Infiltration of Blood-Derived Macrophages Contributes to the Development of Diabetic Neuropathy

Abstract

Background and Objective. Diabetic neuropathic pain (DNP) is a common complication associated with diabetes. Currently, its underlying pathomechanism remains unknown. Studies have revealed that the recruitment of blood monocyte-derived macrophages (MDMs) to the spinal cord plays a pivotal role in different models of central nervous system injury. Therefore, the present study aimed at exploring the infiltration and function of MDMs in DNP using a mice model. Methods. Diabetes was induced using streptozotocin in male A/J mice. Mechanical withdrawal thresholds were measured weekly to characterize neuropathy phenotype. Quantitative analysis of CD11b was performed and visualized by immunofluorescence. Spinal cord cells were isolated from myelin and debris by Percoll gradient. Flow cytometry was used to label CD11b and CD45 antibodies to differentiate MDMs (CD45highCD11b+) from resident microglia (CD45lowCD11b+). Mice were injected with clodronate liposomes to investigate the role of MDMs in DNP. The successful depletion of monocytes was determined by flow cytometry. Results. The DNP mice model was successfully established. Compared with nondiabetic mice, diabetic mice displayed a markedly higher level of CD11b immunofluorescence in the spinal cord. The number of CD11b-positive microglia/macrophages gradually increased over the 28 days of testing after STZ injection, and a significant increase was observed on Day 14 (P<0.01) and 28 (P<0.01). Further analysis by flow cytometry showed that the infiltration of peripheral macrophages began to increase in 2 weeks (P<0.001) and reached a maximum at 4 weeks (P<0.001) post-STZ injection compared to the control. The depletion of MDMs by clodronate liposomes alleviated diabetes-induced tactile allodynia (P<0.05) and reduced the infiltration of MDMs (P<0.001) as well as the expression of IL-1β and TNF-α in the spinal cord (P<0.05). Conclusions. The infiltration of blood MDMs in the spinal cord may promote the development of painful neuropathy in diabetes.

Spinal microglia-neuron interactions in chronic pain

“…CD45 expression analysis confirmed the infiltration of CD45 hi CD11b + macrophages at 12 wk in a murine neuropathy model induced by LP‐BM5 virus infection 23 . Flow cytometry also showed that the infiltration into the spinal cord began in 2 wk after streptozotocin injection in the murine diabetic neuropathic pain model 24 . Both activated microglia and macrophages in the spinal cord are involved in neuroplasticity by inducing and modulating cellular responses and contribute to neuroinflammation, 14 for the establishment or maintenance of pain.…”

Peripheral Nerve Resident Macrophages and Schwann Cells Mediate Cancer-Induced Pain

“…Depletion of the two MΦ populations by the homodimerizer agent, AP20187, in MaFIA mice abolished the mechanical/cold hypersensitivity and spontaneous nociception. In neuropathic pain models, including partial nerve injury (6,35), constriction of the infraorbital nerve (5), and diabetic neuropathy (36) nor mechanical/cold hypersensitivity. Additional evidence that cancer-evoked mechanical/cold hypersensitivity and spontaneous nociception is dependent on rMΦs was obtained in MΦ-depleted MaFIA mice, whose tumor microenvironment, but not the nerve bundle, was replenished with peritoneal MΦs from donor mice.…”

Amyloid Proteins and Peripheral Neuropathy

“…In support of this notion, clinical trials aimed at inhibiting IL-1β in T2DM patients showed improved β-cell function [ 247 ]. With regard to DPN, diabetes-induced neuropathy is associated with infiltration of blood-derived macrophages in the spinal cord [ 275 ], a proinflammatory phenotype of blood monocyte-derived macrophages [ 276 ] and activated spinal microglia [ 277 ].…”