Iron regulates the quiescence of naive CD4 T cells by controlling mitochondria and cellular metabolism

In response to an immune challenge, naive T cells undergo a transition from a quiescent to an activated state acquiring the effector function. Concurrently, these T cells reprogram cellular metabolism, which is regulated by iron. We and others have shown that iron homeostasis controls proliferation and mitochondrial function, but the underlying mechanisms are poorly understood. Given that iron derived from heme makes up a large portion of the cellular iron pool, we investigated iron homeostasis in T cells using mice with a T cell-specific deletion of the heme exporter, FLVCR1 [referred to as knockout (KO)]. Our finding revealed that maintaining heme and iron homeostasis is essential to keep naive T cells in a quiescent state. KO naive CD4 T cells exhibited an iron-overloaded phenotype, with increased spontaneous proliferation and hyperactive mitochondria. This was evidenced by reduced IL-7R and IL-15R levels but increased CD5 and Nur77 expression. Upon activation, however, KO CD4 T cells have defects in proliferation, IL-2 production, and mitochondrial functions. Iron-overloaded CD4 T cells failed to induce mitochondrial iron and exhibited more fragmented mitochondria after activation, making them susceptible to ferroptosis. Iron overload also led to inefficient glycolysis and glutaminolysis but heightened activity in the hexosamine biosynthetic pathway. Overall, these findings highlight the essential role of iron in controlling mitochondrial function and cellular metabolism in naive CD4 T cells, critical for maintaining their quiescent state.

Epidermal ZBP1 stabilizes mitochondrial Z-DNA to drive UV-induced IFN signaling in autoimmune photosensitivity

Photosensitivity is observed in numerous autoimmune diseases and drives poor quality of life and disease flares. Elevated epidermal type I interferon (IFN) production primes for photosensitivity and enhanced inflammation, but the substrates that sustain and amplify this cycle remain undefined. Here, we show that IFN-induced Z-DNA binding protein 1 (ZBP1) stabilizes ultraviolet (UV)B-induced cytosolic Z-DNA derived from oxidized mitochondrial DNA. ZBP1 is significantly upregulated in the epidermis of adult and pediatric patients with autoimmune photosensitivity. Strikingly, lupus keratinocytes accumulate extensive cytosolic Z-DNA after UVB, and transfection of keratinocytes with Z-DNA results in stronger IFN production through cGAS-STING activation compared to B-DNA. ZBP1 knockdown abrogates UV-induced IFN responses, whereas overexpression results in a lupus-like phenotype with spontaneous Z-DNA accumulation and IFN production. Our results highlight Z-DNA and ZBP1 as critical mediators for UVB-induced inflammation and uncover how type I IFNs prime for cutaneous inflammation in photosensitivity.

Non-canonical activation of IRE1α during Candida albicans infection enhances macrophage fungicidal activity

Infection by intracellular pathogens can trigger activation of the IRE1α branch of the unfolded protein response (UPR), which then modulates innate immunity and infection outcomes during bacterial or viral infection. However, the mechanisms by which infection activates IRE1α have not been fully elucidated. While recognition of microbe-associated molecular patterns can activate IRE1α, it is unclear whether this depends on the canonical role of IRE1α in detecting misfolded proteins. Here, we report that Candida albicans infection of macrophages results in IRE1α activation through C-type lectin receptor signaling, reinforcing a role for IRE1α as a central regulator of host responses to infection by a broad range of pathogens. However, IRE1α activation was not preceded by protein misfolding in response to either C. albicans infection or lipopolysaccharide treatment, implicating a non-canonical mode of IRE1α activation after recognition of microbial patterns. Investigation of the phenotypic consequences of IRE1α activation in macrophage antimicrobial responses revealed that IRE1α activity enhances the fungicidal activity of macrophages. Macrophages lacking IRE1α activity displayed inefficient phagolysosomal fusion, enabling C. albicans to evade fungal killing and escape the phagosome. Together, these data provide mechanistic insight for the non-canonical activation of IRE1α during infection, and reveal central roles for IRE1α in macrophage antifungal responses.

