CaMKK-CaMK1a, a new post-traumatic signalling pathway induced in mouse somatosensory neurons

Development of a biomarker prediction model for post-trauma multiple organ failure/dysfunction syndrome based on the blood transcriptome

BACKGROUND

Multiple organ failure/dysfunction syndrome (MOF/MODS) is a major cause of mortality and morbidity among severe trauma patients. Current clinical practices entail monitoring physiological measurements and applying clinical score systems to diagnose its onset. Instead, we aimed to develop an early prediction model for MOF outcome evaluated soon after traumatic injury by performing machine learning analysis of genome-wide transcriptome data from blood samples drawn within 24 h of traumatic injury. We then compared its performance to baseline injury severity scores and detection of infections.

METHODS

Buffy coat transcriptome and linked clinical datasets from blunt trauma patients from the Inflammation and the Host Response to Injury Study ("Glue Grant") multi-center cohort were used. According to the inclusion/exclusion criteria, 141 adult (age ≥ 16 years old) blunt trauma patients (excluding penetrating) with early buffy coat (≤ 24 h since trauma injury) samples were analyzed, with 58 MOF-cases and 83 non-cases. We applied the Least Absolute Shrinkage and Selection Operator (LASSO) and eXtreme Gradient Boosting (XGBoost) algorithms to select features and develop models for MOF early outcome prediction.

RESULTS

The LASSO model included 18 transcripts (AUROC [95% CI]: 0.938 [0.890-0.987] (training) and 0.833 [0.699-0.967] (test)), and the XGBoost model included 41 transcripts (0.999 [0.997-1.000] (training) and 0.907 [0.816-0.998] (test)). There were 16 overlapping transcripts comparing the two panels (0.935 [0.884-0.985] (training) and 0.836 [0.703-0.968] (test)). The biomarker models notably outperformed models based on injury severity scores and sex, which we found to be significantly associated with MOF (APACHEII + sex-0.649 [0.537-0.762] (training) and 0.493 [0.301-0.685] (test); ISS + sex-0.630 [0.516-0.744] (training) and 0.482 [0.293-0.670] (test); NISS + sex-0.651 [0.540-0.763] (training) and 0.525 [0.335-0.714] (test)).

CONCLUSIONS

The accurate assessment of MOF from blood samples immediately after trauma is expected to aid in improving clinical decision-making and may contribute to reduced morbidity, mortality and healthcare costs. Moreover, understanding the molecular mechanisms involving the transcripts identified as important for MOF prediction may eventually aid in developing novel interventions.

High-Throughput Screening for Extracellular Inhibitors of the FLT3 Receptor Tyrosine Kinase Reveals Chemically Diverse and Druggable Negative Allosteric Modulators

Inhibiting receptor tyrosine kinases is commonly achieved by two main strategies targeting either the intracellular kinase domain by low molecular weight compounds or the extracellular ligand-binding domain by monoclonal antibodies. Identifying small molecules able to inhibit RTKs at the extracellular level would be highly desirable to gain exquisite selectivity but is believed to be challenging owing to the size of RTK endogenous ligands (cytokines, growth factors) and the topology of RTK extracellular domains. We here report the high-throughput screening of the French Chemical Library (48K compounds) for extracellular inhibitors of the Fms-like tyrosine kinase 3 (FLT3) receptor tyrosine kinase, by a homogeneous time-resolved fluorescence competition assay. A total of 679 small molecular weight ligands (1.4%) were confirmed to strongly inhibit (>75%) the binding of the fluorescent labeled FLT3 ligand (FL cytokine) to FLT3 overexpressed in HEK-293 cells, at two different concentrations (5 and 20 μM). Concentration-response curves, obtained for 111 lead-like molecules, confirmed the unexpected tolerance of the FLT3 extracellular domain for low molecular weight druggable inhibitors exhibiting submicromolar potencies, chemical diversity, and promising pharmacokinetic properties. Further investigation of one hit confirmed inhibitory properties in dorsal root ganglia neurons and in a mouse model of neuropathic pain.

