Macrophage colony-stimulating factor in the pathogenesis of HIV infection: potential target for therapeutic intervention

Time-series transcriptomic analysis of bronchoalveolar lavage cells from virulent and low virulent PRRSV-1-infected piglets

Porcine reproductive and respiratory syndrome virus (PRRSV) has evolved to escape the immune surveillance for a survival advantage leading to a strong modulation of host’s immune responses and favoring secondary bacterial infections. However, limited data are available on how the immunological and transcriptional responses elicited by virulent and low-virulent PRRSV-1 strains are comparable and how they are conserved during the infection. To explore the kinetic transcriptional signature associated with the modulation of host immune response at lung level, a time-series transcriptomic analysis was performed in bronchoalveolar lavage cells upon experimental in vivo infection with two PRRSV-1 strains of different virulence, virulent subtype 3 Lena strain or the low-virulent subtype 1 3249 strain. The time-series analysis revealed overlapping patterns of dysregulated genes enriched in T-cell signaling pathways among both virulent and low-virulent strains, highlighting an upregulation of co-stimulatory and co-inhibitory immune checkpoints that were disclosed as Hub genes. On the other hand, virulent Lena infection induced an early and more marked “negative regulation of immune system process” with an overexpression of co-inhibitory receptors genes related to T-cell and NK cell functions, in association with more severe lung lesion, lung viral load, and BAL cell kinetics. These results underline a complex network of molecular mechanisms governing PRRSV-1 immunopathogenesis at lung level, revealing a pivotal role of co-inhibitory and co-stimulatory immune checkpoints in the pulmonary disease, which may have an impact on T-cell activation and related pathways. These immune checkpoints, together with the regulation of cytokine-signaling pathways, modulated in a virulence-dependent fashion, orchestrate an interplay among pro- and anti-inflammatory responses.

IMPORTANCE Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the major threats to swine health and global production, causing substantial economic losses. We explore the mechanisms involved in the modulation of host immune response at lung level performing a time-series transcriptomic analysis upon experimental infection with two PRRSV-1 strains of different virulence. A complex network of molecular mechanisms was revealed to control the immunopathogenesis of PRRSV-1 infection, highlighting an interplay among pro- and anti-inflammatory responses as a potential mechanism to restrict inflammation-induced lung injury. Moreover, a pivotal role of co-inhibitory and co-stimulatory immune checkpoints was evidenced, which may lead to progressive dysfunction of T cells, impairing viral clearance and leading to persistent infection, favoring as well secondary bacterial infections or viral rebound. However, further studies should be conducted to evaluate the functional role of immune checkpoints in advanced stages of PRRSV infection and explore a possible T-cell exhaustion state.

Brain tissue transcriptomic analysis of SIV-infected macaques identifies several altered metabolic pathways linked to neuropathogenesis and poly (ADP-ribose) polymerases (PARPs) as potential therapeutic targets

Despite improvements in antiretroviral therapy, human immunodeficiency virus type 1 (HIV-1)-associated neurocognitive disorders (HAND) remain prevalent in subjects undergoing therapy. HAND significantly affects individuals' quality of life, as well as adherence to therapy, and, despite the increasing understanding of neuropathogenesis, no definitive diagnostic or prognostic marker has been identified. We investigated transcriptomic profiles in frontal cortex tissues of Simian immunodeficiency virus (SIV)-infected Rhesus macaques sacrificed at different stages of infection. Gene expression was compared among SIV-infected animals (n = 11), with or without CD8+ lymphocyte depletion, based on detectable (n = 6) or non-detectable (n = 5) presence of the virus in frontal cortex tissues. Significant enrichment in activation of monocyte and macrophage cellular pathways was found in animals with detectable brain infection, independently from CD8+ lymphocyte depletion. In addition, transcripts of four poly (ADP-ribose) polymerases (PARPs) were up-regulated in the frontal cortex, which was confirmed by real-time polymerase chain reaction. Our results shed light on involvement of PARPs in SIV infection of the brain and their role in SIV-associated neurodegenerative processes. Inhibition of PARPs may provide an effective novel therapeutic target for HIV-related neuropathology.

Genome-Wide Association Study Identifies Novel Colony Stimulating Factor 1 Locus Conferring Susceptibility to Cryptococcosis in Human Immunodeficiency Virus-Infected South Africans

BACKGROUND

Cryptococcus is the most common cause of meningitis in human immunodeficiency virus (HIV)-infected Africans. Despite universal exposure, only 5%-10% of patients with HIV/acquired immune deficiency syndrome and profound CD4+ T-cell depletion develop disseminated cryptococcosis: host genetic factors may play a role. Prior targeted immunogenetic studies in cryptococcosis have comprised few Africans.