Cardiolipin coordinates inflammatory metabolic reprogramming through regulation of Complex II disassembly and degradation

Macrophage metabolic plasticity enables repurposing of electron transport from energy generation to inflammation and host defense. Altered respiratory complex II function has been implicated in cancer, diabetes, and inflammation, but regulatory mechanisms are incompletely understood. Here, we show that macrophage inflammatory activation triggers Complex II disassembly and succinate dehydrogenase subunit B loss through sequestration and selective mitophagy. Mitochondrial fission supported lipopolysaccharide-stimulated succinate dehydrogenase subunit B degradation but not sequestration. We hypothesized that this Complex II regulatory mechanism might be coordinated by the mitochondrial phospholipid cardiolipin. Cardiolipin synthase knockdown prevented lipopolysaccharide-induced metabolic remodeling and Complex II disassembly, sequestration, and degradation. Cardiolipin-depleted macrophages were defective in lipopolysaccharide-induced pro-inflammatory cytokine production, a phenotype partially rescued by Complex II inhibition. Thus, cardiolipin acts as a critical organizer of inflammatory metabolic remodeling.

Amino acids suppress macropinocytosis and promote release of CSF1 receptor in macrophages

The internalization of solutes by macropinocytosis provides an essential route for nutrient uptake in many cells. Macrophages increase macropinocytosis in response to growth factors and other stimuli. To test the hypothesis that nutrient environments modulate solute uptake by macropinocytosis, this study analyzed the effects of extracellular amino acids on the accumulation of fluorescent fluid-phase probes in murine macrophages. Nine amino acids, added individually or together, were capable of suppressing macropinocytosis in murine bone marrow-derived macrophages stimulated with the growth factors colony stimulating factor 1 (CSF1) or interleukin 34, both ligands of the CSF1 receptor (CSF1R). The suppressive amino acids did not inhibit macropinocytosis in response to lipopolysaccharide, the chemokine CXCL12, or the tumor promoter phorbol myristate acetate. Suppressive amino acids promoted release of CSF1R from cells and resulted in the formation of smaller macropinosomes in response to CSF1. This suppression of growth factor-stimulated macropinocytosis indicates that different nutrient environments modulate CSF1R levels and bulk ingestion by macropinocytosis, with likely consequences for macrophage growth and function.

The Mitochondrial Fission Regulator DRP1 Controls Post-Transcriptional Regulation of TNF-α

The mitochondrial network plays a critical role in the regulation of innate immune signaling and subsequent production of proinflammatory cytokines such as IFN-β and IL-1β. Dynamin-related protein 1 (DRP1) promotes mitochondrial fission and quality control to maintain cellular homeostasis during infection. However, mechanisms by which DRP1 and mitochondrial dynamics control innate immune signaling and the proinflammatory response are incompletely understood. Here we show that macrophage DRP1 is a positive regulator of TNF-α production during sterile inflammation or bacterial infection. Silencing macrophage DRP1 decreased mitochondrial fragmentation and TNF-α production upon stimulation with lipopolysaccharide (LPS) or methicillin-resistant Staphylococcus aureus (MRSA) infection. The defect in TNF-α induction could not be attributed to changes in gene expression. Instead, DRP1 was required for post-transcriptional control of TNF-α. In contrast, silencing DRP1 enhanced IL-6 and IL-1β production, indicating a distinct mechanism for DRP1-dependent TNF-α regulation. Our results highlight DRP1 as a key player in the macrophage pro-inflammatory response and point to its involvement in post-transcriptional control of TNF-α production.

An Allosteric Shift in CD11c Affinity Activates a Proatherogenic State in Arrested Intermediate Monocytes

Intermediate monocytes (iMo; CD14⁺CD16⁺) increase in number in the circulation of patients with unstable coronary artery disease (CAD), and their recruitment to inflamed arteries is implicated in events leading to mortality following MI. Monocyte recruitment to inflamed coronary arteries is initiated by high affinity β2-integrin (CD11c/CD18) that activates β1-integrin (VLA-4) to bind endothelial VCAM-1. How integrin binding under shear stress mechanosignals a functional shift in iMo toward an inflammatory phenotype associated with CAD progression is unknown. Whole blood samples from patients treated for symptomatic CAD including non-ST elevation MI, along with healthy age-matched subjects, were collected to assess chemokine and integrin receptor levels on monocytes. Recruitment on inflamed human aortic endothelium or rVCAM-1 under fluid shear stress was assessed using a microfluidic-based artery on a chip (A-Chip). Membrane upregulation of high affinity CD11c correlated with concomitant activation of VLA-4 within focal adhesive contacts was required for arrest and diapedesis across inflamed arterial endothelium to a greater extent in non-ST elevation MI compared with stable CAD patients. The subsequent conversion of CD11c from a high to low affinity state under fluid shear activated phospho-Syk- and ADAM17-mediated proteolytic cleavage of CD16. This marked the conversion of iMo to an inflammatory phenotype associated with nuclear translocation of NF-κB and production of IL-1β⁺ We conclude that CD11c functions as a mechanoregulator that activates an inflammatory state preferentially in a majority of iMo from cardiac patients but not healthy patients.

