Communication Between Enteric Neurons, Glia, and Nociceptors Underlies the Effects of Tachykinins on Neuroinflammation

Background & Aims

Tachykinins are involved in physiological and pathophysiological mechanisms in the gastrointestinal tract. The major sources of tachykinins in the gut are intrinsic enteric neurons in the enteric nervous system and extrinsic nerve fibers from the dorsal root and vagal ganglia. Although tachykinins are important mediators in the enteric nervous system, how they contribute to neuroinflammation through effects on neurons and glia is not fully understood. Here, we tested the hypothesis that tachykinins contribute to enteric neuroinflammation through mechanisms that involve intercellular neuron-glia signaling.

Methods

We used immunohistochemistry and quantitative real-time polymerase chain reaction, and studied cellular activity using transient-receptor potential vanilloid-1 (TRPV1)tm1(cre)Bbm/J::Polr2atm1(CAG-GCaMP5g,-tdTomato)Tvrd and Sox10CreERT2::Polr2atm1(CAG-GCaMP5g,-tdTomato)Tvrd mice or Fluo-4. We used the 2,4-di-nitrobenzene sulfonic acid (DNBS) model of colitis to study neuroinflammation, glial reactivity, and neurogenic contractility. We used Sox10::CreERT2+/-/Rpl22tm1.1Psam/J mice to selectively study glial transcriptional changes.

Results

Tachykinins are expressed predominantly by intrinsic neuronal varicosities whereas neurokinin-2 receptors (NK2Rs) are expressed predominantly by enteric neurons and TRPV1-positive neuronal varicosities. Stimulation of NK2Rs drives responses in neuronal varicosities that are propagated to enteric glia and neurons. Antagonizing NK2R signaling enhanced recovery from colitis and prevented the development of reactive gliosis, neuroinflammation, and enhanced neuronal contractions. Inflammation drove changes in enteric glial gene expression and function, and antagonizing NK2R signaling mitigated these changes. Neurokinin A-induced neurodegeneration requires glial connexin-43 hemichannel activity.

Conclusions

Our results show that tachykinins drive enteric neuroinflammation through a multicellular cascade involving enteric neurons, TRPV1-positive neuronal varicosities, and enteric glia. Therapies targeting components of this pathway could broadly benefit the treatment of dysmotility and pain after acute inflammation in the intestine.

Peptide welding technology - A simple strategy for generating innovative ligands for G protein coupled receptors

Based on their high selectivity of action and low toxicity, naturally occurring peptides have great potential in terms of drug development. However, the pharmacokinetic properties of peptides, in particular their half life, are poor. Among different strategies developed for reducing susceptibility to peptidases, and thus increasing the duration of action of peptides, the generation of branched peptides has been described. However, the synthesis and purification of branched peptides are extremely complicated thus limiting their druggability. Here we present a novel and facile synthesis of tetrabranched peptides acting as GPCR ligands and their in vitro and vivo pharmacological characterization. Tetrabranched derivatives of nociceptin/orphanin FQ (N/OFQ), N/OFQ related peptides, opioid peptides, tachykinins, and neuropeptide S were generated with the strategy named peptide welding technology (PWT) and characterized by high yield and purity of the desired final product. In general, PWT derivatives displayed a pharmacological profile similar to that of the natural sequence in terms of affinity, pharmacological activity, potency, and selectivity of action in vitro. More importantly, in vivo studies demonstrated that PWT peptides are characterized by increased potency associated with long lasting duration of action. In conclusion, PWT derivatives of biologically active peptides can be viewed as innovative pharmacological tools for investigating those conditions and states in which selective and prolonged receptor stimulation promotes beneficial effects.

The effects of particulate matter on inflammation of respiratory system: Differences between male and female

Air pollution is known to exacerbate respiratory diseases and epidemiological studies have shown that women present more chronic respiratory symptoms than man exposed to traffic pollution, however, the reason why is unclear. This study evaluated the inflammatory differences in BALB/c mouse males (n=34) and females (n=111) in three phases of the estrous cycle that were exposed to ambient air (AA) or concentrated ambient particles (CAPs). Tracheal hyperreactivity to methacholine, bronchoalveolar lavage fluid (BALF) and immunohistochemical of airways and lung parenchyma were studied. Hyperreactivity increased in CAPs-exposed female mice compared with AA-exposed mice in estrus (p<0.05) and proestrus phases (p<0.05) and decreased in CAPs-exposed males compared with those exposed to AA (p<0.05). Males had increased numbers of total cells (p=0.037) and macrophages (p=0.028) compared to females. BALF levels of cyclooxygenase-2(COX-2) (p=0.000), transforming growth factor alpha (TGF-α) (p=0.001) and IL-8 receptor alpha (IL-8Rα) (p=0.014) were increased in males compared with proestrus, estrus and diestrus females, independent of exposure. Proestrus females exhibited significantly higher cadherin expression in lung parenchyma than did males (p=0.005). CAPs exposure increased matrix metalloproteinase-9 (MMP-9) (p=0.024) and isoprostane (p=0.003) expression in the airways of both, males and females. The level of substance P (SP) (p=0.001) increased in lung parenchyma in males compared with females, while IL-17 levels in airways (p=0.042) and in lung parenchyma (p=0.008) increased in females. MMP-9 levels (p=0.024) were significantly lower in the lung parenchyma of CAPs-exposed females. TGF-α (p=0.007) levels increased in the lung parenchyma of CAPs-exposed females compared to AA-exposed females. These results suggest that inflammatory markers differentially expressed in male mice were mostly linked to acute inflammation (IL-1β, IL-8Rα, COX-2), whereas in females, markers that may lead to a chronic inflammatory process such as IL-17 and remodeling (MMP-9) were increased.

Emerging targets for addiction neuropharmacology: From mechanisms to therapeutics

Drug abuse represents a considerable burden of disease and has enormous economic impacts on societies. Over the years, few medications have been developed for clinical use. Their utilization is endowed with several limitations, including partial efficacy or significant side effects. On the other hand, the successful advancement of these compounds provides an important proof of concept for the feasibility of drug development programs in addiction. In recent years, a wealth of information has been generated on the psychological mechanisms, genetic or epigenetic predisposing factors, and neurobiological adaptations induced by drug consumption that interact with each other to contribute to disease progression. It is now clear that addiction develops through phases, from initial recreational use to excessive consumption and compulsive drug seeking, with a shift from positive to negative reinforcement driving motivated behaviors. A greater understanding of these mechanisms has opened new vistas in drug development programs. Researchers' attention has been shifted from investigation of classical targets associated with reward to biological substrates responsible for negative reinforcement, impulse loss of control, and maladaptive mechanisms resulting from protracted drug use. From this research, several new biological targets for the development of innovative therapies have started to emerge. This chapter offers an overview of targets currently under scrutiny for the development of new medications for addiction. This work is not exhaustive but rather it provides a few examples of how this research has advanced in recent years by virtue of studies carried out in our laboratory.