METHODS

We analyzed genome-wide single-nucleotide polymorphism (SNP) genotype data from 524 patients of African descent: 243 cases (advanced HIV with cryptococcal antigenemia and/or cryptococcal meningitis) and 281 controls (advanced HIV, no history of cryptococcosis, negative serum cryptococcal antigen).

RESULTS

Six loci upstream of the colony-stimulating factor 1 (CSF1) gene, encoding macrophage colony-stimulating factor (M-CSF) were associated with susceptibility to cryptococcosis at P < 10-6 and remained significantly associated in a second South African cohort (83 cases; 128 controls). Meta-analysis of the genotyped CSF1 SNP rs1999713 showed an odds ratio for cryptococcosis susceptibility of 0.53 (95% confidence interval, 0.42-0.66; P = 5.96 × 10-8). Ex vivo functional validation and transcriptomic studies confirmed the importance of macrophage activation by M-CSF in host defence against Cryptococcus in HIV-infected patients and healthy, ethnically matched controls.

CONCLUSIONS

This first genome-wide association study of susceptibility to cryptococcosis has identified novel and immunologically relevant susceptibility loci, which may help define novel strategies for prevention or immunotherapy of HIV-associated cryptococcal meningitis.

Recent advances in colony stimulating factor-1 receptor/c-FMS as an emerging target for various therapeutic implications

Colony stimulating factor-1 (CSF-1) is one of the most common proinflammatory cytokine responsible for various inflammatory disorders. It has a remarkable role in the development and progression of osteoarthritis, cancer and other autoimmune disease conditions. The CSF-1 acts by binding to the receptor, called colony stimulating factor-1 receptor (CSF-1R) also known as c-FMS resulting in the cascade of signalling pathway causing cell proliferation and differentiation. Interleukin-34 (IL-34), recently identified as another ligand for CSF-IR, is a cytokine protein. Both, CSF-1 and IL-34, although two distinct cytokines, follow the similar signalling pathway on binding to the same receptor, CSF-1R. Like CSF-1, IL-34 promotes the differentiation and survival of monocyte, macrophages and osteoclasts. This CSF-1R/c-FMS is over expressed in many cancers and on tumour associated macrophages, consequently, have been exploited as a drug target for promising treatment for cancer and inflammatory diseases. Some CSF-1R/c-FMS inhibitors such as ABT-869, Imatinib, AG013736, JNJ-40346527, PLX3397, DCC-3014 and Ki20227 have been successfully used in these disease conditions. Many c-FMS inhibitors have been the candidates of clinical trials, but suffer from some side effects like cardiotoxicity, vomiting, swollen eyes, diarrhoea, etc. If selectivity of cFMS inhibition is achieved successfully, side effects can be overruled and this approach may become a novel therapy for treatment of various therapeutic interventions. Thus, successful targeting of c-FMS may result in multifunctional therapy. With this background of information, the present review focuses on the recent developments in the area of CSF-1R/c-FMS inhibitors with emphasis on crystal structure, mechanism of action and various therapeutic implications in which c-FMS plays a pivotal role. The review on structure activity relationship of various compounds acting as the inhibitors of c-FMS which gives the selection criteria for the development of novel molecules is also being presented.

Effect of chronic morphine administration on circulating dendritic cells in SIV-infected rhesus macaques

We studied the effect of chronic morphine administration on the circulating dendritic cell population dynamics associated with SIV infection using rhesus macaques. Animals were either first infected with SIV and then given chronic morphine, or visa versa. SIV infection increased the numbers of myeloid DCs (mDCs), but morphine treatment attenuated this mDC expansion. In contrast, morphine increased the numbers of plasmacytoid DCs (pDCs) in SIV-infected animals. Finally, chronic morphine administration (no SIV) transiently increased the numbers of circulating pDCs. These results show that chronic morphine induces a significant alteration in the available circulating levels of critical antigen-presenting cells.

