Persistence of exon 2 skipping and dystrophin expression at 18 months after U7snRNA-mediated therapy in the Dup2 mouse model.

Duchenne muscular dystrophy (DMD) is a progressive X-linked disease caused by mutations in the DMD gene that prevent the expression of a functional dystrophin protein. Exon duplications represent 6%-11% of mutations, and duplications of exon 2 (Dup2) are the most common (∼11%) of duplication mutations. An exon-skipping strategy for Dup2 mutations presents a large therapeutic window. Skipping one exon copy results in full-length dystrophin expression, whereas skipping of both copies (Del2) activates an internal ribosomal entry site (IRES) in exon 5, inducing the expression of a highly functional truncated dystrophin isoform. We have previously confirmed the therapeutic efficacy of AAV9.U7snRNA-mediated skipping in the Dup2 mouse model and showed the absence of off-target splicing effects and lack of toxicity in mice and nonhuman primates. Here, we report long-term dystrophin expression data following the treatment of 3-month-old Dup2 mice with the scAAV9.U7.ACCA vector. Significant exon 2 skipping and robust dystrophin expression in the muscles and hearts of treated mice persist at 18 months after treatment, along with the partial rescue of muscle function. These data extend our previous findings and show that scAAV9.U7.ACCA provides long-term protection by restoring the disrupted dystrophin reading frame in the context of exon 2 duplications.

Systemic PPMO-mediated dystrophin expression in the Dup2 mouse model of Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a devastating muscle-wasting disease that arises due to the loss of dystrophin expression, leading to progressive loss of motor and cardiorespiratory function. Four exon-skipping approaches using antisense phosphorodiamidate morpholino oligomers (PMOs) have been approved by the FDA to restore a DMD open reading frame, resulting in expression of a functional but internally deleted dystrophin protein, but in patients with single-exon duplications, exon skipping has the potential to restore full-length dystrophin expression. Cell-penetrating peptide-conjugated PMOs (PPMOs) have demonstrated enhanced cellular uptake and more efficient dystrophin restoration than unconjugated PMOs. In the present study, we demonstrate widespread PPMO-mediated dystrophin restoration in the Dup2 mouse model of exon 2 duplication, representing the most common single-exon duplication among patients with DMD. In this proof-of-concept study, a single intravenous injection of PPMO targeting the exon 2 splice acceptor site induced 45% to 68% exon 2-skipped Dmd transcripts in Dup2 skeletal muscles 15 days post-injection. Muscle dystrophin restoration peaked at 77% to 87% average dystrophin-positive fibers and 41% to 51% of normal signal intensity by immunofluorescence, and 15.7% to 56.8% of normal by western blotting 15 to 30 days after treatment. These findings indicate that PPMO-mediated exon skipping is a promising therapeutic strategy for muscle dystrophin restoration in the context of exon 2 duplications.

Systemic delivery of an AAV9 exon-skipping vector significantly improves or prevents features of Duchenne muscular dystrophy in the Dup2 mouse.

Duchenne muscular dystrophy (DMD) is typically caused by mutations that disrupt the DMD reading frame, but nonsense mutations in the 5' part of the gene induce utilization of an internal ribosomal entry site (IRES) in exon 5, driving expression of a highly functional N-truncated dystrophin. We have developed an AAV9 vector expressing U7 small nuclear RNAs targeting DMD exon 2 and have tested it in a mouse containing a duplication of exon 2, in which skipping of both exon 2 copies induces IRES-driven expression, and skipping of one copy leads to wild-type dystrophin expression. One-time intravascular injection either at postnatal days 0-1 or at 2 months results in efficient exon skipping and dystrophin expression, and significant protection from functional and pathologic deficits. Immunofluorescence quantification showed 33%-53% average dystrophin intensity and 55%-79% average dystrophin-positive fibers in mice treated in adulthood, with partial amelioration of DMD pathology and correction of DMD-associated alterations in gene expression. In mice treated neonatally, dystrophin immunofluorescence reached 49%-85% of normal intensity and 76%-99% dystrophin-positive fibers, with near-complete correction of dystrophic pathology, and these beneficial effects persisted for at least 6 months. Our results demonstrate the robustness, durability, and safety of exon 2 skipping using scAAV9.U7snRNA.ACCA, supporting its clinical use.

Absence of Significant Off-Target Splicing Variation with a U7snRNA Vector Targeting DMD Exon 2 Duplications.

