先前研究指出，肥胖的人會有較高的雌激素或雌二醇，雌激素或雌二醇會被代謝成雌激素代謝物，其中2-羥基雌二醇(2OHE2)和4-羥基雌二醇(4OHE2)是雌二醇的代謝物，分別由CYP1A1/2和CYP1B1催化。4-羥基雌二醇也是一種致癌代謝物，其可能導致DNA斷裂，並且在大多數乳腺癌細胞株中高度表達。相比之下，2-羥基雌二醇可以抑制癌症的增殖，發炎和血管生成。這兩種化合物可能透過代謝腦中停留的雌激素存在於中樞神經系統(CNS)。然而，兩種雌激素代謝物在腦中的作用尚不清楚。在本研究中，我們觀察2OHE2和4OHE2對星狀膠質細胞的生理功能的影響，星狀膠質細胞是保持離子和神經遞質穩態並在中樞神經系統中支持神經能量代謝的神經膠質細胞群。結果表明，用5和10μM的4OHE2處理24小時後，星狀膠質細胞的形態從平坦的形態轉變成細長的形態。然而，2OHE2處理後沒有觀察到對星狀膠質細胞形態的影響。在10 μM 4OHE2處理七天後也有觀察到細胞形態的改變。此外，4OHE2與2OHE2都會降低星狀膠質細胞的細胞活性。而處理4OHE2與2OHE2後DNA修補能力會下降。只有經4OHE2處理後的星狀膠細胞有內質網壓力產生。當星狀膠質細胞處理2OHE2和4OHE2時，粒線體功能有下降。此外，2OHE2和4OHE2處理的星狀膠質細胞中清楚地觀察到脂質累積。在經過2OHE2和4OHE2處理後，mRNA表現量與蛋白質表現量都會受到影響。總之，雌激素代謝物2OHE2和4OHE2可以通過內質網壓力和線粒體功能障礙的增加而破壞星狀膠細胞體內平衡，可能導致星狀膠質細胞胞內代謝失調。

Previous studies have reported that obese people have higher estrogen or estradiol, which can be metabolized into estrogen metabolites. 2-hydroxyestradiol (2OHE2) and 4-hydroxyestradiol (4OHE2) are converted from estradiol by the catalysis of CYP1A1/2 and CYP1B1, respectively. 4OHE2 is known as a carcinogenic metabolite by generating single-strand DNA breaks in the most of breast cancer cell lines. In contrast, 2OHE2 can inhibit cancer proliferation, inflammation, and angiogenesis. The two compounds may be present in the central nervous system (CNS) by metabolizing the estrogen that remains in the brain. Yet, the effect of the two estrogen metabolites on the brain cells are unclear. In this study, we examined the effect of 2OHE2 and 4OHE2 on the physiological function of astrocytes, a glial cell population in the CNS, that maintain ion and neurotransmitter homeostasis and supports neural energy metabolism in the CNS. Our results first showed that the morphology of astrocytes was transformed from a flat fibroblast-like shape into a mesenchymal-like form after treatment with 5 and 10 M of 4OHE2 for 24 hours. Moreover, exposure to 4OHE2and 2OHE2reduced the cell viability of astrocytes.DNA repair efficiency also declined after exposure to 2OHE2 or 4OHE2 for 24 hours. Mitochondrial function was decreased when astrocytes treated with 2OHE2 or 4OHE2.Furthermore, the lipid accumulation was clearly observed in astrocytes treated with 4OHE2and 2OHE2.PPAR- mRNA expression and protein levels in astrocytes were altered by 2OHE2 and 4OHE2.Endoplasmic reticulum (ER) stress was only detected in astrocytes treated with 4OHE2. Altogether, estrogen metabolites,2OHE2 and 4OHE2, can disrupt astrocytic homeostasis by an increase in ER stress and mitochondrial dysfunction, possibly leading to metabolic imbalance in astrocytes.

Abbott N.J., Ronnback L., and Hansson E. 2006. Astrocyteendothelial interactions at the blood-brain barrier. Nat Rev Neurosci 7:41-53.

Anne-Lieke F. van Deijk NC, Jaap Timmerman, Tim Heistek,Jos F. Brouwers,Floriana Mogavero,Huibert D. Mansvelder,August B. Smit,Mark H.G. Verheijen. 2017. Astrocyte lipid metabolism is critical for synapse development and function in vivo. Glia 65:670-682.