Role for cFMS in maintaining alternative macrophage polarization in SIV infection: implications for HIV neuropathogenesis

BACKGROUND

Macrophage-colony stimulating factor (M-CSF) has been implicated in HIV neuropathogenesis through its ability to modulate activation of macrophages (MΦs) and microglia, as well as enhance the susceptibility of these cells to infection and promote virus production. We have recently reported that MΦs accumulating perivascularly and within nodular lesions in archival brain tissue of simian immunodeficiency virus (SIV)-infected rhesus macaques with encephalitis (SIVE) express M-CSF. In contrast, IL-34, which shares the same receptor, cFMS, was observed more often in parenchymal cells.

METHODS

Frontal white and grey matter from non-infected and SIV-infected rhesus macaques with and without SIVE were examined by single- and double-label immunohistochemistry for M-CSF, IL-34, and CD163 expression. Primary rhesus macaque and human peripheral blood mononuclear cells were cultured with and without 2.5 ng/ml M-CSF or IL-34 alone and with 470 nM or 4.7 μM of GW2580, a receptor tyrosine kinase inhibitor with high specificity for cFMS. After 24 h, cells were analyzed by flow cytometry to examine the effect of these cytokines on promoting an M2 monocyte/MΦ phenotype.

RESULTS

Here, we demonstrate that in SIVE brain, accumulating M-CSF(+) MΦs are also CD163(+), while IL-34 does not appear to co-localize significantly with CD163 in the parenchyma. We further demonstrate that M-CSF and IL-34 are expressed by neurons in normal brain but are altered in SIV and SIVE. Through in vitro studies, we show that M-CSF and IL-34 upregulate CD163, a marker for type 2 activation of MΦs (M2), by primary monocytes, which is attenuated by the addition of GW2580.

CONCLUSIONS

Together, these data suggest that both cFMS ligands may promote and/or prolong M2 activation of MΦs and microglia in brains of SIV-infected animals with encephalitis. As such, cFMS signaling may be an attractive target for eliminating long-lived MΦ reservoirs of HIV infection in brain, as well as other tissues.

Macrophage colony stimulating factor regulation by nuclear factor kappa B: a relevant pathway in human immunodeficiency virus type 1 infected macrophages

Macrophage colony stimulating factor (M-CSF) is a cytokine that promotes monocyte differentiation and survival. When overexpressed, M-CSF contributes to pathology in a wide variety of diseases, including osteoporosis, obesity, certain human cancers, and in human immunodeficiency virus type 1 (HIV-1) infection, particularly with respect to monocyte/macrophage infection and the development of HIV-1 associated central nervous system disorders. In this study, our aim was to expand the current knowledge of M-CSF regulation, focusing on nuclear factor kappa B (NF-κB), a transcription factor playing a prominent role during inflammation and HIV-1 infection. Our results suggest that tumor necrosis factor alpha (TNF-α) promotes M-CSF secretion in primary macrophages and activates the -1310/+48 bp M-CSF promoter in Mono-Mac 1 cells. Inhibitors of the NF-κB pathway diminish this response. We identified four putative NF-κB and four CCAAT-enhancer-binding protein beta binding sites within the M-CSF promoter. Our findings, using promoter constructs mutated at individual NF-κB sites within the M-CSF promoter region, suggest that these sites are redundant with respect to NF-κB regulation. TNF-α treatment promoted NF-κB p65 binding to the M-CSF promoter in phorbol 12-myristate 13-acetate (PMA) treated U937 cells chronically infected with HIV-1 (U1 cells), but not in PMA treated uninfected U937 cells, suggesting that the presence of HIV-1 increases the NF-κB response. In conclusion, our findings demonstrate that NF-κB induces M-CSF expression on a promoter level via multiple functional NF-κB binding sites and that this pathway is likely relevant in HIV-1 infection of macrophages.

Anti-apoptotic genes in the survival of monocytic cells during infection

Macrophages are cells of the immune system that protect organisms against invading pathogens by fulfilling critical roles in innate and adaptive immunity and inflammation. They originate from circulating monocytes and show a high degree of heterogeneity, which reflects the specialization of function given by different anatomical locations. Differentiation of monocytes towards a macrophage phenotype is also accompanied by an increase of resistance against various apoptotic stimuli, a required characteristic that allows macrophages to accomplish their function in a stressful environment.

Apoptosis, a form of programmed cell death, is a tightly regulated process, needed to maintain homeostasis by balancing proliferation with cellular demise. Caspases, a family of cysteine proteases that are highly conserved in multicellular organisms, function as central regulators of apoptosis. FLIP (FLICE-inhibitory protein), anti-apoptotic members of the Bcl2 family and inhibitors of apoptosis (IAP) are the main three groups of anti-apoptotic genes that counteract caspase activation through both the extrinsic and intrinsic apoptotic pathways.

