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Advanced Neurology Dysregulation of cAMP signaling pathway in MT2KO mice

MT1 receptor transduced several cellular responses in MT2KO mice. Then, we used Aβ ELISA to determine
through both pertussis toxin-sensitive and -insensitive the amount of Aβ40 and Aβ42 and found a relatively high
pathways. Activation of the MT1 receptor through G i Aβ42 level in MT2KO mice but a comparable Aβ40 level
protein inhibited forskolin-stimulated cyclic adenosine in three types of knockout mice. A3981, a special antibody,
monophosphate (cAMP) formation, PKA activity, and was used to label the senile plaque; we found that there
phosphorylation of the cAMP-responsive element- were lots of plaque in the hippocampus of MT2KO mice.
binding protein (CREB) and through G increases Golgi staining and Western blot showed that postsynaptic
[2]
q
intracellular calcium . Activation of recombinant proteins were obviously decreased in MT2KO mice due to
[3]
MT2 receptors expressed in mammalian cells inhibited the disruption of cAMP-related signaling pathway.
forskolin-stimulated cAMP formation [4,5] . In COS-7 cells
expressing the hMT2 receptor, melatonin induces c-Jun 2. Materials and methods
N-terminal kinase through pertussis toxin-sensitive (G) 2.1. Animals
i
[6]
and –insensitive (G16) proteins .
The transgenic mice were obtained from Professor D.
It was already known that melatonin abnormality is Weaver of the University of Massachusetts Medical School.
involved in the pathogenesis of many diseases, such as autism, All animals were kept in a room on a 12 h light-dark
and Alzheimer’s disease (AD) [7,8] . In AD patients, the MT2 cycle and set at 25°C and were given sufficient food and
expression was decreased significantly, but the expression water. All animal experiments were carried out according
of MT1 was increased . During neurodegeneration, the to the “Policies on the Use of Animals and Humans in
[9]
cytoskeleton can be erroneously assembled in neuron Neuroscience Research” revised and approved by the
and a deficit in signal transduction could happen in Society for Neuroscience in 1995. A total of 40 mice were
neuron [10,11] . Melatonin has been demonstrated to accelerate divided into four groups: C3H, MT2KO mice, MT1KO
cytoskeletal remodeling through a melatonin receptor- mice, and DKO mice.
dependent pathway to promote nerve regeneration
after telangiectasia . MT2 stimulated axonogenesis 2.2. Step-down inhibitory avoidance task
[12]
and enhances synaptic transmission by activating the
Akt signaling pathway . Our experiment results also The step-down inhibitory avoidance task was carried
[13]
demonstrated that melatonin could effectively ameliorate out in adherence to the procedures described in detail
tau hyperphosphorylation induced by wortmannin, elsewhere. The testing apparatus consisted of an acrylic box
(30 × 30 × 30 cm) with a floor made of a parallel stainless
calyculin A, and okadaic acid [14-17] .
steel grid (1.0 mm in diameter) spaced 1 cm apart. A safe
Melatonin has also been shown to significantly platform (5 cm in height, 5 cm in diameter) was fixed at
decrease amyloid-β peptide (Aβ) production [18,19] . It one corner of the box. Each mouse was placed initially
has been reported that melatonin could reduce soluble on the safe platform and an electric shock (36 V, 1.5 mA,
amyloid precursor protein (APP) by disturbing APP alternate current, 50 Hz) was delivered to the grid. Before
maturation and finally reducing Aβ . The APP mRNA testing commenced, each mouse was habituated to the
[20]
was significantly decreased in PC12 cells following apparatus for 3 min. When the mice stepped down onto
pretreatment with melatonin, but this effect was not the grid floor, they received a foot shock and jumped back
present in human neuroblastoma . In addition, the onto the safe platform. For a while, the mice went up and
[21]
binding of melatonin with Aβ40 and Aβ42 in vitro strongly down between the platform and the grid, and eventually,
inhibited the formation of senile plaque and β-folding . they remained on the platform. The time the mice spent
[18]
The binding occurred at the residue of 29–40, which shows on learning on the platform continuously for 5 min was
[22]
hydrophobic properties . recorded as the latency of the acquisition test (day 1). The
Our results showed that melatonin could effectively mice were tested for retention 24 h later (day 2) and were
reduce Aβ in wild-type N2a and N2a/APP . However, it tested for recall 5 days later (day 7), by placing the mice on
[23]
has also been reported that melatonin does not affect the the platform, and the step-down latency was recorded for
stability of Aβ40 and Aβ42 . These results demonstrated a maximum of 3 min.
[24]
that melatonin has a strong effect on the Aβ, but it was
unknown how melatonin executes its effect on AD, 2.3. Functional magnetic resonance imaging and NMR
considering its antioxidant properties. Here, we used the The volume of the hippocampus was measured from the
melatonin receptor knockout mice, including C3H, MT1 in vivo anatomical images with a manual approach. The
knockout (MT1KO), MT2 knockout (MT2KO), and volume of the hippocampus of each animal was measured
double knockout mice (DKO). We found cognition damage from the anatomical images in their native space by

Volume 2 Issue 3 (2023) 2 https://doi.org/10.36922/an.0974