Araque A, Parpura V, Sanzgiri R.P., Haydon P.G. 1999. Tripartite synapses: glia, the unacknowledged partner. Trends Neurosci 22:208-215.

Barnea E.R., MacLusky, N.J., Naftolin F. 1983. Kinetics of catechol estrogen–estrogen receptor dissociation: a possible factor underlying differences in catechol estrogen biological activity. Steroids 41:643– 656.

Bazan N.G. 2003. Synaptic lipid signaling: significance of polyunsaturated fatty acids and platelet-activating factor. J Lipid Res 44:2221-2233.

Brian P. K., Amita K., Kathryn A. G., Kim L. K., James P. G., Joseph R. K., Toni E. Z., and Ei T.2013.Neuroestradiol in the Hypothalamus Contributes to the Regulation of Gonadotropin Releasing Hormone Release. Neuroscience 33:19051–19059

Chistyakov DV,Aleshin SE, Astakhova AA, Sergeeva MG, Reiser G. 2015. Regulation of peroxisome proliferator-activated receptors (PPAR) α and -γ of rat brain astrocytes in the course of activation by toll-like receptor agonists. J Neurochem 134:113-124.

Chrast R, Saher, G., Nave, K. A., and Verheijen, M. H. 2011. Lipid metabolism in myelinating glial cells: lessons from human inherited disorders and mouse models. J Lipid Res 52:419–434.

Cristiano L, Cimini A, Moreno S, Ragnelli AM, Paola Cerù M. 2005. Peroxisome proliferator-activated receptors (PPARs) and related transcription factors in differentiating astrocyte cultures. Neuroscience 131:577-587.
Desvergne B ,Wahli W. 1999. Peroxisome proliferator-activated receptors: nuclear control of metabolism. Endocr Rev 20:649-688.

Dietschy JM, and Turley, S. D. 2004. Thematic review series: Brain Lipids. Cholesterol metabolism in the central nervous system during early development and in the mature animal. J. Lipid Res 45:1375-1397.

Edmond J.,Robbins R. A., Bergstrom J. D., Cole R. A., and de Vellis J. 1987. Capacity for substrate utilization in oxidative metabolism by neurons, astrocytes, and oiigodendrocytes from developing brain in primary culture. J Neurosci 18:551-561.

Fotsis T, Zhang, Y., Pepper, M.S., Aldecreutz, H., Montesano, R., Nawroth, P.P., Schwelgerer, L. 1994. The endogenous oestrogen metabolite 2-methoxyestradiol inhibits angiogenesis and suppresses tumor growth. Nature 368:237–239.

Han X, Liehr, J.G. 1994. 8-Hydroxylation of guanine bases in kidney and liver DNA of hamsters treated with estradiol: role of free radicals in estrogen-induced carcinogenesis. Cancer Res 54:5515– 5517.

Han X, Liehr, J.G. 1994. DNA single-strand breaks in kidneys of Syrian hamsters treated with steroidal estrogens: hormone-induced free radical damage preceding renal malignancy. Carcinogenesis 15:997-1000.

Hiraku Y, Yamashita, N., Nishiguchi, M., Kawanishi, S. 2001. Catechol estrogens induce oxidative DNA damage and estradiol enhances cell proliferation. Int J Cancer 92:333-337.

Hemsell DL, Grodin JM, Brenner PF, Siiteri PK, MacDonald PC. 1974. Plasma precursors of estrogen II. Correlation of the extent of conversion of plasma androstenidione to estrone with age. J Clin Endocrinol Metab;38:76–9.

Hofmann S ,Cherkasova V, Bankhead P, Bukau B, Stoecklin G. 2012. Translation suppression promotes stress granule formation and cell survival in response to cold shock. Molecular Biology of the Cell 23:3786–3800.

Leihr J.G, Ulubelen, A.A., Strobel, H.W. 1986. Cytochrome P-450-mediated redox cycling of estrogens. J Biol Chem 261:16865–16870.

