Targeting foamy macrophages by manipulating ABCA1 expression to facilitate lesion healing in the injured spinal cord

Spinal cord injury (SCI) triggers a complex cascade of events, including myelin loss, neuronal damage, neuroinflammation, and the accumulation of damaged cells and debris at the injury site. Infiltrating bone marrow derived macrophages (BMDMϕ) migrate to the epicenter of the SCI lesion, where they engulf cell debris including abundant myelin debris to become pro-inflammatory foamy macrophages (foamy Mϕ), participate neuroinflammation, and facilitate the progression of SCI. This study aimed to elucidate the cellular and molecular mechanisms underlying the functional changes in foamy Mϕ and their potential implications for SCI. Contusion at T10 level of the spinal cord was induced using a New York University (NYU) impactor (5 g rod from a height of 6.25 mm) in male mice. ABCA1, an ATP-binding cassette transporter expressed by Mϕ, plays a crucial role in lipid efflux from foamy cells. We observed that foamy Mϕ lacking ABCA1 exhibited increased lipid accumulation and a higher presence of lipid-accumulated foamy Mϕ as well as elevated pro-inflammatory response in vitro and in injured spinal cord. We also found that both genetic and pharmacological enhancement of ABCA1 expression accelerated lipid efflux from foamy Mϕ, reduced lipid accumulation and inhibited the pro-inflammatory response of foamy Mϕ, and accelerated clearance of cell debris and necrotic cells, which resulted in functional recovery. Our study highlights the importance of understanding the pathologic role of foamy Mϕ in SCI progression and the potential of ABCA1 as a therapeutic target for modulating the inflammatory response, promoting lipid metabolism, and facilitating functional recovery in SCI.

PI3K signaling promotes formation of lipid-laden foamy macrophages at the spinal cord injury site

After spinal cord injury (SCI), infiltrating macrophages undergo excessive phagocytosis of myelin and cellular debris, forming lipid-laden foamy macrophages. To understand their role in the cellular pathology of SCI, investigation of the foamy macrophage phenotype in vitro revealed a pro-inflammatory profile, increased reactive oxygen species (ROS) production, and mitochondrial dysfunction. Bioinformatic analysis identified PI3K as a regulator of inflammation in foamy macrophages, and inhibition of this pathway decreased their lipid content, inflammatory cytokines, and ROS production. Macrophage-specific inhibition of PI3K using liposomes significantly decreased foamy macrophages at the injury site after a mid-thoracic contusive SCI in mice. RNA sequencing and in vitro analysis of foamy macrophages revealed increased autophagy and decreased phagocytosis after PI3K inhibition as potential mechanisms for reduced lipid accumulation. Together, our data suggest that the formation of pro-inflammatory foamy macrophages after SCI is due to the activation of PI3K signaling, which increases phagocytosis and decreases autophagy.

Extrinsic lipoid pneumonia due to chronic polyethylene glycol consumption: A case report

Extrinsic lipoid pneumonia (ELP) results from the aspiration of lipid-containing substances. Tissue or cell histopathology after Oil-Red-O staining can confirm the diagnosis, which requires proper tissue handling and preparation during bronchoscopy. Here, we report a case of ELP in a quadriplegic patient with a long history of dysphagia and polyethylene glycol consumption. Computed tomography (CT) of the chest revealed multiple, progressively enlarging, fat-attenuated, nodular pulmonary lesions. Bronchoscopy with bronchoalveolar lavage (BAL) and a transbronchial forceps biopsy confirmed the diagnosis of lipoid pneumonia. We discuss the clinical, radiological, and pathological features of ELP and highlight the preparatory steps required for obtaining a successful diagnosis.

Profiling alveolar macrophage responses to inhaled compounds using in vitro high content image analysis

One of the main hurdles in the development of new inhaled medicines is the frequent observation of foamy macrophage (FM) responses in non-clinical studies in experimental animals, which raises safety concerns and hinders progress into clinical trials. We have investigated the potential of a novel multi-parameter high content image analysis (HCIA) assay as an in vitro safety screening tool to predict drug induced FM. Rat (NR8383) and human U937-derived alveolar macrophages were exposed in vitro to a panel of model compounds with different biological activity, including inhaled bronchodilators, inhaled corticosteroids (ICS), phospholipidosis inducers and proapoptotic agents. An HCIA was utilized to produce drug-induced cell response profiles based on individual cell health, morphology and lipid content parameters. The profiles of both rat and human macrophage cell lines differentiated between cell responses to marketed inhaled drugs and compounds known to induce phospholipidosis and apoptosis. Hierarchical clustering of the aggregated data allowed identification of distinct cell profiles in response to exposure to phospholipidosis and apoptosis inducers. Additionally, in NR8383 cell responses formed two distinct clusters, associated with increased vacuolation with or without lipid accumulation. U937 cells presented a similar trend but appeared less sensitive to drug exposure and presented a narrower range of responses. These results indicate that our multi-parameter HCIA assay is suitable to generate characteristic drug-induced macrophage response profiles, thus enabling differentiation of foamy macrophage phenotypes associated with phospholipidosis and apoptosis. This approach shows great potential as pre-clinical in vitro screening tool for safety assessment of candidate inhaled medicines.

