Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (21 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2016)

The clearance of enteric bacteria by phagocytes plays an essential role in the host response of infection. Previously, we have reported that BAI1 (Brain Angiogenesis Inhibitor 1) binds bacterial Lipopolysaccharide (LPS) and facilitates engulfment of Gram-negative bacteria by activating ELMO1 (Engulfment and cell motility protein 1). Using Salmonella as a model organism, we hypothesized that ELMO1 regulates bacterial clearance, activates autophagy and modulates the endosomal lysosomal pathway. The data from Salmonella infection in J774 murine macrophages with depleted ELMO1 expression, by genetic modification, suggest that ELMO1 is important for LC3BII accumulation. There was a compounded decrease in LC3BII accumulation when ELMO1 and ATG-5 were simultaneously inhibited. These observations suggest that ELMO1 is upstream of ATG-5 and important for its function. The effect of ULK-1 depleted macrophages on LC3BII accumulation was insignificant when compared to control macrophages. Therefore, it appears that Salmonella is cleared mostly by LC3-associated phagocytosis in an ELMO1-dependent manner. ELMO1-depleted macrophages showed delayed bacterial clearance post infection. ELMO1 was found to interact with the late endosomal protein Rab9, which is involved in lysosome biogenesis and cellular trafficking. The accumulation of the lysosomal enzyme cathepsin B varried in a time-dependent manner and decreased in ELMO1-depleted macrophages compared to control macrophages 12 h post infection. The expression of genes associated with the Salmonella Pathogenicity Island-2 (SPI-2), important for bacterial survival inside macrophages, decreased in ELMO1-depleted macrophages compared to control macrophages at 6 hours post infection. The understanding of the host response to enteric infections is important because they persistently reoccur.

    Cover page: The Role of ELMO1 in the Pathogenesis of Infections with Gram-Negative Bacteria
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2018)
    Animal models have been tremendously useful to translational research, but there is a need to maximize their predictive value to human disease. This Comment proposes novel strategies that consider evolutionary history and the presence, absence or modification of molecular networks in one species that are being studied in the other.
      Cover page: Of mice, men and immunity: a case for evolutionary systems biology
      • Thesis
      • Peer Reviewed
      UC San Diego Electronic Theses and Dissertations (2017)

      Millions of people worldwide suffer from food borne illness caused by the Salmonella bacterial species. Disease caused by Salmonella infection is more devastating and likely fatal in immunocompromised individuals or those in economically disadvantaged conditions. These infections start at the gastrointestinal epithelium and translocate subsequently into the lamina propria, where they encounter immune and inflammatory cells such as macrophages.Following infection, macrophages release pro-inflammatory cytokines, such as IL-1, to coordinate inflammatory responses that help clear the infection. We previously demonstrated that engulfment and cell motility protein 1 (ELMO1) expressed by macrophages is essential for the induction of many pro-inflammatory cytokine responses. Here, the role of ELMO1 in the regulation of IL-1 was investigated following Salmonella infection. The murine macrophage cell line J774 was stably transfected with control or ELMO1 shRNA, resulting in a 90% decrease in ELMO1 expression. In turn, cells were infected with Salmonella enterica Serovar typhimurium. Mature IL-1 levels, detected by western blot and ELISA, decreased significantly after Salmonella challenge in ELMO1-inhibited cells. Furthermore, luciferase assays showed a 2-fold increase in NFB activation, a transcription factor regulating many pro-inflammatory cytokines including IL-1b, in ELMO1 overexpressed cells. Additionally, co-transfection of ELMO1 and NOD2, a cytosolic bacteria-sensing protein, revealed an increase in NFB activation. In contrast, ELMO1 did not reproducibly regulate the post-translational activation of IL-1b by caspase 1. These results suggest ELMO1 regulates the NFB pathway and the subsequent expression of pro-inflammatory cytokines after bacterial infection. Understanding the mechanisms by which ELMO1 regulates inflammation can reveal new therapeutic targets for people suffering from chronic inflammation and related immune-mediated disorders.

