Effects of aerobic exercise combined with spirulina nutrition supplement on learning and memory in type 2 diabetes rats and its mechanism
About 65% of patients with type 2 diabetes are accompanied by brain cognitive dysfunction, which is manifested in their early stage and worsens with the prolongation of the course of disease. The clinical manifestations of cognitive dysfunction in diabetes are mainly learning and memory ability, especially the decline of spatial positioning ability, and even Alzheimer’s disease, which has become a global medical and public health problem. It is known that drug treatment is necessary in the learning and memory treatment of diabetes, but the clinical treatment effect is not ideal, and there are many adverse reactions. Recently, more and more studies believe that the use of natural products to prevent diabetes learning and memory can produce the same effect with less adverse reactions. Spirulina is a nutritionally comprehensive and balanced pure natural food, with biological functions including anti fatigue, anti-aging, and immune regulation. The related research on spirulina and diabetes mainly focuses on its lowering blood sugar, inhibiting renal inflammatory signaling pathway and anti-inflammatory. The latest discovery shows that spirulina has an anti Alzheimer’s disease effect on memory impairment in mice. However, little research has been done on the effect of spirulina on learning and memory in diabetes. Aerobic exercise is the basis of learning and memory function to prevent and treat diabetes. Kim and other studies have shown that traditional aerobic treadmill exercise can improve short-term memory and spatial learning ability of diabetes rats. But so far, the effect of aerobic exercise combined with spirulina supplementation on learning and memory of diabetes remains unclear.

Therefore, this study intends to use the model of type 2 diabetes rats to study the effects of aerobic exercise and spirulina on the improvement of learning and memory in diabetes rats, and on extracellular signal regulated kinase (ERK), cAMP response element binding protein (CREB) signal pathway proteins and hippocampal cell apoptosis, so as to provide experimental data for finding new methods to improve learning and memory in diabetes and the application of spirulina in sports medicine.

Oral glucose tolerance test (OGTT) is currently the gold standard for evaluating glucose metabolism status, and is also a commonly used method for clinical assessment of pancreatic beta cell function and insulin sensitivity. This study followed the method of Hou et al. and conducted OGTT test on rats fed high-fat diet for 5 weeks. It was found that the rats exhibited fasting hyperglycemia and hyperinsulinemia, indicating impaired glucose tolerance and insulin resistance. Combined with the selective destruction of pancreatic beta cells by STZ injection, after one week, the symptoms of excessive drinking, eating, and urination in the model rats became increasingly obvious. At the same time, during the experiment, the rats showed weight loss, sparse hair with yellow and dull color, loose stools, and slow movements. After 8 weeks of experimental cycle, the main clinical characteristics of hyperglycemia and hyperinsulinemia still appeared in the model rats of type 2 diabetes, indicating that the model rats of type 2 diabetes have been successfully induced. The reason for the higher insulin levels in the model mice during the experiment may be related to the decrease in insulin receptor content on the target cell membrane, the reduced efficiency of insulin action, and the excessive compensatory secretion of insulin by the body. Eight weeks of aerobic exercise can reduce the blood sugar and insulin levels of rats, but has no obvious effect on body weight. The reason may be related to that regular exercise can increase the insulin receptor sensitivity of skeletal muscle in diabetes rats, promote the direct uptake of glucose by skeletal muscle, and reduce blood sugar; And this effect does not depend on weight loss.

Studies have confirmed that the high-fat diet and STZ induced diabetes model rats have learning and memory disorders. Morris water maze test also showed that the hyperglycemic type 2 diabetes rats induced by this study had a significant decline in spatial learning and memory ability, which was consistent with previous studies. Animal studies have confirmed that high blood sugar can cause cell apoptosis. This study found that, compared with the control group, the apoptosis rate of hippocampal cells in the hyperglycemic model rats increased significantly, indicating that the high glucose status of diabetes caused a more significant increase in hippocampal cell apoptosis, which was consistent with previous studies. At the same time, the escape latency of rats was significantly prolonged and the number of times of crossing the platform was significantly reduced, indicating that the decline of learning and memory ability in diabetes was closely related to the apoptosis of hippocampal neurons. Aerobic exercise has an anti apoptotic effect on hippocampal cells. After eight weeks of treadmill exercise, the apoptosis rate of hippocampal cells in the model mice was significantly reduced, and the learning and memory function was improved. This indicates that long-term aerobic exercise has the effect of anti apoptotic damage of hippocampal cells and enhancing the learning and memory of diabetes, which may be related to its hypoglycemic effect.

