Crosstalk between Metabolic Disorders and Immune Cells

Macrophage: Hidden Criminal in Therapy Resistance

BACKGROUND

Although substantial efforts have been made by researchers to develop drugs, a disappointing reality is that the emergence of drug resistance is an unavoidable reality for the majority of patients. In recent years, emerging evidence suggests a connection between drug resistance and immune dysregulation.

SUMMARY

As a ubiquitously distributed, versatile innate immune cell, macrophages play essential roles in maintaining tissue homeostasis in a steady state. Nevertheless, it is becoming aware that macrophages undermine the action of therapeutic drugs across various disease types. Reprogramming macrophage function has been proven to be effective in restoring patient responsiveness to treatment. Herein, we comprehensively reviewed how macrophages respond to drugs and the mechanisms by which they contribute to treatment unresponsiveness in cancer, inflammatory diseases, and metabolic diseases. In addition, future prospects in macrophage-based combination therapy were discussed.

KEY MESSAGES

Targeting macrophages is a promising strategy for overcoming drug resistance in immune disorders.

Role of IL-34 and its receptors in inflammatory diseases

In recent years, IL-34 has been widely discussed as a novel cytokine. IL-34 is a pro-inflammatory cytokine binding four distinct receptors, namely CSF-1R, syndecan-1, PTP-ζ and TREM2. Previous studies have shown that IL-34 and its receptors play important roles in the development and progression of various inflammatory diseases. Therefore, IL-34 has the potential to be a biomarker and therapeutic target for inflammatory diseases. However, further study is still needed to identify the specific mechanism through which IL-34 contributes to illness. In this article, we review the recent advances in the biological roles of IL-34 and its receptors as well as their roles in the development and therapeutic application of inflammatory diseases.

Reframing the link between metabolism and NLRP3 inflammasome: therapeutic opportunities

Inflammasomes are multiprotein signaling platforms in the cytosol that senses exogenous and endogenous danger signals and respond with the maturation and secretion of IL-1β and IL-18 and pyroptosis to induce inflammation and protect the host. The inflammasome best studied is the Nucleotide-binding oligomerization domain, leucine-rich repeat-containing family pyrin domain containing 3 (NLRP3) inflammasome. It is activated in a two-step process: the priming and the activation, leading to sensor NLRP3 oligomerization and recruitment of both adaptor ASC and executioner pro-caspase 1, which is activated by cleavage. Moreover, NLRP3 inflammasome activation is regulated by posttranslational modifications, including ubiquitination/deubiquitination, phosphorylation/dephosphorylation, acetylation/deacetylation, SUMOylation and nitrosylation, and interaction with NLPR3 protein binding partners. Moreover, the connection between it and metabolism is receiving increasing attention in this field. In this review, we present the structure, functions, activation, and regulation of NLRP3, with special emphasis on regulation by mitochondrial dysfunction-mtROS production and metabolic signals, i.e., metabolites as well as enzymes. By understanding the regulation of NLRP3 inflammasome activation, specific inhibitors can be rationally designed for the treatment and prevention of various immune- or metabolic-based diseases. Lastly, we review current NLRP3 inflammasome inhibitors and their mechanism of action.

Unraveling the roles of endoplasmic reticulum-associated degradation in metabolic disorders

Misfolded proteins retained in the endoplasmic reticulum cause many human diseases. ER-associated degradation (ERAD) is one of the protein quality and quantity control system located at ER, which is responsible for translocating the misfolded proteins or properly folded but excess proteins out of the ER for proteasomal degradation. Recent studies have revealed that mice with ERAD deficiency in specific cell types exhibit impaired metabolism homeostasis and metabolic diseases. Here, we highlight the ERAD physiological functions in metabolic disorders in a substrate-dependent and cell type-specific manner.

Mechanisms of Oxidative Stress in Metabolic Syndrome

Metabolic syndrome is a cluster of conditions associated with the risk of diabetes mellitus type 2 and cardiovascular diseases (CVDs). Metabolic syndrome is closely related to obesity. Increased adiposity promotes inflammation and oxidative stress, which are precursors of various complications involving metabolic syndrome components, namely insulin resistance, hypertension, and hyperlipidemia. An increasing number of studies confirm the importance of oxidative stress and chronic inflammation in the etiology of metabolic syndrome. However, few studies have reviewed the mechanisms underlying the role of oxidative stress in contributing to metabolic syndrome. In this review, we highlight mechanisms by which reactive oxygen species (ROS) increase mitochondrial dysfunction, protein damage, lipid peroxidation, and impair antioxidant function in metabolic syndrome. Biomarkers of oxidative stress can be used in disease diagnosis and evaluation of severity.

