Antonina Akk

Disruption of T cell signaling networks and development by Grb2 haploid insufficiency.

The developmental processes of positive and negative selection in the thymus shape the T cell antigen receptor (TCR) repertoire and require the integration of multiple signaling networks. These networks involve the efficient assembly of macromolecular complexes and are mediated by multimodular adaptor proteins that permit the functional integration of distinct signaling molecules. We show here that decreased expression of the adaptor protein Grb2 in Grb2+/− mice weakens TCR-induced c-Jun N-terminal kinase (JNK) and p38, but not extracellular signal–regulated kinase (ERK), activation. In turn, this selective effect decreases the ability of thymocytes to undergo negative, but not positive, selection. We also show that there are differences in the signaling thresholds of the three mitogen-activated protein kinase (MAPK) families. These differences may provide a mechanism by which quantitative differences in signal strength can alter the balance of downstream signaling pathways to induce the qualitatively distinct biological outcomes of proliferation, differentiation or apoptosis.

Dipeptidyl Peptidase I-Dependent Neutrophil Recruitment Modulates the Inflammatory Response to Sendai Virus Infection

The role of innate immunity in the pathogenesis of asthma is unclear. Although increased presence of neutrophils is associated with persistent asthma and asthma exacerbations, how neutrophils participate in the pathogenesis of asthma remains controversial. In this study, we show that the absence of dipeptidyl peptidase I (DPPI), a lysosomal cysteine protease found in neutrophils, dampens the acute inflammatory response and the subsequent mucous cell metaplasia that accompanies the asthma phenotype induced by Sendai virus infection. This attenuated phenotype is accompanied by a significant decrease in the accumulation of neutrophils and the local production of CXCL2, TNF, IL-1β, and IL-6 in the lung of infected DPPI−/− mice. Adoptive transfer of DPPI-sufficient neutrophils into DPPI−/− mice restored the levels of CXCL2 and enhanced cytokine production on day 4 postinfection and subsequent mucous cell metaplasia on day 21 postinfection. These results indicate that DPPI and neutrophils play a critical role in Sendai virus-induced asthma phenotype as a result of a DPPI-dependent neutrophil recruitment and cytokine response.

Peptide-siRNA nanocomplexes targeting NF-κB subunit p65 suppress nascent experimental arthritis

The NF-κB signaling pathway is implicated in various inflammatory diseases, including rheumatoid arthritis (RA); therefore, inhibition of this pathway has the potential to ameliorate an array of inflammatory diseases. Given that NF-κB signaling is critical for many immune cell functions, systemic blockade of this pathway may lead to detrimental side effects. siRNAs coupled with a safe and effective delivery nanoplatform may afford the specificity lacking in systemic administration of small-molecule inhibitors. Here we demonstrated that a melittin-derived cationic amphipathic peptide combined with siRNA targeting the p65 subunit of NF-κB (p5RHH-p65) noncovalently self-assemble into stable nanocomplexes that home to the inflamed joints in a murine model of RA. Specifically, administration of p5RHH-p65 siRNA nanocomplexes abrogated inflammatory cytokine expression and cellular influx into the joints, protected against bone erosions, and preserved cartilage integrity. The p5RHH-p65 siRNA nanocomplexes potently suppressed early inflammatory arthritis without affecting p65 expression in off-target organs or eliciting a humoral response after serial injections. These data suggest that this self-assembling, largely nontoxic platform may have broad utility for the specific delivery of siRNA to target and limit inflammatory processes for the treatment of a variety of diseases.

Suppression of NF-κB activity via nanoparticle-based siRNA delivery alters early cartilage responses to injury.

Significance Osteoarthritis is a common debilitating joint disease that affects millions in the United States and for which there are few therapeutic options. Critical barriers to the successful development of osteoarthritis treatment include limited understanding of the pathways governing early cartilage degradation and ineffective delivery of therapeutic agents to the resident chondrocytes in the avascular cartilage. Using a peptidic nanoparticle carrying siRNA that specifically suppresses NF-κB, we show that early antiinflammatory intervention reduces chondrocyte death caused by joint injury, a known predisposing factor for osteoarthritis. The peptidic nanoparticle deeply penetrates human cartilage to deliver its therapeutic cargo to the chondrocytes, demonstrating its ability to permeate the dense cartilage matrix. This approach promises to overcome the barriers to effectively treat osteoarthritis. Osteoarthritis (OA) is a major cause of disability and morbidity in the aging population. Joint injury leads to cartilage damage, a known determinant for subsequent development of posttraumatic OA, which accounts for 12% of all OA. Understanding the early molecular and cellular responses postinjury may provide targets for therapeutic interventions that limit articular degeneration. Using a murine model of controlled knee joint impact injury that allows the examination of cartilage responses to injury at specific time points, we show that intraarticular delivery of a peptidic nanoparticle complexed to NF-κB siRNA significantly reduces early chondrocyte apoptosis and reactive synovitis. Our data suggest that NF-κB siRNA nanotherapy maintains cartilage homeostasis by enhancing AMPK signaling while suppressing mTORC1 and Wnt/β-catenin activity. These findings delineate an extensive crosstalk between NF-κB and signaling pathways that govern cartilage responses postinjury and suggest that delivery of NF-κB siRNA nanotherapy to attenuate early inflammation may limit the chronic consequences of joint injury. Therapeutic benefits of siRNA nanotherapy may also apply to primary OA in which NF-κB activation mediates chondrocyte catabolic responses. Additionally, a critical barrier to the successful development of OA treatment includes ineffective delivery of therapeutic agents to the resident chondrocytes in the avascular cartilage. Here, we show that the peptide–siRNA nanocomplexes are nonimmunogenic, are freely and deeply penetrant to human OA cartilage, and persist in chondrocyte lacunae for at least 2 wk. The peptide–siRNA platform thus provides a clinically relevant and promising approach to overcoming the obstacles of drug delivery to the highly inaccessible chondrocytes.

