Sphingosine and FTY720 modulate pacemaking activity in interstitial cells of Cajal from mouse small intestine

Structural mechanisms of TRPM7 activation and inhibition

The transient receptor potential channel TRPM7 is a master regulator of the organismal balance of divalent cations that plays an essential role in embryonic development, immune responses, cell mobility, proliferation, and differentiation. TRPM7 is implicated in neuronal and cardiovascular disorders, tumor progression and has emerged as a new drug target. Here we use cryo-EM, functional analysis, and molecular dynamics simulations to uncover two distinct structural mechanisms of TRPM7 activation by a gain-of-function mutation and by the agonist naltriben, which show different conformational dynamics and domain involvement. We identify a binding site for highly potent and selective inhibitors and show that they act by stabilizing the TRPM7 closed state. The discovered structural mechanisms provide foundations for understanding the molecular basis of TRPM7 channelopathies and drug development.

Knockdown of TRPM7 attenuates apoptosis and inflammation in neonatal necrotizing enterocolitis model cell IEC-6 via modulating TLR4/NF-κB and MEK/ERK pathways

OBJECTIVES

Neonatal necrotizing enterocolitis (NEC) is the most common gastrointestinal critical illness in neonatal infants. TRPM7 reportedly plays a role in human inflammatory bowel disease (IBD) and colorectal cancer, but the role of TRPM7 in the pathogenesis of NEC remains vague.

MATERIALS AND METHODS

The expression of TRPM7 was determined in intestinal tissues of NEC patients and lipopolysaccharide (LPS)-induced IEC-6 cells. Subsequently, a loss-of-function assay was performed to assess the effects of TRPM7 on cell apoptosis and inflammatory response in IEC-6 cells after LPS induction. Furthermore, the modulation of TRPM7 on TLR4/NF-κB and MEK/ERK signaling pathways was validated.

RESULTS

The expression of TRPM7 was higher in the intestinal tissues of NEC patients compared with the normal human intestinal tissues. Moreover, the expression level of TRPM7 was elevated in LPS stimulation IEC-6 cells. Knockdown of TRPM7 enhanced cell viability and suppressed apoptosis, accompanied by the decreased Bax/Bcl-1 ratio and cleaved-caspase3 expression in LPS-induced IEC-6 cells. Additionally, TRPM7 silencing attenuated LPS-induced expressions and secretions of proinflammatory cytokines. Mechanistically, TRPM7 knockdown inhibited the TLR4/NF-κB activation, while enhancing the MEK/ERK activation in LPS-treated IEC-6 cells. Overexpression of TLR4 or inhibition of MEK attenuated the inhibitory effects of TRPM7 knockdown on LPS-induced apoptosis and inflammation in IEC-6 cells.

CONCLUSION

Knockdown of TRPM7 attenuated LPS-induced IEC-6 cell apoptosis and inflammation by modulating TLR4/NF-κB and MEK/ERK pathways.

The sphingosine analog fingolimod (FTY720) enhances tone and contractility of rat gastric fundus smooth muscle

BACKGROUND

Sphingosine and its metabolite sphingosine phosphate (S1P) regulate a multitude of biological functions, including the contractile state of smooth. Gastrointestinal side effects have been reported in patients treated with FTY720, a sphingosine analog that is approved for the treatment of multiple sclerosis. The aim of this study was to characterize the effects of FTY720 on rat gastric fundus smooth muscle under basal conditions and during activation induced by high-K⁺ solution.

METHODS

Isometric contractions of isolated circular strips of gastric fundus smooth muscle were recorded using the organ bath method. The effects of FTY720 or vehicle were recorded under control conditions and in the presence of indomethacin, L-NAME, HA-1100, nifedipine, JTE-013, and suramin. Tone and contractions recorded in the presence of FTY720 or vehicle are reported as % of the amplitude of an initial high-K⁺ contraction obtained under control conditions.

