Ruxana T. Sadikot

Mitochondria are increasingly recognized as important contributors to immune function, in addition to energy production. They exert this influence through modulation of various signaling pathways that regulate cellular metabolism and immune function in response to pathogens. Peroxisome proliferator-activated receptor (PPAR) coactivator 1 alpha (PGC-1α) is the primary transcription factor and regulator involved in mitochondrial biogenesis. Long known to be involved in immune function, zinc (Zn) is also required for proper mitochondrial function. It is increasingly recognized that many cellular immunometabolic activities are also Zn-dependent. Taken together, we investigated the role of Zn deficiency, both dietary and genetically induced, and Zn supplementation in PGC-1α-mediated macrophage mitochondrial biogenesis and immune function following infection with Mycobacterium avium complex (MAC). Our novel findings show that Zn is an important regulator of PGC-1α, TFAM and mitochondrial biogenesis, leading to enhanced bacterial phagocytosis and bacterial killing in macrophages. Mechanistically, we show that the Zn importer ZIP8 (Zrt/Irt-like protein) orchestrates Zn-mediated effects on PGC-1α and mitochondrial function. Taken together, defective Zn biodistribution may increase susceptibility to infection, whereas Zn supplementation may provide a tractable host-directed therapy to enhance the innate immune response in patients vulnerable to MAC infection.

Mitochondria are increasingly recognized as important contributors to immune function in addition to energy production. They do this through modulation of various signaling pathways that regulate cellular metabolism and immune function in response to pathogens. Peroxisome proliferator-activated receptor (PPAR) coactivator 1 alpha (PGC-1) is the primary transcription factor and regulator involved in mitochondrial biogenesis. Long known to be involved in immune function, zinc (Zn) is also required for proper mitochondrial function. It is increasingly recognized that many cellular immunometabolic activities are also Zn dependent. Taken together, we investigated the role of Zn deficiency, both dietary and genetically induced, and Zn supplementation in PGC-1α-mediated macrophage mitochondrial biogenesis and immune function following infection with Mycobacterium avium complex (MAC). Our novel findings show that Zn is an important regulator of PGC-1α and TFAM and mitochondrial biogenesis, leading to enhanced bacterial phagocytosis and bacterial killing in macrophages. Mechanistically, we show that the Zn importer ZIP8 (Zrt/Irt-like protein) orchestrates Zn-mediated effects on PGC-1α and mitochondrial function. Taken together, defective Zn biodistribution may increase susceptibility to infection, whereas Zn supplementation may provide a tractable host-directed therapy to enhance the innate immune response in patients vulnerable to MAC infection.

Chronic obstructive pulmonary disease (COPD) is a clinical syndrome that presents as airflow limitation with poor reversibility accompanied by dynamic hyperinflation of the lung. It is a complex disease with chronic inflammatory airway changes caused by exposure to noxious particles or gases, such as cigarette smoke. The disease involves persistent inflammation and oxidative stress, perpetuated by frequent exacerbations. The prevalence of COPD is on the rise, with the prediction that it will be the leading cause of morbidity and mortality over the next decade. Despite the global burden of COPD and its associated morbidity and mortality, treatment remains limited. Although the understanding of the pathogenesis of COPD has increased over the last two decades, molecular approaches to develop new therapies for the treatment of COPD have lagged. Here, we review the molecular approaches that have the potential for developing novel therapies for COPD.

Nontuberculous Mycobacteria (NTM) are a heterogeneous group of environmental microorganisms with distinct human pathogenesis. Their incidence and prevalence are rising worldwide, due in part to elevated antimicrobial resistance which complicates treatment and potential successful outcomes. Although information exists on the clinical significance of NTMs, little is known about host immune response to infection. NTM infections alter macrophage mitochondrial capacity and decrease ATP production, efficient immune response, and bacterial clearance. Transcription factor peroxisome proliferator activated receptor (PPAR) γ coactivator-1α (PGC-1α) is a master regulator of mitochondrial biogenesis, influencing metabolism, mitochondrial pathways, and antioxidant response. Mitochondrial transcription factor A (TFAM) is a protein essential for mitochondrial DNA (mtDNA) genome stability, integrity, and metabolism. Both PGC-1α and TFAM regulate mitochondrial biogenesis and activity, and their disruption is linked to inflammatory signaling and altered macrophage function. We show that NTM causes macrophage mitochondrial damage and disrupted bioenergetics. Mechanistically we show that this is related to attenuation of expression of PGC-1α and TFAM in infected macrophages. Importantly, rescuing expression of PGC-1α and TFAM using pharmacologic approaches restored macrophage immune function. Our results suggest that pharmacologic approaches to enhance mitochondrial function provide a novel approach to target macrophage immune function and means to combat NTM infections.

Pneumonia, as well as other types of acute and chronic lung injuries, remain the leading causes of death in individuals living with HIV. Individuals with HIV who are on antiretroviral therapy continue to have a greater risk for pneumonia, including bacterial and mycobacterial infections. Alveolar macrophages and lung epithelial cells constitute the first line of host defense against invading pathogens. The predisposition of individuals living with HIV to infections despite ante-retroviral therapy is mechanistically related to HIV pro-viruses integrating into host cells, including airway epithelial cells and alveolar macrophages. Alveolar macrophages harbor latent HIV even when individuals appear to have complete suppression on ART. In parallel, pneumonia can irreversibly impair lung function in HIV-infected individuals. Cells that Macrophages exposed to HIV or HIV-related proteins have been shown to secrete exosomes that contain miRNAs. These exosomes can regulate several innate and acquired immune functions by stimulating cytokine production and inflammatory responses. Furthermore, these secreted exosomal miRNAs can shuttle between cells, causing cellular dysfunction in the case of epithelial cells; they disrupt lung epithelial barrier dysfunction, which leads to a predisposition to bacterial infections. We discuss the common bacterial infections that occur in patients living with HIV and provide mechanistic insights into how the intercellular communication of miRNAs results in cellular dysfunction.

