SIV-induced impairment of neurovascular repair: a potential role for VEGF

Abstract

Peripheral nerves and blood vessels travel together closely during development but little is known about their interactions post-injury. The SIV-infected pigtailed macaque model of human immunodeficiency virus (HIV) recapitulates peripheral nervous system pathology of HIV infection. In this study, we assessed the effect of SIV infection on neurovascular regrowth using a validated excisional axotomy model. Six uninfected and five SIV-infected macaques were studied 14 and 70 days after axotomy to characterize regenerating vessels and axons. Blood vessel extension preceded the appearance of regenerating nerve fibers suggesting that vessels serve as scaffolding to guide regenerating axons through extracellular matrix. Vascular endothelial growth factor (VEGF) was expressed along vascular silhouettes by endothelial cells, pericytes, and perivascular cells. VEGF expression correlated with dermal nerve (r=0.68, p= 0.01) and epidermal nerve fiber regrowth (r=0.63, p=0.02). No difference in blood vessel growth was observed between SIV-infected and control macaques. In contrast, SIV-infected animals demonstrated altered length, pruning and arborization of nerve fibers as well as alteration of VEGF expression. These results reinforce earlier human primate findings that vessel growth precedes and influences axonal regeneration. The consistency of these observations across human and non-human primates validates the use of the pigtailed-macaque as a preclinical model.

Persistent Peripheral Nervous System Damage in Simian Immunodeficiency Virus—Infected Macaques Receiving Antiretroviral Therapy

“…Epidermal nerve fiber lengths from footpad biopsies were quantified with unbiased stereology methodology utilizing the space ball probe of Stereo Investigator software (MBF Bioscience, Williston, VT) (31–33). Briefly, 3 50-µm-thick PGP9.5-immunostained sections from 1 plantar footpad biopsy from each animal were measured.…”

Combining In Vivo Corneal Confocal Microscopy with Deep Learning-based Analysis Reveals Sensory Nerve Fiber Loss in Acute SIV Infection

“…In contrast with the SIV-infected macaques, corneal nerve fiber length in uninfected control animals imaged at comparable repeat timepoints were not significantly different (P = 0.34; paired t-test). These data demonstrate the ability of the combination of IVCM and automated analysis to detect corneal nerve fiber loss during acute infection, an early timepoint when SIV replicates in sensory ganglia macrophages and induces both immune activation and metabolic alterations (4,7,24). Similar to corneal nerve fiber length, fractal dimension also declined with SIV infection with 10 of the 12 animals with lower counts after SIV infection (Figure 7; P = 0.008, paired t-test).…”

“…(3)(4)(5)(6) Concordant loss of epidermal nerve fibers in the skin of the hind feet can be detected at 14 days post-SIV infection. (7) The current gold standard to measure sensory nerve fiber loss in both research and clinical settings is to calculate epidermal nerve fiber density in skin biopsies after PGP9.5 immunostaining to identify the small sensory nerve fibers. (8) We have adapted and validated similar approaches for use in macaques; however, serial biopsies are problematic for animals and human subjects, as it requires repeat sampling within the same local region of sensory innervation.…”

Tracking Epidermal Nerve Fiber Changes in Asian Macaques

“…Additionally, stereologic algorithms provide an estimate of the total length of objects in a specimen by systematic random sampling (SRS), which saves time compared to analyzing an entire specimen. To measure length of epidermal nerve fibers in macaque footpad samples, we used the Stereo Investigator space ball probe (MBF Biosciences, Williston, VT, Version 9), similar to the method described by Ebenezer and colleagues (2011) and (2012). Three, 50µm thick, PGP9.5 immunostained skin sections were evaluated per animal.…”