Featured Papers in 2018

TrkB-BDNF signaling is responsible and involved in cell proliferation, differentiation, cell survival, and long-term potentiation.

In a recent game changing paper, Zahavi et al. elegantly and remarkably refute the current model of tyrosine kinase receptor activation. TrkB, the receptor for BDNF, does not undergo dimerization at the cell membrane following BDNF activation.

The authors show that TrkB signals as a monomer from the plasma membrane upon activation through a series of complex experiments involving recombinant/chimeric proteins, immunostaining and microscopy. Alomone Labs human BDNF-Biotin (#B-250-B) plays a pivotal role in this explicitly controversial, formidable, and exciting paper. Using biotinylated BDNF, the authors show that monomeric TrkB receptors bind BDNF (Figure 1) by a coordinated lateral movement of both proteins.

Following stimulation by BDNF, the receptor-ligand complex is internalized in endosomes where the signal is propagated spatially and temporally. Biotinylated BDNF is shown to internalize with TrkB into endosomes. However, in endosomes, TrkB appears as a dimer and the authors propose that a ligand-dependent dimerization occurs within signaling endosomes. This study leads to open questions like what factors are involved in TrkB dimerization in the endosome.

Figure 1. TrkB binds to BDNF at the plasma membrane.Live TIRF imaging of TrkB-ACP-488 and labeled BDNF co-movement in HEK293T (HEK). Cells treated with streptavidin-647-labeled human BDNF-Biotin (#B-250-B) for 5 minutes and imaged at 8 fps. Arrowhead marks co-localized TrkB-BDNF particle. Scale bar = 2 µm. Right: color trace shows movement trajectory of TrkB-ACP-488 and BDNF-647 particles over time (blue- start, red- end of trajectory) Scale bar = 1 µm.Unpublished data from Zahavi, E.E. et al. (2018) Sci. Signal. 11, eaao4006. Figure generously provided by Dr. Eran Perlson, Dept. of Physiology and Pharmacology, Tel-Aviv University, Tel-Aviv, Israel.

A fundamental step in nociception requires glutamatergic signaling between primary nociceptors and secondary neurons in the spinal dorsal horn.

Presynaptic K_V3.4 channel was found to play an important role in transmitting and relaying nociceptive signaling to the glutamatergic pathway. Expression of K_V3.4 was demonstrated by immunohistochemical staining of rat cervical spinal cord sections using Anti-K_V3.4 Antibody (#APC-019). K_V3.4 immunostaining was observed in peptidergic nociceptive fibers with calcitonin gene-related peptide (CGRP), (Figure 1), and with non-peptidergic nociceptive fibers as well as with the presynaptic VGLUT2 marker.

Electrophysiological experiments indicate an important regulatory role for K_V3.4 in glutamatergic signaling in nociception. The authors suggest that increasing the activity of K_V3.4 in DRGs may represent analgesic effects.

Figure 1. Expression of K_V3.4 in rat dorsal horn.Immunohistochemical staining of rat spinal cord sections using Anti-K_V3.4 Antibody (#APC-019). K_V3.4 staining (green) is observed in dorsal horn laminae I–III. K_V3.4 immunoreactivity partially co-localizes with CGRP staining (red).Adapted from Muqeem, T. et al. (2018) J. Neurosci. 38, 3729. with permission of the Society for Neuroscience.

In this study, Lipopolysaccharides (LPS) from bacteria-causing urinary tract infection was found to activate BK/K_Ca1.1 channel in bladder umbrella cells.

Electrophysiological recordings first identified K⁺ currents in bladder umbrella cells. One type of K⁺ current identified was Ca²⁺-sensitive which could be blocked by Iberiotoxin (#STI-400), a large-conductance K⁺ channel blocker. BK currents were later on showed to be directly activated by LPS.

In addition, immunohistochemical staining of mouse bladder sections using Anti-K_Ca1.1 (BK_Ca) (extracellular) Antibody (#APC-151) showed that the channel is expressed in urothelium (where umbrella cells reside) and detrusor layer (Figure 1).

This work sets the ground for further studies on BK channel and its role in urinary tract infection.

Figure 1. Expression of K_Ca1.1 channel in mouse bladder.Immunohistochemical staining of mouse bladder sections using Anti-K_Ca1.1 (BK_Ca) (extracellular) Antibody (#APC-151). BK staining (red) is detected in urothelium layer (panels 1, a) and in detrusor layer (panels 1, b). Negative control using secondary antibody only shows insignificant background staining (panel 2). DAPI is used to stain nuclei. Panels a, and b are high magnifications of panel 1.Adapted from Lu, M. et al. (2018) Am. J. Physiol. 314, C643. with permission of the American Physiological Society.

Intracerebral hemorrhage (ICH) is a type of stroke in which 50% of affected patients die within 48 hrs as a result of brain edema. Brain edema is caused by an increase in blood brain barrier (BBB) permeability.