Exon skipping therapies for Duchenne muscular dystrophy that restore an open reading frame can be induced by the use of noncoding U7 small nuclear RNA (U7snRNA) modified by an antisense exon-targeting sequence delivered by an adeno-associated virus (AAV) vector. We have developed an AAV vector (AAV9.U7-ACCA) containing four U7snRNAs targeting the splice donor and acceptor sites of dystrophin exon 2, resulting in highly efficient exclusion of DMD exon 2. We assessed the specificity of splice variation induced by AAV9.U7-ACCA delivery in the Dmd exon 2 duplication (Dup2) mouse model through an unbiased RNA-seq approach. Treatment-related effects on pre-mRNA splicing were quantified using local splicing variation (LSV) analysis. Filtering the transcriptome for differences in treatment-related splicing resulted in only 16 candidate off-target LSVs. Only a single candidate off-target LSV was found in both skeletal and cardiac muscle tissue and occurred at a known variable cassette exon. In contrast, four LSVs represented significant on-target correction of Dmd exon 2 splicing and transcriptome analysis showed correction of known dystrophin-deficient gene dysregulation. We conclude that the absence of off-target splicing induced by treatment with the U7-ACCA vector supports the continued clinical development of this approach.

Lack of Toxicity in Nonhuman Primates Receiving Clinically Relevant Doses of an AAV9.U7snRNA Vector Designed to Induce DMD Exon 2 Skipping.

Therapeutic exon skipping as a treatment for Duchenne muscular dystrophy (DMD) has largely concentrated on the delivery of antisense oligomers to treat out-of-frame exon deletions. Here we report on the preclinical development of an adeno-associated virus (AAV)-encapsidated viral vector containing four copies of the noncoding U7 small nuclear RNA (U7snRNA), each targeted to either the splice donor or the splice acceptor sites of DMD exon 2. We have previously shown that delivery of this vector (scAAV9.U7.ACCA) to the Dup2 mouse model results in expression of full-length dystrophin from wild-type DMD mRNA, as well as an internal ribosome entry site (IRES)-driven isoform translated only in the absence of exon 2 (deletion exon 2 [Del2] mRNA). Here we present the data from a rigorous dose escalation toxicity study in nonhuman primates, encompassing two doses (3 × 1013 and 8 × 1013 vg/kg) and two time points (3 and 6 months postinjection). No evidence for significant toxicity was seen by biochemical, histopathologic, or clinical measures, providing evidence for safety that led to initiation of a first-in-human clinical trial.

Conserved structural and functional aspects of the tripartite motif gene family point towards therapeutic applications in multiple diseases.

The tripartite motif (TRIM) gene family is a highly conserved group of E3 ubiquitin ligase proteins that can establish substrate specificity for the ubiquitin-proteasome complex and also have proteasome-independent functions. While several family members were studied previously, it is relatively recent that over 80 genes, based on sequence homology, were grouped to establish the TRIM gene family. Functional studies of various TRIM genes linked these proteins to modulation of inflammatory responses showing that they can contribute to a wide variety of disease states including cardiovascular, neurological and musculoskeletal diseases, as well as various forms of cancer. Given the fundamental role of the ubiquitin-proteasome complex in protein turnover and the importance of this regulation in most aspects of cellular physiology, it is not surprising that TRIM proteins display a wide spectrum of functions in a variety of cellular processes. This broad range of function and the highly conserved primary amino acid sequence of family members, particularly in the canonical TRIM E3 ubiquitin ligase domain, complicates the development of therapeutics that specifically target these proteins. A more comprehensive understanding of the structure and function of TRIM proteins will help guide therapeutic development for a number of different diseases. This review summarizes the structural organization of TRIM proteins, their domain architecture, common and unique post-translational modifications within the family, and potential binding partners and targets. Further discussion is provided on efforts to target TRIM proteins as therapeutic agents and how our increasing understanding of the nature of TRIM proteins can guide discovery of other therapeutics in the future.

Treatment with Recombinant Human MG53 Protein Increases Membrane Integrity in a Mouse Model of Limb Girdle Muscular Dystrophy 2B.