Protective Effect of Glycomacropeptide on the Inflammatory Response of U937 Macrophages

Macrophages play crucial roles in inflammation and oxidative stress associated with noncommunicable diseases, such as cardiovascular diseases, diabetes, and cancer. Glycomacropeptide (GMP) is a bioactive peptide derived from milk κ-casein that contains abundant sialic acid and has shown anti-inflammatory, antioxidative, anti-obesity, and anti-diabetic properties when is orally administered. The aim of this study was to evaluate the effect of GMP on the regulation of the inflammatory response in human macrophages and the participation of sialic acid in this activity. GMP pretreatment decreased by 35%, 35%, and 49% the production of nitrites, interleukin (IL)-1β, and tumor necrosis factor (TNF)-α, respectively, in activated human macrophages U937. The same effect was obtained when cells were pretreated with asialo GMP, and no change on the gene expression of the lectins associated with the recognition of sialic acids, SIGLEC5, 7, and 9, was induced by GMP on macrophages, which suggests that sialic acid might not be involved in this immunoregulatory effect. Interestingly, GMP increased 8.9- and 3.5-fold the gene expression of the canonical anti-inflammatory protein SOCS3 and the antioxidant enzyme HMOX1, respectively, in U937 cells. Thus, GMP exerts anti-inflammatory and antioxidative activities on activated macrophages in a sialic acid-independent manner, which might be related to its in vivo reported bioactivity.

Oxidative stress as a culprit in diabetic kidney disease

Diabetic kidney disease (DKD) has become the leading cause of end-stage renal disease (ESRD), and the prevalence of DKD has increased worldwide during recent years. DKD is associated with poor therapeutic outcomes in most patients, but there is limited understanding of its pathogenesis. This review suggests that oxidative stress interacts with many other factors in causing DKD. Highly active mitochondria and NAD(P)H oxidase are major sources of oxidants, and they significantly affect the risk for DKD. Oxidative stress and inflammation may be considered reciprocal causes of DKD, in that each is a cause and an effect of DKD. Reactive oxygen species (ROS) can act as second messengers in various signaling pathways and as regulators of metabolism, activation, proliferation, differentiation, and apoptosis of immune cells. Epigenetic modifications, such as DNA methylation, histone modifications, and non-coding RNAs can modulate oxidative stress. The development of new technologies and identification of new epigenetic mechanisms may provide novel opportunities for the diagnosis and treatment of DKD. Clinical trials demonstrated that novel therapies which reduce oxidative stress can slow the progression of DKD. These therapies include the NRF2 activator bardoxolone methyl, new blood glucose-lowering drugs such as sodium-glucose cotransporter 2 inhibitors, and glucagon-like peptide-1 receptor agonists. Future studies should focus on improving early diagnosis and the development of more effective combination treatments for this multifactorial disease.

Susceptibility of Fat Tissue to SARS-CoV-2 Infection in Female hACE2 Mouse Model

The coronavirus disease (COVID-19) is a highly contagious viral illness caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). COVID-19 has had a catastrophic effect globally causing millions of deaths worldwide and causing long-lasting health complications in COVID-19 survivors. Recent studies including ours have highlighted that adipose tissue can act as a reservoir where SARS-CoV-2 can persist and cause long-term health problems. Here, we evaluated the effect of SARS-CoV-2 infection on adipose tissue physiology and the pathogenesis of fat loss in a murine COVID-19 model using humanized angiotensin-converting enzyme 2 (hACE2) mice. Since epidemiological studies reported a higher mortality rate of COVID-19 in males than in females, we examined hACE2 mice of both sexes and performed a comparative analysis. Our study revealed for the first time that: (a) viral loads in adipose tissue and the lungs differ between males and females in hACE2 mice; (b) an inverse relationship exists between the viral loads in the lungs and adipose tissue, and it differs between males and females; and (c) CoV-2 infection alters immune signaling and cell death signaling differently in SARS-CoV-2 infected male and female mice. Overall, our data suggest that adipose tissue and loss of fat cells could play important roles in determining susceptibility to CoV-2 infection in a sex-dependent manner.

Obese visceral fat tissue inflammation: from protective to detrimental?