In recent years, the study of the relationship between changes in signal transduction pathways in the nervous system and learning and memory has become a new research hotspot. ERK is widely distributed in the central nervous system, with significant expression in areas such as the hippocampus, striatum, and prefrontal cortex, and is closely related to learning and memory. CREB is a nuclear protein that has the function of regulating gene transcription. CREB is one of the most important downstream signaling molecules of ERK. Activated ERK regulates synaptic plasticity and improves brain learning and memory abilities by activating the expression of downstream CREB. The intracellular ERK/CREB signaling pathway plays a “switch” role in regulating brain learning and memory abilities as well as synaptic plasticity. Phosphorylation of signaling molecules is a way of activating signaling pathways. The results of this study showed that compared with the control group, the levels of p-ERK/ERK and p-CREB/CREB in model rats were significantly reduced, suggesting that hyperglycemia in diabetes could cause the down-regulation of ERK/CREB signals. After aerobic treadmill exercise, the levels of p-ERK/ERK and p-CREB/CREB in the model rats increased significantly, indicating that moderate exercise can affect the expression of ERK/CREB signaling proteins, repair hippocampal neuron damage, and improve learning and memory. Aerobic exercise is a non pharmacological method that directly affects the hippocampus and neural synapses. Long term aerobic exercise can promote the expression of hippocampal memory related proteins such as ERK and CREB, achieving the effect of repairing hippocampal neuronal cell damage and improving learning and memory. Research has also shown that silencing CREB expression can promote apoptosis of cortical neurons subjected to oxygen glucose deprivation/reoxygenation. The upregulation of ERK and CREB signaling pathway proteins has anti apoptotic effects, achieving neuroprotective effects through this pathway. The ERK signaling pathway may be a common mechanism for inducing synaptic plasticity in multiple hippocampus. Cystinyl aspartate specific protease-3 (caspase-3) is a driver and key executive molecule of cell apoptosis, and its activation is an important step in cell protein cleavage during programmed cell death. This study shows that aerobic exercise upregulates ERK/CREB signaling, reduces the expression of activated caspase-3, and inhibits cell apoptosis. It is speculated that aerobic exercise under this experimental condition may reduce blood glucose, up regulate ERK/CREB signaling pathway, reduce the expression of cleaved caspase-3, enhance the ability of hippocampus to resist apoptosis, promote the repair of hippocampal neurons, and thus prevent the decline of spatial learning and memory related to diabetes. At present, there is little research on ERK/CREB signal and aerobic exercise anti diabetes learning and memory. ERK/CREB signal mediated anti apoptosis effect on hippocampal cells may be one of the neuroprotective mechanisms of exercise improving learning and memory in diabetes.

Spirulina has many functions, such as hypoglycemic, antioxidant, and so on. It is called the source of human protein in the 21st century. At present, many countries make spirulina into nutritional health food, which is used to supplement human nutrition needs and prevent and treat various diseases (such as diabetes, hypertension, and so on). Recent studies have found that spirulina has neuroprotective effects on enhancing memory and resisting memory damage. Its mechanism is related to increasing the expression of nNOS, inhibiting the expression of GSK-3 β protein, and improving cognitive dysfunction in rats caused by A β 1-42 protein deposition. However, there is no report about spirulina improving the learning and memory of diabetes. Whether Spirulina can improve or enhance the learning and memory of diabetes rats by reducing blood glucose and affecting ERK/CREB signaling pathway is still unclear.

