Cell. Mol. Life Sci. (2016) 73:201–215

Sex hormone-related neurosteroids differentially rescue bioenergetic deficits induced by amyloid-β or hyperphosphorylated tau protein

 

Amandine Grimm 1,2,3, Emily E. Biliouris 1,2, Undine E. Lang 2, Jürgen Götz 4, Ayikoe Guy Mensah-Nyagan 3, Anne Eckert 1,2

1 Neurobiology Laboratory for Brain Aging and Mental Health, Transfaculty Research Platform, Molecular and Cognitive Neuroscience, University of Basel, Wilhelm Klein-Str. 27, 4012 Basel, Switzerland

2 Psychiatric University Clinics, University of Basel, Wilhelm Klein-Str. 27, 4012 Basel, Switzerland

3 Biopathologie de la Myéline, Neuroprotection et Stratégies Thérapeutiques, INSERM U1119, Fédération de Médecine Translationnelle de Strasbourg (FMTS), Université de Strasbourg, Bâtiment 3 de la Faculté de Médecine, 11 rue Humann, 67 000 Strasbourg, France

4 Clem Jones Centre for Ageing Dementia Research (CJCADR), Queensland Brain Institute (QBI), The University of Queensland, Brisbane 4072, QLD, Australia

 

Abstract:

Alzheimer’s disease (AD) is an age-related neurodegenerative disease marked by a progressive cognitive decline. Metabolic impairments are common hallmarks of AD, and amyloid-β (Aβ) peptide and hyperphosphorylated tau protein—the two foremost histopathological signs of AD—have been implicated in mitochondrial dysfunction. Neurosteroids have recently shown promise in alleviating cognitive and neuronal sequelae of AD. The present study evaluates the impact of neurosteroids belonging to the sex hormone family (progesterone, estradiol, estrone, testosterone, 3α-androstanediol) on mitochondrial dysfunction in cellular models of AD: human neuroblastoma cells (SHSY5Y) stably transfected with constructs encoding (1) the human amyloid precursor protein (APP) resulting in overexpression of APP and Aβ, (2) wild-type tau (wtTau), and (3) mutant tau (P301L), that induces abnormal tau hyperphosphorylation. We show that while APP and P301L cells both display a drop in ATP levels, they present distinct mitochondrial impairments with regard to their bioenergetic profiles. The P301L cells presented a decreased maximal respiration and spare respiratory capacity, while APP cells exhibited, in addition, a decrease in basal respiration, ATP turnover, and glycolytic reserve. All neurosteroids showed beneficial effects on ATP production and mitochondrial membrane potential in APP/Aβ overexpressing cells while only progesterone and estradiol increased ATP levels in mutant tau cells. Of note, testosterone was more efficient in alleviating Aβ-induced mitochondrial deficits, while progesterone and estrogen were the most effective neurosteroids in our model of AD-related tauopathy. Our findings lend further support to the neuroprotective effects of neurosteroids in AD and may open new avenues for the development of gender specific therapeutic approaches in AD.

PMID: 26198711

 

Supplement:

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder that currently affects about 2% of the population in industrialized countries and accounts for more than 60% of all dementia cases. The disease is marked by a progressive physical and cognitive decline, coupled with a large brain hypometabolism. Increasing evidence support that mitochondrial deficits are a prominent and early event of the disease, and the two foremost histopathological signs of AD, namely the presence of extracellular senile plaques, composed of aggregated amyloid-β peptide (Aβ), as well as intracellular neurofibrillary tangles (NFT), consisting of aggregates of abnormally hyperphosphorylated tau protein, have been implicated in mitochondrial dysfunction [1].

