Immune recognition of self nucleic acids driven by endogenous antimicrobial peptides: role in autoimmunity

Innate immune recognition of extracellular host-derived self-DNA and self-RNA is prevented by endosomal seclusion of the Toll-like receptors (TLRs) in the dendritic cells (DCs). However, in psoriasis plasmacytoid dendritic cells have been found to be able to sense self-DNA molecules in complex with the endogenous cationic antimicrobial peptide LL37, which are internalized into the endosomal compartments and thus can access TLR9. We investigated whether this endogenous peptide can also interact with extracellular self-RNA and lead to DC activation. We found that LL37 binds self-RNA as well as self-DNA going into an electrostatic interaction; forms micro-aggregates of nano-scale particles protected from enzymatic degradation and transport it into the endosomal compartments of both plasmacytoid and myeloid dendritic cells. In the plasmacytoid DCs, the self-RNA-LL37 complexes activate TLR7 and like the self-DNA-LL37 complexes, trigger the production of IFN-α in the absence of induction of maturation or production of IL-6 and TNF-α. In contrast to the self-DNA-LL37 complexes, the self-RNA-LL37 complexes are also internalized into the endosomal compartments of myeloid dendritic cells and trigger activation through TLR8, leading to the production of TNF-α and IL-6, and the maturation of the myeloid DCs. Furthermore, we found that these self nucleic acid-LL37 complexes can be found in vivo in the skin lesions of the cutaneous autoimmune disease psoriasis, where they are associated with mature mDCs in situ. On the other hand, in the systemic autoimmune disease systemic lupus erythematosus, self-DNA-LL37 complexes were found to be a constituent of the circulating immune complexes isolated from patient sera. This interaction between the endogenous peptide with the self nucleic acid molecules present in the immune complexes was found to be electrostatic and it confers resistance to enzymatic degradation of the nucleic acid molecules in the immune complexes. Moreover, autoantibodies to these endogenous peptides were found to trigger neutrophil activation and release of neutrophil extracellular traps composed of DNA, which are potential sources of the self nucleic acid-LL37 complexes present in SLE immune complexes. Our results demonstrate that the cationic antimicrobial peptide LL37 drives the innate immune recognition of self nucleic acid molecules through toll-like receptors in human dendritic cells, thus elucidating a pathway for innate sensing of host cell death. This pathway of autoreactivity was found to be pathologically relevant in human autoimmune diseases psoriasis and SLE, and thus this study provides new insights into the mechanisms autoimmune diseases.

Natriuretic peptides and nitric oxide stimulate cGMP synthesis in different cellular compartments.

Cyclic nucleotide-gated (CNG) channels are a family of ion channels activated by the binding of cyclic nucleotides. Endogenous channels have been used to measure cyclic nucleotide signals in photoreceptor outer segments and olfactory cilia for decades. Here we have investigated the subcellular localization of cGMP signals by monitoring CNG channel activity in response to agonists that activate either particulate or soluble guanylyl cyclase. CNG channels were heterologously expressed in either human embryonic kidney (HEK)-293 cells that stably overexpress a particulate guanylyl cyclase (HEK-NPRA cells), or cultured vascular smooth muscle cells (VSMCs). Atrial natriuretic peptide (ANP) was used to activate the particulate guanylyl cyclase and the nitric oxide donor S-nitroso-n-acetylpenicillamine (SNAP) was used to activate the soluble guanylyl cyclase. CNG channel activity was monitored by measuring Ca2+ or Mn2+ influx through the channels using the fluorescent dye, fura-2. We found that in HEK-NPRA cells, ANP-induced increases in cGMP levels activated CNG channels in a dose-dependent manner (0.05-10 nM), whereas SNAP (0.01-100 microM) induced increases in cGMP levels triggered little or no activation of CNG channels (P < 0.01). After pretreatment with 100 microM 3-isobutyl-1-methylxanthine (IBMX), a nonspecific phosphodiesterase inhibitor, ANP-induced Mn2+ influx through CNG channels was significantly enhanced, while SNAP-induced Mn2+ influx remained small. In contrast, we found that in the presence of IBMX, both 1 nM ANP and 100 microM SNAP triggered similar increases in total cGMP levels. We next sought to determine if cGMP signals are compartmentalized in VSMCs, which endogenously express particulate and soluble guanylyl cyclase. We found that 10 nM ANP induced activation of CNG channels more readily than 100 muM SNAP; whereas 100 microM SNAP triggered higher levels of total cellular cGMP accumulation. These results suggest that cGMP signals are spatially segregated within cells, and that the functional compartmentalization of cGMP signals may underlie the unique actions of ANP and nitric oxide.

