Tubular microdomains of Rab7-endosomes retrieve TrkA, a mechanism disrupted in Charcot-Marie-Tooth 2B

Axonal survival and growth requires signalling from tropomyosin receptor kinases (Trks). To transmit their signals, receptor-ligand complexes are endocytosed and retrogradely trafficked to the soma where downstream signalling occurs. Vesicles transporting neurotrophic receptors to the soma are reported to be Rab7-positive late endosomes/multi vesicular bodies where receptors localize within so-called intraluminal vesicles. Therefore, one challenging question is how downstream signalling is possible given the insulating properties of intraluminal vesicles. In this study, we report that Rab7-endosomes/multi vesicular bodies retrieve TrkA through tubular microdomains. Interestingly, this phenotype is absent for the EGF-receptor. Further, we found that EndophilinA1, EndophilinA2 and EndophilinA3 together with WASH1 are involved in the tubulation process. In Charcot-Marie-Tooth 2B, a neuropathy of the peripheral nervous system, this tubulating mechanism is disrupted. In addition, the ability to tubulate correlates with the phosphorylation levels of TrkA as well as with neurite length in neuronal cultures from dorsal root ganglia. In all, we report a new retrieval mechanism of late Rab7-endosomes, which enables TrkA signalling and sheds new light onto how neurotrophic signalling is disrupted in CMT2B.

Matrix metalloproteinases, purinergic signaling, and epigenetics, hubs in the spinal neuroglial network following nerve injury.

The neuroglial network characterizes synaptic transmission and accounts for both cellular elements (neurons and glia) and neural extracellular matrix (nECM) roles. Glial cells, neuron, and nECMnetwork is strongly interconnected, in physiological and pathological conditions as shownin several neurodegenerative diseases. Purinergic activation and matrix metalloproteinases (MMPs) remodeling of the spinal cord is pivotal in maladaptive plastic changes following peripheral nerve injury (PNI). To understand how purinergic and MMPs inhibition may modulate and potentially reverse the neuroglial network failure, we used the spared nerve injury (SNI) model of the sciatic nerve. Molecular and morphological analysis of astrocytic and microglial activation, purinergic and neurotrophic receptors, Histone Deacetylase (HDAC)1, HDAC2 were analyzed to define the pathways in response to the purinergic and MMPs inhibition. The data suggest complex protein interconnections, which are not passively influenced by epigenetics but actively contribute to modify the transcriptomics machinery. The present study contributes to unveiling the spinal network consistency and ultimately encourages new paths for targeted treatments in neurological diseases with benefits of neuroprotection, plasticity, and functional recovery.

Impact of neurotrophic factors combination therapy on retinitis pigmentosa

Objective We aimed to determine the location of neurotrophic receptors tropomyosin receptor kinase (Trk)B, TrkC, and ciliary neurotrophic factor receptor (CNTFR)α in the retina of retinal degeneration ( rd) mice and to explore the dynamic changes of B-cell lymphoma-2 (Bcl-2), Bcl-2-associated X-protein (Bax), and microtubule-associated protein light chain 3 (LC3) expression and ultrastructure in the retina of rd mice intravitreally injected with neurotrophic factors. Methods Rd mice aged 2 and 3 weeks post-natally (PN) received intravitreal injections of neurotrophic factors. Two weeks later, their retinas were harvested for the detection of Bax, Bcl-2, and LC3 mRNA and protein expression. Results TrkB and TrkC expression levels were lower at 3 weeks PN compared with 0, 1, and 2 weeks PN, but CNTFRα expression was still detected in certain layers. The three receptors were expressed in different retinal layers at the same timepoint. Bax expression was downregulated in, rhBDNF + rhCNTF, rhBDNF + rhNT-3, groups 2 weeks after intravitreal injection; Bcl-2 expression was upregulated in the rhBDNF + rhCNTF + rhNT-3 group at PN-4w; and LC3 expression was upregulated in rhBDNF + rhCNTF + rhNT-3 groups. Conclusions The combined use of neurotrophic factors had a more significant effect on Bax, Bcl-2, and LC3 expression than the same factors used alone.

Parasite-Derived Neurotrophic Factor/trans-Sialidase of Trypanosoma cruzi Links Neurotrophic Signaling to Cardiac Innate Immune Response

ABSTRACTThe Chagas' disease parasiteTrypanosoma cruzielicits a potent inflammatory response in acutely infected hearts that keeps parasitism in check and triggers cardiac abnormalities. A most-studied mechanism underlying innate immunity inT. cruziinfection is Toll-like receptor (TLR) activation by lipids and other parasite molecules. However, yet-to-be-identified pathways should exist. Here, we show thatT. cruzistrongly upregulates monocyte chemoattractant protein 1 (MCP-1)/CCL2 and fractalkine (FKN)/CX3CL1 in cellular and mouse models of heart infection. Mechanistically, upregulation of MCP-1 and FKN stems from the interaction of parasite-derived neurotrophic factor (PDNF)/trans-sialidase with neurotrophic receptors TrkA and TrkC, as assessed by pharmacological inhibition, neutralizing antibodies, and gene silencing studies. Administration of a single dose of intravenous PDNF to naive mice results in a dose-dependent increase in MCP-1 and FKN in the heart and liver with pulse-like kinetics that peak at 3 h postinjection. Intravenous PDNF also augments MCP-1 and FKN in TLR signaling-deficient MyD88-knockout mice, underscoring the MyD88-independent action of PDNF. Although single PDNF injections do not increase MCP-1 and FKN receptors, multiple PDNF injections at short intervals up the levels of receptor transcripts in the heart and liver, suggesting that sustained PDNF triggers cell recruitment at infection sites. Thus, given that MCP-1 and FKN are chemokines essential to the recruitment of immune cells to combat inflammation triggers and to enhance tissue repair, our findings uncover a new mechanism in innate immunity againstT. cruziinfection mediated by Trk signaling akin to an endogenous inflammatory and fibrotic pathway resulting from cardiomyocyte-TrkA recognition by matricellular connective tissue growth factor (CTGF/CCN2).