Effect Of The Dihydrotestosterone On Postsynaptic Density Injuries Induced By Aβ Oligomers

BackgroundAlzheimer’s disease (AD) is the most common dementia type in the elderly, with the clinic characteristics of the progressive decline of cognitive function. Multiple studies have proved that the degree of synaptic loss is best related with dementia and AD stages. Synaptic loss, one of the significant pathological alterations in early AD development, is the basis for memory impairment and it can induce the impairment even before the formation of senile plaque.Soluble β amyloid (Aβ) protein has been demonstrated to induce the cognitive decline, especially during the early onset of the AD development. Experiments on animals show Aβ oligomers lead to rapid disruption of learning, the synaptic mechanisms underlying memory, and injury of the post-synaptic density (PSD) in the post-synaptic membranes. Being the critical functional region, PSD takes an important part in contacts between pre-and post-synaptic molecules as well as the regulation of synaptic function, making it one of the main structural and functional units of the synapse.As the key structural unit of the postsynaptic membrane, PSD, at the molecular level, is made up of the core molecules such as post-synaptic density protein-95 (PSD-95), Homer-1 and Shank. The development of synapse and dendrite spine positively correlates with the PSD area. It is therefore not surprising that the abnormal structure and dysfunction of the PSD would directly affect the development and function of synapses. Thus, it is of great importance to discuss the effects of Aβ on PSD scaffolding proteins such as PSD-95 and Homer-1 for the illustration of mechanisms of Alzheimer’s synaptotoxity and improvement of cognitive function in AD patients.On the other hand, the level of androgens in the brain goes down significantly as a normal consequence of aging in men. Age-related androgens decline adversely affects not only muscle and bone mass, sexual function, but also brain functions such as mood, cognition, and memory. Interestingly, androgens depletion is also associated with the development of age-related neurodegenerative disorders such as AD. In adult animals, androgens have been linked to neuronal plasticity as well as regulation of synapse density in the CA1 region of hippocampus, suggesting that androgens may have a protective role in synapse.Previous studies have proved that androgens have a neuroprotective action on neurons and neurogliocytes by activating the PI3K/Akt and/or MAPK/ERK pathways. Meanwhile, evidences have been found that the PI3K/Akt and MAPK/ERK pathways play vital roles in modulation of the neuronal synaptic structure and function. Consequently, through exploring the possible protective effect and its mechanisms of androgen for synapses in the brain, this study might provide clinical and pharmacological reference for the prevention and treatment of synaptic-damage diseases including AD.ObjectivesTo observe the synaptotoxity effect of A β on the neuron model SH-SY5Y, to uncover whether dihydrotestosterone has a neuroprotective role in synapse against A β, and to discuss the potential mechanisms in the protection process.Methods1. Effect induced by Aβ on the expression of PSD scaffolding proteins and PI3K/Akt、MAPK/ERK pathways in SH-SY5Y neurons1.1 Effect induced by Aβ on the expression of PSD scaffolding proteins in SH-SY5Y neuronsSH-SY5Y neurons were treated with different concentrations of Aβ1-42 and A β25-35 separately. The expression of PSD-95 and Homer-1 were examined by Western blot.1.2 Effect induced by A 3 on the PI3K/Akt、MAPK/ERK pathways in SH-SY5Y neuronsSH-SY5Y neurons were treated with different concentrations of Aβ1 and Aβ25-35 as the former step separately. The phosphorylations of p-Akt and p-ERK1/2 were examined by Western blot.2. Effect conducted by DHT on the expression of PSD scaffolding proteins and PI3K/Akt、 MAPK/ERK pathways in SH-SY5Y neurons2.1 Effect conducted by DHT on the expression of PSD scaffolding proteins in SH-SY5Y neuronsSH-SY5Y neurons were intervened with different concentrations of DHT. The expression of PSD-95 and Homer-1 were detected by Western blot.2.2 Effect conducted by DHT on the P13K/Akt、MAPK/ERK pathways in SH-SY5Y neuronsSH-SY5Y neurons were intervened with different concentrations of DHT as the former step. The phosphorylations of p-Akt and p-ERK1/2 were detected by Western blot.3. Effect performed by DHT on the down-regulation of PSD scaffolding proteins induced by Aβ in SH-SY5Y neuronsPretreated with DHT before SH-SY5Y neurons were exposed to Aβ1-42 or Aβ25-35, or LY294002/U0126 was administered before DHT, the expression of PSD-95 and Homer-1 were detected by Western blot.4. Morphological effect of Aβ1-42, Aβ25-35 and DHT on neurons and PSD regionsAfter treated separately with Aβ1-42, Aβ25-35 or/and DHT, utilizing indirect immunofluorescence method by the Homer-1 protein, morphological changes of the synaptic structure such as dendrite number and dendrite length as well as synaptic contacts and PSD region were observed under the confocal microscopy.Results1.Aβ1-42 and Aβ25-35 down-regulated the expression of PSD proteins PSD-95 and Homer-1 and inhibited the phosphorylations of p-Akt and p-ERK1/2 in concentration dependent manner.2. DHT up-regulated the expression of PSD proteins PSD-95 and Homer-1 and promoted the phosphorylations of p-Akt and p-ERK1/2 in concentration dependent manner.3. DHT significantly prevented the down-regulation of PSD proteins PSD-95 and Homer-1 induced by Aβ1-42 and Aβ25-35 in SH-SY5Y neurons, while PI3K inhibitor LY294002 and MEK inhibitor 10126 prevented DHT effect in the process.4. We found by confocal microscopy that after exposure to Aβ1-42 and A β25-35 oligomers, there was a markedly decline in both dendrite number and dendrite length as well as synaptic contacts, which was greatly alleviated by DHT pretreatment.Conclusions1. We found that both A β1-42 and A β25-35 reduce the expression of scaffolding proteins PSD-95 and Homer-1 in SH-SY5Y neurons; Meanwhile, Aβ1-42 and Aβ25-35 can inhibit the phosphorylation of Akt and ERK1/2, consequently blocking the PI3K/Akt and MAPK/ERK pathways.2. DHT can obviously prevent the down-regulation of PSD proteins PSD-95 and Homer-1 induced by Aβ in SH-SY5Y neurons; at the same time, DHT can promote the phosphorylation of Akt and ERK1/2, consequently activating the PI3K/Akt and MAPK/ERK pathways. In addition, PI3K inhibitor LY294002 and MEK inhibitor U0126 can prevent DHT effect in the former process. Therefore, we inferred that DHT may protect the PSD proteins PSD-95 and Homer-1 against A β by activating the PI3K/Akt and MAPK/ERK pathways.3. Morphologically, we found by confocal microscopy that A β1-42 and A β25-35 seriously block the growth and development of the synapses, while DHT may greatly alleviate the synaptotoxity induced by Aβ1-42 and A β25-35.Hence, we proved the protective effect of DHT against synaptotoxity of A β1-42 and Aβ25-35.