The antibiotic doxycycline mimics the NGF signaling in PC12 cells: A relevant mechanism for neuroprotection.

Doxycycline has been used as antibiotic since the 1960s. Recently, studies have shown that doxycycline is neuroprotective in models of neurodegenerative diseases and brain injuries, mainly due to anti-inflammatory and anti-apoptotic effects. However, it is not known if doxycycline has neurotrophic potential, which is relevant, considering the role of axonal degeneration at the early stages of neurodegeneration in Alzheimer's disease, Amyotrophic Lateral Sclerosis and Parkinson's disease as well as in normal aging. Axons are preceded by the formation of neurites, the hallmark of the neuronal differentiation induced by neurotrophins like NGF. Therefore, the modulation of neurotrophin receptors aimed at formation and regeneration of axons has been proposed as a strategy to delay the progression of neurodegeneration and has gained relevance as new techniques for early diagnosis arise. Based on these premises, we investigated the potential of doxycycline to mimic the effects of Nerve Growth Factor (NGF) with focus on the signaling pathways and neuronal modulators of neurite initiation, growth and branching. We used PC12 cells, a neuronal model widely employed to study the neurotrophic pathways and mechanisms induced by NGF. Results showed that doxycycline induced neurite outgrowth via activation of the trkA receptor and the downstream signaling pathways, PI3K/Akt and MAPK/ERK, without inducing the expression of NGF. Doxycycline also increased the expression of GAP-43, synapsin I and NF200, proteins involved in axonal and synaptic plasticity. Altogether, these data demonstrate, for the first time, the neurotrophic potential of doxycycline, which might be useful to restore the neuronal connectivity lost at the initial phase of neurodegeneration.