A phase 2a trial investigating ninerafaxstat – a novel cardiac mitotrope for the treatment of diabetic cardiomyopathy (IMPROVE-DiCE)

Background

Type 2 diabetes (T2D) is a significant, independent contributor to the development of heart failure (HF), driven by energetic, metabolic, structural and functional myocardial changes. The T2D heart is characterised by over-reliance on fatty acid utilisation, shows reduced glucose oxidation and inhibition of pyruvate dehydrogenase (PDH). This results in a diminished myocardial energy reserve and blunted adenosine triphosphate (ATP) generation as well as cardiac steatosis, contributing to lipotoxicity, and diastolic dysfunction.

Purpose

We assessed the effects of ninerafaxstat – a novel cardiac mitotrope designed to shift myocardial substrate utilisation in favour of glucose and thus, restore myocardial energy homeostasis – on cardiac metabolism & diastolic function in patients with T2D and obesity.

Methods

In this open-label, mechanistic phase 2a trial, we enrolled 21 patients with T2D & obesity (HbA1c median 7.0% (IQR 6.6, 7.8), weight 97kg (90, 102)) and subsequently treated them with 200mg ninerafaxstat twice daily for 4 or 8 weeks; (Fig. 1). Cardiac metabolism and function were assessed pre- & post-treatment using magnetic resonance imaging (MRI), 31P-, 1H- and, in a subset of n=9, hyperpolarized [1-13C]pyruvate MR spectroscopy.

Results

T2D patients at baseline presented with impaired myocardial energetics with a markedly reduced PCr/ATP (1.6 [1.4, 2.1]), myocardial steatosis (myocardial triglycerides 2.2% [1.5, 3.2]) left ventricular (LV) hypertrophy (LV mass 130g [98, 152]), and diastolic dysfunction (peak diastolic strain rate 0.86 1/s [0.82, 1.06]). Ninerafaxstat significantly improved myocardial energetics (PCr/ATP median by 32%, p<0.01), reduced myocardial triglyceride content (by 34%, p=0.03) and improved LV diastolic function (peak circumferential diastolic strain rate by 10%, peak LV filling rate by 11%, both p<0.05) (Fig. 2). PDH flux was increased in 7/9 subjects (mean 45%, p=0.08), consistent with improved glucose utilisation. Left ventricular volumes and mass, heart rate and blood pressure remained unchanged.

Conclusions

Treatment with ninerafaxstat significantly improves myocardial energetics, reduces myocardial steatosis and improves diastolic function in patients with T2D and obesity.

Funding Acknowledgement

Type of funding sources: Private company. Main funding source(s): Imbria Pharmaaceuticals

Impaired myocardial energetics limits cardiac functional reserve and leads to exercise-induced pulmonary congestion in heart failure with preserved ejection fraction

Background

Abnormal cardiac mitochondrial function and energetics may be a unifying feature in the pathogenesis of heart failure with preserved ejection fraction (HFpEF). Transient pulmonary congestion during exercise is emerging as an important determinant of reduced exercise capacity and symptoms in patients with HFpEF.

Purpose

We sought to determine if impaired myocardial energetics limits cardiac exercise reserve and leads to exercise-induced pulmonary congestion in HFpEF.

Methods

42 patients across the spectrum of diastolic dysfunction and HFpEF (controls n=10; type 2 diabetes (T2DM) n=9; HFpEF n=14; severe diastolic dysfunction due to cardiac amyloid n=9) (Fig. 1a) underwent assessment of cardiac energetics (myocardial phosphocreatine to adenosine triphosphate ratio, PCr/ATP) and function using cardiovascular magnetic resonance (CMR) imaging and echocardiography, and lung-water using a novel pulmonary proton-density MR sequence. Studies were performed at rest and during exercise (20W for 6 minutes) using a CMR-ergometer.

