Series Editors: Michael J. Parnham · Achim Schmidtko

Progress in Inflammation Research 87

CarloRossetti

FrancescoPeri Editors

TheRole ofToll-Like

Receptor 4 in

Infectious and

Non Infectious

Inflammation

Progress in Inammation Research

Volume 87

Series Editors

MichaelJ.Parnham

Inst of Clinical Pharmacology

Goethe University Frankfurt,

Frankfurt am Main,Germany

AchimSchmidtko

Inst Pharmacology and Clinical Pharmacy

Goethe University Frankfurt

Frankfurt am Main,Germany

The last few years have seen a revolution in our understanding of how blood and

tissue cells interact and of the intracellular mechanisms controlling their activation.

This has not only provided multiple targets for potential anti-inammatory and

immunomodulatory therapy, but has also revealed the underlying inammatory

pathology of many diseases.

This series provides up-to-date information on the latest developments in the

pathology, mechanisms and therapy of inammatory disease. Areas covered include:

vascular responses, skin inammation, pain, neuroinammation, arthritis cartilage

and bone, airways inammation and asthma, allergy, cytokines and inammatory

mediators, cell signalling, and recent advances in drug therapy.

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and industrial biomedical researchers, drug development personnel and

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requiring regular scientic updates.

More information about this series at http://www.springer.com/series/4983

Carlo Rossetti • Francesco Peri

Editors

The Role of Toll-Like

Receptor 4in Infectious and

Non Infectious Inammation

ISSN 0379-0363 ISSN 2296-4517 (electronic)

Progress in Inammation Research

ISBN 978-3-030-56318-9 ISBN 978-3-030-56319-6 (eBook)

https://doi.org/10.1007/978-3-030-56319-6

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Editors

Carlo Rossetti

Department of Medicine and Surgery

University of Insubria

Varese, Italy

Francesco Peri

Department of Biotechnology and

Biosciences

University of Milano Bicocca

Milan, Italy

Preface

Toll-like receptors (TLRs) are essential regulators of innate and adaptive immune

responses and their complexity continues to intrigue researchers, including the

authors of this book. Because of their importance, when they are mutated and not

functioning as they should, autoimmune, inammatory, and infectious diseases can

develop.

The aim of this book is to present an update on the role of TLR4, the most stud-

ied TLR, in inammatory and infectious diseases with special focus on central ner-

vous system (CNS) pathologies.

We also give an outlook on what emerged in the past years on the molecular

aspects of extracellular TLR4 activation and intracellular signaling, its regulation by

miRNA, and crosstalk with other metabolic pathways.

To this end, a group of internationally recognized experts has kindly accepted to

present recent results on TLR4 function and role in health and disease.

TLR4 was the rst TLR identied by Medzhitov and coworkers in 1997 and was

then characterized by Beutler and coworkers as a pattern recognition receptor. TLR4

has an exquisite ligand selectivity that has remained largely unchanged through the

course of evolution allowing for an immediate and sensitive response to gram-

negative bacterial lipopolysaccharide (LPS).

The understanding of molecular features of extracellular TLR4 activation has

contributed to unravel the physiological and pathological role of TLR4. We have

now information on the structural biology of the molecular actors of LPS transfer:

LBP and CD14 proteins, the M-shaped dimeric (TLR4-MD2-LPS)

complex, and

of the intracellular signaling proteins, belonging to the so-called MyD88-dependent

and MyD88-independent pathways. The LPS-binding protein CD14 not only takes

part in LPS extraction from aggregates in solution and shuttling to TLR4/MD-2/

LPS dimer, but it also exerts autonomous functions by regulating endocytic pro-

cesses or by activating dedicated signaling pathways, as critically reviewed by

M.Di Gioia and I.Zanoni.

Starting from the knowledge of the supramolecular interactions among LPS and

LBP, CD14 and MD-2, the structure–activity relationship of TLR4 ligands, espe-

cially of lipid A variants, has been extensively studied. These studies allow the

structure-based rational design of synthetic or semisynthetic lipid A variants as vac-

cine adjuvants as reviewed by A.Shimoyama and K.Fukase.

Natural TLR4 ligands, LPS and LOS, and their synthetic variants are amphiphi-

lic molecules that aggregate in solution. A.B. Schromm and K.Brandenburg dis-

cuss from a biophysical perspective the most recent achievements in the study of the

role of aggregates in the biological activity of TLR4 ligands, with special focus on

the very recent ndings on LPS interaction with intracellular caspases and subse-

quent induction of the non-canonical inammasome.

To complete the complex and fascinating view of TLR4 signaling at a molecular

level, N.Kuzmich dissected from the structural biology point of view the two dis-

tinct intracellular pathways activated upon TLR4 dimerization: the MyD88-

dependent pathway and the TRIF/IRF3 pathway leading to interferon production.

He discussed the molecular events including phosphorylation and ubiquitination

that allow the regulation of the pathways.

Septic shock or excessive inammation are possibly the most severe outcomes

due to inadequate negative regulation of TLR4 signaling leading to excessive pro-

inammatory cytokine production. Similarly, TLR4 excessive stimulation by

endogenous molecules derived from necrotic or damaged tissues (danger-associated

molecular patterns, DAMPs) has been associated to a wide array of inammatory

and autoimmune diseases, including neuroinammations and vascular

inammations.

In this perspective, M.Christodoulides reviewed the molecular mechanism of

Neisseria lipooligosaccharide (LOS) interaction with TLR4 and discussed the role

of TLR4in meningococcal and gonococcal infections in the therapeutic perspective

to target Neisseria infections with TLR4 antagonists or investigating the role of

TLR4in Neisseria-vaccine-induced immune responses.

