Biology subjects

Rittner, H.

Publications and source records attributed to Rittner, H..

5 recordsLinked to original sources

bioRxiv2024

Neuropathic pain and distinct CASPR2 autoantibody IgG subclasses drive neuronal hyperexcitability

Patients with autoantibodies (aAbs) against the contactin-associated protein-like 2 (CASPR2) suffer from a variety of clinical syndromes including neuropathic pain, in some patients even as the only symptom. CASPR2 is an adhesion protein of the neurexin IV family and part of the voltage-gated potassium channel complex (VGKC) in neurons of dorsal root ganglia (DRG). The subsequent pathological mechanisms following the binding of CASPR2 aAbs and their association with pain are only partially understood. CASPR2 aAbs are mainly of the IgG4 subclass. Previous studies have neglected subclass-dependent effects. Here we investigated 49 subclassified patient serum samples positive for CASPR2 aAbs. To unravel underlying molecular mechanisms, we used a combination of super-resolution lattice structural illumination microscopy (SIM2) and functional readouts by calcium imaging and electrophysiological recordings. CASPR2-positive patient sera subclassified in IgG4 together with at least one other IgG subclass (IgGX) and patients with only IgG4 were further subdivided into the pain and no pain group. Patient subclassification shed further light on the pathological mechanisms of CASPR2 aAbs. A decrease of CASPR2 expression after long-term exposure to CASPR2 aAbs was only observed for the patient group without pain. Upon withdrawal of the CASPR2 aAbs, CASPR2 expression returned to normal level. Structural alterations were obtained by increased distances between CASPR2 and associated potassium channels along DRG axons using high-resolution lattice SIM2 microscopy but only following binding of CASPR2 aAbs from patients with pain. Similarly, CASPR2 aAbs of patients with pain significantly increased overall neuronal excitability of cultured DRG neurons as measured by calcium imaging. Patch-clamp recordings revealed significantly decreased current amplitudes of voltage-gated potassium (Kv) channels after incubation with all four CASPR2 aAbs subclassifications with the most prominent effect of serum samples harboring IgG4 aAbs. Notably, a patient serum sample lacking IgG4 did not alter Kv channel function. Withdrawal of aAbs rescued Kv channel function to normal levels suggesting that the affected potassium channel function is rather due to a functional block of the VGKC rather than altered structural integrity of the VGKC. Taken together, we found IgG4 aAbs to be a major modifier of potassium channel function. The increase in DRG excitability is primarily due to impaired Kv channel conductance as a consequence of CASPR2 aAbs binding but additional and so far unidentified signal pathways contribute to this process in patients with neuropathic pain.

neuroscience↗

bioRxiv2024

TAM receptors mediate the Fpr2-driven pain resolution and fibrinolysis after nerve injury

Nerve injury causes neuropathic pain and multilevel nerve barrier disruption. Nerve barriers consist of perineurial, endothelial, and myelin barriers. So far, it is unclear whether resealing nerve barriers fosters pain resolution and recovery. To this end, we analysed the nerve barrier property portfolio, pain behaviour battery, and lipidomics for precursors of specialized pro-resolving meditators (SPMs) and their receptors in chronic constriction injury of rat sciatic nerve to identify targets for pain resolution by resealing the selected nerve barriers. Of the three nerve barriers - perineurium, capillaries, and myelin - only capillary tightness specifically against larger molecules, such as fibrinogen, recuperated with pain resolution. Fibrinogen immunoreactivity was not only elevated in rats at the time of neuropathic pain but also in nerve biopsies from patients with (but not without) painful polyneuropathy indicating that sealing of the vascular barrier might be novel approach in pain treatment. 15R-HETE (hydroxyeicosatetraenoic acid), a precursor of aspirin-triggered lipoxin A4, were specifically upregulated at the beginning of pain resolution. Repeated local application of resolvin D1-laden nanoparticles or Fpr2 agonists sex-independently resulted in accelerated pain resolution and fibrinogen removal. Clearing macrophages (Cd206) and fibrinolytic pathways (Plat) were also induced while inflammation (Tnf) and inflammasomes (Nlrp3) were unaffected by this treatment. Blocking TAM receptors (Tyro3, Axl, and Mer) and tyrosine kinase receptors linking haemostasis and inflammation completely inhibited all the effects. In summary, nanoparticles can be used as transporters for fleeting lipids, such as SPMs, and therefore expand the array of possible therapeutic agents. Thus, the Fpr2-Cd206-TAM receptor axis may be a suitable target for strengthening the capillary barrier, removing endoneurial fibrinogen, and boosting pain resolution in patients with chronic neuropathic pain.

