Proline dehydrogenase is essential for proline protection against hydrogen peroxide-induced cell death

Proline metabolic reprogramming modulates cardiac remodeling induced by pressure overload in the heart

Metabolic reprogramming is critical in the onset of pressure overload-induced cardiac remodeling. Our study reveals that proline dehydrogenase (PRODH), the key enzyme in proline metabolism, reprograms cardiomyocyte metabolism to protect against cardiac remodeling. We induced cardiac remodeling using transverse aortic constriction (TAC) in both cardiac-specific PRODH knockout and overexpression mice. Our results indicate that PRODH expression is suppressed after TAC. Cardiac-specific PRODH knockout mice exhibited worsened cardiac dysfunction, while mice with PRODH overexpression demonstrated a protective effect. In addition, we simulated cardiomyocyte hypertrophy in vitro using neonatal rat ventricular myocytes treated with phenylephrine. Through RNA sequencing, metabolomics, and metabolic flux analysis, we elucidated that PRODH overexpression in cardiomyocytes redirects proline catabolism to replenish tricarboxylic acid cycle intermediates, enhance energy production, and restore glutathione redox balance. Our findings suggest PRODH as a modulator of cardiac bioenergetics and redox homeostasis during cardiac remodeling induced by pressure overload. This highlights the potential of PRODH as a therapeutic target for cardiac remodeling.

L-Proline: A Promising Tool for Boosting Cryotolerance and Fertilizing Ability of Cryopreserved Sperm in Animals

Sperm cryopreservation technology significantly contributes to the safeguarding of genetic resources, particularly for endangered species, and supports the use of artificial insemination in domestic animals. Therefore, cryopreservation can negatively affect sperm health and function leading to reduce the freezing ability and fertility potential. Therefore, it is essential to prioritize the improvement of cryotolerance in cryopreserved sperm to enhance reproductive efficiency and ensure sustainability in livestock herds. The main reason for sperm dysfunction after thawing may be related to the excessive amount of oxidative stress (OS) produced during cryopreservation. Scientists have different ways for counteracting this OS including the use of plant extracts, enzymes, minerals, anti-freezing proteins, and amino acids. Recently, one such amino acid is L-proline (LP), which has multiple roles such as osmotic and OS defense, nitrogen, and carbon metabolism, as well as cell survival and signaling. LP has been found in seminal plasma and has recently been added to the freezing extender to improve the various post-thaw parameters of sperm. This improvement is related to the ability of LP to reduce the OS, sustain the plasma membrane and to act as an osmoregulatory agent. Moreover, LP can suppress cell apoptosis by modulating intracellular redox in sperm. This review addresses the ongoing research on the addition of L-proline as an osmoregulatory agent in freezing extenders to increase the cryotolerance of animal spermatozoa to freeze-thaw.

Using a metabolomics approach to investigate the sensitivity of a potential Arctic-invader and its Arctic sister-species to marine heatwaves and traditional harvesting disturbances

Coastal species are threatened by fishing practices and changing environmental conditions, such as marine heatwaves (MHW). The mechanisms that confer tolerance to such stressors in marine invertebrates are poorly understood. However, differences in tolerance among different species may be attributed to their geographical distribution. To test the tolerance of species occupying different thermal ranges, we used two closely related bivalves the softshell clam Mya arenaria (Linnaeus, 1758), a cold-temperate invader with demonstrated potential for establishment in the Arctic, and the blunt gaper Mya truncata (Linnaeus, 1758), a native polar species. Clams were subjected to a thermal stress, mimicking a MHW, and harvesting stress in a controlled environment. Seven acute temperature changes (2, 7, 12, 17, 22, 27, and 32 °C) were tested at two harvesting disturbance intensities (with, without). Survival was measured after 12 days and three tissues (gills, mantle, and posterior adductor muscle) collected from surviving individuals for targeted metabolomic profiling. MHW tolerance differed significantly between species: 26.9 °C for M. arenaria and 17.8 °C for M. truncata, with a negligeable effect of harvesting. At the upper thermal limit, M. arenaria displayed a more profound metabolomic remodelling when compared to M. truncata, and this varied greatly between tissue types. Network analysis revealed differences in pathway utilization at the upper MHW limit, with M. arenaria displaying a greater reliance on multiple DNA repair and expression and cell signalling pathways, while M. truncata was limited to fewer pathways. This suggests that M. truncata is ill equipped to cope with warming environments. MHW patterning in the Northwest Atlantic may be a strong predictor of population survival and future range shifts in these two clam species. As polar environments undergo faster rates of warming compared to the global average, M. truncata may be outcompeted by M. arenaria expanding into its native range.

