The intracellular cation channel TMEM176B as a dual immunoregulator

Characterizing immune regulatory pathways is critical to understand physiological and pathophysiological processes as well as to identify novel immunotherapeutic targets. The cation channel TMEM176B has emerged in the last years as a potential new immunoregulatory player and pharmacological target. Here, we review how expression data, clinical associations of genetic variants and functional studies support a dual role for TMEM176B in regulating immune responses. Thus, TMEM176B can inhibit effector immune responses in some settings whereas it may also promote immunity by supporting antigen presentation in others. We also discuss a potential role for TMEM176B in regulating type 2 and 3 immunity and comment recent data on modulation of DC biology and inflammasome activation as well as CD8⁺ T cell responses. Understanding the role of TMEM176B in immunity is critical to propose rational pharmacological approaches targeting this channel.

PD-1/PD-L1 blockade abrogates a dysfunctional innate-adaptive immune axis in critical β-coronavirus disease

Severe COVID-19 is associated with hyperinflammation and weak T cell responses against SARS-CoV-2. However, the links between those processes remain partially characterized. Moreover, whether and how therapeutically manipulating T cells may benefit patients are unknown. Our genetic and pharmacological evidence demonstrates that the ion channel TMEM176B inhibited inflammasome activation triggered by SARS-CoV-2 and SARS-CoV-2-related murine β-coronavirus. Tmem176b^-/- mice infected with murine β-coronavirus developed inflammasome-dependent T cell dysfunction and critical disease, which was controlled by modulating dysfunctional T cells with PD-1 blockers. In critical COVID-19, inflammasome activation correlated with dysfunctional T cells and low monocytic TMEM176B expression, whereas PD-L1 blockade rescued T cell functionality. Here, we mechanistically link T cell dysfunction and inflammation, supporting a cancer immunotherapy to reinforce T cell immunity in critical β-coronavirus disease.

Effects of sequential osteoporosis treatments on trabecular bone in adult rats with low bone mass

We used an osteopenic adult ovariectomized (OVX) rat model to evaluate various sequential treatments for osteoporosis, using FDA-approved agents with complementary tissue-level mechanisms of action. Sequential treatment for 3 months each with alendronate (Aln), followed by PTH, followed by resumption of Aln, created the highest trabecular bone mass, best microarchitecture, and highest bone strength.

INTRODUCTION

Individual agents used to treat human osteoporosis reduce fracture risk by ∼ 50-60%. As agents that act with complementary mechanisms are available, sequential therapies that mix antiresorptive and anabolic agents could improve fracture risk reduction, when compared with monotherapies.

METHODS

We evaluated bone mass, bone microarchitecture, and bone strength in adult OVX, osteopenic rats, during different sequences of vehicle (Veh), parathyroid hormone (PTH), Aln, or raloxifene (Ral) in three 90-day treatment periods, over 9 months. Differences among groups were evaluated. The interrelationships of bone mass and microarchitecture endpoints and their relationship to bone strength were studied.

RESULTS

Estrogen deficiency caused bone loss. OVX rats treated with Aln monotherapy had significantly better bone mass, microarchitecture, and bone strength than untreated OVX rats. Rats treated with an Aln drug holiday had bone mass and microarchitecture similar to the Aln monotherapy group but with significantly lower bone strength. PTH-treated rats had markedly higher bone endpoints, but all were lost after PTH withdrawal without follow-up treatment. Rats treated with PTH followed by Aln had better bone endpoints than those treated with Aln monotherapy, PTH monotherapy, or an Aln holiday. Rats treated initially with Aln or Ral, then switched to PTH, also had better bone endpoints, than monotherapy treatment. Rats treated with Aln, then PTH, and returned to Aln had the highest values for all endpoints.

CONCLUSION

Our data indicate that antiresorptive therapy can be coupled with an anabolic agent, to produce and maintain better bone mass, microarchitecture, and strength than can be achieved with any monotherapy.

Induction of non-specific suppressor cells and myeloregulatory effects of an immunomodulatory azaspirane, SK&F 105685

Administration of the immunosuppressive agent, SK&F 105685, has demonstrated immunosuppressive activity in several animal models of autoimmunity such as adjuvant arthritis and experimental autoimmune encephalomyelitis. The mechanism of action of SK&F 105685 in these autoimmune disease models appears to be the induction of non-specific suppressor cells (SC) detected in the spleen and bone marrow of treated animals. In this study we have examined the kinetics of SC appearance in the spleen and bone marrow following treatment with 30 mg/kg/day, p.o., for 1-6 days. SC activity was apparent following a single dose and increased with successive treatments. Treatment with SK&F 105685 also resulted in significantly enhanced myelopoiesis as measured by a 128% increase in the frequency of bone marrow myeloid progenitors (CFU-GM). Mechanistic studies indicated that in vitro treatment of bone marrow stromal cell cultures with SK&F 105685 upregulated the production of colony stimulating activity (CSA) detectable in a rat CFU-GM assay. Further, in vitro studies revealed that the SC in the bone marrow or spleens of SK&F 105685-treated rats admixed with normal marrow cells inhibited CFU-GM formation at a six-fold less cell concentration than cells obtained from control rats. These in vitro results suggest that the SK&F 105685-induced myelopoiesis is regulated by the subsequent generation of SC.

Beneficial effects of long-term treatment with SK&F 105685 in murine lupus nephritis

MRL/Mp-lpr/lpr (MRL/lpr) mice were studied from 6 to 19 weeks of age. Proteinuria began to increase at 15 weeks, and continued to increase until the animals were sacrificed at 19 weeks. This proteinuria was associated with lymphadenopathy and splenomegaly, as well as changes in lymph node cell phenotype and histologic changes in the glomeruli. Oral administration of SK&F 105685 starting at 12 weeks of age prevented the increased urinary protein loss, inhibited the histologic changes in the glomeruli, reduced the increase in spleen and lymph node weight and modified the phenotypic profile of the lymphoid cells. SK&F 105685 appears to act by increasing the number/activity of nonspecific suppressor cells in MRL/lpr mice. On the basis of this evidence, we conclude that SK&F 105685 can attenuate the progression of renal damage in MRL/lpr mice by exerting a unique effect on cells which may be involved in the autoimmune process.

Protective effect of SK&F 86002, a novel dual inhibitor of arachidonic acid metabolism, in murine models of endotoxin shock: inhibition of tumor necrosis factor as a possible mechanism of action

The effect of a new, structurally novel, dual inhibitor of arachidonic acid (AA) metabolism, SK&F 86002, was studied in two murine models of endotoxin shock. The first model was the injection of C57BL/6 mice with lipopolysaccharide (LPS) in combination with D-galactosamine (D-gal), which resulted in death within 6-48 hr. Treatment of these mice with SK&F 86002 (100 mg/kg, p.o.) 30 min to 2 hr prior to the administration of D-gal and LPS protected the animals from mortality. Protection was also provided by treatment with the corticosteroid dexamethasone, whereas only partial protection was afforded by the dual inhibitor of AA metabolism phenidone and the cyclooxygenase inhibitors naproxen and indomethacin. In a similar dosing protocol, SK&F 86002 also protected mice in a second endotoxin shock model in which mice sensitized with Proprionibacterium acnes received LPS 10 days later. Moreover, partial protection was obtained when SK&F 86002 was administered therapeutically after LPS injection. The administration of SK&F 86002 to P. acnes/LPS-treated mice decreased serum levels of tumor necrosis factor (TNF), which was not observed following naproxen or indomethacin treatment. Consistent with the role of TNF in this model of endotoxin shock was the observation that treatment with antibodies against TNF also prevented or reduced mortality.