Alterations in content and localization of defensins in rat ileum and jejunum following ischemia-reperfusion. Specific peptides, in specific places, for specific jobs?

Objective: To determine alterations in quantities and distributions of natural antimicrobials following ischemia-reperfusion injury. We hypothesized that these compounds would be upregulated in areas of small intestine where changes in permeability and cellular disruption were likely and where protective mechanisms would be initiated. Methods: Rats with ischemia-reperfusion underwent superior mesenteric artery clamping and reperfusion. Shams were subjected to laparotomy but no clamping. Ileum and jejunum were harvested and sectioned, and subjected to fluorescence deconvolution microscopy for determinations of content and localization of rat beta defensins, 1, 2, 3; rat neutrophil protein-1; and cathelicidin LL-37. Modeling was performed to determine cellular location of antimicrobials. Results: Ischemia-reperfusion increased neutrophil defensin alpha (RNP-1) in jejunum; rat beta defensin 1 was increased 2-fold in ileal mucosa and slightly reduced in jejunal mucosa; rat beta defensin 2 was reduced by ischemia-reperfusion in ileum, but slightly increased in jejunum; rat beta defensin 3 was concentrated in the muscularis externa and myenteric plexus of the jejunum; ischemia-reperfusion did not alter cathelicidin LL-37 content in the small intestine, although a greater concentration was seen in jejunum compared with ileum. Conclusion: Ischemia-reperfusion injury caused changes in antimicrobial content in defined areas, and these different regulations might reflect the specific roles of jejunum versus ileum.

Eluding antibiotic resistance: capitalizing on antimicrobial peptides interaction with the lipid bilayer

It is widely accepted that the emergence of drug-resistant pathogens is the result of the overuse and misuse of antibiotics. Infectious Disease Society of America, Center for Disease Control and World Health Organization continue to view, with concern, the lack of antibiotics in development, especially those against Gram-negative bacteria. Antimicrobial peptides (AMPs) have been proposed as an alternative to antibiotics due to their selective activity against microbes and minor ability to induce resistance. For example, the Food and Drug Administration approved Daptomycin (DAP) in 2003 for treatment of severe skin infections caused by susceptible Gram-positive organisms. Currently, there are 12 to 15 examples of modified natural and synthetic AMPs in clinical development. But most of these agents are against Gram-positive bacteria. Therefore, there is unmet medical need for antimicrobials used to treat infections caused by Gram-negative bacteria. In this study, we show that a pro-apoptotic peptide predominantly used in cancer therapy, (KLAKLAK)2, is an effective antimicrobial against Gram-negative laboratory strains and clinical isolates. Despite the therapeutic promise, AMPs development is hindered by their susceptibility to proteolysis. Here, we demonstrate that an all-D enantiomer of (KLAKLAK)2, resistant to proteolysis, retains its activity against Gram-negative pathogens. In addition, we have elucidated the specific site and mechanism of action of D(KLAKLAK)2 through a repertoire of whole-cell and membrane-model assays. Although it is considered that development of resistance does not represent an obstacle for AMPs clinical development, strains with decreased susceptibility to these compounds have been reported. Staphylococci resistance to DAP was observed soon after its approval for use and has been linked to alterations of the cell wall (CW) and cellular membrane (CM) properties. Immediately following staphylococcal resistance, Enterococci resistance to DAP was seen, yet the mechanism of resistance in enterococci remains unknown. Our findings demonstrate that, similar to S. aureus, development of DAP-resistance in a vancomycin-resistant E. faecalis isolate is associated with alterations of the CW and properties of the CM. However, the genes linked to these changes in enterococci appear to be different from those described in S. aureus.