Obesity usually is accompanied by inflammation of fat tissue, with a prominent role of visceral fat. Chronic inflammation in obese fat tissue is of a lower grade than acute immune activation for clearing the tissue from an infectious agent. It is the loss of adipocyte metabolic homeostasis that causes activation of resident immune cells for supporting tissue functions and regaining homeostasis. Initially, the excess influx of lipids and glucose in the context of overnutrition is met by adipocyte growth and proliferation. Eventual lipid overload of hypertrophic adipocytes leads to endoplasmic reticulum stress and the secretion of a variety of signals causing increased sympathetic tone, lipolysis by adipocytes, lipid uptake by macrophages, matrix remodeling, angiogenesis, and immune cell activation. Pro-inflammatory signaling of adipocytes causes the resident immune system to release increased amounts of pro-inflammatory and other mediators resulting in enhanced tissue-protective responses. With chronic overnutrition, these protective actions are insufficient, and death of adipocytes as well as senescence of several tissue cell types is seen. This structural damage causes the expression or release of immunostimulatory cell components resulting in influx and activation of monocytes and many other immune cell types, with a contribution of stromal cells. Matrix remodeling and angiogenesis is further intensified as well as possibly detrimental fibrosis. The accumulation of senescent cells also may be detrimental via eventual spread of senescence state from affected to neighboring cells by the release of microRNA-containing vesicles. Obese visceral fat inflammation can be viewed as an initially protective response in order to cope with excess ambient nutrients and restore tissue homeostasis but may contribute to tissue damage at a later stage.

The regulation of efferocytosis signaling pathways and adipose tissue homeostasis in physiological conditions and obesity: Current understanding and treatment options

Obesity is associated with changes in the resolution of acute inflammation that contribute to the clinical complications. The exact mechanisms underlying unresolved inflammation in obesity are not fully understood. Adipocyte death leads to pro-inflammatory adipose tissue macrophages, stimulating additional adipocyte apoptosis. Thus, a complex and tightly regulated process to inhibit inflammation and maintain homeostasis after adipocyte apoptosis is needed to maintain health. In normal condition, a specialized phagocytic process (efferocytosis) performs this function, clearing necrotic and apoptotic cells (ACs) and controlling inflammation. For efficient and continued efferocytosis, phagocytes must internalize multiple ACs in physiological conditions and handle the excess metabolic burden in adipose tissue. In obesity, this control is lost and can be an important hallmark of the disease. In this regard, the deficiency of efferocytosis leads to delayed resolution of acute inflammation and can result in ongoing inflammation, immune system dysfunction, and insulin resistance in obesity. Hence, efficient clearance of ACs by M2 macrophages could limit long-term inflammation and ensue clinical complications, such as cardiovascular disease and diabetes. This review elaborates upon the molecular mechanisms to identify efferocytosis regulators in obesity, and the mechanisms that can improve efferocytosis and reduce obesity-related complications, such as the use of pharmacological agents and regular exercise.

Adipokines as potential biomarkers for type 2 diabetes mellitus in cats

Type 2 diabetes mellitus (T2DM) is no longer only a disease of humans, but also of domestic animals, and it particularly affects cats. It is increasingly thought that because of its unique characteristics, T2DM may belong not only to the group of metabolic diseases but also to the group of autoimmune diseases. This is due to the involvement of the immune system in the inflammation that occurs with T2DM. Various pro- and anti-inflammatory substances are secreted, especially cytokines in patients with T2DM. Cytokines secreted by adipose tissue are called adipokines, and leptin, adiponectin, resistin, omentin, TNF-α, and IL-6 have been implicated in T2DM. In cats, approximately 90% of diabetic cases are T2DM. Risk factors include older age, male sex, Burmese breed, presence of obesity, and insulin resistance. Diagnosis of a cat requires repeated testing and is complicated compared to human diagnosis. Based on similarities in the pathogenesis of T2DM between humans and cats, adipokines previously proposed as biomarkers for human T2DM may also serve in the diagnosis of this disease in cats.

Leukocyte subtypes, gelatinases, and their tissue inhibitors in a group of subjects with asymptomatic carotid atherosclerosis