Results

Paralleling the stepwise decline in diastolic function across the groups (E/e' ratio, p<0.0001) was an increase in NT-pro BNP (p<0.0001, Fig. 1b) and reduction in PCr/ATP (control 2.00 [1.86,2.15], T2DM 1.71 [1.61,1.91], HFpEF 1.66 [1.44,1.89], amyloid 1.30 [1.16,1.53], p<0.0001, Fig. 1c). During exercise, there was progressive blunting of left ventricular (LV) diastolic filling (p<0.0001) (Fig. 2a-b), left atrial (LA) dilatation (p<0.0001), failure of RVEF augmentation (p=0.003), RV-PA uncoupling (RV stroke volume to end-systolic volume (SV/ESV) ratio, p=0.0002), and right atrial (RA) dilatation (p<0.0001) across the groups (Fig. 2b). LV diastolic filling (r 0.41, p=0.008), LA dilatation (r −0.35, p=0.03), RVEF augmentation (r 0.46, p=0.003), RV-PA uncoupling (r 0.36, p=0.02), and RA dilatation (r −0.68, p<0.001) during exercise were strongly linked with impaired myocardial energetics (Fig. 2b).

The novel pulmonary proton-density sequence provided images that scaled linearly with water content (validated using a water-doped sponge phantom; r 0.98, p<0.0001), and revealed a progressive increase in lung water signal/pulmonary congestion (Fig. 2c) post-exercise (p<0.0001) across the groups (controls: +0.25% [−1.8, 3.1], p=0.82; T2DM: +0.8% [−1.7, 1.9], p=0.82; HFpEF: +4.4% [0.5, 6.4], p=0.002; amyloid: +6.4% [3.3, 10.0], p=0.004). Pulmonary congestion was associated with impaired LV diastolic filling (r −0.32, p=0.04), RV-PA uncoupling (r −0.39, p=0.01) and RA dilatation (r 0.4, p=0.01) during exercise, and impaired myocardial energetics (r −0.36, p=0.02).

Conclusion

A gradient of myocardial energetic deficit exists across the spectrum of HFpEF. This energetic deficit is related to markedly abnormal cardiac exercise responses, which leads to transient pulmonary congestion. The findings support an energetic basis for impaired cardiac reserve and exercise-induced pulmonary congestion in HFpEF.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): British Heart Foundation Baseline clinical and CMR parametersExercise cardiopulmonary parameters

The intrinsically disordered protein LEA7 from Arabidopsis thaliana protects the isolated enzyme lactate dehydrogenase and enzymes in a soluble leaf proteome during freezing and drying

The accumulation of Late Embryogenesis Abundant (LEA) proteins in plants is associated with tolerance against stresses such as freezing and desiccation. Two main functions have been attributed to LEA proteins: membrane stabilization and enzyme protection. We have hypothesized previously that LEA7 from Arabidopsis thaliana may stabilize membranes because it interacts with liposomes in the dry state. Here we show that LEA7, contrary to this expectation, did not stabilize liposomes during drying and rehydration. Instead, it partially preserved the activity of the enzyme lactate dehydrogenase (LDH) during drying and freezing. Fourier-transform infrared (FTIR) spectroscopy showed no evidence of aggregation of LDH in the dry or rehydrated state under conditions that lead to complete loss of activity. To approximate the complex influence of intracellular conditions on the protective effects of a LEA protein in a convenient in-vitro assay, we measured the activity of two Arabidopsis enzymes (glucose-6-P dehydrogenase and ADP-glucose pyrophosphorylase) in total soluble leaf protein extract (Arabidopsis soluble proteome, ASP) after drying and rehydration or freezing and thawing. LEA7 partially preserved the activity of both enzymes under these conditions, suggesting its role as an enzyme protectant in vivo. Further FTIR analyses indicated the partial reversibility of protein aggregation in the dry ASP during rehydration. Similarly, aggregation in the dry ASP was strongly reduced by LEA7. In addition, mixtures of LEA7 with sucrose or verbascose reduced aggregation more than the single additives, presumably through the effects of the protein on the H-bonding network of the sugar glasses.