Anti-complement activity of the Ixodes scapularis salivary protein Salp20.

Complement, a major component of innate immunity, presents a rapid and robust defense of the intravascular space. While regulatory proteins protect host cells from complement attack, when these measures fail, unrestrained complement activation may trigger self-tissue injury, leading to pathologic conditions. Of the three complement activation pathways, the alternative pathway (AP) in particular has been implicated in numerous disease and injury states. Consequently, the AP components represent attractive targets for therapeutic intervention. The common hard-bodied ticks from the family Ixodidae derive nourishment from the blood of their mammalian hosts. During its blood meal the tick is exposed to host immune effectors, including the complement system. In defense, the tick produces salivary proteins that can inhibit host immune functions. The Salp20 salivary protein of Ixodes scapularis inhibits the host AP pathway by binding properdin and dissociating C3bBbP, the active C3 convertase. In these studies we examined Salp20 activity in various complement-mediated pathologies. Our results indicate that Salp20 can inhibit AP-dependent pathogenesis in the mouse. Its efficacy may be part in due to synergic effects it provides with the endogenous AP regulator, factor H. While Salp20 itself would be expected to be highly immunogenic and therefore inappropriate for therapeutic use, its emergence speaks for the potential development of a non-immunogenic Salp20 mimic that replicates its anti-properdin activity.

Neutrophil Proteases Promote Experimental Abdominal Aortic Aneurysm via Extracellular Trap Release and Plasmacytoid Dendritic Cell Activation

Objective—We previously established that neutrophil-derived dipeptidyl peptidase I (DPPI) is essential for experimental abdominal aortic aneurysm (AAA) development. Because DPPI activates several neutrophil serine proteases, it remains to be determined whether the AAA-promoting effect of DPPI is mediated by neutrophil serine proteases. Approach and Results—Using an elastase-induced AAA model, we demonstrate that the absence of 2 neutrophil serine proteases, neutrophil elastase and proteinase-3, recapitulates the AAA-resistant phenotype of DPPI-deficient mice. DPPI and neutrophil serine proteases direct the in vitro and in vivo release of extracellular structures termed neutrophil extracellular traps (NETs). Administration of DNase1, which dismantles NETs, suppresses elastase-induced AAA in wild-type animals and in DPPI-deficient mice reconstituted with wild-type neutrophils. NETs also contain the cathelicidin-related antimicrobial peptide that complexes with self-DNA in recruiting plasmacytoid dendritic cells (pDCs), inducing type I interferons (IFNs) and promoting AAA in DPPI-deficient mice. Conversely, depletion of pDCs or blockade of type I IFNs suppresses experimental AAA. Moreover, we find an abundance of human cathelicidin peptide, a 37 amino acid sequence starting with 2 leucines and the human orthologue of cathelicidin-related antimicrobial peptide, in the vicinity of pDCs in human AAA tissues. Increased type I IFN mRNA expression is observed in human AAA tissues and circulating IFN-&agr; is detected in ≈50% of the AAA sera examined. Conclusions—These results suggest that neutrophil protease–mediated NET release contributes to elastase-induced AAA through pDC activation and type I IFN production. These findings increase our understanding of the pathways underlying AAA inflammatory responses and suggest that limiting NET, pDC, and type I IFN activities may suppress aneurysm progression.

Anti-Mouse Properdin TSR 5/6 Monoclonal Antibodies Block Complement Alternative Pathway-dependent Pathogenesis

The complement alternative pathway (AP) is a major contributor to a broad and growing spectrum of diseases that includes age-related macular degeneration, atypical hemolytic uremic syndrome, and preeclampsia. As a result, there is much interest in the therapeutic disruption of AP activity. Properdin, the only positive regulator of the AP, is a particularly promising AP target. Several issues need to be clarified before the potential for properdin-directed therapy can be realized. In this report we use a portion of the mouse properdin protein, expressed in a bacterial system, to raise rabbit polyclonal and hamster monoclonal antibodies that block properdin-dependent pathogenesis. These antibodies, when employed with AP-dependent mouse disease models, can help evaluate the feasibility of properdin-directed therapy.