In a cohort of subjects with asymptomatic carotid atherosclerosis (ACA), we have evaluated the neutrophil and lymphocyte count and their ratio (NLR), the gelatinases (MMP-2 and MMP-9) and their tissue inhibitors (TIMP-1 and TIMP-2). At baseline, no difference was observed between ACA subjects and subject control group regarding neutrophil and lymphocyte count while was evident in ACA subjects a significant increase in MMP-2, MMP-9 and TIMP-2 associated to a significant decrease in TIMP-1. Dividing the ACA according to the number of cardiovascular risk factors (CRFs) we have observed an increase in lymphocyte count in the subgroup with 3-5 CRFs. Evaluating the leukocyte subtypes according to all the surrogate markers of insulin resistance has been noted, in the subgroups that exceed the medians of these markers, a significant increase in neutrophil and lymphocyte count without any variation of the NLR. Effecting the same evaluation for the MMP/TIMP pattern we observed, instead, that the same subgroups tend to show a decrease in MMP-2 and an increase in MMP-9. No difference instead for TIMP-1 and TIMP-2. The abnormality of the MMP/TIMP pattern, bearing in mind the cardiometabolic clustering present in this cohort of ACA subjects, would induce to use drugs able not only to cure the cardiometabolic risk factors but also to influence the MMP/TIMP profile.

Chromosomal Aberrations and Oxidative Stress in Psoriatic Patients with and without Metabolic Syndrome

Psoriasis and metabolic syndrome (MetS), a common comorbidity of psoriasis, are associated with mild chronic systemic inflammation that increases oxidative stress and causes cell and tissue damage. At the cellular level, chromosomal and DNA damage has been documented, thus confirming their genotoxic effect. The main objective of our study was to show the genotoxic potential of chronic inflammation and determine whether the presence of both pathologies increases chromosomal damage compared to psoriasis alone and to evaluate whether there are correlations between selected parameters and chromosomal aberrations in patients with psoriasis and MetS psoriasis. Clinical examination (PASI score and MetS diagnostics according to National Cholesterol Education Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults; NCE/ATPIII criteria), biochemical analysis of blood samples (fasting glucose, total cholesterol, low density and high density lipoproteins; LDL, HDL, non-HDL, and triglycerides;TAG), DNA/RNA oxidative damage, and chromosomal aberration test were performed in 41 participants (20 patients with psoriasis without MetS and 21 with MetS and psoriasis). Our results showed that patients with psoriasis without metabolic syndrome (nonMetS) and psoriasis and MetS had a higher rate of chromosomal aberrations than the healthy population for which the limit of spontaneous, natural aberration was <2%. No significant differences in the aberration rate were found between the groups. However, a higher aberration rate (higher than 10%) and four numerical aberrations were documented only in the MetS group. We found no correlations between the number of chromosomal aberrations and the parameters tested except for the correlation between aberrations and HDL levels in nonMetS patients (rho 0.44; p < 0.02). Interestingly, in the MetS group, a higher number of chromosomal aberrations was documented in non-smokers compared to smokers. Data from our current study revealed an increased number of chromosomal aberrations in patients with psoriasis and MetS compared to the healthy population, especially in psoriasis with MetS, which could increase the genotoxic effect of inflammation and the risk of genomic instability, thus increasing the risk of carcinogenesis.

Linking Inflammatory Adipose Tissue to Placental Abnormalities in Obese Preeclamptic Pregnancies

Preeclampsia (PE), a pregnancy-specific disorder, is characterized by maternal hypertension and proteinuria or another accompanying sign/symptom of multi-organ dysfunction. Maternal symptoms resolve with delivery of the baby and, importantly, the placenta. Therefore, the placenta plays a causal role in PE. However, the precise cause of abnormal placental development and/or function is unknown. Women with obesity have an increased risk of developing PE that is potentially related to the increased inflammation that accompanies increased maternal adiposity. Furthermore, inflammatory adipokines, i.e., leptin, have been linked to the development of systemic inflammation, hypertension, and other adverse outcomes associated with PE. Rodent models that recapitulate key pathophysiologic features of the maternal and fetal syndrome have been used translationally to study PE. This review covers inflammatory adipokines, immune cells and impaired placental development associated with PE in women and in rodent models of PE that utilize functional genomics to test causation.