Mitochondria are critical in numerous cellular processes, including energy generation. Bacterial pathogens target host cell mitochondria through various mechanisms to disturb the host response and improve bacterial survival. We review recent advances in the understanding of how bacteria cause mitochondrial dysfunction through perturbations in mitochondrial cell-death pathways, energy production, mitochondrial dynamics, mitochondrial quality control, DNA repair, and the mitochondrial unfolded protein response. We also briefly highlight possible therapeutic approaches aimed at restoring the host mitochondrial function as a novel strategy to enhance the host response to bacterial infection.

SARS-CoV-2 infection triggers distinct patterns of disease development characterized by significant alterations in host regulatory responses. Severe cases exhibit profound lung inflammation and systemic repercussions. Remarkably, critically ill patients display a “lipid storm”, influencing the inflammatory process and tissue damage. Sphingolipids (SLs) play pivotal roles in various cellular and tissue processes, including inflammation, metabolic disorders, and cancer. In this study, we employed high-resolution mass spectrometry to investigate SL metabolism in plasma samples obtained from control subjects (n = 55), COVID-19 patients (n = 204), and convalescent individuals (n = 77). These data were correlated with inflammatory parameters associated with the clinical severity of COVID-19. Additionally, we utilized RNAseq analysis to examine the gene expression of enzymes involved in the SL pathway. Our analysis revealed the presence of thirty-eight SL species from seven families in the plasma of study participants. The most profound alterations in the SL species profile were observed in patients with severe disease. Notably, a predominant sphingomyelin (SM d18:1) species emerged as a potential biomarker for COVID-19 severity, showing decreased levels in the plasma of convalescent individuals. Elevated SM levels were positively correlated with age, hospitalization duration, clinical score, and neutrophil count, as well as the production of IL-6 and IL-8. Intriguingly, we identified a putative protective effect against disease severity mediated by SM (d18:1/24:0), while ceramide (Cer) species (d18:1/24:1) and (d18:1/24:0)were associated with increased risk. Moreover, we observed the enhanced expression of key enzymes involved in the SL pathway in blood cells from severe COVID-19 patients, suggesting a primary flow towards Cer generation in tandem with SM synthesis. These findings underscore the potential of SM as a prognostic biomarker for COVID-19 and highlight promising pharmacological targets. By targeting sphingolipid pathways, novel therapeutic strategies may emerge to mitigate the severity of COVID-19 and improve patient outcomes.

G protein‐coupled receptors (GPCRs) are the largest and most diverse class of signaling receptors. GPCRs regulate many functions in the human body and have earned the title of “most targeted receptors”. About one‐third of the commercially available drugs for various diseases target the GPCRs. Fibroblasts lay the architectural skeleton of the body, and play a key role in supporting the growth, maintenance, and repair of almost all tissues by responding to the cellular cues via diverse and intricate GPCR signaling pathways. This review discusses the dynamic architecture of the GPCRs and their intertwined signaling in pathological conditions such as idiopathic pulmonary fibrosis, cardiac fibrosis, pancreatic fibrosis, hepatic fibrosis, and cancer as opposed to the GPCR signaling of fibroblasts in physiological conditions. Understanding the dynamics of GPCR signaling in fibroblasts with disease progression can help in the recognition of the complex interplay of different GPCR subtypes in fibroblast‐mediated diseases. This review highlights the importance of designing and adaptation of next‐generation strategies such as GPCR‐omics, focused target identification, polypharmacology, and effective personalized medicine approaches to achieve better therapeutic outcomes for fibrosis and fibrosis associated malignancies.

Viral reservoirs constitute an obstacle to curing HIV-1 diseases, despite antiretroviral therapy. Macrophages serve as viral reservoirs in HIV infection by promoting long-term replication and latency.

SARS-CoV-2 infection triggers distinct patterns of disease development, characterized by significant alterations in host regulatory responses. Severe cases exhibit profound lung inflammation and systemic repercussions. Remarkably, critically ill patients display a "lipid storm", influencing the inflammatory process and tissue damage. Sphingolipids (SL) play pivotal roles in various cellular and tissue processes, including inflammation, metabolic disorders, and cancer. In this study, we employed high-resolution mass spectrometry to investigate SL metabolism in plasma samples obtained from control subjects (n=55), COVID-19 patients (n=204), and convalescent individuals (n=77). These data were correlated with inflammatory parameters associated with the clinical severity of COVID-19. Additionally, we utilized RNAseq analysis to examine the gene expression of enzymes involved in the SL pathway. Our analysis revealed the presence of thirty-eight SL species from seven families in the plasma of study participants. The most profound alterations in the SL species profile were observed in patients with severe disease. Notably, the predominant sphingomyelin (SM d18:1) species emerged as a potential biomarker for COVID-19 severity, showing decreased levels in the plasma of convalescent individuals. Elevated SM levels were positively correlated with age, hospitalization duration, clinical score, neutrophil count, as well as the production of IL-6 and IL-8. Intriguingly, we identified a putative protective effect against disease severity mediated by SM (d18:1/24:0), while ceramide (Cer) d18:1/24:1 and d18:1/24:0 was associated with increased risk. Moreover, we observed enhanced expression of key enzymes involved in SL pathway, in blood cells from severe COVID-19 patients, suggesting a primary flow towards Cer generation in tandem with SM synthesis. These findings underscore the potential of SM as a prognostic biomarker for COVID-19 and highlight promising pharmacological targets. By targeting sphingolipid pathways, novel therapeutic strategies may emerge to mitigate the severity of COVID-19 and improve patient outcomes.