Perilipin-2 limits remyelination by preventing lipid droplet degradation

Foamy macrophages and microglia containing lipid droplets (LDs) are a pathological hallmark of demyelinating disorders affecting the central nervous system (CNS). We and others showed that excessive accumulation of intracellular lipids drives these phagocytes towards a more inflammatory phenotype, thereby limiting CNS repair. To date, however, the mechanisms underlying LD biogenesis and breakdown in lipid-engorged phagocytes in the CNS, as well as their impact on foamy phagocyte biology and lesion progression, remain poorly understood. Here, we provide evidence that LD-associated protein perilipin-2 (PLIN2) controls LD metabolism in myelin-containing phagocytes. We show that PLIN2 protects LDs from lipolysis-mediated degradation, thereby impairing intracellular processing of myelin-derived lipids in phagocytes. Accordingly, loss of Plin2 stimulates LD turnover in foamy phagocytes, driving them towards a less inflammatory phenotype. Importantly, Plin2-deficiency markedly improves remyelination in the ex vivo brain slice model and in the in vivo cuprizone-induced demyelination model. In summary, we identify PLIN2 as a novel therapeutic target to prevent the pathogenic accumulation of LDs in foamy phagocytes and to stimulate remyelination.

Tumor-associated mononuclear cells in the tumor bed of triple-negative breast cancer associate with clinical outcomes in the post-neoadjuvant chemotherapy setting

PURPOSE

To evaluate the clinical role of tumor-associated macrophages, including foamy (FM) and hemosiderin-laden macrophages (HLM) in the tumor bed (TB) of triple-negative breast cancer (TNBC) post-neoadjuvant chemotherapy (NACT).

METHODS

We conducted a pathologic review of 129 women, diagnosed with TNBC between 2002 and 2016 at our institute. The residual cancer burden (RCB) was calculated. We estimated the percentage of tumor-infiltrating lymphocytes (TILs) in the core needle biopsy (CNB), and FM, HLM, and TILs (in TB) [the combined cells are designated as tumor-associated mononuclear cells (TAMNC)]. The information on patient demographics, chemotherapy regimen, recurrence-free survival (RFS), and overall survival (OS) was extracted from the medical records.

RESULTS

Pathologic complete response (pCR) was achieved in 34.1% of the women. TILs (10% increment in CNB) only were associated with pCR in the multivariable analysis [odds ratio 1.04 (1.02, 1.06) (p = 0.0003)]. Immune cells associated with better OS included TAMNC (≤ 30%) [hazard ratio (HR) 4.32 (1.93, 9.66) (p = 0.0004)], and FM (0%) [HR 2.30 (1.06, 4.98) (p = 0.036)]. While increased HLM (10% increment) was statistically significant with HR 0.93 and 95% CI (0.88 to 0.98) (p = 0.0061), using a cutoff of 0%, HLM (0%: negative vs. ≥ 1%: positive) achieved only borderline significance with HR 2.05 (0.98, 4.31) (p = 0.058). Similarly, these immune cells were also associated with better RFS: TAMNC (≤ 30%) [HR 4.57 (2.04, 10.21) (p = 0.0002)], FM (0%) [HR 2.80 (1.23, 6.35) (p = 0.014)], and HLM (0%) [HR 2.34 (1.07, 5.11) (p = 0.03)]. TILs (in TB) were not associated with any clinical outcomes.

CONCLUSIONS

Although TILs may play a role in the response to NACT, they may not be critical to the prognosis after NACT. Instead, FM and HLM may assume this role. More studies are warranted.

