Exosomes Secreted by Adipose-Derived Stem Cells Following FK506 Stimulation Reduce Autophagy of Macrophages in Spine after Nerve Crush Injury.

Pao-Jen Kuo,Chia-Jung Wu,Shao-Chun Wu,Cheng-Shyuan Rau,Yi-Chan Wu,Ching-Hua Hsieh,Chia-Wei Lin,Tsu-Hsiang Lu,Lien-Hung Huang,Chia-Wen Tsai

doi:10.3390/ijms22179628

Abstract

Macrophages emerge in the milieu around innervated neurons after nerve injuries. Following nerve injury, autophagy is induced in macrophages and affects the regulation of inflammatory responses. It is closely linked to neuroinflammation, while the immunosuppressive drug tacrolimus (FK506) enhances nerve regeneration following nerve crush injury and nerve allotransplantation with additional neuroprotective and neurotrophic functions. The combined use of FK506 and adipose-derived stem cells (ADSCs) was employed in cell therapy for organ transplantation and vascularized composite allotransplantation. This study aimed to investigate the topical application of exosomes secreted by ADSCs following FK506 treatment (ADSC-F-exo) to the injured nerve in a mouse model of sciatic nerve crush injury. Furthermore, isobaric tags for relative and absolute quantitation (iTRAQ) were used to profile the potential exosomal proteins involved in autophagy. Immunohistochemical analysis revealed that nerve crush injuries significantly induced autophagy in the dorsal root ganglia and dorsal horn of the spinal segments. Locally applied ADSC-F-exo significantly reduced autophagy of macrophages in the spinal segments after nerve crush injury. Proteomic analysis showed that of the 22 abundant exosomal proteins detected in ADSC-F-exo, heat shock protein family A member 8 (HSPA8) and eukaryotic translation elongation factor 1 alpha 1 (EEF1A1) are involved in exosome-mediated autophagy reduction.

Highlights

Our findings indicate that nerve crush injuries significantly induce autophagy in the dorsal root ganglia and dorsal horn of the spinal segments
Previous studies have shown that HIF-1α leads to the transcription of BCL2 interacting protein 3 (BNIP3), which competes with Bcl-2 and Bcl-XL for interaction with Beclin to induce autophagy [43]
The results of this study provide evidence supporting that the exosomes secreted by adiposederived stem cells (ADSCs) following FK506 treatment reduced autophagy in the spinal segments after nerve crush injury, shedding light on the new potential therapeutic application in the regulation of inflammation and neuropathic pain after nerve crush injury

Summary

Introduction

A remote cell body response in axotomized neurons is induced following a sciatic nerve injury [1]. This strong response indicates the neuronal release of cytokines and chemokines, the induction of neuron-intrinsic growth programs, the activation of resident macrophages [2,3,4], and invasion of macrophages from the peripheral circulation [5,6]. The proliferation of resident and invasive macrophages is abundant and peaks three days after injury [7], with an increased (proportional) influx of hematogenous macrophages after day 4 [7]. The secreted molecules and phagocytosis activity of these macrophages can magnify immune and inflammatory responses in the local milieu, influence the surrounding neurons [8], and further contribute to secondary damage and the further loss of neurons [9]

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