The effect of long-term food restriction on te expression of glucocorticoid receptor in the rat forebrain during aging

Dugotrajna restrikcija hrane produžava životni vek i odlaže pojavu mnogih bolesti koje se javljaju sa starenjem. Brojni literaturni podaci ukazuju da kod životinja kojima je unos hrane smanjen izostaje karakterističan starosno-zavistan pad u kognitivnim funkcijama, međutim, mehanizam ovakvog neuroprotektivnog dejstva restrikcije hrane nije u potpunosti razjašnjen. U isto vreme, kod životinja na dugotrajnoj restrikciji hrane se povećava nivo kortikosterona u plazmi što ukazuje da ovaj tretman deluje kao blagi stresor. Do sada nije ispitivano do kakvih promena u signalnom putu glukokortikoida dovodi smanjeni unos hrane tokom starenja u mozgu. Centralno polje istraživanja procesa starenja neizbežno podrazumeva ispitivanje promena do kojih dolazi u korteksu i hipokampusu, strukturama mozga koje su ključne za kognitivne funkcije. Sa druge strane, iste strukture učestvuju u regulaciji HHA ose kao važni regioni delovanja negativne povratne sprege. Cilj doktorske disertacije je da se ispita uloga signalnog puta glukokortikoida u korteksu i hipokampusu pacova tokom starenja i pod uticajem dugotrajne restrikcije hrane. Eksperimentalne životinje (mužjaci pacova soja Wistar) starosti 6 meseci su podeljene u dve grupe. Prva grupa, označena kao ad libitum (AL), je imala neograničen pristup hrani, dok je druga grupa (označena kao DR) podvrgnuta režimu redukovane ishrane koji je podrazumevao dobijanje 100% dnevnog unosa hrane AL životinja svakog drugog dana. Životinje su analizirane kada su dostigle starost od 18 i 24 meseca. Životinje stare 6 meseci su predstavljale kontrolnu grupu. Glukokortikoidna signalizacija u ispitivanim strukturama je praćena na prereceptorskom nivou, kao i na nivou ekspresije i aktivacije glukokortikoidnog receptora primenom imunoesej, imunoblot i PCR metoda, kao i imunohistohemijske analize. Rezultati doktorske disertacije pokazuju da tokom starenja dolazi do povećanja koncentracije kortikosterona u korteksu pacova, dok dugotrajna restrikcija hrane povećava nivo kortikosterona u obe ispitivane strukture. Utvrđeno je da nivo ključnog enzima koji u moždanom tkivu reguliše dostupnost kortikosterona za receptore, 11β-HSD1, raste u hipokampusu pacova koji imaju neograničen pristup hrani. Tretman dugotrajnom restrikcijom hrane dovodi do povećanja nivoa 11β-HSD1 u korteksu, dok u hipokampusu izostaje efekat na nivo ovog enzima...Moderate restriction in food intake (dietary restriction, DR) extends the life-span and delays the onset of many age-related diseases. In addition, food-restricted animals exhibit attenuated cognitive deficits during aging as they perform better in learning and memory tasks than their ad libitum fed counterparts. At the same time, the animals on chronic food restriction have elevated levels of plasma corticosterone, which implies that this treatment could be considered as a mild stressor. So far, there are no literature data regarding the effects of food restriction on glucocorticoid signaling in the brain during aging and the mechanisms by which DR exhibits its neuroprotective effects are poorly understood. Two brain regions of interest are cortex and hippocampus, regions particularly prone to age-related changes. The same regions are also involved in cognition and regulation of the hypothalamic–pituitary–adrenal (HPA) axis activity. The aim of the present study was to evaluate the effect of long-term food restriction on glucocorticoid signaling pathway in the cortex and hippocampus of rats during aging. Experimental animals (male Wistar rats, 6 months old) were divided into two groups. The AL group was fed ad libitum, whereas the food restricted group (DR) received 100% of the mean daily intake of the AL animals every other day. The animals were examined at the age of 18 and 24 months. Six-month-old animals were used as a control. Glucocorticoid signaling in specific brain regions was examined at the pre-receptor level, as well as regarding the level of expression and glucocorticoid receptor activity by using immunoassays, Western blot, PCR and immunohistochemistry. The results of this study demonstrate an age-related increase in cortical corticosterone concentration. The increase in the hormone level was further detected in DR animals, in both brain regions examined. However, 11β-HSD1, a key enzyme in brain tissue that regulates the availability of corticosterone to its receptors, was increased only in the hippocampi of AL rats and in the cortex of rats subjected to the long-term food restriction. The most pronounced changes in the level of glucocorticoid receptor during aging were observed in the hippocampi of AL animals..