Modulation of the apoptotic machinery during viral and bacterial infections, as well as in various malignancies, is a wellestablished mechanism that promotes the survival of affected cells. The involvement of anti-apoptotic genes in the survival of monocytes/macrophages, either physiological or pathological, will be described in this review. How viral and bacterial infections that target cells of the monocytic lineage affect the expression of anti-apoptotic genes is important in understanding the pathological mechanisms that lead to manifested disease. The latest therapeutic approaches that target anti-apoptotic genes will also be discussed.

Exploring the relationship of macrophage colony-stimulating factor levels on neuroaxonal metabolism and cognition during chronic human immunodeficiency virus infection

Macrophage colony-stimulating factor (M-CSF) promotes macrophage differentiation, increases susceptibility of macrophages to viral infection, and enhances human immunodeficiency virus (HIV) replication in infected macrophages. Given the current model of HIV neuropathogenesis, which involves monocyte trafficking into the central nervous system, immune factors linked with macrophage maturation and survival may be associated with cognitive decline (measured by neuropsychological z-score [NPZ-8] or Memorial Sloan-Kettering [MSK] score) and alterations in a marker of neuronal integrity, N-acetylaspartate (NAA). Fifty-four chronically infected HIV+ subjects underwent neuropsychological assessment, magnetic resonance spectroscopic imaging, and quantification of M-CSF in plasma and cerebrospinal fluid (CSF) at baseline. Thirty-nine of those subjects underwent further examination at 3 and 10 months after initiation of combination antiretroviral therapy (ART) regimens. Within 3 months of therapy use, CSF M-CSF and viral RNA levels were reduced, whereas NAA concentrations in many brain regions were increased. Neither baseline levels nor the change in M-CSF levels had the ability to predict changes in NAA levels observed after 10 months of combination ART use. At study entry those with the lowest M-CSF levels in the CSF had the least cognitive impairment (NPZ-8). Those who had higher baseline CSF M-CSF levels and exhibited larger decreases in M-CSF after therapy, tended to have greater cognitive improvement after 10 months. Increased prevalence of M-CSF in the setting of HIV infection could contribute to neuronal injury and may be predictive of cognitive impairment.

HIV and bone loss

The use of antiretroviral therapy has significantly reduced the number of deaths due to HIV/AIDS. However, no current therapy can suppress the virus completely, and as the HIV-infected population continues to live longer new complications are emerging from the persistence of the virus and use of antiretroviral therapy. This review summarizes the clinical evidence linking HIV-associated osteoporosis to direct infection and antiretroviral therapy (ART) use. The purported molecular mechanisms involved in bone loss are also reviewed. Additionally, recommendations regarding the pharmacologic management of HIV/ART-related osteoporosis are given.

Human immunodeficiency virus and leishmaniasis

The Leishmaniases are a group of diseases transmitted to humans by the bite of a sandfly, caused by protozoan parasites of the genus Leishmania. Various Leishmania species infect humans, producing a spectrum of clinical manifestations. It is estimated that 350 million people are at risk, with a global yearly incidence of 1-1.5 million for cutaneous and 500,000 for visceral Leishmaniasis (VL). VL is a major cause of morbidity and mortality in East Africa, Brazil and the Indian subcontinent. Co-infection with human immunodeficiency virus (HIV) alters the immune response to the disease. Here we review the immune response to Leishmania in the setting of HIV co-infection. Improved understanding of the immunology involved in co-infections may help in designing prophylactic and therapeutic strategies against Leishmaniasis.

Alterations in the immuno-skeletal interface drive bone destruction in HIV-1 transgenic rats

Osteoporosis and bone fractures are increasingly recognized complications of HIV-1 infection. Although antiretroviral therapy itself has complex effects on bone turnover, it is now evident that the majority of HIV-infected individuals already exhibit reduced bone mineral density before therapy. The mechanisms responsible are likely multifactorial and have been difficult to delineate in humans. The HIV-1 transgenic rat recapitulates many key features of human AIDS. We now demonstrate that, like their human counterparts, HIV-1 transgenic rats undergo severe osteoclastic bone resorption, a consequence of an imbalance in the ratio of receptor activator of NF-kappaB ligand, the key osteoclastogenic cytokine, to that of its physiological decoy receptor osteoprotegerin. This imbalance stemmed from a switch in production of osteoprotegerin to that of receptor activator of NF-kappaB ligand by B cells, and was further compounded by a significantly elevated number of osteoclast precursors. With the advancing age of individuals living with HIV/AIDS, low bone mineral density associated with HIV infection is likely to collide with the pathophysiology of skeletal aging, leading to increased fracture risk. Understanding the mechanisms driving bone loss in HIV-infected individuals will be critical to developing effective therapeutic strategies.