KEY RESULTS

From a concentration of 10 μmol L^-1 onwards, FTY720 increased the tone, reaching 8.9% ± 7.5% at 100 μmol L^-1 (P < .05). With indomethacin in the solution, the effects of FTY720 were enhanced (32.1% ± 7.7%; P < .001). The FTY720-induced increase in tone was abolished in the absence of extracellular Ca²⁺ and reduced by nifedipine, HA-1100, JTE-013, and suramin. Furthermore, FTY720 increased high-K⁺ contractions in the presence of indomethacin.

CONCLUSIONS & INFERENCES

FTY720 increases tone and contractile responses to depolarization in gastric fundus smooth muscle by triggering calcium entry and calcium sensitization in a S1P receptor-dependent manner. Taken together, the experimental results presented in this work suggest that FTY720 may increase gastric tone and contractility in patients.

Depolarizing Effects of Daikenchuto on Interstitial Cells of Cajal from Mouse Small Intestine

Background:

Daikenchuto (DKT; TJ-100, TU-100), a traditional herbal medicineis used in modern medicine to treat gastrointestinal (GI) functional disorders. Interstitial cells of Cajal (ICCs) are the pacemaker cells of the GI tract and play important roles in the regulation of GI motility.

Objective:

The objective of this study was to investigate the effects of DKT on the pacemaker potentials (PPs) of cultured ICCs from murine small intestine.

Materials and Methods:

Enzymatic digestions were used to dissociate ICCs from mouse small intestine tissues. All experiments on ICCs were performed after 12 h of culture. The whole-cell patch-clamp configuration was used to record ICC PPs (current clamp mode). All experiments were performed at 30-32°C.

Results:

In current-clamp modeDKT depolarized and concentration-dependently decreased the amplitudes of PPs. Y25130 (a 5-HT₃ receptor antagonist) or SB269970 (a 5-HT₇ receptor antagonist) did not block DKT-induced PP depolarization, but RS39604 (a 5-HT₄ receptor antagonist) did. Methoctramine (a muscarinic M₂ receptor antagonist) failed to block DKT-induced PP depolarization, but pretreating 4-diphenylacetoxy-N-methylpiperidine methiodide (a muscarinic M₃ receptor antagonist) facilitated blockade of DKT-induced PP depolarization. Pretreatment with an external Ca²⁺-free solution or thapsigargin abolished PPsand under these conditions, DKT did not induce PP depolarization. Furthermore Ginseng radix and Zingiberis rhizomes depolarized PPs, whereas Zanthoxyli fructus fruit (the third component of DKT) hyperpolarized PPs.

Conclusion:

These results suggest that DKT depolarizes ICC PPs in an internal or external Ca²⁺-dependent manner by stimulating 5-HT₄ and M₃ receptors. Furthermore, the authors suspect that the component in DKT largely responsible for depolarization is probably also a component of Ginseng radix and Zingiberis rhizomes.

SUMMARY

Daikenchuto (DKT) depolarized and concentration-dependently decreased the amplitudes of pacemaker potentials (PPs)

Y25130 (a 5-HT₃ receptor antagonist) or SB269970 (a 5-HT₇ receptor antagonist) did not block DKT-induced PP depolarization, but RS39604 (a 5-HT₄ receptor antagonist) did

Methoctramine (a muscarinic M₂ receptor antagonist) failed to block DKT-induced PP depolarization, but pretreating 4-DAMP (a muscarinic M₃ receptor antagonist) facilitated blockade of DKT-induced PP depolarization

Ginseng radix and Zingiberis rhizomes depolarized PPswhereas Zanthoxyli fructus fruit (the third component of DKT) hyperpolarized PPs.

Abbreviation used: DKT: Daikenchuto, GI: Gastrointestinal, ICCs: Interstitial cells of Cajal, PPs: Pacemaker Potentials.

