mTOR activation due to APPL1 deficiency exacerbates hyperalgesia via Rab5/Akt and AMPK signaling pathway in streptozocin-induced diabetic rats

Abstract

Painful diabetic neuropathy is a common complication of diabetes mellitus with obscure underlying mechanisms. The adaptor protein APPL1 is critical in mediating the insulin sensitizing and insulin signaling. In neurons, APPL1 reportedly affects synaptic plasticity, while its role in the pathogenesis of painful diabetic neuropathy is masked. Our Western blotting revealed significantly decreased APPL1 expression in the dorsal horn in streptozocin-induced rats versus the control rats, coupled with concomitant mechanical and thermal hyperalgesia. Afterward, the determination of exact localization of APPL1 in spinal cord by immunofluorescent staining assay revealed highly expressed APPL1 in the lamina of spinal dorsal horn in control rats, with the overexpression in neurons, microglia, and underexpression in astrocytes. The APPL1 expression in laminae I and II was significantly downregulated in painful diabetic neuropathy rats. In addition, APPL1 deficiency or overexpression contributed to the increase or decrease of Map and Bassoon, respectively. The localization and immunoactivity of APPL1 and mammalian target of rapamycin (mTOR) were determined in spinal dorsal horn in painful diabetic neuropathy rats and control rats by immunohistochemistry, suggesting pronounced decrease in APPL1 expression in the superficial layer of the spinal cord in painful diabetic neuropathy rats, with p-mTOR expression markedly augmented. APPL1 knockdown by infection with lentiviral vector facilitated the activation of mTOR and abrogated mechanical withdrawal threshold values in painful diabetic neuropathy rats. Genetically overexpressed APPL1 significantly eliminated the activation of mTOR and resulted in the augmented mechanical withdrawal threshold values and thermal withdrawal latency values. Furthermore, the APPL1 levels affect phosphorylation of adenosine monophosphate-activated protein kinase (AMPK), and Akt, as well as the small GTPase, Rab5 expression in painful diabetic neuropathy rats. Our results uncovered a novel mechanism by which APPL1 deficiency facilitates the mTOR activation and thus exacerbates the hyperalgesia in streptozocin-induced diabetic rats, presumably via the regulation of Rab5/Akt and AMPK signaling pathway.

Active APPL1 sequestration by Plasmodium favors liver-stage development

“…The phosphorylation of another APPL1 effector kinase-AMPK was elevated only in hRab5_Q79L-expressing cells and not the PbRab5b variants, which was particularly interesting given previous studies indicating the negative effect of AMPK activation on EEF size (Ruivo et al, 2016). A reduction in the activity of AMPK upon depletion of APPL1 was previously demonstrated (Zhou et al, 2009), while APPL1 has been associated with the negative regulation of mTOR via Akt and AMPK in the model of painful diabetic neuropathy (He et al, 2019). We speculate in this case that removal of APPL1 may be associated with disabling AMPK activity in the host cell, where the WT EEF is unable to effectively do so in the presence of hRab5_Q79L-positive endosomes.…”

β-Nicotinamide Mononucleotide (NMN) Administrated by Intraperitoneal Injection Mediates Protection Against UVB-Induced Skin Damage in Mice

“…It mediates a variety of cell signaling pathways, regulates the inflammatory response of cells, and has antioxidant and anti-arteriosclerotic effects. 75 LKB1 is a kinase upstream of AMPK and is mainly localized in the nucleus. It can directly phosphorylate threonine 172 on the α subunit of AMPK to activate AMPK, thereby regulating the energy metabolism of cells.…”

Improving NKCC1 Function Increases the Excitability of DRG Neurons Exacerbating Pain Induced After TRPV1 Activation of Primary Sensory Neurons

“…The time for lifting did not exceed 30 s, and the stimulation intensity was the same when measured. The measurement was repeated three times at each time point, with at least 5 min interval, and the average was referred to as the thermal withdrawal latency (TWL) ( He et al, 2019 ). The lower the TWL value is, the more severe the hyperalgesia of the rat under thermal stimulation.…”