The PhD thesis is devoted to the important scientific problem of modern neurobiology, concerning the study of morpho-functional changes in neurons and glial cells of the ventromedial nucleus of the hypothalamus (VMH) of rats with the experimental type 2 diabetes mellitus (T2DM), including the development of endoplasmic reticulum (ER) stress, neurogliosis, apoptosis and autophagy of neurons. In addition, the influence of combined administration of metformin and sodium propionate on abovementioned processes was investigated in order to develop the possible pharmacological schemes for the neuroprotection on the background of the development of diabetic encephalopathy.
Obesity, metabolic syndrome (MS) and type 2 diabetes mellitus are considered among the most urgent public health problems in the 21st century. Genetic, environmental and molecular factors, the influence of diet, behavior and lifestyle altogether contribute to the development of MS and T2DM, associated with a number of complications, including diabetic neuropathy and encephalopathy, which dramatically reduce the quality of life of patients. However, the pathogenetic mechanisms of the neuronal damage under the influence of the combination of impaired glucose and lipid homeostasis remain unexplored. Research on experimental animal models allow to analyze the intracellular mechanisms of cerebral regulation of homeostasis, especially in hypothalamic structures, and to study the impairments of central regulation on the background of diabetes mellitus, and also to elucidate the new trends in treatment options. Hypothalamus is the center of regulation of metabolism. The main structures of hypothalamus that are responsible for the central mechanisms of regulation of glucose and lipid metabolism to ensure the energy balance of the organism are neurons of ventromedial, lateral and arcuate nuclei. Dysregulation of the functional activity of the hypothalamic nuclei leads to the impaired glucose metabolism and, as a consequence, the development of T2DM. One of the reasons is the low-grade inflammation of the nervous tissue, in particular, the hypothalamus, the resistance of hypothalamic neurons to leptin and an impaired neurogenesis. The neurobiological basis of leptin resistance remains unclear. Therefore, there are several hypotheses of the development of this condition: an inflammation in the hypothalamic nuclei, disturbances in the process of neuronal autophagy, ER stress in neurons. ER stress activates the signaling way of unfolded protein response (UPR). Therefore, our study was devoted to the investigation of structural changes in ER of rat VMH neurons, the state of UPR system associated with an imbalance of intracellular homeostasis, apoptosis and autophagy of neurons on the background of experimental T2DM.
To correct the disturbances in the functioning of nervous tissue, caused by T2DM, we chose metformin – a well-known medication, that is considered the "gold standard" for the treatment of type 2 diabetes mellitus, and sodium propionate (here and throughout the text, propionate) – salt of propionic acid (short-chain fatty acid), which is a dietary supplement and an additional component for the treatment of patients with neurodegenerative autoimmune diseases. The propose of the study was to determine the morpho-functional changes of neurons and glial cells of the ventromedial nucleus of the hypothalamus under experimental type 2 diabetes mellitus and after its possible correction by metformin and propionate. The following tasks were defined, according to the study purpose:
1. To determine the most effective way to reproduce the experimental model of T2DM in rats via monitoring the biochemical parameters and studying the spectrum of fatty acids in animal tissues.
2. To investigate ultrastructural changes of neurons and glial cells of the ventromedial nucleus of the hypothalamus rats with T2DM and after its correction by metformin and propionate.
3. To study the functional state of the endoplasmic reticulum of VMH neurons in rats with type 2 diabetes mellitus and under its correction by studying the parameters of UPR system (particularly, proteins GRP78, PERK, ATF6, IRE1).
4. To determine the functional markers of glial cells (Iba1, GFAP, ZO-1) in the VMH on the background of type 2 diabetes mellitus and after its correction.
5. To study the functional markers of autophagy (LC3, Beclin-1) and apoptosis (Bcl_xl, BAX, caspase-3) in the VMH of rats with T2MD and under the action of metformin and propionate.
6. To outline the molecular mechanisms of the pharmacological effect of combined administration of metformin and propionate on the state of neurons and glial cells of the ventromedial nucleus of hypothalamus in order to scientifically substantiate the use of these drugs on the background of T2MD.