APPLICATIONS OF EPHB4 RECEPTOR SPECIFIC PEPTIDES IN TARGETED CANCER IMAGING AND THERAPY

EphB4 receptors, a member of the largest family of receptor tyrosine kinases, are found over-expressed in a variety of tumors cells including glioma cells as well as angiogenic blood vessels. Noninvasive imaging of EphB4 could potentially increase early detection rates, monitor response to therapy directed against EphB4, and improve patient outcomes. Targeted delivery of EphB4 receptor specific peptide conjugated hollow gold nanoshells (HAuNS) into tumors has great potential in cancer imaging and photothermal therapy. In this study, we developed an EphB4 specific peptide named TNYL-RAW and labeled with radioisotope 64Cu and Cy5.5 dye. We also conjugate this specific peptide with hollow gold nanoshells (HAuNS) to evaluate targeted photothermal therapy of cancers. In vitro, 64Cu-DOTA-TNYL- RAW specifically bind to CT26 and PC-3M cells but not to A549 cells. In vivo, Small-animal PET/CT clearly showed the significant uptake of 64Cu-DOTA-TNYL-RAW in CT26 and PC-3M tumors but not in A549 tumors. Furthermore, µPET/CT and near-infrared optical imaging clearly showed the uptake of the dual labeled TNYL-RAW peptide in both U251 and U87 tumors in the brains of nude mice. In U251 tumors, Cy5.5-labeled peptide can bind to EphB4-expressing tumor blood vessels and tumors cells. But in U87 models, dual labeled peptide only could bind to tumor associated blood vessels. Also, Irradiation of PC-3M and CT-26 cell treated with TNYL-PEG-HAuNS nanopatilces with near-infrared (NIR) laser resulted in selective destruction of these cells in vitro. EphB4 targeted TNYL-PEG-HAuNS showed more photothermal killing effect on CT26 tumor model than PEG-HAuNS did. In summary, tumors with overexpression of EphB4 receptors can be noninvasively visualized by micro PET/CT with 64Cu labeled or dual labeled TNYL-RAW peptide. Targeted delivery of TNYL-RAW conjugated HAuNS into tumors can greatly improve the treatment effect of photothermal therapy. The information acquired with this study should be advantageous in improving diagnostics and future applications in photothermal ablation therapy in clinical.

Modulatory effects of bag cell peptides in {\it Aplysia}: Behavioral and electrophysiological studies

Reproductive hormones have effects on the nervous system not directly related to reproductive function. In the rat, for example, luteinizing hormone releasing hormone has dramatic effects on learning and memory. The present work attempts to examine the effects of reproductive hormones on non-reproductive behaviors and the neural loci and mechanisms underlying these effects in Aplysia, an animal whose behaviors, reproductive hormones and neural circuitry have been well characterized.^ In Aplysia, the neurosecretory bag cells release several peptides that are responsible for eliciting egg laying. The effects of these peptides on the defensive tail-siphon withdrawal reflex, as well as sensitization of this reflex, were examined. Sensitization, a simple form of nonassociative learning, refers to the behavioral enhancement of a response to a test stimulus after the presentation of a strong stimulus, that may last minutes (short-term) or days (long-term). An extract of the bag cells (BCE) inhibited the baseline siphon component of the tail-siphon withdrawal reflex and suppressed long-term, but not short-term, sensitization of the reflex. Preliminary experiments suggest that BCE also affects the tail component of the tail-siphon withdrawal reflex.^ To determine the neural mechanisms underlying the inhibition of the baseline reflex, electrophysiological studies were performed using an in vitro analogue of the tail-siphon withdrawal reflex to examine the ability of BCE, as well as the individual bag cell peptides (BCPs), to modulate the circuitry of the reflex. Bag cell extract attenuated the synaptic strength of the monosynaptic connections between tail sensory neurons and tail motor neurons. When individually applied only $\beta$-BCP produced a similar attenuation. This effect of $\beta$-BCP was not dependent on changes in duration of the presynaptic action potential.^ An in vitro analogue of long-term sensitization training was developed to examine the mechanisms by which the BCPs may affect long-term sensitization of the tail-siphon withdrawal reflex. This analogue exhibited both short- and long-term facilitation of the connections between the tail sensory and motor neurons.^ The results of these behavioral and electrophysiological experiments suggest that the BCPs inhibit the tail-siphon withdrawal reflex, at least in part, by modulating the synaptic strength of the connections between the sensory neurons and motor neurons underlying the reflex. One candidate for this effect is $\beta$-BCP. Thus, the peptides which elicit egg laying may also serve other functions such as the inhibition of defensive reflexes. In addition, these experiments raise the possibility that BCPs may exert a long lasting effect ($>$24 hr), suppressing long-term sensitization of the tail-siphon withdrawal reflex. ^