Western blot analysis showed that TRPV4 expression increases in the ipsilateral hemisphere following ICH. Immunohistochemical staining of rat brain sections 24 hours post-ICH was carried out. Using Anti-TRPV4 Antibody (#ACC-034), immunostaining of the channel was detected on neurovascular structures, perivascular astrocytes and endothelial cells in the perihematomal area. TRPV4 staining coincided with that of GFAP, an astrocyte marker and von Willebrand factor (vWF), a marker of BBB (Figure 1).

The increase in TRPV4 expression was accompanied by an increase in BBB permeability. Subjecting rats to TRPV4 blockers following ICH induction, prevented the disruption of BBB.

The data presented indicate that blocking TRPV4 following ICH may represent a novel approach for treating secondary brain injury.

Figure 1. Expression of TRPV4 in Rat Perihematomal Area Following ICH.Immunohistochemical staining of rat brain sections 24 hours after intracerebral hemorrhage (ICH) induction using Anti-TRPV4 Antibody (#ACC-034). At 24 hours post-ICH, TRPV4 immunostaining (red) was detected on neurovascular structures, perivascular astrocytes and endothelial cells in the perihematomal area. TRPV4 staining coincided with that of GFAP (lower panels), an astrocyte marker and von Willebrand factor (vWF) (upper panels), a marker of BBB. Nuclei were stained using DAPI.Adapted from Zhao, H. et al. (2018) Front. Mol. Neurosci. 11, 97.with permission of Frontiers.

Neuropathic pain is caused by injuries to peripheral nerve fibers. A study was set out to see how uninjured adjacent nerve fibers relate to neighbor injuries by making use of the spared nerve injury (SNI) model system. In this system a lesion of two to three terminal branches of the sciatic nerve is achieved, while leaving the sural nerve intact.

Immunohistochemical staining using Anti-Ca_V3.2 Antibody (#ACC-025) demonstrated that the T-type channel is expressed in the normal rat sural nerve (Figure 1). Ca_V3.2 staining partially colocalizes with neurofilament 200 (Figure 1A) and significantly colocalizes with calcitonin gene-related peptide (CGRP), a marker for nociceptive peptidergic fibers (Figure 1B). Western blot analysis revealed that Ca_V3.2 accumulates in the uninjured sural nerve following SNI.                 

Aβ-, Aδ and C-fibers of the uninjured sural nerve were highly sensitized following SNI; an effect directly related to the increase in Ca_V3.2 expression in the sural nerve.  Application of Alomone Labs TTA-P2 (#T-155) caused a significant increase in mechanical thresholds, suggesting that accumulation of Ca_V3.2 in the uninjured sural nerve contributes to mechanical allodynia following SNI.

Figure 1. Expression of Ca_V3.2 in Rat Sural Nerve.Immunohistochemical staining of rat sural nerve sections using Anti-Ca_V3.2 Antibody (#ACC-025). A. Ca_V3.2 staining (green) partially colocalizes with neurofilament 200. B. Ca_V3.2 staining (green) significantly colocalizes with calcitonin gene-related peptide (CGRP, red), a marker for nociceptive peptidergic fibers.Adapted from Chen, W. et al. (2018) Front. Mol. Neurosci. 11, 24. with permission of Frontiers.

Pancreatitis is a mechanical injury caused to the pancreas which can be easily induced by simple blows to the abdomen.

In this study, Romac et al.¹ investigate the molecular determinants of pancreatitis. They confirm the expression of Piezo1 by the application of Yoda1, a Piezo1 activator, and by immunohistochemical staining of mouse pancreas sections. Piezo1 staining in pancreas acinar cells was detected using Anti-Piezo1 Antibody (#APC-087).  Piezo1, a member of non-selective cationic mechanosensitive channel family has been gaining tremendous attention since its discovery in 2010².

The authors show that activation of Piezo1 is sufficient for causing pressure-induced pancreatitis. Conversely, cell-specific knockout of Piezo1 in acinar cells (as shown in immunohistochemical staining (Figure 1.)) or blockade of Piezo1 by GsMTx-4 protect from pressure-induced pancreatitis.

Overall, the data strongly suggest that inhibiting Piezo1 could be used when manipulation of the pancreas is required.

Figure 1. Expression of Piezo1 in Mouse Pancreas.Immunohistochemical staining of mouse pancreas sections using Anti-Piezo1 Antibody (#APC-087). Piezo1 staining (red) is detected in acinar cells. Piezo1^aci KO mice (right panel) do not express Piezo1. Trypsin staining is shown in green and nuclei are stained with DAPI (blue).Adapted from Romac, J.M. et al. (2018) Nat. Commun. 9, 1715. with permission of SPRINGER NATURE.

References
1. Romac, J.M. et al. (2018) Nat. Commun. 9, 1715.
2. Coste, B. et al. (2010) Science 330, 55.