Quantifying progression and regression of thrombotic risk in experimental atherosclerosis

Currently, there are no generally applicable noninvasive methods for defining the relationship between atherosclerotic vascular damage and risk of focal thrombosis. Herein, we demonstrate methods to delineate the progression and regression of vascular damage in response to an atherogenic diet by quantifying the in vivo accumulation of semipermeable 200‐300 nm per‐fluorocarbon core nanoparticles (PFC‐NP) in ApoE null mouse plaques with [19F] magnetic resonance spectroscopy (MRS). Permeability to PFC‐NP remained minimal until 12 weeks on diet, then increased rapidly following 12 weeks, but regressed to baseline within 8 weeks after diet normalization. Markedly accelerated clotting (53.3% decrease in clotting time) was observed in carotid artery preparations of fat‐fed mice subjected to photochemical injury as defined by the time to flow cessation. For all mice on and off diet, an inverse linear relationship was observed between the permeability to PFC‐NP and accelerated thrombosis (P = 0.02). Translational feasibility for quantifying plaque permeability and vascular damage in vivo was demonstrated with clinical 3 T MRI of PFC‐NP accumulating in plaques of atherosclerotic rabbits. These observations suggest that excessive permeability to PFC‐NP may indicate prothrombotic risk in damaged atherosclerotic vasculature, which resolves within weeks after dietary therapy.—Palekar, R. U., Jallouk, A. P., Goette, M. J., Chen, J., Myerson, J. W., Allen, J. S., Akk, A., Yang, L., Tu, Y., Miller, M. J., Pham, C. T. N., Wickline, S. A., Pan, H. Quantifying progression and regression of thrombotic risk in experimental atherosclerosis. FASEB J. 29, 3100‐3109 (2015). www.fasebj.org

Neutrophil Extracellular Traps Enhance Early Inflammatory Response in Sendai Virus-Induced Asthma Phenotype

Paramyxoviral infection in childhood has been linked to a significant increased rate of asthma development. In mice, paramyxoviral infection with the mouse parainfluenza virus type I, Sendai virus (Sev), causes a limited bronchiolitis followed by persistent asthma traits. We have previously shown that the absence of cysteine protease dipeptidyl peptidase I (DPPI) dampened the acute lung inflammatory response and the subsequent asthma phenotype induced by Sev. Adoptive transfer of wild-type neutrophils into DPPI-deficient mice restored leukocyte influx, the acute cytokine response, and the subsequent mucous cell metaplasia that accompanied Sev-induced asthma phenotype. However, the exact mechanism by which DPPI-sufficient neutrophils promote asthma development following Sev infection is still unknown. We hypothesize that neutrophils recruited to the alveolar space following Sev infection elaborate neutrophil extracellular traps (NETs) that propagate the inflammatory cascade, culminating in the eventual asthma phenotype. Indeed, we found that Sev infection was associated with NET formation in the lung and release of cell-free DNA complexed to myeloperoxidase in the alveolar space and plasma that peaked on day 2 post infection. Absence of DPPI significantly attenuated Sev-induced NET formation in vivo and in vitro. Furthermore, concomitant administration of DNase 1, which dismantled NETs, or inhibition of peptidylarginine deiminase 4 (PAD4), an essential mediator of NET formation, suppressed the early inflammatory responses to Sev infection. Lastly, NETs primed bone marrow-derived cells to release cytokines that can amplify the inflammatory cascade.

Contribution of Adipose-Derived Factor D/Adipsin to Complement Alternative Pathway Activation: Lessons from Lipodystrophy

Factor D (FD) is an essential component of the complement alternative pathway (AP). It is an attractive pharmaceutical target because it is an AP-specific protease circulating in blood. Most components of the complement activation pathways are produced by the liver, but FD is highly expressed by adipose tissue. Two critical questions are: 1) to what degree does adipose tissue contribute to circulating FD levels and 2) what quantity of FD is sufficient to maintain a functional AP? To address these issues, we studied a novel mouse strain with complete lipodystrophy (LD), the fld mouse with partial LD, an FD-deficient mouse, and samples from lipodystrophic patients. FD was undetectable in the serum of LD mice, which also showed minimal AP function. Reconstitution with purified FD, serum mixing experiments, and studies of partial LD mice all demonstrated that a low level of serum FD is sufficient for normal AP activity in the mouse system. This conclusion was further supported by experiments in which wild-type adipose precursors were transplanted into LD mice. Our results indicate that almost all FD in mouse serum is derived from adipose tissue. In contrast, FD levels were reduced ∼50% in the sera of patients with congenital generalized LD. Our studies further demonstrate that a relatively small amount of serum FD is sufficient to facilitate significant time-dependent AP activity in humans and in mice. Furthermore, this observation highlights the potential importance of obtaining nearly complete inhibition of FD in treating alternative complement activation in various autoimmune and inflammatory human diseases.