Limb girdle muscular dystrophy type 2B (LGMD2B) and other dysferlinopathies are degenerative muscle diseases that result from mutations in the dysferlin gene and have limited treatment options. The dysferlin protein has been linked to multiple cellular functions including a Ca2+-dependent membrane repair process that reseals disruptions in the sarcolemmal membrane. Recombinant human MG53 protein (rhMG53) can increase the membrane repair process in multiple cell types both in vitro and in vivo. Here, we tested whether rhMG53 protein can improve membrane repair in a dysferlin-deficient mouse model of LGMD2B (B6.129-Dysftm1Kcam/J). We found that rhMG53 can increase the integrity of the sarcolemmal membrane of isolated muscle fibers and whole muscles in a Ca2+-independent fashion when assayed by a multi-photon laser wounding assay. Intraperitoneal injection of rhMG53 into mice before acute eccentric treadmill exercise can decrease the release of intracellular enzymes from skeletal muscle and decrease the entry of immunoglobulin G and Evans blue dye into muscle fibers in vivo. These results indicate that short-term rhMG53 treatment can ameliorate one of the underlying defects in dysferlin-deficient muscle by increasing sarcolemmal membrane integrity. We also provide evidence that rhMG53 protein increases membrane integrity independently of the canonical dysferlin-mediated, Ca2+-dependent pathway known to be important for sarcolemmal membrane repair.

Lipidomic Adaptations in White and Brown Adipose Tissue in Response to Exercise Demonstrate Molecular Species-Specific Remodeling.

Exercise improves whole-body metabolic health through adaptations to various tissues, including adipose tissue, but the effects of exercise training on the lipidome of white adipose tissue (WAT) and brown adipose tissue (BAT) are unknown. Here, we utilize MS/MSALL shotgun lipidomics to determine the molecular signatures of exercise-induced adaptations to subcutaneous WAT (scWAT) and BAT. Three weeks of exercise training decrease specific molecular species of phosphatidic acid (PA), phosphatidylcholines (PC), phosphatidylethanolamines (PE), and phosphatidylserines (PS) in scWAT and increase specific molecular species of PC and PE in BAT. Exercise also decreases most triacylglycerols (TAGs) in scWAT and BAT. In summary, exercise-induced changes to the scWAT and BAT lipidome are highly specific to certain molecular lipid species, indicating that changes in tissue lipid content reflect selective remodeling in scWAT and BAT of both phospholipids and glycerol lipids in response to exercise training, thus providing a comprehensive resource for future studies of lipid metabolism pathways.

Bioengineering of injectable encapsulated aggregates of pluripotent stem cells for therapy of myocardial infarction.

It is difficult to achieve minimally invasive injectable cell delivery while maintaining high cell retention and animal survival for in vivo stem cell therapy of myocardial infarction. Here we show that pluripotent stem cell aggregates pre-differentiated into the early cardiac lineage and encapsulated in a biocompatible and biodegradable micromatrix, are suitable for injectable delivery. This method significantly improves the survival of the injected cells by more than six-fold compared with the conventional practice of injecting single cells, and effectively prevents teratoma formation. Moreover, this method significantly enhances cardiac function and survival of animals after myocardial infarction, as a result of a localized immunosuppression effect of the micromatrix and the in situ cardiac regeneration by the injected cells.

Role of phosphatidylinositol-4,5-bisphosphate 3-kinase signaling in vesicular trafficking.

Phosphatidylinositol-4,5-bisphosphate 3-kinases (PI3Ks) are regulatory enzymes involved in the generation of lipid species that modulate cellular signaling pathways through downstream effectors to influence a variety of cellular functions. Years of intensive study of PI3Ks have produced a significant body of literature in many areas, including that PI3K can mediate intracellular vesicular trafficking and through these actions contribute to a number of important physiological functions. This review focuses on the crucial roles that PI3K and AKT, a major downstream partner of PI3K, play in the regulation of vesicle trafficking during various forms of vesicular endocytosis and exocytosis.

miR-155 Deletion in Female Mice Prevents Diet-Induced Obesity.

