illnesses with external origins, so our focus turned inward to focus on disorders with internal origins that commonly affect the aged. Aging has only been more formally classified as a conquerable disease in 1983 when Klass et al. isolated the first long lived strains of Caenorhabditis elegans mainly through dietary restrictions which has since shown to extend lifespan in seemingly all tested eukaryotic species as well as non-human primates (Colman et al., 2009; Fontana et al., 2010; Mattison et al., 2012). This served as a proof of concept that life can be extended and from this point, medical science began more fervently defining the characteristics of aging and elucidating the pathways for each component. Even today, many details of the aging process remain a mystery, but astounding progress is being made with ever more sophisticated methods of analysis.
López-Otín et al. in a 2013 review made parallels to cancer and aging, coming to the conclusion that although seemingly different, each “can be regarded as two different manifestations of the same underlying process—namely, the accumulation of cellular damage.” Cumulative cellular and molecular damage leading to a loss of function is, in essence, the definition of aging. As the DNA damages accumulate and stem cell reserves become unable to maintain proper tissue homeostasis and function, the organism gradually loses the ability to heal itself and tries to compensate via the upregulation of certain pathways which originally served a useful purpose but, now under excessive conditions, begin to exacerbate the problem and cause irreversible damage as in the case of Reactive Oxygen Species (ROS) stress (Rossi et al., 2007, Hekimi et al., 2011). Hekimi et al. in 2011 reevaluated the role of ROS as we age stating that it normally acts as a cell signal to propagate, even showing some examples where knock-out organisms with higher ROS production tended to live longer (Lapointe et al. 2008). The caveat was that during the second half of our lives, ROS overproduction overwhelms the cell’s protective measures and begins to cause increasing amounts of cellular and DNA damage.
Aging tends to affect the entire organism and all cells. The body will not have the plasticity of youth and signs of aging can manifest themselves in recognizable visible symptoms. However, especially in more social animals such as mammals, these symptoms are sometimes most apparent in changes in the interactions and behaviors of the animal and its surroundings. The cerebral cortex is the most evolved structure in the mammalian brain, with a prominent role in governing cognition, behavior, emotion and decision making (Bechara et al. 2000). However, this region is highly impacted by aging as it begins to atrophy and thin to the point where magnetic resonance imaging shows a noticeable difference by middle age (Salat et al. 2004). As the cortex continues aging, unusual behavior and decision making may develop and be readily tolerated among the elderly in our own society because of the familial and social buffers helping prevent grave errors in judgement, but among aged animals in the wild, unnecessary risks combined with impaired motor function can easily be fatal. Therefore the brain, and the cerebral cortex in particular, can be considered one of the most crucial areas impacted by aging.
We chose to experiment with adipose derived stem cells (ADSC) because previous experiments have shown that they provide neuroprotection if administered intravenously to ischemic stroke rat models shortly after inducing a stroke, and neurogenesis and repair when administered weeks or more after the stroke (Gutiérrez-Fernández et al. 2015). This all points to ADSCs being able to adequately permeate the blood brain barrier and provide relief in the damaged area if administered with the low risk intravenous method. ADSCs are pluripotent and so are able to differentiate themselves depending on their surrounding tissue. This would be beneficial to stroke patients as they tend to be at an advanced age at stroke onset and would benefit from a holistic approach to therapy in their weakened state. Furthermore, there is evidence that damaged neural tissues respond positively to just the extract of ADSCs even in tissues where donor cells are not found, confirming that secreted factors likely also confer therapeutic effects and that these effects may help integrate both host and donor cells to repair brain damage together and more robustly (Zhao et al. 2017).