Palmitate induces integrated stress response and lipoapoptosis in trophoblasts

Maternal obesity increases the risk of childhood obesity and programs the offspring to develop metabolic syndrome later in their life. Palmitate is the predominant saturated free fatty acid (FFA) that is transported across the placenta to the fetus. We have recently shown that saturated FFA in the maternal circulation as a result of increased adipose tissue lipolysis in third trimester of pregnancy induces trophoblast lipoapoptosis. Here, we hypothesized that palmitate induces integrated stress response by activating mitogen-activated protein kinases (MAPKs), endoplasmic reticulum (ER) stress and granular stress and lipoapoptosis in trophoblasts. Choriocarcinoma-derived third-trimester placental trophoblast-like cells (JEG-3 and JAR) referred as trophoblasts were exposed to various concentrations of palmitate (PA). Apoptosis was assessed by nuclear morphological changes and caspase 3/7 activity. Immunoblot and immunofluorescence analysis was performed to measure the activation of MAPKs, ER stress and granular stress response pathways. Trophoblasts exposed to pathophysiological concentrations of PA showed a concentration-dependent increase in trophoblast lipoapoptosis. PA induces a caspase-dependent trophoblast lipoapoptosis. Further, PA induces MAPK activation (JNK and ERK) via phosphorylation, and activation of ER stress as evidenced by an increased phosphorylation eIF2α & IRE1α. PA also induces the activation of stress granules formation. Two pro-apoptotic transcriptional mediators of PA-induced trophoblast lipoapoptosis, CHOP and FoxO3 have increased nuclear translocation. Mechanistically, PA-induced JNK is critical for trophoblast lipoapoptosis. However, PA-induced activation of ERK and stress granule formation were shown to be cell survival signals to combat subcellular stress due to PA exposure. In conclusion, PA induces the activation of integrated stress responses, among which small molecule inhibition of JNK demonstrated that activation of JNK is critical for PA-induced trophoblast lipoapoptosis and small molecule activation of stress granule formation significantly prevents PA-induced trophoblast lipoapoptosis.

Proline and Proline Analogues Improve Development of Mouse Preimplantation Embryos by Protecting Them against Oxidative Stress

The culture of embryos in the non-essential amino acid L-proline (Pro) or its analogues pipecolic acid (PA) and L-4-thiazolidine carboxylic acid (L4T) improves embryo development, increasing the percentage that develop to the blastocyst stage and hatch. Staining of 2-cell and 4-cell embryos with tetramethylrhodamine methyl ester and 2',7'-dichlorofluorescein diacetate showed that the culture of embryos in the presence of Pro, or either of these analogues, reduced mitochondrial activity and reactive oxygen species (ROS), respectively, indicating potential mechanisms by which embryo development is improved. Inhibition of the Pro metabolism enzyme, proline oxidase, by tetrahydro-2-furoic-acid prevented these reductions and concomitantly prevented the improved development. The ways in which Pro, PA and L4T reduce mitochondrial activity and ROS appear to differ, despite their structural similarity. Specifically, the results are consistent with Pro reducing ROS by reducing mitochondrial activity while PA and L4T may be acting as ROS scavengers. All three may work to reduce ROS by contributing to the GSH pool. Overall, our results indicate that reduction in mitochondrial activity and oxidative stress are potential mechanisms by which Pro and its analogues act to improve pre-implantation embryo development.