This study shows that after spirulina supplementation, the learning and memory of diabetes model rats are significantly improved, while the blood glucose and insulin content are decreased, the ERK/CREB signal in the hippocampus is significantly increased, and the cleaved caspase-3 and apoptosis rate are significantly reduced. It suggests that spirulina can improve learning and memory by reducing blood glucose and repairing the function of damaged pancreatic islet cells. Its mechanism may be achieved by enhancing the ERK/CREB signal in the hippocampus and inhibiting apoptosis of hippocampal cells. Previous studies have found that spirulina upregulates the brain-derived neurotrophic factor (BDNF) signaling in the hippocampus and improves hippocampal injury in exercise fatigue model rats. Brain derived neurotrophic factor (BDNF) binds to its tyrosine kinase receptor B (TrkB) and can induce CREB activation by activating ERK, resulting in sustained CREB signaling; Enhancing the ERK/CREB signaling of BDNF/TrkB is beneficial for improving hippocampal learning and memory. In the study of app/ps1 mice, it was found that an increase in β – amyloid protein levels downregulated CREB phosphorylation, leading to a downregulation of TrkB autophosphorylation induced by BDNF in the hippocampus and a decrease in CREB expression activated by ERK, which can cause a decline in learning and memory abilities. Spirulina can significantly up regulate ERK, CREB and other key signal molecules in learning and memory of hippocampal neurons, and inhibit cell apoptosis to a certain extent, which may be one of its new brain protective mechanisms against learning and memory damage in diabetes.

The study further found that after 8 weeks of exercise combined with spirulina, the learning and memory improvement effect of diabetes rats was also better than that of the single aerobic exercise group and spirulina group, indicating that exercise combined with spirulina has synergistic effect. Exercise therapy, as a supplement to drug therapy, has good application prospects. The enhancement effect of aerobic exercise combined with spirulina is consistent with the neuroprotective effect of aerobic exercise combined with resveratrol in type 2 diabetes model. The mechanism study showed that the levels of p-ERK/ERK and p-CREB/CREB in the exercise spirulina combination group were significantly higher than those in the single aerobic exercise and spirulina group, the expression of cleaved caspase-3 was significantly reduced, and the rate of apoptosis was significantly reduced, suggesting that the exercise combined with spirulina supplementation may further activate the ERK/CREB signaling pathway, promote the activation of the key proteins ERK and CREB in hippocampus memory, effectively inhibit the apoptosis of hippocampal cells, thereby playing a neuroprotective role in reducing blood sugar and improving learning and memory in diabetes rats. This may be an important reason why exercise combined with spirulina can improve the learning and memory of diabetes. Exercise combined with nutrition supplement may become a new way to improve learning and memory in diabetes related neurodegenerative diseases.

It is worth noting that the insulin level of the DES group in this study has basically recovered to the normal level in the late intervention period (the 8th week), and although its blood glucose concentration has significantly improved, it is still significantly higher than the normal level, suggesting that diabetes is a continuous progressive disease, exercise and spirulina can not restore blood glucose to the normal state in a limited time, but can repair the damaged islet cell function, so that insulin secretion tends to be normal. It is suggested that type 2 diabetes patients should adhere to regular aerobic exercise for a long time, and pay attention to the appropriate supplement of spirulina in the diet.

It can be seen that under the conditions of this experiment, aerobic exercise and spirulina can effectively reduce blood sugar, improve the learning and memory of type 2 diabetes rats, and exercise combined with spirulina has a more obvious application effect, which is superior to simple aerobic exercise and spirulina. Its mechanism is related to its up regulation of ERK/CREB signal in the hippocampus, reduction of the expression of cleaved caspase-3, inhibition of cell apoptosis to a certain extent, and play a protective role in hippocampal neurons. ERK/CREB signaling pathway may become a potential target for aerobic exercise and spirulina to improve the learning and memory of hippocampus in diabetes.