neuroscience↗

bioRxiv2024

Neuronal toxicity and recovery from early bortezomib-induced neuropathy: targeting the blood nerve barrier but not the dorsal root ganglion

The use of the first in class proteasome inhibitor Bortezomib (BTZ) is highly effective in the treatment of multiple myeloma. However, its long-term use is limited by the fact, that most treated patients develop dose limiting painful polyneuropathy. In some of the treated patients, pain resolves after variable timeframes, in others it persists, despite the discontinuation of treatment, with the underlying mechanisms poorly understood. One condition of neural toxicity is the ability to penetrate the blood nerve barrier. Here we present pathways involved in early bortezomib-induced polyneuropathy (BIPN) development and its resolution, in rats and in myeloma patients. One cycle of BTZ elicited transient mechanical hyperalgesia and cold allodynia in rats. Transcriptomic signature and network analysis revealed regulation of circadian, extracellular matrix, and immune genes within the nerve and modest changes in the dorsal root ganglia. Recovery processes resealed the small molecule leakiness of the perineurial barrier, reversed axonal swelling, and normalized small fiber density in the skin. Expression of the microtubule-associated cytoskeletal protein cortactin matched this process in the perineurium. Netrin-1 (Ntn1) as a known barrier sealer was also upregulated in pain resolution in nerve and skin. In patients with painful BIPN skin NTN1 was independent of axonal damage. In summary, our data demonstrate that early BTZ toxicity targets mainly the nerve and indicates that pain resolution could be supported by protective growth factors like Ntn1 for remodeling of the extracellular matrix and neuronal barriers. SummaryBortezomib leads to dose-limiting painful polyneuropathy. Already in the first cycle, BTZ toxicity weakens the blood nerve barrier which reseals upon upregulation of netrin-1.

neuroscience↗

bioRxiv2020

Antinociceptive modulation by the adhesion-GPCR CIRL promotes mechanosensory signal discrimination

Adhesion-type G protein-coupled receptors (aGPCRs) participate in a vast range of physiological processes. Correspondingly, these receptors are associated with diverse human diseases, such as developmental disorders, defects of the nervous system, allergies and cancer. Several aGPCRs have recently been linked to mechanosensitive functions suggesting that processing of mechanical stimuli may be a common feature of this receptor family. CIRL (ADGRL/Latrophilin, LPHN), one of the oldest members of the aGPCR family, sensitizes sensory responses of larval Drosophila to gentle touch and sound by amplifying mechanosensory signal transduction in low-threshold mechanoreceptors (Scholz et al., 2015; 2017). In the present study, we show that Cirl is also expressed in high-threshold mechanical nociceptors where it adjusts nocifensive behaviour under physiological and pathophysiological conditions. Optogenetic in vivo experiments indicate that CIRL quenches cAMP levels in both mechanosensory submodalities. However, contrasting its effect in touch sensitive neurons, CIRL dampens the response of nociceptors to mechanical stimulation. Consistent with this finding, rat nociceptors display a drop in Cirl1 expression during allodynia. Taken together, these results demonstrate that CIRL exerts opposing modulatory functions in low-threshold mechanosensors and high-threshold nociceptors. This intriguing bipolar action likely facilitates the separation of mechanosensory signals carrying different physiological information.

physiology↗

bioRxiv2019

Claudin-12 deficiency causes nerve barrier breakdown, mechanical hypersensitivity and painful neuropathy

Peripheral nerves and their axons are shielded by the blood-nerve and the myelin barrier, but understanding of how these barriers impact nociception is limited. Here, we identified a regulatory axis of the tight junction protein claudin-12, sex-dependently controlling perineurial and myelin barrier integrity. In nerve biopsies, claudin-12 in Schwann cells was lost in male and postmenopausal female patients with painful but not painless polyneuropathy. Global Cldn12 gene-knockout selectively increased perineurial/myelin barrier leakage, damaged tight junction protein expression and morphology, increased proinflammatory cytokines and induced mechanical hypersensitivity in naive and neuropathic male mice, respectively. Other barriers and neurological function remained intact. In vitro transfection studies documented claudin-12 plasma membrane localisation without interaction with other tight junction proteins or intrinsic sealing properties. Rather, claudin-12 had a regulatory tight junction protein function on the myelin barrier via the morphogen SHH in vivo in Cldn12-KO and after local siRNA knockdown. Fertile female mice were completely protected. Collectively, these studies reveal the critical role of claudin-12 maintaining the myelin barrier and highlight restoration of the claudin-12/SHH pathway as a potential target for painful neuropathy.

neuroscience↗