Calcium in Neuronal and Glial Response to Axotomy

Neurotrauma assumes an instant or delayed disconnection of axons (axotomy), which affects not only neurons, but surrounding glia as well. Not only mechanically injured glia near the site of disconnection, especially transection, is subjected to the damage, but also glia that is remote from the lesion site. Glial cells, which surround the neuronal body, in turn, support neuron survival, so there is a mutual protection between neuron and glia. Calcium signaling is a central mediator of all post-axotomy events, both in neuron and glia, playing a critical role in their survival/regeneration or death/degeneration. The involvement of calcium in post-axotomy survival of the remote, mechanically intact glia is poorly studied. The purpose of this review is to sum up the calcium-involving mechanisms in responses of neurons and glial cells to axotomy to show their importance and to give some suggestions for future research of remote glia in this context.

Polymorphisms in CAMKK2 associate with susceptibility to sensory neuropathy in HIV patients treated without stavudine

HIV-associated sensory neuropathy (HIV-SN) is a debilitating neurological complication of HIV infection potentiated by the antiretroviral drug stavudine. While stavudine is no longer used, HIV-SN now affects around 15% of HIV+ Indonesians. Here, we investigate whether polymorphisms within the P2X-block (P2X4R, P2X7R, CAMKK2) and/or ANAPC5 mark susceptibility to HIV-SN in this setting. As polymorphisms in these genes associated with HIV-SN in African HIV patients receiving stavudine, the comparison can identify mechanisms independent of stavudine. HIV patients who had never used stavudine (n = 202) attending clinics in Jakarta were screened for neuropathy using the AIDS Clinical Trials Group Brief Peripheral Neuropathy Screen. Open-array technology was used to type 48 polymorphisms spanning the four genes. Haplotypes were derived for each gene using fastPHASE. Haplogroups were constructed with median-joining methods. Multivariable models optimally predicting HIV-SN were based on factors achieving p < 0.2 in bivariate analyses. Minor alleles of three co-inherited polymorphisms in CAMKK2 (rs7975295*C, rs1560568*A, rs1132780*T) associated with a reduced prevalence of HIV-SN individually and after adjusting for lower CD4 T cell count and viremia (p = 0.0002, pseudo R² = 0.11). The optimal model for haplotypes linked HIV-SN with viremia and lower current CD4 T cell count, plus CAMKK2 haplotypes 6 and 11 and P2X7R haplotypes 2 and 12 (p = 0.0002; pseudo R² = 0.11). CAMKK2 haplogroup A (includes 16 haplotypes and all instances of rs7975295*C, rs1560568*A, rs1132780*T) associated with reduced rates of HIV-SN (p = 0.02, OR = 0.43 CI = 0.21-0.88). These findings support a protective role for these three alleles, suggesting a role in the pathogenesis of HIV-SN that is independent of stavudine.

Inhibition of neuronal FLT3 receptor tyrosine kinase alleviates peripheral neuropathic pain in mice

Peripheral neuropathic pain (PNP) is a debilitating and intractable chronic disease, for which sensitization of somatosensory neurons present in dorsal root ganglia that project to the dorsal spinal cord is a key physiopathological process. Here, we show that hematopoietic cells present at the nerve injury site express the cytokine FL, the ligand of fms-like tyrosine kinase 3 receptor (FLT3). FLT3 activation by intra-sciatic nerve injection of FL is sufficient to produce pain hypersensitivity, activate PNP-associated gene expression and generate short-term and long-term sensitization of sensory neurons. Nerve injury-induced PNP symptoms and associated-molecular changes were strongly altered in Flt3-deficient mice or reversed after neuronal FLT3 downregulation in wild-type mice. A first-in-class FLT3 negative allosteric modulator, discovered by structure-based in silico screening, strongly reduced nerve injury-induced sensory hypersensitivity, but had no effect on nociception in non-injured animals. Collectively, our data suggest a new and specific therapeutic approach for PNP.

Sensitisation of dorsal root ganglia neurons contributes to neuropathic pain. Here the authors demonstrate the cytokine FL contributes to sensitisation of DRGs via its receptor FLT3 expressed on neurons, and identify a novel FLT3 inhibitor that attenuates neuropathic pain in mice.