Porcine circovirus type 2 (PCV2) induces cell proliferation, fusion, and chemokine expression in swine monocytic cells in vitro

Granulomatous lymphadenitis is one of the pathognomonic lesions in post-weaning multisystemic wasting syndrome (PMWS)-affected pigs. This unique lesion has not been reported in direct association with viral infection in pigs. The objective of the present study was to evaluate whether porcine circovirus type 2 (PCV2) alone is able to induce functional modulation in porcine monocytic cells in vitro to elucidate its possible role in the development of granulomatous inflammation. It was found that the proliferation activity of blood monocytes (Mo) and monocyte-derived macrophages (MDM) was significantly enhanced by PCV2. During monocyte-macrophage differentiation, the PCV2 antigen-containing rate and formation of multinucleated giant cells (MGC) were significantly increased in MDM when compared to those in Mo. The MDM-derived MGC displayed a significantly higher PCV2 antigen-containing rate than did the mono-nucleated MDM. Supernatants from PCV2-inoculated MDM at 24 h post-inoculation induced an increased tendency of chemotactic activity for blood Mo. At the same inoculation time period, levels of mRNA expression of the monocytic chemokines, monocyte chemoattractant protein-1 and macrophage inflammatory protein-1, also significantly increased in PCV2-inoculated MDM. The results suggest that PCV2 alone may induce cell proliferation, fusion, and chemokine expression in swine monocytic cells. Thus, PCV2 itself may play a significant role in the induction of granulomatous inflammation in PMWS-affected pigs.

CNS inflammation and macrophage/microglial biology associated with HIV-1 infection

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system (CNS) can result in neurological dysfunction with devastating consequences in a significant proportion of individuals with acquired immune deficiency syndrome. HIV-1 does not infect neurons directly but induces damage indirectly through the accumulation of activated macrophage/microglia (M/M) cells, some of which are infected, that release neurotoxic mediators including both cellular activation products and viral proteins. One mechanism for the accumulation of activated M/M involves the development in infected individuals of an activated peripheral blood monocyte population that traffics through the blood-brain barrier, a process that also serves to carry virus into CNS and establish local infection. A second mechanism involves the release by infected and activated M/M in the CNS of chemotactic mediators that recruit additional monocytes from the periphery. These activated M/M, some of which are infected, release a number of cytokines and small molecule mediators as well as viral proteins that act on bystander cells and in turn activate them, thus amplifying the cascade. These viral proteins and cellular products have neurotoxic properties as well, both directly and through induction of astrocyte dysfunction, which ultimately lead to neuronal injury and death. In patients effectively treated with antiretroviral therapy, frank dementia is now uncommon and has been replaced by milder forms of neurocognitive impairment, with less frequent and more focal neuropathology. This review summarizes key findings that support the critical role and mechanisms of monocyte/macrophage activation and inflammation as a major component for HIV-1 encephalitis or HIV-1 associated dementia.

Regulation of complement component C3 in astrocytes by IL-1beta and morphine

Substances of abuse, such as opiates, and astroglial-derived proinflammatory cytokines, such as interleukin (IL)-1beta, likely contribute to the neuroinflammatory and neurodegenerative processes observed in NeuroAIDS in injection drug users. Furthermore, uncontrolled synthesis and activation of complement component C3 in the brain can also lead to inflammation and neurodegeneration. We hypothesized that morphine may alter regulation of the C3 gene by IL-1beta in astrocytes. Our studies demonstrate that IL-1beta induces C3 promoter activity in a CAAT/enhancer-binding protein (C/EBP)-dependent manner. Inhibition of IL-1beta mediated C3 promoter activation by the dominant negative mutant of p38-alpha mitogen-activated protein kinase suggests that IL-1beta induces C3 expression through the activation of C/EBP. Morphine (0.01 microM) in combination with IL-1beta further induced C3 promoter activity. Similarly, the C/EBP-beta isoform liver activating protein and C/EBP-delta-induced C3 promoter activity were upregulated by morphine and IL-1beta. Taken together, this study illustrates that morphine modulates IL-1beta-mediated C3 expression in astrocytic cells.