Effects of Prunus mume Siebold & Zucc. in the pacemaking activity of interstitial cells of Cajal in murine small intestine

Interstitial cells of Cajal (ICCs) function as pacemaker cells in the gastrointestinal (GI) tract and therefore, serve an important role in regulating GI motility. The effects of a species of plum (Prunus mume Siebold & Zucc.) on cultured ICC cluster-induced pacemaker potentials in the mouse small intestine were investigated, and the effects of a methanolic extract of Prunus mume (m-PM) on ICC pacemaker activities were examined using the whole-cell patch-clamp technique. ICC pacemaker membrane potentials were depolarized by m-PM in a concentration dependent manner in current clamp mode. 4-Diphenylacetoxy-N-methyl-piperidine methiodide, which is a muscarinic 3 (M₃) receptor antagonist, was able to block m-PM-induced pacemaker potential increases, whereas methoctramine, which is a muscarinic 2 (M₂) receptor antagonist, was not. When 1 mM guanosine diphosphate β-5 was present in the pipette solution, m-PM induced slight pacemaker depolarization. Following pretreatment in bath solution of Ca²⁺-free solution or a Ca²⁺-ATPase inhibitor in endoplasmic reticulum, the pacemaker currents were inhibited. Furthermore, pretreatment with PD98059, SB203580 or SP600125, which is a c-jun NH2-terminal kinase inhibitor, blocked m-PM-induced ICC potential depolarization. Furthermore, m-PM inhibited transient receptor potential melastatin (TRPM) 7 channels, but did not affect Ca²⁺-activated Cl^- channels. These results suggest that m-PM is able to modulate pacemaker potentials through the muscarinic M₃ receptor, via G-protein and external and internal Ca²⁺, in a mitogen-activated protein kinase and TRPM7-dependent manner. Therefore, m-PM may provide a basis for the development of a novel gastroprokinetic agent.

Berberine induces pacemaker potential inhibition via cGMP-dependent ATP-sensitive K+ channels by stimulating mu/delta opioid receptors in cultured interstitial cells of Cajal from mouse small intestine

Berberine is traditionally used to treat gastrointestinal (GI) motility disorders. The interstitial cells of Cajal (ICCs) are the pacemaker cells of the gastrointestinal tract, which are responsible for the production of gut movements. The present study aimed to investigate the effects of berberine on pacemaker potentials (PPs) in cultured ICC clusters from the mouse small intestine, and sought to identify the receptors involved and the underlying mechanisms of action. All experiments were performed on cultured ICCs, and a whole‑cell patch‑clamp configuration was used to record PPs from ICC clusters (current clamp mode). Under current clamp mode, berberine was shown to decrease the amplitude and frequency of PPs. However, these effects were suppressed by treatment with glibenclamide, a specific ATP‑sensitive K+ channel blocker. Nor‑binaltorphimine dihydrochloride (a kappa opioid receptor antagonist) did not suppress berberine‑induced PP inhibition, whereas ICI 174,864 (a delta opioid receptor antagonist) and CTOP (a mu opioid receptor antagonist) did suppress the inhibitory effects of berberine. Pretreatment with SQ‑22536 (an adenylate cyclase inhibitor) or with KT‑5720 (a protein kinase A inhibitor) did not suppress the effects of berberine; however, pretreatment with 1H‑[1,2,4] oxadiazolo [4,3‑a] quinoxalin‑1‑one (a guanylate cyclase inhibitor) or KT‑5823 [a protein kinase G (PKG) inhibitor] did. In addition, berberine stimulated cyclic guanosine monophosphate (cGMP) production in ICCs. These observations indicate that berberine may inhibit the pacemaker activity of ICC clusters via ATP‑sensitive K+ channels and the cGMP‑PKG‑dependent pathway by stimulating mu and delta opioid receptors. Therefore, berberine may provide a basis for the development of novel agents for the treatment of GI motility dysfunction.

Natural and Synthetic Modulators of the TRPM7 Channel

Transient receptor potential cation channel subfamily M member 7 (TRPM7) is a bi-functional protein comprising a TRP ion channel segment linked to an α-type protein kinase domain. Genetic inactivation of TRPM7 revealed its central role in magnesium metabolism, cell motility, proliferation and differentiation. TRPM7 is associated with anoxic neuronal death, cardiac fibrosis and tumor progression highlighting TRPM7 as a new drug target. Recently, several laboratories have independently identified pharmacological compounds inhibiting or activating the TRPM7 channel. The recently found TRPM7 modulators were used as new experimental tools to unravel cellular functions of the TRPM7 channel. Here, we provide a concise overview of this emerging field.