Effects of Treatment of Treadmill Combined with Electro-Acupuncture on Tibia Bone Mass and Substance PExpression of Rabbits with Sciatic Nerve Injury

The peripheral nervous system may play an important role in normal bone maintenance and remodeling. Substance P (SP) is a neuropeptide associated with bone loss and formation that may mediate the effects of the nervous system. The purpose of this study is to determine if treadmill running combined with electro-acupuncture at Jiaji acupoints (Jiaji-EA) affects tibial bone mass and SP expression in rabbits with sciatic nerve injury. Twenty-four juvenile male New Zealand white rabbits were randomly assigned to one of 4 groups: sham injury control (sham), sciatic never crush control (SNCr), treadmill running (treadmill), and Jiaji-EA combined with treadmill running (ET group). The SNCr, treadmill, and ET groups all had an induced sciatic never crush injury of approximately 2mm. Control groups received no intervention; the treadmill and ET groups were trained by treadmill; the ET group also received Jiaji-EA. After the 4 weeks of treatment, toe-spreading index (TSI), BMD, bone strength, and SP expression in the tibia were significantly lower in the nerve injury groups (SNCr, treadmill, and ET) compared to the sham groups (p<0.05). Treatment (treadmill and ET groups) increased all measures compared to the SNCr group (p<0.05). Further, TSI, BMD, bone strength, and SP expression in the ET group were higher than the treadmill group (p<0.05). Our results indicate that treadmill therapy combined with electro-acupuncture at Jiaji acupoints prevents bone loss in rabbit tibias after sciatic nerve injury. This may occur in two ways: indirectly in association with axon regeneration and directly via loading on the bone mediated through increased SP expression. This study provides important evidence for the clinical treatment of bone loss after peripheral nerve injury.

Fxyd2 regulates Aδ- and C-fiber mechanosensitivity and is required for the maintenance of neuropathic pain

Identification of the molecular mechanisms governing sensory neuron subtype excitability is a key requisite for the development of treatments for somatic sensory disorders. Here, we show that the Na,K-ATPase modulator Fxyd2 is specifically required for setting the mechanosensitivity of Aδ-fiber low-threshold mechanoreceptors and sub-populations of C-fiber nociceptors, a role consistent with its restricted expression profile in the spinal somatosensory system. We also establish using the spared nerve injury model of neuropathic pain, that loss of Fxyd2 function, either constitutively in Fxyd2^−/− mice or acutely in neuropathic rats, efficiently alleviates mechanical hypersensitivity induced by peripheral nerve lesions. The role of Fxyd2 in modulating Aδ- and C-fibers mechanosensitivity likely accounts for the anti-allodynic effect of Fxyd2 knockdown. Finally, we uncover the evolutionarily conserved restricted expression pattern of FXYD2 in human dorsal root ganglia, thus identifying this molecule as a potentially promising therapeutic target for peripheral neuropathic pain management.

Nicotine effects on muscarinic receptor-mediated free Ca[Formula: see text] level changes in the facial nucleus following facial nerve injury

It was suggested that muscarinic, and nicotinic receptors increase free Ca[Formula: see text] levels in the facial nerve nucleus via various channels following facial nerve injury. However, intracellular Ca[Formula: see text] overload can trigger either necrotic or apoptotic cell death. It is assumed that, following facial nerve injury, the interactions of nicotinic and muscarinic acetylcholine receptors in facial nerve nucleus may negatively regulate free Ca[Formula: see text] concentrations in the facial nerve nucleus, which provide important information for the repair and regeneration of the facial nerve. The present study investigated the regulatory effects of nicotine on muscarinic receptor-mediated free calcium ion level changes in the facial nucleus in a rat model of facial nerve injury at 7, 30, and 90 days following facial nerve injury using laser confocal microscopy. The dose-dependent regulation of nicotine on muscarinic receptor-mediated free calcium ion level changes in the facial nucleus may decrease the range of free Ca[Formula: see text] increases following facial nerve injury, which is important for nerve cell regeneration. It is concluded that the negative effects of nicotine on muscarinic receptors are related to the [Formula: see text] subtype of nicotinic receptors.

Molecular mechanisms of protein kinase regulation by calcium/calmodulin

Many human protein kinases are regulated by the calcium-sensor protein calmodulin, which binds to a short flexible segment C-terminal to the enzyme's catalytic kinase domain. Our understanding of the molecular mechanism of kinase activity regulation by calcium/calmodulin has been advanced by the structures of two protein kinases-calmodulin kinase II and death-associated protein kinase 1-bound to calcium/calmodulin. Comparison of these two structures reveals a surprising level of diversity in the overall kinase-calcium/calmodulin arrangement and functional readout of activity, as well as complementary mechanisms of kinase regulation such as phosphorylation.