Application of multi-omics combined with bioinformatics techniques to assess salinity stress response and tolerance mechanisms of Pacific oyster (Crassostrea gigas) during depuration

Depuration is a vital stage to ensure the safety of oyster consumption, and salinity had a great impact on the environmental adaptability of oysters, but the underlying molecular mechanism was poorly understood during depuration stage. Here, Crassostrea gigas was depurated for 72 h at different salinity (26, 29, 32, 35, 38 g/L, corresponding to ±20%, ±10% salinity fluctuation away from oyster's production area) and then analyzed by using transcriptome, proteome, and metabolome combined with bioinformatics techniques. The transcriptome showed that the salinity stress led to 3185 differentially expressed genes and mainly enriched in amino acid metabolism, carbohydrate metabolism, lipid metabolism, etc. A total of 464 differentially expressed proteins were screened by the proteome, and the number of up-regulated expression proteins was less than the down-regulated, indicating that the salinity stress would affect the regulation of metabolism and immunity in oysters. 248 metabolites significantly changed in response to depuration salinity stress in oysters, including phosphate organic acids and their derivatives, lipids, etc. The results of integrated omics analysis indicated that the depuration salinity stress induced abnormal metabolism of the citrate cycle (TCA cycle), lipid metabolism, glycolysis, nucleotide metabolism, ribosome, ATP-binding cassette (ABC) transport pathway, etc. By contrast with Pro-depuration, more radical responses were observed in the S38 group. Based on the results, we suggested that the 10% salinity fluctuation was suitable for oyster depuration and the combination of multi-omics analysis could provide a new perspective for the analysis of the mechanism changes.

Effects of Fe2+ addition to sugarcane molasses on poly-γ-glutamic acid production in Bacillus licheniformis CGMCC NO. 23967

BACKGROUND

Poly-γ-glutamic acid (γ-PGA) is biodegradable, water-soluble, environment-friendly, and edible. Consequently, it has a variety of industrial applications. It is crucial to control production cost and increase output for industrial production γ-PGA.

RESULTS

Here γ-PGA production from sugarcane molasses by Bacillus licheniformis CGMCC NO. 23967 was studied in shake-flasks and bioreactors, the results indicate that the yield of γ-PGA could reach 40.668 g/L in a 5L stirred tank fermenter. Further study found that γ-PGA production reached 70.436 g/L, γ-PGA production and cell growth increased by 73.20% and 55.44%, respectively, after FeSO₄·7H₂O was added. Therefore, we investigated the metabolomic and transcriptomic changes following FeSO₄·7H₂O addition. This addition resulted in increased abundance of intracellular metabolites, including amino acids, organic acids, and key TCA cycle intermediates, as well as upregulation of the glycolysis pathway and TCA cycle.

CONCLUSIONS

These results compare favorably with those obtained from glucose and other forms of biomass feedstock, confirming that sugarcane molasses can be used as an economical substrate without any pretreatment. The addition of FeSO₄·7H₂O to sugarcane molasses may increase the efficiency of γ-PGA production in intracellular.

Yield, quality and physiological variation of strawberry in response to irrigation regimes and exogenous proline with a cost benefit analysis

Strawberry (Fragaria × ananassa Duch.) production is a major aspect of the agricultural economy in Turkey's Mediterranean region, offering high rates of employment and farm revenue. The effects of treatment of the exogenous amino acid on yield, quality, and physiological diversity for strawberry production was analyzed considering the economic aspects. To achieve this, 4 different irrigation regimes (IR (irrigation) 125, IR100, IR75, IR50) with proline treatment was tested. The total berry yield, photosynthesis and leaf water potential (LWP) significantly decreased as irrigation application rates declined. The IR125 treatment with proline (PIR125) produced the highest overall berry production. The use of proline significantly increased berry production by 23%. Exogenous proline generated 3.5 kg/1 m³ greater yields than control in terms of irrigation water use efficiency (IWUE). Under the IR50 conditions, the treatment of proline yielded a 32% higher than the control. Moreover, proline significantly increased fruit soluble solids content (SSC) by 6.4%. The production system achieves the highest cost-benefit ratio (CBR) under PIR125 whereas the lowest cost-benefit ratio under IR50. When each scenario was considered at individually, it was evident that the more water used the more efficient high tunnel strawberry production. The fact that proline generated an increase in CBR in all four irrigation regimes proves this amino acid's economic effectiveness. As a result, PIR125 is recommended for the highest efficiency and CBR in Mediterranean environment. However, it has been discovered that using proline to alleviate this problem in areas where water is limited could be quite helpful.