Functional characterization of selected LEA proteins from Arabidopsis thaliana in yeast and in vitro

Expression of eight LEA genes enhanced desiccation tolerance in yeast, including two LEA_2 genes encoding atypical, stably folded proteins. The recombinant proteins showed enzyme, but not membrane protection during drying. To screen for possible functions of late embryogenesis abundant (LEA) proteins in cellular stress tolerance, 15 candidate genes from six Arabidopsis thaliana LEA protein families were expressed in Saccharomyces cerevisiae as a genetically amenable eukaryotic model organism. Desiccation stress experiments showed that eight of the 15 LEA proteins significantly enhanced yeast survival. While none of the proteins belonging to the LEA_1, LEA_5 or AtM families provided protection to yeast cells, two of three LEA_2 proteins, all three LEA_4 proteins and three of four dehydrins were effective. However, no significantly enhanced tolerance toward freezing, salt, osmotic or oxidative stress was observed. While most LEA proteins are highly hydrophilic and intrinsically disordered, LEA_2 proteins are "atypical", since they are more hydrophobic and possess a stable folded structure in solution. Because nothing was known about the functional properties of LEA_2 proteins, we expressed the three Arabidopsis proteins LEA1, LEA26 and LEA27 in Escherichia coli. The bacteria expressed all three proteins in inclusion bodies from which they could be purified and refolded. Correct folding was ascertained by Fourier transform Infrared (FTIR) spectroscopy. None of the proteins was able to stabilize liposomes during freezing or drying, but they were all able to protect the enzyme lactate dehydrogenase (LDH) from inactivation during freezing. Significantly, only LEA1 and LEA27, which also protected yeast cells during drying, were able to stabilize LDH during desiccation and subsequent rehydration.

LEA polypeptide profiling of recalcitrant and orthodox legume seeds reveals ABI3-regulated LEA protein abundance linked to desiccation tolerance

In contrast to orthodox seeds that acquire desiccation tolerance during maturation, recalcitrant seeds are unable to survive drying. These desiccation-sensitive seeds constitute an interesting model for comparative analysis with phylogenetically close species that are desiccation tolerant. Considering the importance of LEA (late embryogenesis abundant) proteins as protective molecules both in drought and in desiccation tolerance, the heat-stable proteome was characterized in cotyledons of the legume Castanospermum australe and it was compared with that of the orthodox model legume Medicago truncatula. RNA sequencing identified transcripts of 16 homologues out of 17 LEA genes for which polypeptides are detected in M. truncatula seeds. It is shown that for 12 LEA genes, polypeptides were either absent or strongly reduced in C. australe cotyledons compared with M. truncatula seeds. Instead, osmotically responsive, non-seed-specific dehydrins accumulated to high levels in the recalcitrant cotyledons compared with orthodox seeds. Next, M. truncatula mutants of the abscisic acid insensitive3 (ABI3) gene were characterized. Mature Mtabi3 seeds were found to be desiccation sensitive when dried below a critical water content of 0.4 g H2O g DW(-1). Characterization of the LEA proteome of the Mtabi3 seeds revealed a subset of LEA proteins with severely reduced abundance that were also found to be reduced or absent in C. australe cotyledons. Transcripts of these genes were indeed shown to be ABI3 responsive. The results highlight those LEA proteins that are critical to desiccation tolerance and suggest that comparable regulatory pathways responsible for their accumulation are missing in both desiccation-sensitive genotypes, revealing new insights into the mechanistic basis of the recalcitrant trait in seeds.

