Identification of adrenergic presynaptic and postsynaptic protein locations at neuromuscular junctions, their...

Area of Science:

• Neuroscience
• Aging Research
• Molecular Biology

Background:

• Neuromuscular junctions (NMJs) are critical for motor control, receiving input from both motor and sympathetic nerves.
• Sympathetic modulation of motor innervation declines with age, but the underlying mechanisms remain unclear.
• Understanding age-related changes at the NMJ is vital for addressing functional decline.

Purpose of the Study:

• To investigate the impact of aging on sympathetic nerves and associated synaptic proteins at mouse NMJs.
• To determine if nicotinamide mononucleotide (NMN) can ameliorate age-related deficits at the NMJ.

Main Methods:

• Immunohistochemistry was used to visualize sympathetic nerves (tyrosine hydroxylase), presynaptic (vesicular monoamine transporter 2), and postsynaptic (β2-adrenergic receptors) proteins at mouse NMJs.
• Comparisons were made between adult, aged, and NMN-treated aged mice.
• Quantitative analysis of protein signal intensity was performed.

Main Results:

• While sympathetic nerve marker (tyrosine hydroxylase) intensity remained unchanged with age, presynaptic (vesicular monoamine transporter 2) and postsynaptic (β2-adrenergic receptors) protein levels declined in aged mice.
• Nicotinamide mononucleotide (NMN) administration for one month restored vesicular monoamine transporter 2 and β2-adrenergic receptor levels to those seen in adult mice.
• NMN did not affect tyrosine hydroxylase expression levels.

Conclusions:

• Aging leads to a functional decline in sympathetic innervation at the NMJ, characterized by reduced presynaptic and postsynaptic protein expression.
• Nicotinamide mononucleotide (NMN) effectively reverses these age-related molecular deficits at the NMJ, suggesting a therapeutic potential for age-related neuromuscular dysfunction.