Obesity is a growing epidemic in developed countries. Obese individuals are susceptible to comorbidities, including cardiovascular disease and metabolic disorder. Increasing the ability of adipose tissue to expend excess energy could improve protection from obesity. One promising target is microRNA (miR)-155-5p. We demonstrate that deletion of miR-155 (-5p and -3p) in female mice prevents diet-induced obesity. Body weight gain did not differ between wild-type (WT) and miR-155 knockout (KO) mice fed control diet (CD); however, miR-155 KO mice fed high-fat diet (HFD) gained 56% less body weight and 74% less gonadal white adipose tissue (WAT) than WT mice. Enhanced WAT thermogenic potential, brown adipose tissue differentiation, and/or insulin sensitivity might underlie this obesity resistance. Indeed, miR-155 KO mice on HFD had 21% higher heat release than WT HFD mice. Compared to WT adipocytes, miR-155 KO adipocytes upregulated brown (Ucp1, Cidea, Pparg) and white (Fabp4, Pnpla2, AdipoQ, Fasn) adipogenic genes, and glucose metabolism genes (Glut4, Irs1). miR-155 deletion abrogated HFD-induced adipocyte hypertrophy and WAT inflammation. Therefore, miR-155 deletion increases adipogenic, insulin sensitivity, and energy uncoupling machinery, while limiting inflammation in WAT, which together could restrict HFD-induced fat accumulation. Our results identify miR-155 as a novel candidate target for improving obesity resistance.

Adipocyte reporter assays: application for identification of anti-inflammatory and antioxidant properties of mangosteen xanthones.

SCOPE: Three fluorescence biosensors were developed based on a 3T3-L1 preadipocyte line that stably expressed Nfkb-RE/GFP, Fabp4-P/CFP, and Nrf2-P/YFP fluorescent reporters. We hypothesized that nutraceuticals' inflammatory, adipogenic, and antioxidant status will be identified based on the change in fluorescence in reporter adipocytes. We validated these assays with activators of NFκB, FABP4-regulating peroxisome proliferator activated receptor gamma, NFR2 and, thereafter, tested known and unknown properties of mangostines (MGs), the xanthone metabolites in mangosteen fruit. METHODS AND RESULTS: We validated inflammatory and adipogenic properties of α-MG using an Nfkb-RE/GFP biosensor assay. Next, we identified unique properties of γ-MG, a minor MG xanthone. γ-MG suppressed adipogenesis and expression of adiponectin, but inhibited the Nfkb-RE/GFP reporter and secretion of inflammatory monocyte chemotactic protein 1 as compared to the control adipocytes. We found that the inhibition of adipogenesis and Nfkb-mediated inflammation depends on a dose-dependent reduction of Nrf2 promoter activity by α-MG. The Nrf2 inhibition resulted in the reduced Pparg expression. α-MG did not directly influence Pparg activity in Fabp4-P/CFP adipocytes. CONCLUSION: α-MG-mediated antioxidant response via Nrf2 is a mechanism preventing adipogenesis and inflammation in adipocytes. Combined application of high-throughput biosensors could provide an effective platform for the identification of nutraceuticals and the mechanism of their actions in adipocytes and, potentially, in obese patients.

Air pollution-mediated susceptibility to inflammation and insulin resistance: influence of CCR2 pathways in mice.

BACKGROUND: Epidemiologic and experimental studies support an association between PM2.5 exposure and insulin resistance (IR). Innate immune cell activation has been suggested to play a role in the pathogenesis of these effects. OBJECTIVES: We sought to evaluate the role of CC-chemokine receptor 2 (CCR2) in PM2.5-mediated inflammation and IR. METHODS: Wild-type C57BL/6 and CCR2-/- male mice were fed a high-fat diet and exposed to either concentrated ambient PM2.5 or filtered air for 17 weeks via a whole-body exposure system. We evaluated glucose tolerance and insulin sensitivity. At euthanasia, blood, spleen, and visceral adipose tissue (VAT) were collected, and inflammatory cells were measured using flow cytometry. We used standard immunoblots, immunohistochemical methods, and quantitative PCR (polymerase chain reaction) to assess pathways of interest involving insulin signaling, inflammation, and lipid and glucose metabolism in various organs. Vascular function was assessed using myography. RESULTS: PM2.5 exposure resulted in whole-body IR and increased hepatic lipid accumulation in the liver, which was attenuated in CCR2-/- mice by inhibiting SREBP1c-mediated transcriptional programming, decreasing fatty acid uptake, and suppressing p38 MAPK activity. Abnormal phosphorylation levels of AKT, AMPK in VAT, and adipose tissue macrophage content in wild-type mice were not present in CCR2-/- mice. However, the impaired whole-body glucose tolerance and reduced GLUT-4 in skeletal muscle in response to PM2.5 was not corrected by CCR2 deficiency. CONCLUSIONS: PM2.5 mediates IR by regulating VAT inflammation, hepatic lipid metabolism, and glucose utilization in skeletal muscle via both CCR2-dependent and -independent pathways. These findings provide new mechanistic links between air pollution and metabolic abnormalities underlying IR.