Cardiolipin dynamics regulate proinflammatory cytokine production in methicillin-resistant Staphylococcus aureus--infected macrophages

During the immune response, mitochondria serve as a hub for innate immune signaling molecules, such as mitochondrial antiviral signaling protein (MAVS) and Nod Like Receptor Family Pyrin Domain Containing 3 (NLRP3). Cardiolipin, a class of phospholipids found primarily in the inner mitochondrial membrane (IMM), regulates mitochondrial function and cellular stress. In lipopolysaccharide (LPS)-stimulated macrophages, CL translocates from the IMM to the outer mitochondrial membrane (OMM) and recruits NLRP3 to promote inflammasome activation. However, the role of CL in macrophage antibacterial responses remains ill defined. Here, we have made CL-deficient RAW264.7 (RAW) cells by stably knocking down Cardiolipin Synthase (Crls1). Upon infection with methicillin-resistant Staphylococcus aureus (MRSA), Crls1 KD RAW cells showed markedly decreased expression and production of cytokines IL-6, IL-1β, and IFN-β compared to control cells, while TNF-α levels remained similar. For IL-6 and IFN-β, transcript and protein levels in Crls1 KD RAW cells were comparable to unstimulated controls. Surprisingly, these cells showed normal MRSA killing and NF-kB p65 nuclear translocation. These findings suggest a novel role for CL in transcript-level regulation of cytokines during infection. To further investigate CL-dependent innate immune functions, we will use RAW cells expressing a GFP-tagged CL-binding protein, Stomatin-like Protein-2-GFP, to track CL dynamics at membrane-level resolution using 3D structured illumination microscopy. This approach supports earlier studies that describe increased CL OMM localization in response to LPS. Our data suggest an underappreciated role for CL in macrophage responses to MRSA infection.

A Mouse Model to Assess Innate Immune Response to Staphylococcus aureus Infection

Staphylococcus aureus (S. aureus) infections, including methicillin resistant stains, are an enormous burden on the healthcare system. With incidence rates of S. aureus infection climbing annually, there is a demand for additional research in its pathogenicity. Animal models of infectious disease advance our understanding of the host-pathogen response and lead to the development of effective therapeutics. Neutrophils play a primary role in the innate immune response that controls S. aureus infections by forming an abscess to wall off the infection and facilitate bacterial clearance; the number of neutrophils that infiltrate an S. aureus skin infection often correlates with disease outcome. LysM-EGFP mice, which possess the enhanced green fluorescent protein (EGFP) inserted in the Lysozyme M (LysM) promoter region (expressed primarily by neutrophils), when used in conjunction with in vivo whole animal fluorescence imaging (FLI) provide a means of quantifying neutrophil emigration noninvasively and longitudinally into wounded skin. When combined with a bioluminescent S. aureus strain and sequential in vivo whole animal bioluminescent imaging (BLI), it is possible to longitudinally monitor both the neutrophil recruitment dynamics and in vivo bacterial burden at the site of infection in anesthetized mice from onset of infection to resolution or death. Mice are more resistant to a number of virulence factors produced by S. aureus that facilitate effective colonization and infection in humans. Immunodeficient mice provide a more sensitive animal model to examine persistent S. aureus infections and the ability of therapeutics to boost innate immune responses. Herein, we characterize responses in LysM-EGFP mice that have been bred to MyD88-deficient mice (LysM-EGFP×MyD88-/- mice) along with wild-type LysM-EGFP mice to investigate S. aureus skin wound infection. Multispectral simultaneous detection enabled study of neutrophil recruitment dynamics by using in vivo FLI, bacterial burden by using in vivo BLI, and wound healing longitudinally and noninvasively over time.

α-Toxin Regulates Local Granulocyte Expansion from Hematopoietic Stem and Progenitor Cells in Staphylococcus aureus-Infected Wounds