LUNG AND CHEST WALL MECHANICAL PROPERTIES IN METFORMIN-TREATED AND UNTREATED MODELS OF TYPE 2 DIABETES

The adverse respiratory consequences of type-2 diabetes mellitus (T2DM) may reflect compromised lung function and/or alterations of the chest wall because of skeletal muscle stiffening. We assessed the separate contributions of these compartments to respiratory complications in diabetes and explored the effects of metformin on respiratory abnormalities. Experiments were performed in untreated rats (control, n=7), high-fat diet-fed rats receiving streptozotocin (T2DM, n=7), and metformin-treated diabetic rats (MET, n=6). Newtonian resistance, tissue damping, and elastance were separately assessed for lung and chest wall components by measuring the esophageal pressure during forced oscillations at low (0 cmH₂O), medium (3 cmH₂O), and high positive end-expiratory pressure (PEEP) (6 cmH₂O). Tissue hysteresivity was calculated as damping/elastance. Blood gas parameters were used to assess gas exchange, and lung histology was performed to characterize collagen expression. T2DM at low PEEP compromised airway and lung tissue mechanics in association with gas-exchange defects and collagen overexpression. Abnormal chest wall mechanics in T2DM was indicated only by decreased tissue hysteresivity. No difference in lung or chest wall mechanics, gas exchange, or lung histology was observed between the MET and control groups. These findings suggest the primary involvement of the pulmonary system in the respiratory consequences of T2DM, with chest wall properties only disturbed by a shift toward the dominance of elastic forces at low PEEP. The adequacy of metformin to treat the adverse respiratory consequences of diabetes was also revealed, in addition to its well-established beneficial effects on other organs.

Overview of Memory NK Cells in Viral Infections: Possible Role in SARS-CoV-2 Infection

NK cells have usually been defined as cells of the innate immune system, although they are also involved in adaptative responses. These cells belong to the innate lymphocyte cells (ILC) family. They remove unwanted cells, tumoral cells and pathogens. NK cells are essential for viral infection clearance and are involved in tolerogenic responses depending on the dynamic balance of the repertoire of activating and inhibitory receptors. NK plasticity is crucial for tissue function and vigilant immune responses. They directly eliminate virus-infected cells by recognising viral protein antigens using a non-MHC dependent mechanism, recognising viral glycan structures and antigens by NCR family receptors, inducing apoptosis by Fas-Fas ligand interaction, and killing cells by antibody-dependent cell cytotoxicity via the FcγIII receptor. Activating receptors are responsible for the clearance of virally infected cells, while inhibitory KIR receptor activation impairs NK responses and facilitates virus escape. Effective NK memory cells have been described and characterised by a low NKG2A and high NKG2C or NKG2D expression. NK cells have also been used in cell therapy. In SARS-CoV-2 infection, several contradicting reports about the role of NK cells have been published. A careful analysis of the current data and possible implications will be discussed.

Intramuscular adipogenesis in cattle: Effects of body fat distribution and macrophage infiltration

Ectopic fat is defined by the deposition of adipose tissue within non-adipose tissue such as skeletal muscle. Japanese Black cattle (Wagyu) are characterized by the ability to accumulate high amounts of intramuscular adipose tissue. Obese conditions enhance the accumulation of ectopic fat. This review shows the effects of subcutaneous and visceral fat distribution on Wagyu intramuscular adipogenesis. Obese conditions also stimulate the macrophage infiltration into adipose tissues. Adipose tissue macrophages have reported to regulate adipose tissue growth and ectopic fat accumulation in humans and rodents. Wagyu is characterized by the higher capacity for intramuscular adipogenesis than Holsteins. This review discusses the depot-specific effects of macrophage infiltration among subcutaneous, visceral, and intramuscular adipose tissue on intramuscular adipogenesis in Wagyu and Holstein cattle. Recently, metabolome analysis has been used to identify obesity-related biomarkers by comparing the biological samples between lean and obese patients. This review introduces the metabolomic profiles of plasma and intramuscular adipose tissue between Wagyu and Holsteins.

Roles of extracellular vesicles associated non-coding RNAs in Diabetes Mellitus

Extracellular vesicles (EVs), especially exosomes (50 to 150 nm), have been shown to play important roles in a wide range of physiological and pathological processes, including metabolic diseases such as Diabetes Mellitus (DM). In the last decade, several studies have demonstrated how EVs are involved in cell-to-cell communication. EVs are enriched in proteins, mRNAs and non-coding RNAs (miRNAs, long non-coding RNAs and circRNAS, among others) which are transferred to recipient cells and may have a profound impact in either their survival or functionality. Several studies have pointed out the contribution of exosomal miRNAs, such as miR-l42-3p and miR-26, in the development of Type 1 and Type 2 DM (T1DM and T2DM), respectively. In addition, some miRNA families such as miR-let7 and miR-29 found in exosomes have been associated with both types of diabetes, suggesting that they share common etiological features. The knowledge about the role of exosomal long non-coding RNAs in this group of diseases is more immature, but the exosomal lncRNA MALAT1 has been found to be elevated in the plasma of individuals with T2DM, while more than 169 lncRNAs were reported to be differentially expressed between healthy donors and people with T1DM. Here, we review the current knowledge about exosomal non-coding RNAs in DM and discuss their potential as novel biomarkers and possible therapeutic targets.