Moderate vitamin A supplementation in obese mice regulates tissue factor and cytokine production in a sex-specific manner.

Vitamin A (vitA) regulates obesity, insulin resistance, inflammation, dyslipidemia and hemostasis through its metabolites retinaldehyde (Rald) and retinoic acid (RA) produced in endogenous enzymatic reactions. Combination of at least 3 of these conditions leads to development of metabolic syndrome (Msyn) and, consequently, type 2 diabetes and/or cardiovascular disease. Although many foods are fortified with vitA, it remains unknown what conditions of Msyn are influenced by moderate dietary vitA supplementation. A family of aldehyde dehydrogenase 1 (Aldh1) enzymes is a key contributor to obesity via sex- and fat depot-specific production of RA in adipose tissue. Therefore, we studied effects of moderate vitamin A supplementation of an obesogenic high-fat (HF) diet (4 IU vitA/g and 20 IU vitA/g HF diet) on multiple conditions and mediators of Msyn in wild-type (WT, C57Bl/6) and Aldh1a1(-/-) mice. We found that mild vitamin A supplementation did not influence obesity, fat distribution, and glucose tolerance in males and females of the same genotype. In contrast, multiplex analysis of bioactive proteins in blood showed moderately increased concentrations (10-15%) of inflammatory IL-18 and MIP-1γ in vitA supplemented vs. control WT males. Marked decrease (28-31%) in concentrations of lymphotactin and tissue factor, a key protein contributing to thrombogenesis during injury, was achieved by vitA supplementation in WT females compared to control WT females. Aldh1a1 deficiency reduced obesity, insulin resistance, suppressed many pro-inflammatory cytokines, and abolished the effects of vitA supplementation seen in WT mice. Our study revealed specific inflammatory and pro-thrombotic proteins in plasma regulated by dietary vitamin A and the critical role of endogenous vitA metabolism in these processes. The sex-specific decrease of plasma tissue factor concentrations by moderate dietary vitA supplementation could potentially reduce pro-thrombotic states in obese females.

Aliskiren effect on plaque progression in established atherosclerosis using high resolution 3D MRI (ALPINE): a double-blind placebo-controlled trial.

BACKGROUND: The renin-angiotensin system is well recognized as a mediator of pathophysiological events in atherosclerosis. The benefits of renin inhibition in atherosclerosis, especially when used in combination with angiotensin-converting enzyme inhibitors/angiotensin receptor blockers (ACEIs/ARBs) are currently not known. We hypothesized that treatment with the renin inhibitor aliskiren in patients with established cardiovascular disease will prevent the progression of atherosclerosis as determined by high-resolution magnetic resonance imaging (MRI) measurements of arterial wall volume in the thoracic and abdominal aortas of high-risk patients with preexisting cardiovascular disease. METHODS AND RESULTS: This was a single-center, randomized, double-blind, placebo-controlled trial in patients with established cardiovascular disease. After a 2-week single-blind placebo phase, patients were randomized to receive either placebo (n=37, mean ± SD age 64.5 ± 8.9 years, 3 women) or 150 mg of aliskiren (n=34, mean ± SD age 63.9 ± 11.5 years, 9 women). Treatment dose was escalated to 300 mg at 2 weeks and maintained during the remainder of the study. Patients underwent dark-blood, 3-dimensional MRI assessment of atherosclerotic plaque in the thoracic and abdominal segments at baseline and on study completion or termination (up to 36 weeks of drug or matching placebo). Aliskiren use resulted in significant progression of aortic wall volume (normalized total wall volume 5.31 ± 6.57 vs 0.15 ± 4.39 mm(3), P=0.03, and percentage wall volume 3.37 ± 2.96% vs 0.97 ± 2.02%, P=0.04) compared with placebo. In a subgroup analysis of subjects receiving ACEI/ARB therapy, atherosclerosis progression was observed only in the aliskiren group, not in the placebo group. CONCLUSIONS: MRI quantification of atheroma plaque burden demonstrated that aliskiren use in patients with preexisting cardiovascular disease resulted in an unexpected increase in aortic atherosclerosis compared with placebo. Although preliminary, these results may have implications for the use of renin inhibition as a therapeutic strategy in patients with cardiovascular disease, especially in those receiving ACEI/ARB therapy. CLINICAL TRIAL REGISTRATION: URL: http://ClinicalTrials.gov Unique identifier: NCT01417104.