The immune response to Staphylococcus aureus infection in skin involves the recruitment of polymorphonuclear neutrophils (PMNs) from the bone marrow via the circulation and local granulopoiesis from hematopoietic stem and progenitor cells (HSPCs) that also traffic to infected skin wounds. We focus on regulation of PMN number and function and the role of pore-forming α-toxin (AT), a virulence factor that causes host cell lysis and elicits inflammasome-mediated IL-1β secretion in wounds. Infection with wild-type S. aureus enriched in AT reduced PMN recruitment and resulted in sustained bacterial burden and delayed wound healing. In contrast, PMN recruitment to wounds infected with an isogenic AT-deficient S. aureus strain was unimpeded, exhibiting efficient bacterial clearance and hastened wound resolution. HSPCs recruited to infected wounds were unaffected by AT production and were activated to expand PMN numbers in proportion to S. aureus abundance in a manner regulated by TLR2 and IL-1R signaling. Immunodeficient MyD88-knockout mice infected with S. aureus experienced lethal sepsis that was reversed by PMN expansion mediated by injection of wild-type HSPCs directly into wounds. We conclude that AT-induced IL-1β promotes local granulopoiesis and effective resolution of S. aureus-infected wounds, revealing a potential antibiotic-free strategy for tuning the innate immune response to treat methicillin-resistant S. aureus infection in immunodeficient patients.

Nasal valve dysfunction after Mohs surgery for skin cancer of the nose

BACKGROUND

The nasal valve is the narrowest part of the nasal vestibule and is an important regulator of airflow. Nasal valve insufficiency (NVI), which can be caused by nasal surgery, results in nasal stuffiness, or resistance to airflow on inspiration. This entity has not been well described in the dermatologic surgery literature.

OBJECTIVE

To study nasal valve insufficiency in 100 consecutive patients who had Mohs surgery for skin cancer of the nose, review the literature, and report methods for prevention of this complication.

METHODS

One hundred consecutive nasal Mohs surgery cases were studied retrospectively. Symptomatic patients were evaluated based on several parameters to determine causative and exacerbating factors, and possible methods of prevention. The pertinent literature was reviewed.

RESULTS

Out of 100 patients, 92 responded--38 (41.3%) of whom were determined to be "at risk" for NVI based on the anatomic location of their defects. Out of those 38, five (13.2%) had new onset nasal stuffiness. An additional three of the 38 (7.9%) reported an exacerbation of prior nasal obstructive symptoms. Healing by secondary intention, bulky flaps, inadequate cartilaginous support, inappropriate choice of flap, mucosal scarring, and sacrifice of nasalis and levator labii superioris alaeque nasi fibers were identified as contributors to postoperative NVI.

CONCLUSION

NVI is a relatively common complication of Mohs surgery and reconstruction of the lower third of the nose. Treatment is difficult, but prevention is possible in many instances. Therefore, surgeons should be well aware of this entity and techniques that may aid in its prevention.

Legal review: auto-authentication of medical records raises verification concerns

In summary, federal and state laws require hospitals and practitioners to be accountable for the accuracy and completeness of medical records. The inevitable introduction of computer systems into the process of authenticating medical records evokes novel legal issues. Any computer system that does not require the review of reports after they are transcribed raises serious concerns regarding accountability for the accuracy and completeness of those documents. While federal and state laws have recognized that a signature on a document may be made by electronic or other means, regulatory and accrediting agencies restrict the auto-authentication of medical records. Systems have been proposed that would require the practitioner to see the report and would restrict the final signature authority to the practitioner after his or her review. These systems are likely to be closely scrutinized by regulatory authorities but may ultimately receive their approval. Currently, however, any system that does not require the physician to review and affix his or her signature to each document after reviewing the document creates serious risks for the health care facility implementing that system. Whether future changes in applicable laws will allow more flexibility for such systems is by no means certain.

Special report on licensure, accreditation and CON. JCAHO adopts shorter, more concise standards for 1992

The 1992 AMH is a key step in what will be major ongoing changes in the JCAHO's approach to accreditation. After January 1992, hospital administrators and medical staff leadership should expect that JCAHO surveyors will be looking for indications of a diligent effort to interpret and apply the continuous quality improvement requirements. Meeting the new and revised standards will require rapid implementation of the continuous quality improvement approach. The JCAHO has provided two resources to assist hospitals in this process. The first is a description of the continuous quality improvement process, in both the Introduction and in the Quality Assessment and Improvement chapter of the 1992 AMH. Also, the JCAHO has published a booklet entitled "Transitions from Quality Assurance to Continuous Quality Improvement," which is available from the JCAHO Customer Service Department. It is important that hospital administrators and medical staff leadership review the 1992 AMH promptly and make any changes necessary to comply with the new standards. Despite the fact that JCAHO has been criticized in recent years, accreditation remains important to the viability of the vast majority of hospitals, primarily because of its importance to licensing agencies and third party payors. As accreditation standards become more comparable to the Medicare Conditions of Participation, hospital accreditation will become even more closely linked to a facility's ability to receive or maintain Medicare provider status.