Neurosteroids constitute a category of steroids that are synthetized within the nervous system, independently of peripheral endocrine glands, and act on the nervous system in an auto/paracrine configuration. Neurosteroids are involved in a broad range of brain-specific functions and a growing body of evidence attests that neurosteroids possess strong neuroprotective properties. In particular, many studies are focused on estradiol which is also known to boost bioenergetic metabolism in cells [2]. In a previous study, we tested the effects of a panel of neurosteroids (progesterone, estradiol, estrone, testosterone, 3α-androstanediol, dehydroepiandrosterone (DHEA) and allopregnanolone) on cellular bioenergetics using human SH-SY5Y neuroblastoma cells [3]. Most of the neurosteroids we tested improved the bioenergetic metabolism in neuronal cells by increasing ATP levels, mitochondrial membrane potential and basal mitochondrial respiration, possibly via nuclear steroid receptor activation.

Based on these findings, we hypothesized that neurosteroids were able to alleviate AD-related bioenergetic deficits.

Thus, we aimed to investigate whether neurosteroids, and more specifically steroids that also belong to the sex hormones family (progesterone, estradiol, estrone, testosterone, 3α-androstanediol), could attenuate the toxic effects of Aβ and abnormal tau on bioenergetic parameters, such as ATP production and mitochondrial respiration using cellular models of AD (SH-SY5Y neuroblastoma cells overexpressing either the human amyloid precursor protein (APP/Aβ) or mutant tau (P301L) compared to control cells expressing the empty vector (Mock cells) and the wildtype form of tau protein (wtTau), respectively). Total ATP content was determined using a bioluminescence assay (ViaLighTM HT; Cambrex Bio Science) according to the instructions of the manufacturer, and the investigation of mitochondrial respiration was performed using the Seahorse Bioscience XF24 analyzer.

 

Table 1: Sex hormone-related neurosteroids increase mitochondrial bioenergetics in cellular models of AD.

Table 1APP: amyloid precursor protein (APP); Mock: empty vector; P301L: mutant tau protein; wtTau: wild-type tau protein; single arrow ↑: increase with all the neurosteroids tested; ↑(T): increase only with testosterone; ↑(T, 3α): increase only with testosterone and 3α-androstanediol; ↑(P, E2): increase only with progesterone and estradiol.

 

 

We first demonstrated that the presence of APP/Aβ and mutant tau protein differentially impacted mitochondrial respiration [4]. In line with previous studies, both AD pathogenic features induced a decrease in ATP levels (Table 1). However, the presence of abnormal tau protein (in P301L cells) only impaired the maximal mitochondrial respiration and spare respiratory capacity, whereas the overexpression of APP/Aβ induced, in addition, a decrease in basal respiration and ATP turnover. Of note, in previous publications, we demonstrated that APP/Aβ overexpressing cells present an impairment in mitochondrial complex IV activity [5], whereas complex I activity was impacted in P301L cells [6] (Figure 1). These findings can explain the different bioenergetic output observed between APP/Aβ and abnormal tau-overexpressing cells.

All the neurosteroids tested showed beneficial effects on ATP production and mitochondrial membrane potential in APP/Aβ overexpressing cells. Interestingly, only progesterone (P) and estradiol (E2) increased ATP levels in mutant tau cells (P301L) (Table 1). In addition, we showed that testosterone (T), that is also the main male steroid hormone, was more efficient to alleviate mitochondrial deficits induced by APP/Aβ by increasing the basal respiration, ATP turnover, maximal respiration and spare respiratory capacity (Table 1). In contrast, neurosteroids belonging to the family of female steroid hormones, progesterone and estradiol, increased these bioenergetic parameters only in our cellular model of AD-related tauopathies (Table 1). This protective pattern was not only evident under physiological but also in oxidative stress conditions induced by a treatment with hydrogen peroxide (H2O2).

It is very interesting to observe that sex steroid hormones present distinct mitochondrial improvements with regard to their bioenergetic profiles in the presence of Aβ-related or tau-related mitochondrial dysfunction (Figure 1). Epidemiological studies report that two third of AD patients are women, and exhibit also greater senile plaque deposition than men as well as a higher vulnerability to oxidative damage [2]. Accordingly, the sudden drop of estrogen after the menopause, as well as the age-related decrease in sex hormone levels, has been proposed to be one risk factor in AD. And based on these observations and on the data we obtained, one can ask the question whether women and men differently respond to mitochondrial insults mediated by either Aβ or abnormal tau.