Effects of a novel pharmacologic inhibitor of myeloperoxidase in a mouse atherosclerosis model.

Inflammation and oxidative stress play fundamental roles in the pathogenesis of atherosclerosis. Myeloperoxidase has been extensively implicated as a key mediator of inflammatory and redox-dependent processes in atherosclerosis. However, the effect of synthetic myeloperoxidase inhibitors on atherosclerosis has been insufficiently studied. In this study, ApoE(-/-) mice were randomized to low- and high-dose INV-315 groups for 16 weeks on high-fat diet. INV-315 resulted in reduced plaque burden and improved endothelial function in response to acetylcholine. These effects occurred without adverse events or changes in body weight or blood pressure. INV-315 treatment resulted in a decrease in iNOS gene expression, superoxide production and nitrotyrosine content in the aorta. Circulating IL-6 and inflammatory CD11b(+)/Ly6G(low)/7/4(hi) monocytes were significantly decreased in response to INV-315 treatment. Acute pretreatment with INV-315 blocked TNFα-mediated leukocyte adhesion in cremasteric venules and inhibited myeloperoxidase activity. Cholesterol efflux was significantly increased by high-dose INV-315 via ex-vivo reverse cholesterol transport assays. Our results suggest that myeloperoxidase inhibition may exert anti-atherosclerotic effects via inhibition of oxidative stress and enhancement of cholesterol efflux. These findings demonstrate a role for pharmacologic modulation of myeloperoxidase in atherosclerosis.

High-resolution crystal structure of spectrin SH3 domain fused with a proline-rich peptide.

A new chimeric protein, named WT-CIIA, was designed by connecting the proline-rich decapeptide PPPVPPYSAG to the C-terminus of the alpha-spectrin SH3 domain through a natural twelve-residue linker to obtain a single-chain model that would imitate intramolecular SH3-ligand interaction. The crystal structure of this fusion protein was determined at 1.7 Å resolution. The asymmetric unit of the crystal contained two SH3 globules contacting with one PPPVPPY fragment located between them. The domains are related by the two-fold non-crystallographic axis and the ligand lies in two opposite orientations with respect to the conservative binding sites of SH3 domains.

Solution structure and dynamics of the chimeric SH3 domains, SHH- and SHA-"Bergeracs".

Two chimeric proteins, SHcapital EN, Cyrillic and SHA of the "SH3-Bergerac" family (where the beta-turn N47D48 in spectrin SH3 domain was substituted for KITVNGKTYE or KATANGKTYE sequences, respectively), were analyzed by high-resolution NMR to resolve their spatial structures and to analyze their dynamics. Although the presence of a stable beta-hairpin in the region of the insertion was confirmed, the introduced extension of the polypeptide chain in SHcapital EN, Cyrillic (approximately 17%) practically did not affect the total molecule topology. Interestingly, the introduced beta-hairpin had higher mobility in comparison with other protein regions. Finally, we performed a disorder prediction with the PONDR VSL2 algorithm and discovered that the inserted beta-hairpin in both SHH and SHA proteins exhibited significant propensity for intrinsic disorder and therefore for high mobility. In agreement with the experimental data, the predisposition for the increased intramolecular mobility was noticeably higher in SHA.

Structural and thermodynamic studies of Bergerac-SH3 chimeras.

Bergerac-type chimeras of spectrin SH3 were designed by extending a beta-hairpin by eight amino acids so that the extension protruded from the domain body like a "nose" being exposed to the solvent. A calorimetric study of several Bergerac-SH3 variants was carried out over a wide range of pH values and protein concentrations and the three-dimensional structure of one of them, SHH, was determined. X-ray studies confirmed that the nose had a well defined beta-structure whilst the chimera formed a stable tetramer within the crystal unit because of four tightly packed noses. In the pH range of 4-7 the heat-induced unfolding of some chimeras was complex and concentration dependent, whilst at pH values below 3.5, low protein concentrations of all the chimeras studied, including SHH, seemed to obey a monomolecular two-state unfolding model. The best set of data was obtained for the SHA variant, the unfolding heat effects of which were systematically higher than those of the WT protein (about 16.4 kJ/mol at 323 K), which may be close to the upper limit of the enthalpy gain due to 10 residue beta-hairpin folding. At the same time, the chimeras with high nose stability, which, like SHH, have a hydrophobic (IVY) cluster on their surface, showed a lower apparent unfolding heat effect, much closer to that of the WT protein. The possible reasons for this difference are discussed.