On the other hand, M.Molteni and C.Rossetti analyzed the main families of

endogenous TLR4 stimulators (DAMPs) and discussed DAMP/TLR4 activation

mechanisms that very often differ from the well-known direct TLR4/MD-2 binding

of bacterial endotoxins.

Another aspect still underestimated relative to TLR4 biology is the crosstalk

between TLR4 signaling and metabolic regulations occurring in macrophages and

dendritic cells (DCs). TLR4 stimulation of DCs or macrophages results in increased

glycolytic activity, an essential process to support their pro-inammatory functions.

L.Perrin-Cocon, A.Aublin-Gex, and V.Lotteau reviewed the molecular mecha-

nisms involved in the modulation of central carbon metabolism, from glycolysis,

tricarboxylic acid (TCA) cycle, and oxidative phosphorylation to lipid metabolism,

upon TLR4 signaling in macrophages and DCs.

Molecules called microRNAs (miRNA) have been recently described as negative

regulators of TLR signaling acting as a break on the pathway while others act as

Preface

vii

positive regulators and act as an accelerator. There is increasing evidence that TLR4

and miRNA crosstalk ensures the ne-tuning of inammatory response and subse-

quent healing occurring in tissues after infection or injury. The expression of miR-

NAs inside the cell, after TLR4 triggering, critically contributes both to the activation

and to the shutdown of immune cell response needed for the termination of the

inammatory process. M.Molteni and C.Rossetti gave insight into the intracellular

role of TLR4-miRNA axis in the regulation of inammatory and anti-inammatory

processes.

Interestingly, TLR4 does not only play a role in inducing inammation but also

in inducing tissue regeneration and healing after inammatory insult, and it main-

tains homeostasis in the gut and a state of constant “controlled inammation” due

to the stimulation by commensal bacteria. When there is an imbalance of gut micro-

ora, inammatory bowel diseases can develop.

This dual role of TLR4 signaling is particularly critical in CNS, as discussed by

L.De Filippis and F.Peri. TLR4 is expressed in microglia, which is a master player

in neuroinammatory processes, as well as in neural cells: astrocytes, neurons, oli-

godendrocytes, neural progenitors (NPC), and neural stem cells (NSC). We have

observed that TLR4 stimulation by LPS during differentiation enhances neurono-

genic potential of human NSC and favors both neuronal and oligodendroglial sur-

vival. Consistent with our data, it has been recently reported that endogenous NSC

are actively stimulated to proliferate by TLR4 activation after stroke, thus conrm-

ing the relevant role of TLR4in promoting neurogenesis under non-physiological

conditions. Altogether, these results indicate that in a therapeutic perspective, TLR4

activity should not to be turned on or off, but should be nely tuned in order to pro-

mote neuroregeneration rather than neurodegeneration and to mediate the develop-

ment of healing immunomodulation rather than of detrimental neuroinammation.

Recent insight on the role of TLR4 as mediator of inammatory response in

Alzheimer’s (AD) and Parkinson’s disease (PD) has been reviewed by C.Balducci

and G.Forloni. They reported literature data relating activation of TLR4 and the

presence of β amyloid and their own data showing that the memory damage and

inammatory effects obtained by intraventricular application of β amyloid oligo-

mers was antagonized by TLR4 inhibitor and completely abolished in TLR4-

knockout mice. They also discuss the recently discovered role of TLR4 in the

relationship between gut microbiota dysbiosis and increased risk of developing PD.

M.De Paola presented new data on the potential of Human Induced Pluripotent

Stem Cells (IPSC) and Cerebral Organoids as models to study how TLR4 regulates

immune cell interactions to orchestrate brain development and reaction to injury. He

showed how the development of platforms in which microglia, neurons, and mac-

roglia derived from healthy or diseased subjects grow and mature in a single system

allows to demonstrate the role of TLR4in mediating neuroinammation.

We thank all authors, that are also our good friends, for having accepted the chal-

lenge to compose this multidisciplinary mosaic around TLR4 functions. Their dif-

ferent expertise in the elds of structural biology, biophysics, medicinal chemistry,

Preface

viii

computational biology, biochemistry, immunology, pharmacology, and medicine

made possible the creation of a unique overview on several aspects of physiological

and pathological roles of one of the most fascinating and smart molecules to which

we have dedicated a large part of our scientic adventure.

Varese, Italy CarloRossetti

Milan, Italy FrancescoPeri

Preface

Contents

Chemically Synthesized TLR4 Ligands,

Their Immunological Functions, and Potential as Vaccine Adjuvant . . . . 1

Atsushi Shimoyama and Koichi Fukase

Intracellular TLR4 Signaling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Nikolay N. Kuzmich

TLR4 Ligands: Single Molecules and Aggregates . . . . . . . . . . . . . . . . . . . . 39

Andra B. Schromm and Klaus Brandenburg

CD14: Not Just Chaperone, But a Key-Player in Inflammation . . . . . . . . 57

Marco Di Gioia and Ivan Zanoni

Toll-Like Receptor 4 Interactions with Neisseria . . . . . . . . . . . . . . . . . . . . . 79

Myron Christodoulides

Toll-Like Receptor 4 Activation by Damage-Associated

Molecular Patterns (DAMPs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Monica Molteni and Carlo Rossetti

TLR4 in Neurodegenerative Diseases:

Alzheimer’s and Parkinson’s Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

Claudia Balducci and Gianluigi Forloni

TLR4-Mediated Neuroinflammation in Human Induced

Pluripotent Stem Cells and Cerebral Organoids . . . . . . . . . . . . . . . . . . . . . 119

Massimiliano De Paola

The Role of TLR4 in Neural Stem Cells–Mediated

Neurogenesis and Neuroinflammation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

Lidia De Filippis and Francesco Peri