Temporal profiling of the heat-stable proteome during late maturation of Medicago truncatula seeds identifies a restricted subset of late embryogenesis abundant proteins associated with longevity

Developing seeds accumulate late embryogenesis abundant (LEA) proteins, a family of intrinsically disordered and hydrophilic proteins that confer cellular protection upon stress. Many different LEA proteins exist in seeds, but their relative contribution to seed desiccation tolerance or longevity (duration of survival) is not yet investigated. To address this, a reference map of LEA proteins was established by proteomics on a hydrophilic protein fraction from mature Medicago truncatula seeds and identified 35 polypeptides encoded by 16 LEA genes. Spatial and temporal expression profiles of the LEA polypeptides were obtained during the long maturation phase during which desiccation tolerance and longevity are sequentially acquired until pod abscission and final maturation drying occurs. Five LEA polypeptides, representing 6% of the total LEA intensity, accumulated upon acquisition of desiccation tolerance. The gradual 30-fold increase in longevity correlated with the accumulation of four LEA polypeptides, representing 35% of LEA in mature seeds, and with two chaperone-related polypeptides. The majority of LEA polypeptides increased around pod abscission during final maturation drying. The differential accumulation profiles of the LEA polypeptides suggest different roles in seed physiology, with a small subset of LEA and other proteins with chaperone-like functions correlating with desiccation tolerance and longevity.

Influence of drying on the secondary structure of intrinsically disordered and globular proteins

Circular dichroism (CD) spectroscopy of five Arabidopsis late embryogenesis abundant (LEA) proteins constituting the plant specific families LEA_5 and LEA_6 showed that they are intrinsically disordered in solution and partially fold during drying. Structural predictions were comparable to these results for hydrated LEA_6, but not for LEA_5 proteins. FTIR spectroscopy showed that verbascose, but not sucrose, strongly affected the structure of the dry proteins. The four investigated globular proteins were only mildly affected by drying in the absence, but strongly in the presence of sugars. These data highlight the larger structural flexibility of disordered compared to globular proteins and the impact of sugars on the structure of both disordered and globular proteins during drying.

Structural transitions in the intrinsically disordered plant dehydration stress protein LEA7 upon drying are modulated by the presence of membranes

Dehydration stress-related late embryogenesis abundant (LEA) proteins have been found in plants, invertebrates and bacteria. Most LEA proteins are unstructured in solution, but some fold into amphipathic α-helices during drying. The Pfam LEA_4 (Group 3) protein LEA7 from the higher plant Arabidopsis thaliana was predicted to be 87% α-helical, while CD spectroscopy showed it to be largely unstructured in solution and only 35% α-helical in the dry state. However, the dry protein contained 15% β-sheets. FTIR spectroscopy revealed the β-sheets to be largely due to aggregation. β-Sheet content was reduced and α-helix content increased when LEA7 was dried in the presence of liposomes with secondary structure apparently influenced by lipid composition. Secondary structure was also affected by the presence of membranes in the fully hydrated state. A temperature-induced increase in the flexibility of the dry protein was also only observed in the presence of membranes. Functional interactions of LEA7 with membranes in the dry state were indicated by its influence on the thermotropic phase transitions of the lipids and interactions with the lipid headgroup phosphates.

Interaction of two intrinsically disordered plant stress proteins (COR15A and COR15B) with lipid membranes in the dry state

COR15A and COR15B form a tandem repeat of highly homologous genes in Arabidopsis thaliana. Both genes are highly cold induced and the encoded proteins belong to the Pfam LEA_4 group (group 3) of the late embryogenesis abundant (LEA) proteins. Both proteins were predicted to be intrinsically disordered in solution. Only COR15A has previously been characterized and it was shown to be localized in the soluble stroma fraction of chloroplasts. Ectopic expression of COR15A in Arabidopsis resulted in increased freezing tolerance of both chloroplasts after freezing and thawing of intact leaves and of isolated protoplasts frozen and thawed in vitro. In the present study we have generated recombinant mature COR15A and COR15B for a comparative study of their structure and possible function as membrane protectants. CD spectroscopy showed that both proteins are predominantly unstructured in solution and mainly alpha-helical after drying. Both proteins showed similar effects on the thermotropic phase behavior of dry liposomes. A decrease in the gel to liquid-crystalline phase transition temperature depended on both the unsaturation of the fatty acyl chains and lipid headgroup structure. FTIR spectroscopy indicated no strong interactions between the proteins and the lipid phosphate and carbonyl groups, but significant interactions with the galactose headgroup of the chloroplast lipid monogalactosyldiacylglycerol. These findings were rationalized by modeling the secondary structure of COR15A and COR15B. Helical wheel projection indicated the presence of amphipathic alpha-helices in both proteins. The helices lacked a clear separation of positive and negative charges on the hydrophilic face, but contained several hydroxylated amino acids.