We also considered the common antioxidant and bioactive polyphenol found in green tea (Camellia sinensis), epigallocatechin-3-gallate (EGCG), for this experiment. EGCG is already consumed around the world and previous experiments have confirmed its capability of not only permeating the blood brain barrier but inducing nerve cell proliferation in rat cerebral cortices as well as potentially counteracting axonal growth inhibitors and creating a local environment conducive to neural growth (Lin et al. 2007, Pervin et al. 2016, Gopalakrishna et al. 2016). EGCG has also been shown to positively affect highly damaged post ischemic stroke cortex tissue by attenuating ROS and upregulating glutathione and NRF2 along the Antioxidant Response Element pathway which had a final effect of decreasing the infarction size (Han et al. 2014). Normally, EGCG increases mitochondrial membrane potential and oxidative phosphorylation in both neurons and astrocytes by activating Cytochrome C oxidase (CcO) which causes a net increase in the production of ATP and, at higher doses, ROS (Castellano-González et al. 2016). In their recent work with C. Elegans, Xiong et al. in 2018 found that EGCG causes cellular metabolism to increase in tandem with ROS production which then subsequently activates an antioxidant and cellular proliferation response. This increased the longevity and rate of mitochondrial biogenesis of the organism in a dose dependent manner via the activation of AMPK and SIRT-1, however, this effect was strongest in the first half of the organism’s life and tapered off afterwards.
Sirtuin-1 is a well-known histone deacetylase said to be partly responsible for the enhanced lifespans of experimental models subject to dietary restrictions. However, it also deacetylates its first known nonhistone target, P53, a powerful tumor suppressor, with which it has a strong interplay in tumorigenesis and senescence (Yi et al. 2010). P53 is also known to be activated under conditions of increased ROS or aging, and can even be induced by chemical means that bring about either of these factors (Hsu et al. 2016). Although SIRT-1’s role in aging is still controversial, recent studies have made progress in elucidating ways that SIRT-1 overexpression in the dorsomedial and lateral hypothalamic nuclei areas of the brain can indeed increase the lifespan of mice when combined with increased orexin type 2 receptor (Ox2r) expression (Satoh et al. 2013). This shows that there are still many complexities yet to be understood about this keystone protein as well as its role with P53.
Aging and even a poor diet can decrease an organism’s antioxidant defenses in a pathological manner (Zheltova et al. 2016). Heme oxygenase 1 (HO-1) is an enzyme that catalyzes the conversion of pro-oxidant free floating heme into ferritin and bilirubin, both of which have antioxidant properties. A byproduct of this conversion is carbon monoxide which, in appropriate quantities, ultimately induces anti-apoptotic and anti-inflammatory factors and may even activate Nuclear factor erythroid 2–related factor 2 (Nrf-2) which is an upstream signaling protein for HO-1 (Pae et al. 2008). EGCG is a potent activator of Nrf-2 and recent studies have shown that it functions by disabling the Nrf-2 inhibitor, Kelch-like ECH-associated protein 1 (Keap1) which normally keeps Nrf-2 bound to itself in the cell cytoplasm (Sun et al. 2017). The final result of activating both of these proteins is an increased antioxidant capacity as the Antioxidant Response Element (ARE) within the cell is also activated, protecting the cell from oxide stress induced cell death (Han et al. 2014).
In order to attempt to remedy the regional thinning of the rat cerebral cortex, we tested three comparative alternatives. The first was to inject young ADSCs into aged Wistar rat models. The second was to first precondition the young ADSCs by co-culturing them with EGCG antioxidants before injecting them intravenously into the rat. The third was to co-culture the young ADSCs with a micro RNA (miRNA) 3575 mimic or inhibitor before injection. MiRNA functions as a messenger RNA (mRNA) suppressor, thereby changing the gene and downstream protein coding expression by binding to and silencing the mRNA. MiRNA mimics are synthetic double stranded copies of RNA that mimic the mature target miRNA in the organism and upregulate its function, whereas miRNA inhibitors downregulate the organism’s miRNA’s function by binding to and rendering the target miRNA inactive.
MiRNA 3575 has a looped structure and its active regions are coded as
It has been predicted to target the protein hypoxia-inducible factor-1 alpha (HIF-1α) with a target rank of 3 and a score of 99 (mirbase.org, miRDB.org). HIF-1 plays a key role in mediating the recruitment and homing of progenitor cells to injured tissue under hypoxic conditions, such as would be seen in ischemic stroke, so we included miRNA 3575 in this study to ascertain what effect it would have on the homing, and overall curative, capabilities of the injected ADSCs under normoxia conditions of the damaged aged brain. (Ceradini et al. 2005).