Environmental Influences on the Relation between the 22q11.2 Deletion Syndrome and Mental Health: A Literature Review

22q11.2 deletion syndrome (22q11DS) is a clinically heterogeneous genetic syndrome, associated with a wide array of neuropsychiatric symptoms. The clinical presentation is likely to be influenced by environmental factors, yet little is known about this. Here, we review the available research literature on the role of the environment in 22q11DS. We find that within-patient design studies have mainly investigated the role of parental factors, stress, and substance use, reporting significant effects of these factors on the clinical profile. Case-control studies have been less successful, with almost no reports of significant moderating effects of the environment. We go on to hypothesize which specific environmental measures are most likely to interact with the 22q11 deletion, based on the genes in this region and their involvement in molecular pathways. We end by discussing potential reasons for the limited findings so far, including modest sample sizes and limited availability of environmental measures, and make recommendations how to move forward.

Integrated physiological and transcriptional dissection reveals the core genes involving nutrient transport and osmoregulatory substance biosynthesis in allohexaploid wheat seedlings under salt stress

BACKGROUND

Soil salinization has become a global problem restricting the seed yield and quality of crops, including wheat (Triticum aestivum L.). Salinity significantly alters plant morphology and severely disrupts physiological homeostasis. Salt tolerance of wheat has been widely studied whereas core ion transporters responsive to salt stress remain elusive.

RESULTS

In this study, the wheat seedlings were subjected to salinity toxicity for morpho-physiological and transcriptomic analysis of wheat salt tolerance. There was a inversely proportional relationship between salt concentrations and morpho-physiological parameters. Under the condition of 100 mM NaCl, the H₂O₂, O₂^-, MDA content and membrane permeability were significantly increased whereas the chlorophyll content was markedly decreased. Under salt stress, a larger proportion of Na⁺ was partitioned in the roots than in the shoots, which had a lower Na⁺/K⁺ ratio and proline content. Salt stress also obviously affected the homeostasis of other cations. Genome-wide transcriptomic analysis showed that a total of 2,807 and 5,570 differentially expressed genes (DEGs) were identified in the shoots and roots, respectively. Functionality analysis showed that these DEGs were mainly enriched in the KEGG pathways related to carbon metabolism, phenylalanine, and amino acid biosynthesis, and were primarily enriched in the GO terms involving proline metabolism and redox processes. The Na⁺ transporter genes were upregulated under salt stress, which repressed the gene expression of the K⁺ transporters. Salt stress also significantly elevated the expression of the genes involved in osmoregulation substances biosynthesis, and obviously affected the expression profiling of other cation transporters. Co-expression network analysis identified TaNHX6-D5/TaNHX4-B7 and TaP5CS2-B3 potentially as core members regulating wheat salt tolerance.

CONCLUSIONS

These results might help us fully understand the morpho-physiological and molecular responses of wheat seedlings to salt stress, and provide elite genetic resources for the genetic modification of wheat salt tolerance.

Rapid and Nondestructive Detection of Proline in Serum Using Near-Infrared Spectroscopy and Partial Least Squares

Proline is an important amino acid that widely affects life activities. It plays an important role in the occurrence and development of diseases. It is of great significance to monitor the metabolism of the machine. With the great advantages of deep learning in feature extraction, near-infrared analysis technology has great potential and has been widely used in various fields. This study explored the potential application of near-infrared spectroscopy in the detection of serum proline. We collected blood samples from clinical sources, separated the serum, established a quantitative model, and determined the changes in proline. Four algorithms of SMLR, PLS, iPLS, and SA were used to model proline in serum. The root mean square errors of prediction were 0.00111, 0.00150, 0.000770, and 0.000449, and the correlation coefficients (Rp) were 0.84, 0.67, 0.91, and 0.97, respectively. The experimental results show that the model is relatively robust and has certain guiding significance for the clinical monitoring of proline. This method is expected to replace the current mainstream but time-consuming HPLC, or it can be applied to rapid online monitoring at the bedside.

Chuanzhitongluo capsule ameliorates microcirculatory dysfunction in rats: Efficacy evaluation and metabolic profiles

Background: Ischemic stroke is a leading cause of mortality and disability worldwide. Microcirculatory dysfunction is the foremost hindrance for a good clinical prognosis in ischemic stroke patients. Clinical researches show that Chuanzhitongluo capsule (CZTL) has a curative effect during the recovery period of ischemic stroke, which contributes to a good prognosis. However, it is not known whether CZTL treats ischemic stroke by ameliorating microcirculation dysfunction.