        Cover page: Microbial Sensing by ELMO1 Mediates Intestinal Inflammation
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2022)
        Mast cells (MCs) are immune cells widely distributed in the body, accompanied by diverse phenotypes and functions. Committed mast cell precursors (MCPs) leave the bone marrow and enter the blood circulation, homing to peripheral sites under the control of various molecules from different microenvironments, where they eventually differentiate and mature. Partly attributable to the unique maturation mechanism, MCs display high functional heterogeneity and potentially plastic phenotypes. High plasticity also means that MCs can exhibit different subtypes to cope with different microenvironments, which we call the peripheral immune education system. Under the peripheral immune education system, MCs showed a new character from previous cognition in some cases, namely regulation of allergy and inflammation. In this review, we focus on the mucosal tissues, such as the gastrointestinal tract, to gain insights into the mechanism underlying the migration of MCs to the gut or other organs and their heterogeneity, which is driven by different microenvironments. In particular, the immunosuppressive properties of MCs let us consider that positively utilizing MCs may be a new way to overcome inflammatory and allergic disorders.
          Cover page: Utilizing mast cells in a positive manner to overcome inflammatory and allergic diseases.
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2024)
          Glycoprotein 2 (GP2) is a widely distributed protein in the digestive tract, contributing to mucosal barrier maintenance, immune homeostasis, and antigen-specific immune response, while also being linked to inflammatory bowel disease (IBD) pathogenesis. This review sheds light on the extensive distribution of GP2 within the gastrointestinal tract and its intricate interplay with the immune system. Furthermore, the significance of GP2 autoantibodies in diagnosing and categorizing IBD is underscored, alongside the promising therapeutic avenues for modulating GP2 to regulate immunity and maintain mucosal balance.
            Cover page: Glycoprotein 2 as a gut gate keeper for mucosal equilibrium between inflammation and immunity.
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2022)
            The pancreas contains exocrine glands, which release enzymes (e.g., amylase, trypsin, and lipase) that are important for digestion and islets, which produce hormones. Digestive enzymes and hormones are secreted from the pancreas into the duodenum and bloodstream, respectively. Growing evidence suggests that the roles of the pancreas extend to not only the secretion of digestive enzymes and hormones but also to the regulation of intestinal homeostasis and inflammation (e.g., mucosal defense to pathogens and pathobionts). Organ crosstalk between the pancreas and intestine is linked to a range of physiological, immunological, and pathological activities, such as the regulation of the gut microbiota by the pancreatic proteins and lipids, the retroaction of the gut microbiota on the pancreas, the relationship between inflammatory bowel disease, and pancreatic diseases. We herein discuss the current understanding of the pancreas-intestinal barrier axis and the control of commensal bacteria in intestinal inflammation.
              Cover page: Intestinal homeostasis and inflammation: Gut microbiota at the crossroads of pancreas-intestinal barrier axis.
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2021)
              Over the last several years, many advances have been made in understanding the role of bacteria in the pathogenesis of gastrointestinal cancers. Beginning with Helicobacter pylori being recognized as the first bacterial carcinogen and the causative agent of most gastric cancers, more recent studies have examined the role of enteric microbes in colorectal cancer. In the digestive tract, these communities are numerous and have a complex interrelationship with local immune/inflammatory responses that impact the health of the host. As modifying the microbiome in the stomach has decreased the risk of gastric cancer, modifying the distal microbiome may decrease the risk of colorectal cancers. To date, very few studies have considered the notion that mucosal lymphocyte-dependent immune memory may confound attempts to change the microbial components in these communities. The goal of this review is to consider some of the factors impacting host-microbial interactions that affect colorectal cancer and raise questions about how immune memory responses to the local microbial consortium affect any attempt to modify the composition of the intestinal microbiome.
                Cover page: Microbial-Driven Immunological Memory and Its Potential Role in Microbiome Editing for the Prevention of Colorectal Cancer.
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2017)
                Helicobacter pylori is a gram-negative, microaerophilic bacterium that infects the stomach and can lead to, among other disorders, the development of gastric cancer. The inability of the host to clear the infection results in a chronic inflammatory state with continued oxidative stress within the tissue. Reactive oxygen species and reactive nitrogen species produced by the immune and epithelial cells damage the host cells and can result in DNA damage. H pylori has evolved to evoke this damaging response while blunting the host's efforts to kill the bacteria. This long-lasting state with inflammation and oxidative stress can result in gastric carcinogenesis. Continued efforts to better understand the bacterium and the host response will serve to prevent or provide improved early diagnosis and treatment of gastric cancer.
                  Cover page: Oxidative Stress Resulting From Helicobacter pylori Infection Contributes to Gastric Carcinogenesis
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2015)