The beneficial effects of both ADSCs and EGCG on the mammalian brain is well documented. The purpose of this study is to investigate whether undifferentiated ADSCs co cultured with 10µM of EGCG would have a synergistic ameliorating effect on the aged rat cerebral cortex than either treatment would alone if injected intravenously through the rat tail vein at a concentration of 1 x 106 cells.
This comparative in vivo experiment used 28 male Wistar rat pups (Rattus norvegicus) purchased from LASCO Biotechnology at 8 weeks of age. The animals were maintained in plastic cages with sawdust bedding and fed a standard diet with filtered water access provided ad libitum. They followed a 12-hour light-dark cycle with a controlled ambient temperature and were acclimatized for 1 month before the procedure began. All applicable rules concerning ethical treatment of animals were followed using the guidelines laid out by the Taiwan Society for Laboratory Animals Sciences for the care and use of laboratory animals.
ADSCs were isolated from the adipose tissue of the 3 month old rats following a previously described method (Ren et al. 2012). The primary ADSCs were then cultured in low glucose Dulbecco’s Modified Eagle’s Medium (DMEM-D2902; Sigma-Aldrich, St. Louis, MO, USA) with 10% Fetal Bovine Serum and 1% penicillin/streptomycin up to 80% confluence before subculturing with a 0.25% trypsin/0.02 mM EDTA solution, and seeding at a density of 1 x 104 cells/cm2. The rats were divided into five groups. The control group (N=7) did not receive any treatment, the ADSC group (N=6) received ADSCs, the ADSC + EGCG group (N=6) received ADSCs co-cultured with 10µM of EGCG, the ADSC + miR-3575 mimic group (N=4) received ADSCs co-cultured with 10nM of miR-3575, and the ADSC + miR-3575 inhibitor group (N=5) received ADSCs co-cultured with 20nM of miR-3575 inhibitor. All treated rats received 1 x 106 ADSCs at 20 months of age and were sacrificed at 22 months for analyses.
The whole brains of all rats were extracted, blood was removed with ice cold PBS, the brain tissues were kept in 4% Paraformaldehyde, and the cortex tissue was separated from the hippocampus with extra attention towards the prefrontal cortex. The tissue was homogenized in lysis buffer (iNtRON Pro Prep, cat. 17081) at a concentration of 100mg tissue/3ml of buffer and then placed in -80℃ for 12 hours. The homogenates were then placed on ice for 15 minutes and then centrifuged at 12,000 rpm for 40 minutes. The supernatant from each sample was collected and stored in -80℃ for future analyses.
The cortex tissues were first placed in formalin then encased in paraffin. The slides were immersed in a series of ethanol concentrations (100, 95 and 75%), each for 15 minutes, then stained with hematoxylin and eosin (H&E), and finally rinsed with water. The slides were then dehydrated through serial ethanol concentrations for 15 minutes each, cleaned with xylene, and had their coverslips placed on. Photomicrographs were taken using a Zeiss Axiophot microscope (Zeiss, Oberkochen, Germany). The photos taken all concentrate on the same area of prefrontal cortex at 200x magnification to better observe the cell morphology of the tissues.
A Bradford protein assay was performed using protein dye (Bio-Rad, Richmond, CA, USA, cat.500-0006) and Bovine Serum Albumin (UniRegion Bio-Tech, UR-BSA-001). BSA was first used as the protein standard in serial dilutions with double deionized water (ddH2O), to which the protein assay dye was added, into a 96-well plate and incubated at room temperature for 5 minutes. Changes in optical density were then measured at 595 nm and plotted to elicit the standard curve. Quantification of the cortex samples was done in triplicate by adding previously collected supernatant to the protein dye in a 96 well plate, measuring the absorbance at 595 nm, and comparing the results against the standard curve formula in order to determine accurate protein concentrations. The samples were diluted with ddH2O and loading dye as required and placed on a 100℃ hot plate for 10 minutes then an ice bath for 10 minutes before being stored in -20℃ while not in use.
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