Lopaschuk GD, Ussher, J.R., Folmes, C.D., Jaswal, J.S. and Stanley, W.C. 2010. Myocardial fatty acid metabolism in health and disease. Physiol Rev 90:207-258

Mauch DH, Nagler, K., Schumacher, S., Goritz, C., Muller, E. C., Otto, A., and Pfrieger, F. W. 2001. CNS synaptogenesis promoted by glia-derived cholesterol. Science 294:1354-1357.

McBride HM , Neuspiel M, Wasiak S. 2006. Mitochondria: more than just a powerhouse. Curr Biol 16:551–560.

McMillian MK , Thai L, Hong JS, O'Callaghan JP, Pennypacker KR. 1994. Brain injury in a dish: a model for reactive gliosis. Trends Neurosci 17:138-42.

Moore SA. 2001. Polyunsaturated fatty acid synthesis and release by brain-derived cells in vitro. J Mol Neurosci 16:195-200.

Naaz A, Zakroczymski M, Heine P, Taylor J, Saunders P, Lubahn D, Cooke PS. 2002. Effect of ovariectomy on adipose tissue of mice in the absence of estrogen receptor alpha (ERalpha): a potential role for estrogen receptor beta (ERbeta). Horm Metab Res;34:758–63

Pfrieger FW, and Ungerer, N. 2011. Cholesterol metabolism in neurons and astrocytes. Progress in Lipid Research 50:357-371.

Raff MC,Abney ER, Miller RH. . 1984. Two glial cell lineages diverge prenatally in rat optic nerve. Dev Biol 106:53-60.

Reichenbach A ,Siegel A, Senitz D, Smith TG Jr. 1992. A comparative fractal analysis of various mammalian astroglial cell types. Neuroimage 1:69-77.

Robinson A. M. and Williamson D.H. 1980. Physiological roles of ketone bodies as substrates and signals in mammalian tissues. Physiol Rev 60:143-187.

Runkel ED, Baumeister R, Schulze E. 2014. Mitochondrial stress: balancing friend and foe. Exp Gerontol 56:194–201.

Sandeep Tyagi PG, Arminder SS, Chaitnya K, and Saurabh S. 2011. The peroxisome proliferator-activated receptor: A family of nuclear receptors role in various diseases. J Adv Pharm Technol Res 2:236–240.

Schneider G, Kirschner MA, Berkowitz R, Ertel NH. 1979. Increased estrogen production in obese men.J Clin Endocrinol Metab, 48:633-638.

Schumacher G, Neuhaus, P. 2001. The physiological estrogen metabolite 2-methoxyestradiol reduces tumor growth and induces apoptosis in human solid tumors. J Cancer Res Clin Oncol 127:405-410.

Surojit P,SumantraD, Ranjana P,Pranab K.S. 1996. Role of Thyroid Hormone in the Morphological Differentiation and Maturation of Astrocytes: Temporal Correlation with Synthesis and Organization of Actin. European Journal of Neuroscience 21:26-32.

Tabernero A, Lavado, E. M., Granda, B., Velasco, A.,and Medina, J. M. 2001. Neuronal differentiation is triggered by oleic acid synthesized and released by astrocytes. J Neurochem 79:606-616.

Toran-Allerand CD BenthamW, Miranda RC, Anderson JP. 1991. Insulin influences astroglial morphology and glial fibrillary acidic protein (GFAP) expression in organotypic cultures. Brain Res 558:296-304.

Volgyi K JuhaszG, Kovacs Z, Penke B. 2015. Dysfunction of endoplasmic reticulum (ER) and mitochondria (MT) in Alzheimer’s disease: the role of the ER-MT crosstalk. Curr Alzheimer Res 12:655–672.

Wang MY, Liehr, J.G. 1994. Identification of fatty acid hydroperoxide cofactors in the cytochrome P450-mediated oxidation of estrogens to quinone metabolites. Role and balance of lipid peroxides during estrogen-induced carcinogenesis. J Biol Chem 269:284– 291.

Webber R. J. and Edmond J.. 1979. The in vivo utilization of acetoacetate, D-( -)-3-hydroxybutyrate, and glucose for lipid synthesis in brain in the 18-day-old rat. J Biol Chem 254:3912-3920.

Zhu BT andConneyA H. 1998. Functional role of estrogen metabolism in target cells: review and perspectives. Carcinogenesis 19:1-27.