Importance of this study:

Together, our findings lend further evidence to the neuroprotective effects of sex hormone-related neurosteroids in AD pathology and indicate that these molecules represent promising tools which are able to increase bioenergetics via enhancement of mitochondrial respiration. Our results provide a potential molecular basis for the beneficial and neuroprotective effects of neurosteroids, which may open new avenues for the development of gender-based therapeutic approaches with regard to targeting mitochondria in AD.

 

 

Figure 1

Figure 1: Hypothetic representation of the effects of sex hormone-related neurosteroids on mitochondrial bioenergetics in the presence of Aβ or abnormally hyperphosphorylated tau protein.

Previous studies showed that abnormally hyperphosphorylated tau protein and Aβ impair mitochondrial respiration by inhibiting the electron transport chain complex I and IV, respectively. Based on our own data and those reported by others, we hypothesize that neurosteroids can rescue the AD-induced mitochondrial deficits at two levels by (1) directly boosting mitochondrial function, probably via the regulation of genes involved in mitochondrial respiration; and (2) decreasing amyloid-β (Aβ) accumulation and tau hyperphosphorylation, thereby alleviating mitochondrial impairments induced by Aβ and tau. An interaction between these mechanisms is not excluded. P: progesterone; E2: estradiol; T: testosterone; ♂: male symbol; ♀: female symbol.

 

 

References

  1. Schmitt K, Grimm A, Kazmierczak A, Strosznajder JB, Götz J, Eckert A (2012) Insights into mitochondrial dysfunction: aging, amyloid-beta, and tau-A deleterious trio. Antioxid Redox Signal 16 (12):1456-1466. doi:10.1089/ars.2011.4400
  2. Grimm A, Lim YA, Mensah-Nyagan AG, Götz J, Eckert A (2012) Alzheimer’s disease, oestrogen and mitochondria: an ambiguous relationship. Mol Neurobiol 46 (1):151-160. doi:10.1007/s12035-012-8281-x
  3. Grimm A, Schmitt K, Lang UE, Mensah-Nyagan AG, Eckert A (2014) Improvement of neuronal bioenergetics by neurosteroids: implications for age-related neurodegenerative disorders. Biochim Biophys Acta 1842 (12 Pt A):2427-2438. doi:10.1016/j.bbadis.2014.09.013
  4. Grimm A, Biliouris EE, Lang UE, Götz J, Mensah-Nyagan AG, Eckert A (2016) Sex hormone-related neurosteroids differentially rescue bioenergetic deficits induced by amyloid-beta or hyperphosphorylated tau protein. Cellular and molecular life sciences : CMLS 73 (1):201-215. doi:10.1007/s00018-015-1988-x
  5. Rhein V, Baysang G, Rao S, Meier F, Bonert A, Muller-Spahn F, Eckert A (2009) Amyloid-beta leads to impaired cellular respiration, energy production and mitochondrial electron chain complex activities in human neuroblastoma cells. Cell Mol Neurobiol 29 (6-7):1063-1071. doi:10.1007/s10571-009-9398-y
  6. Schulz KL, Eckert A, Rhein V, Mai S, Haase W, Reichert AS, Jendrach M, Muller WE, Leuner K (2012) A new link to mitochondrial impairment in tauopathies. Mol Neurobiol 46 (1):205-216. doi:10.1007/s12035-012-8308-3

 

Acknowledgments

This work was supported by grants from Synapsis Foundation, Novartis Foundation for Biomedical Research Basel, and the Swiss National Science Foundation (#31003A_149728) to AE.

 

Contact

Prof. Dr. Anne Eckert

Neurobiology Laboratory for Brain Aging and Mental Health, Transfaculty Research Platform, Molecular and Cognitive Neuroscience, Psychiatric University Clinics, University of Basel, Wilhelm Klein-Str. 27, 4012 Basel, Switzerland

anne.eckert@upkbs.ch

https://mcn.unibas.ch/research/neurobiology

http://www.upkbs.ch

 

 

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