Quantitative and Microstructural Changes of the Blood-Nerve Barrier in Peripheral Neuropathy

Abstract

Peripheral neuropathy is accompanied by changes in the neuronal environment. The blood-nerve barrier (BNB) is crucial in protecting the neural homeostasis: Tight junctions (TJ) seal paracellular spaces and thus prevent external stimuli from entering. In different models of neuropathic pain, the BNB is impaired, thus contributing to local damage, immune cell invasion and, ultimately, the development of neuropathy with its symptoms. In this study, we examined changes in expression and microstructural localization of two key tight junction proteins (TJP), claudin-1 and the cytoplasmic anchoring ZO-1, in the sciatic nerve of mice subjected to chronic constriction injury (CCI). Via qPCR and analysis of fluorescence immunohistochemistry, a marked downregulation of mRNA as well as decreased fluorescence intensity were observed in the nerve for both proteins. Moreover, a distinct zig-zag structure for both proteins located at cell-cell contacts, indicative of the localization of TJs, was observed in the perineurial compartment of sham-operated animals. This microstructural location in cell-cell-contacts was lost in neuropathy as semiquantified via computational analysis, based on a novel algorithm. In summary, we provide evidence that peripheral neuropathy is not only associated with decrease in relevant TJPs but also exhibits alterations in TJP arrangement and loss in barrier tightness, presumably due to internalization. Specifically, semiquantification of TJP in cell-cell-contacts of microcompartments could be used in the future for routine clinical samples of patients with neuropathy.

Claudin-12 deficiency causes nerve barrier breakdown, mechanical hypersensitivity and painfulness in polyneuropathy

“…Next, we chose to further examine the well-standardized mononeuropathy CCI in mice, characterized also by an inflammatory reaction due to the ligatures around the SN. Previous data from our and other labs revealed that CCI caused claudin-1, claudin-5, occludin and ZO-1 downregulation in the SN (Moreau et al, 2016;Reinhold et al, 2018;Reinhold et al, 2019). In WT mice, claudin-12-IR was found in myelinating, MBP-positive Schwann cells and S100b-positive Schwann cells (Fig 2A).…”

“…Deletion of Cldn12 gene via KO or siRNA in the SN led to mechanical allodynia. Although nerve injury drives loss of tight junction protein expression and barrier opening in the PNS and spinal cord (4,5,13,51), it is unknown whether this is sufficient to cause pain. Indeed, barrier opening by tissue plasminogen activator (4), by siRNA or peptides against Cldn1 opens the perineurial barrier without causing hypersensitivity (6,11).…”

“…Next, we chose to further examine the well-standardized mononeuropathy CCI in mice, characterized also by an inflammatory reaction due to the ligatures around the SN. Previous data from our and other labs revealed that CCI caused claudin-1, claudin-5, occludin and ZO-1 downregulation in the SN (4,5,13). Since claudin-12 and claudin-19 were affected in patients with painful or severe fiber loss CIDP/non-inflammatory PNP, these tight junction proteins were now specifically examined.…”

“…Certain key claudins [e.g. claudin-1, claudin-5, claudin-19, occludin and zona occludens (ZO-1, TPJ1)] have been identified as relevant for nerve barriers (4,5). Interference with them enhances drug delivery of e.g.…”

“…Among the tight junction protein family, claudins [e.g. claudin-1, claudin-5, claudin-19, occludin and zona occludens (ZO-1, TPJ1)] have been identified as relevant for nerve barriers (Reinhold et al, 2018;Reinhold et al, 2019): Claudin-1 protects the perineurial barrier (Hackel et al, 2012;Sauer et al, 2014) and claudin-5, the major tight junction protein in the blood brain barrier (BBB), serves as a neuroprotector in in the endoneurial vessels (Moreau et al, 2016).…”