MtPM25 is an atypical hydrophobic late embryogenesis-abundant protein that dissociates cold and desiccation-aggregated proteins

Late embryogenesis-abundant (LEA) proteins are one of the components involved in desiccation tolerance (DT) by maintaining cellular structures in the dry state. Among them, MtPM25, a member of the group 5 is specifically associated with DT in Medicago truncatula seeds. Its function is unknown and its classification as a LEA protein remains elusive. Here, evidence is provided that MtPM25 is a hydrophobic, intrinsically disordered protein that shares the characteristics of canonical LEA proteins. Screening protective activities by testing various substrates against freezing, heating and drying indicates that MtPM25 is unable to protect membranes but able to prevent aggregation of proteins during stress. Prevention of aggregation was also found for the water soluble proteome of desiccation-sensitive radicles. This inhibition was significantly higher than that of MtEM6, one of the most hydrophilic LEA protein associated with DT. Moreover, when added after the stress treatment, MtPM25 is able to rapidly dissolve aggregates in a non-specific manner. Sorption isotherms show that when it is unstructured, MtPM25 absorbs up to threefold more water than MtEM6. MtPM25 is likely to act as a protective molecule during drying and plays an additional role as a repair mechanism compared with other LEA proteins.

LEA (late embryogenesis abundant) proteins and their encoding genes in Arabidopsis thaliana

BACKGROUND

LEA (late embryogenesis abundant) proteins have first been described about 25 years ago as accumulating late in plant seed development. They were later found in vegetative plant tissues following environmental stress and also in desiccation tolerant bacteria and invertebrates. Although they are widely assumed to play crucial roles in cellular dehydration tolerance, their physiological and biochemical functions are largely unknown.

RESULTS

We present a genome-wide analysis of LEA proteins and their encoding genes in Arabidopsis thaliana. We identified 51 LEA protein encoding genes in the Arabidopsis genome that could be classified into nine distinct groups. Expression studies were performed on all genes at different developmental stages, in different plant organs and under different stress and hormone treatments using quantitative RT-PCR. We found evidence of expression for all 51 genes. There was only little overlap between genes expressed in vegetative tissues and in seeds and expression levels were generally higher in seeds. Most genes encoding LEA proteins had abscisic acid response (ABRE) and/or low temperature response (LTRE) elements in their promoters and many genes containing the respective promoter elements were induced by abscisic acid, cold or drought. We also found that 33% of all Arabidopsis LEA protein encoding genes are arranged in tandem repeats and that 43% are part of homeologous pairs. The majority of LEA proteins were predicted to be highly hydrophilic and natively unstructured, but some were predicted to be folded.

CONCLUSION

The analyses indicate a wide range of sequence diversity, intracellular localizations, and expression patterns. The high fraction of retained duplicate genes and the inferred functional diversification indicate that they confer an evolutionary advantage for an organism under varying stressful environmental conditions. This comprehensive analysis will be an important starting point for future efforts to elucidate the functional role of these enigmatic proteins.

LEA (late embryogenesis abundant) proteins and their encoding genes in Arabidopsis thaliana

Background

LEA (late embryogenesis abundant) proteins have first been described about 25 years ago as accumulating late in plant seed development. They were later found in vegetative plant tissues following environmental stress and also in desiccation tolerant bacteria and invertebrates. Although they are widely assumed to play crucial roles in cellular dehydration tolerance, their physiological and biochemical functions are largely unknown.

