Transmembrane TNF protects mutant mice against intracellular bacterial infections, chronic inflammation and autoimmunity

Abstract

Using targeted mutagenesis in mice, we have blocked shedding of endogenous murine TNF by deleting its cleavage site. Mutant mice produce physiologically regulated levels of transmembrane TNF (tmTNF), which suffice to support thymocyte proliferation but cannot substitute for the hepatotoxic activities of wild-type TNF following LPS/Dgalactosamine challenge in vivo and are not sufficient to support secondary lymphoid organ structure and function. Notably, however, tmTNF is capable of exerting antiListerial host defenses while remaining inadequate to mediate arthritogenic functions, as tested in the tristetraprolin-deficient model of TNF-dependent arthritis. Most interestingly, in the EAE model of autoimmune demyelination, tmTNF suppresses disease onset and progression and retains the autoimmune suppressive properties of wild-type TNF. Together, these results indicate that tmTNF preserves a subset of the beneficial activities of TNF while lacking detrimental effects. These data support the hypothesis that selective targeting of soluble TNF may offer several advantages over complete blockade of TNF in the treatment of chronic inflammation and autoimmunity.Supporting information for this article is available at: http://www.wiley-vch.de/contents/jc_2040/2006/35921_s.pdf IntroductionOriginally identified as an endotoxin-induced serum factor that causes necrosis of tumors [1] and/or cachexia [2], TNF is currently known to mediate a wide array of biological activities [3, 4]. TNF is produced in response to bacterial toxins, inflammatory products and other stimuli mainly by cells of the myeloid lineage, with additional producers including B and T lymphocytes, NK cells, microglia, astrocytes and adipocytes [3]. TNF is bioactive both as a transmembrane protein and as a homotrimeric secreted molecule [5] and mediates its effects through two distinct TNF receptors, p55TNFR (TNFRI) and p75TNFR (TNFRII) [6]. Transmembrane TNF (tmTNF) appears superior to soluble TNF in activating the p75TNFR, while at physiological concentrations soluble TNF primarily activates the p55TNFR [7]. The two types of TNF receptors share structural homology in the extracellular TNF-binding domains, but they induce separate cytoplasmic signaling pathways following receptor-ligand interaction [8]. Apoptosis and activation of NF-jB are initiated by p55TNFR, whereas p75TNFR appears to play a direct role in only a limited number of TNF responses [6,9]. Several functionally diverse proteins, such as growth factors and cytokines and including TNF, are initially synthesized as biologically active membrane-anchored molecules that are subsequently released from the cell by proteolysis [10]. Thus, surface localization may serve to restrict activity to specific microenvironments, whereas release may lead to distal effects. TNF is synthesized as a 26 kDa type II transmembrane molecule, which can be processed by a TNF-alpha converting enzyme (TACE or ADAM17), to generate secreted 17 kDa monomers that form biologically active homotrimers [11,12]. Indications for a r...

TPL2-mediated activation of ERK1 and ERK2 regulates the processing of pre-TNFα in LPS-stimulated macrophages

“…TPL2 would appear to be an attractive drug target because its inhibition should prevent the activation of ERK1/2 by LPS, TNF␣ and IL-1␤, without affecting the activation of ERK1/2 by other agonists, such as growth factors, which activate this pathway via RAF and not TPL2. Membraneinserted TNF␣ is biologically active (Kriegler et al, 1988) and might be able to partially (Alexopoulou et al, 2006) or weakly (Ruuls et al, 2001) support pro-inflammatory activity in vivo. Therefore, our observation that pre-TNF␣ is not expressed at the cell surface if the activation of ERK1/2 is blocked is important, because it implies that pre-TNF␣ produced when TPL2 is inhibited is unlikely to retain significant pro-inflammatory activity.…”

Cellular source and molecular form of TNF specify its distinct functions in organization of secondary lymphoid organs

“…Analysis of mice expressing only the membrane form of TNF suggested that both soluble and membrane-bound TNF could play important roles in organization of different secondary lymphoid organs and in host defense. 18,34 Our studies using Tm-B-TNF KO mice further demonstrate that soluble TNF produced by B cells is essential for the organization of secondary lymphoid organs and for generation of IgG responses to T-cell-dependent antigens.…”

“…Analysis of mice expressing only the membrane form of TNF suggested that both soluble and membrane-bound TNF could play important roles in organization of different secondary lymphoid organs and in host defense. 18,34 Our studies using Tm-B-TNF KO mice further demonstrate that soluble TNF produced by B cells is essential for the organization of secondary lymphoid organs and for generation of IgG responses to T-cell-dependent antigens.The second complexity of interpreting TNF functions in lymphoid organ maintenance is because TNF effects could be mediated by different cell types in different secondary lymphoid organs. Our data suggest that TNF from B cells plays a major role in the maintenance of spleen, LN, and PP microstructure, while TNF from T cells provides a complementary but distinct signal in spleen and MLNs (supplemental Figure 12), but not in PPs.…”

Genetic ablation of soluble tumor necrosis factor with preservation of membrane tumor necrosis factor is associated with neuroprotection after focal cerebral ischemia

“…17,18 Studies in humans and animal models have yielded significant insight into the function of TNF in neurological diseases, indicating distinct and often opposite roles for solTNF and mTNF. 1,9,[19][20][21][22] TNF has been implicated in many aspects of stroke pathology, 23,24 and it is increased in the blood and cerebrospinal fluid of stroke patients. [25][26][27][28][29] In some studies, this increase has been found to correlate with stroke severity, 27,30,31 in line with recent findings of an association between TNF-a 238G/A, 308G/A, or rs1800628 polymorphisms, resulting in increased serum TNF levels, and an increased risk of stroke.…”