Pathogenesis and Host Immune Response in Leprosy

Leprosy is an ancient insidious disease caused by Mycobacterium leprae, where the skin and peripheral nerves undergo chronic granulomatous infections, leading to sensory and motor impairment with characteristic deformities. Susceptibility to leprosy and its disease state are determined by the manifestation of innate immune resistance mediated by cells of monocyte lineage. Due to insufficient innate resistance, granulomatous infection is established, influencing the specific cellular immunity. The clinical presentation of leprosy ranges between two stable polar forms (tuberculoid to lepromatous) and three unstable borderline forms. The tuberculoid form involves Th1 response, characterized by a well demarcated granuloma, infiltrated by CD4⁺ T lymphocytes, containing epitheloid and multinucleated giant cells. In the lepromatous leprosy, there is no characteristic granuloma but only unstructured accumulation of ineffective macrophages containing engulfed pathogens. Th1 response, characterised by IFN-γ and IL-2 production, activates macrophages in order to kill intracellular pathogens. Conversely, a Th2 response, characterized by the production of IL-4, IL-5 and IL-10, helps in antibody production and consequently downregulates the cell-mediated immunity induced by the Th1 response. M. lepare has a long generation time and its inability to grow in culture under laboratory conditions makes its study challenging. The nine-banded armadillo still remains the best clinical and immunological model to study host-pathogen interaction in leprosy. In this chapter, we present cellular morphology and the genomic uniqueness of M. leprae, and how the pathogen shows tropism for Schwann cells, macrophages and dendritic cells.

Severe pulmonary alveolar proteinosis with respiratory failure treated by intrapulmonary percussive ventilation

Pulmonary alveolar proteinosis (PAP) is a rare disease characterized by abnormal accumulation of surfactant in the alveoli. Whole lung lavage (WLL) is the standard treatment for severe autoimmune PAP (aPAP); however, it is highly invasive. Intrapulmonary percussive ventilation (IPV) is a non-invasive technique that delivers small bursts of high-flow respiratory gas into the lung and mobilizes secretions. As IPV is beneficial for chronic respiratory diseases such as cystic fibrosis and bronchiectasis to reduce sputum, it was hypothesized that IPV will ameliorate aPAP by mobilizing and removing accumulated surfactant and foamy macrophages. Here, we report the case of a 52-year-old female with severe aPAP and progressive respiratory failure. She received intermittent IPV therapy for six months and thereby showed improvement in assessments of chest computed tomography (CT), lung function, and oxygenation. We suggest that IPV should be used as an alternative therapy for patients with aPAP and respiratory failure.

Multiple sclerosis: The resolving lesion revealed

A little studied lesion, the resolving lesion, is described in multiple sclerosis (MS). Unusual features of early resolving lesions comprised a fibrous astrogliotic parenchyma replete with lipid-laden (foamy) microglia/macrophages widely scattered throughout and lined up at the edge, separating demyelinated plaque from myelinated white matter. Ongoing myelin breakdown was absent, as was remyelination. Later resolving lesions displayed the unusual coexistence of macrophages and remyelination within the gliotic parenchyma. Collectively, these observations may provide for the first time evidence for a role in MS for mitigating factors like alternatively-activated (M2) microglia/macrophages, known to have an anti-inflammatory phenotype and to be associated with wound-healing and repair.

Extensive macrophage accumulation in young and old Niemann-Pick C1 model mice involves the alternative, M2, activation pathway and inhibition of macrophage apoptosis

We have studied the pathophysiology of lung disease which occurs in two mouse models of Niemann-Pick C1 disease. We utilized Npc1(-/-) mice transgenic for normal gene expression in glia or neurons and glia at ages several fold the usual and a mouse model of the juvenile form of NPC1, a point mutation, at one age to confirm some findings. Lung weights, as per cent of body weight, increase much more than liver and spleen weights. Although pulmonary function parameters only vary for hysteresis between young and older Npc1(-/-) mice, they are markedly different than those found in normal control mice. Cholesterol accumulation continued in the older mice but sphingosine-1-phosphate was not increased. Bronchoalveolar lavage (BAL) showed a massive increase (26×) in the number of macrophages. Histologic examination from the older, transgenic Npc1(-/-) mice showed small foci of alveolar proteinosis and evidence of hemorrhage, as well as dense macrophage accumulation. A large subset of macrophages was immunopositive for Fizz1 or arginase-1, markers of the alternative activation pathway, while no Fizz1 or arginase-1 positive macrophages were found in wild-type mice. The percentage of marker positive macrophages was relatively stable at 5-10% at various ages and within the 2 transgenic models. Phosphohistone H3 and Ki67 showed low levels of proliferation of these macrophages. Apoptosis was prominent within lung capillary endothelial cells, but limited within macrophages. Thus, activation of the alternative pathway is involved in Niemann-Pick C1 associated pulmonary macrophage accumulation, with low proliferation of these cells balanced by low levels of apoptosis.