Immunochemical interactions of peptides with site-directed polyclonal immunoglobulin G

The objective of this study was to investigate the immunochemical nature of the polyclonal immune response to the 14mer peptide TINKEDDESPGLYG and to identify interactions among antibodies to more than one epitope. Two groups of rabbits were immunized with the 14mer peptide and a Keyhole Limpet hemocyanin (KLH) carrier, but with KLH attached either to the 14mer's N- or C-terminus. Two approximate epitopes were mapped by an antibody-capture enzyme-linked immunosorbent assay method using antiserum obtained when KLH was oriented on the C-terminus of the 14mer. A precise mapping of the epitopes performed with inhibition enzyme immunoassays (iEIAs) resulted in an N-terminal 6mer epitope TINKED and a C-terminal 10mer epitope EDDESPGLYG. The epitopes overlapped by two amino acids. IEIAs and iEIAs incorporating antibody-blocking peptides indicated that the two anti-epitope antibody fractions did not interfere with one anothers' epitope binding. It was postulated that the anti-TINKED and anti-EDDESPGLYG antibody fractions individually bind their respective hydrophobic epitope "core" region at the N- or C-terminal of peptide TINKEDDESPGLYG, while sharing the two hydrophilic overlap amino acids. This antibody "lap joint" binding interaction can be accomplished by each of the anti-epitope antibodies binding an opposite side of the epitope overlap region in the shallow periphery of its binding site. ^

{\it In vivo\/} induction of cytotoxic T lymphocytes against human immunodeficiency virus type 1 by synthetic viral peptides

Cytotoxic T lymphocytes (CTLs) play an important role in the suppression of initial viremia after acute infection with the human immunodeficiency virus (HIV), the causative agent of acquired immune deficiency syndrome (AIDS). Most HIV-infected individuals attain a high titer of anti-HIV antibodies within weeks of infection; however this antibody-mediated immune response appears not to be protective. In addition, anti-HIV antibodies can be detrimental to the immune response to HIV through enhancement of infection and participating in autoimmune reactions as a result of HIV protein mimicry of self antigens. Thus induction and maintenance of a strong HIV-specific CTL immune response in the absence of anti-HIV antibodies has been proposed to be the most effective means of controlling of HIV infection. Immunization with synthetic peptides representing HIV-specific CTL epitopes provides a way to induce specific CTL responses, while avoiding stimulation of anti-HIV antibody. This dissertation examines the capacity of synthetic peptides from the V3 loop region of the gp120 envelope protein from several different strain of HIV-1 to induce HIV-specific, MHC-restricted CD8$\sp+$ CTL response in vivo in a mouse model. Seven synthetic peptides representative of sequences found throughout North America, Europe, and Central Africa have been shown to prime CTLs in vivo. In the case of the MN strain of HIV-1, a 13 amino acid sequence defining the epitope is most efficient for optimal induction of specific CTL, whereas eight to nine amino acid sequences that could define the epitope were not immunogenic. In addition, synthesis of peptides with specific amino acid substitutions that are important for either MHC binding or T cell receptor recognition resulted in peptides that exhibited increased immunogenicity and induced CTLs that displayed altered specificity. V3 loop peptides from HIV-1 MN, SC, and Z321 induced a CTL population that was broadly cross-reactive against strains of HIV-1 found throughout the world. This research confirms the potential efficacy of using synthetic peptides for in vivo immunization to induce HIV-specific CTL-mediated responses and provides a basis for further research into development of synthetic peptide-based vaccines. ^