                  Background

                  Gastric epithelial cells (GECs) undergo apoptosis during H. pylori infection and phagocytes within the mucosa engulf these cells. The recognition and clearance of apoptotic cells is a multifactorial process, enhanced by the presence of various bridging molecules and opsonins which are abundant in serum. However, it is not clear how recognition or clearance may differ in the context of H. pylori infection induced apoptosis. In addition, efferocytosis of sterile apoptotic cells is known to confer anti-inflammatory properties in the engulfing phagocyte, however it is unknown if this is maintained when phagocytes encounter H. pylori-infected cells. Thus, the ability of macrophages to bind and engulf gastric epithelial cells rendered apoptotic by H. pylori infection and the association of these interactions to the modulation of phagocyte inflammatory responses was investigated in the absence and presence of serum with a particular focus on the role of serum protein C1q.

                  Methods

                  Control (uninfected) or H. pylori-infected AGS cells were co-cultured with THP-1 macrophages in the presence or absence of serum or serum free conditions + C1q protein (40-80 μg/mL). Binding of AGS cells to THP-1 macrophages was assessed by microscopy and cytokine (IL-6 and TNF-α) release from LPS stimulated THP-1 macrophages was quantified by ELISA.

                  Results

                  We show that macrophages bound preferentially to cells undergoing apoptosis subsequent to infection with H. pylori. Binding of apoptotic AGS to THP-1 macrophages was significantly inhibited when studied in the absence of serum and reconstitution of serum-free medium with purified human C1q restored binding of macrophages to apoptotic cells. Co-culture of sterile apoptotic and H. pylori-infected AGS cells both attenuated LPS-stimulated cytokine production by THP-1 macrophages. Further, direct treatment of THP-1 macrophages with C1q attenuated LPS stimulated TNF-α production.

                  Conclusions

                  These studies suggest that C1q opsonizes GECs rendered apoptotic by H. pylori. No differences existed in the ability of infected or sterile apoptotic cells to attenuate macrophage cytokine production, however, there may be a direct role for C1q in modulating macrophage inflammatory cytokine production to infectious stimuli.
                    Cover page: The role of C1q in recognition of apoptotic epithelial cells and inflammatory cytokine production by phagocytes during Helicobacter pylori infection
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (2017)
                    Macrophages are specialized phagocytic cells involved in clearing invading pathogens. Previously we reported that engulfment and cell motility protein 1 (ELMO1) in macrophages mediates bacterial internalization and intestinal inflammation. Here we studied the role of ELMO1 in the fate of internalized targets. ELMO1 is present in the intracellular vesicles and enhances accumulation of the protein LC3B following engulfment of Salmonella or treatment with autophagy-inducing rapamycin. The protein ATG5 and the kinase ULK1 are involved in classical autophagy, while LC3-associated phagocytosis is ULK1 independent. ATG5 but not ULK1 cooperated with ELMO1 in LC3 accumulation after infection, suggesting the ELMO1 preferentially regulated LC3-associated phagocytosis. Because LC3-associated phagocytosis delivers cargo for degradation, the contribution of ELMO1 to the lysosome degradation pathways was evaluated by studying pH and cathepsin B activity. ELMO1-depleted macrophages showed a time-dependent increase in pH and a decrease in cathepsin B activity associated with bacterial survival. Together, ELMO1 regulates LC3B accumulation and antimicrobial responses involved in the clearance of enteric pathogens. This paper investigated how innate immune pathways involving ELMO1 work in a coordinated fashion to eliminate bacterial threats. ELMO1 is present in the phagosome and enhances bacterial clearance by differential regulation of lysosomal acidification and enzymatic activity.
                      Cover page: ELMO1 Regulates Autophagy Induction and Bacterial Clearance During Enteric Infection
                      Top