Results

We present a genome-wide analysis of LEA proteins and their encoding genes in Arabidopsis thaliana. We identified 51 LEA protein encoding genes in the Arabidopsis genome that could be classified into nine distinct groups. Expression studies were performed on all genes at different developmental stages, in different plant organs and under different stress and hormone treatments using quantitative RT-PCR. We found evidence of expression for all 51 genes. There was only little overlap between genes expressed in vegetative tissues and in seeds and expression levels were generally higher in seeds. Most genes encoding LEA proteins had abscisic acid response (ABRE) and/or low temperature response (LTRE) elements in their promoters and many genes containing the respective promoter elements were induced by abscisic acid, cold or drought. We also found that 33% of all Arabidopsis LEA protein encoding genes are arranged in tandem repeats and that 43% are part of homeologous pairs. The majority of LEA proteins were predicted to be highly hydrophilic and natively unstructured, but some were predicted to be folded.

Conclusion

The analyses indicate a wide range of sequence diversity, intracellular localizations, and expression patterns. The high fraction of retained duplicate genes and the inferred functional diversification indicate that they confer an evolutionary advantage for an organism under varying stressful environmental conditions. This comprehensive analysis will be an important starting point for future efforts to elucidate the functional role of these enigmatic proteins.

LEA (late embryogenesis abundant) proteins and their encoding genes in Arabidopsis thaliana

BACKGROUND

LEA (late embryogenesis abundant) proteins have first been described about 25 years ago as accumulating late in plant seed development. They were later found in vegetative plant tissues following environmental stress and also in desiccation tolerant bacteria and invertebrates. Although they are widely assumed to play crucial roles in cellular dehydration tolerance, their physiological and biochemical functions are largely unknown.

RESULTS

We present a genome-wide analysis of LEA proteins and their encoding genes in Arabidopsis thaliana. We identified 51 LEA protein encoding genes in the Arabidopsis genome that could be classified into nine distinct groups. Expression studies were performed on all genes at different developmental stages, in different plant organs and under different stress and hormone treatments using quantitative RT-PCR. We found evidence of expression for all 51 genes. There was only little overlap between genes expressed in vegetative tissues and in seeds and expression levels were generally higher in seeds. Most genes encoding LEA proteins had abscisic acid response (ABRE) and/or low temperature response (LTRE) elements in their promoters and many genes containing the respective promoter elements were induced by abscisic acid, cold or drought. We also found that 33% of all Arabidopsis LEA protein encoding genes are arranged in tandem repeats and that 43% are part of homeologous pairs. The majority of LEA proteins were predicted to be highly hydrophilic and natively unstructured, but some were predicted to be folded.

CONCLUSION

The analyses indicate a wide range of sequence diversity, intracellular localizations, and expression patterns. The high fraction of retained duplicate genes and the inferred functional diversification indicate that they confer an evolutionary advantage for an organism under varying stressful environmental conditions. This comprehensive analysis will be an important starting point for future efforts to elucidate the functional role of these enigmatic proteins.

The role of raffinose in the cold acclimation response ofArabidopsis thaliana

In many plants raffinose family oligosaccharides are accumulated during cold acclimation. The contribution of raffinose accumulation to freezing tolerance is not clear. Here, we investigated whether synthesis of raffinose is an essential component for acquiring frost tolerance. We created transgenic lines of Arabidopsis thaliana accessions Columbia-0 and Cape Verde Islands constitutively overexpressing a galactinol synthase (GS) gene from cucumber. GS overexpressing lines contained up to 20 times as much raffinose as the respective wild-type under non-acclimated conditions and up to 2.3 times more after 14 days of cold acclimation at 4 degrees C. Furthermore, we used a mutant carrying a knockout of the endogenous raffinose synthase (RS) gene. Raffinose was completely absent in this mutant. However, neither the freezing tolerance of non-acclimated leaves, nor their ability to cold acclimate were influenced in the RS mutant or in the GS overexpressing lines. We conclude that raffinose is not essential for basic freezing tolerance or for cold acclimation of A. thaliana.