Objective: In this study, we investigated the influence of CZTL on microcirculation and its underlying mechanism.

Methods: A rat model of acute microcirculatory dysfunction was established by stimuli of adrenaline and ice water. The microcirculatory damage in model rats and the efficacy of CZTL were assessed by detecting laser speckle contrast imaging, coagulation function, hemorheology, vasomotor factor and microcirculation function. The potential mechanism of CZTL action was explored by the untargeted metabolomic analysis based on ultra-performance liquid chromatography-quadrupole-time of flight-mass spectrometry.

Results: Laser speckle contrast imaging showed that model rats suffered low perfusion in ears, feet and tails, and CZTL treatment increased microcirculatory blood flow. Coagulation function detection results showed that CZTL diminished the reduction of thrombin time, prothrombin time, activated partial thromboplastin time and the elevated fibrinogen level caused by acute microcirculatory dysfunction. Furthermore, CZTL could recover the increased blood viscosity as well as the abnormal vasomotor and microcirculation function in rats with acute microcirculatory dysfunction. Metabolomics analysis indicated that CZTL might regulate sphingolipid metabolism and arachidonic acid metabolism to exert protective effects on microcirculation.

Conclusion: These results elucidated that CZTL was highly effective against microcirculatory dysfunction and its potential mechanisms related with the modulation of sphingolipid and arachidonic acid metabolic pathways. The present study provided a new perspective on the clinical application of CZTL, and it contribute to explore novel therapeutic drug against microcirculatory dysfunction.

Beneficial Effect of Proline Supplementation on Goat Spermatozoa Quality during Cryopreservation

Sperm cryopreservation contributes to the extensive utilization of artificial insemination (AI) in the daily livestock industry. However, due to the presence of few sperm with good biological function in post-thaw goat sperm, its use has been limited for AI purposes. Hence, its improvement has been the focus of many research studies. This study aimed to investigate the effects of proline supplementation of the freezing medium on goat sperm. The goat semen was cryopreserved with freezing medium supplementation of different concentrations of proline (0, 0.5, 1, 2 and 4 mM). The post-thaw sperm motility patterns, membrane integrity, acrosome integrity, lipid peroxidation (LPO) levels, malondialdehyde (MDA) levels, total antioxidant capacity (T-AOC), proline dehydrogenase (PRODH) activity, superoxide dis-mutase (SOD) activity, glutathione (GSH) levels and GSH/GSSG were evaluated. Likewise, the expression and immunofluorescent localization of PRODH in post-thaw goat sperm was also detected. It was observed that addition of 2 mM proline to the freezing medium significantly enhanced post-thaw goat sperm total motility, progressive motility, straight-linear velocity (VSL), curvilinear velocity (VCL), average path velocity (VAP), straightness (STR), linearity (LIN), membrane integrity and acrosome integrity. Interestingly, PRODH was expressed in post-thaw goat sperm, especially in the post-acrosome and sperm tail. Addition of 2 mM proline also significantly increased the post-thaw sperm PRODH activity compared to the control. Moreover, post-thaw goat sperm LPO levels and MDA levels were reduced by supplementation of 2 mM proline. Furthermore, compared to the control, the values of post-thaw goat sperm T-AOC, SOD activity, GSH level and GSH/GSSG were also significantly increased in 2 mM proline treatment. Reduction of post-thaw goat sperm apoptosis in 2 mM proline treatment was also observed as the levels of Caspase3 and Caspase9 were decreased by the supplementation with 2 mM proline. These observations suggest that the addition of 2 mM proline to the freezing medium increased post-thaw goat sperm quality by reducing oxidative stress during cryopreservation. These findings also provide novel insights into the use of proline as an efficient additive to enhance post-thaw goat sperm quality during cryopreservation.

Metabolomics analysis identifies glutamic acid and cystine imbalances in COVID-19 patients without comorbid conditions. Implications on redox homeostasis and COVID-19 pathophysiology

It is well known that the presence of comorbidities and age-related health issues may hide biochemical and metabolic features triggered by SARS-CoV-2 infection and other diseases associated to hypoxia, as they are by themselves chronic inflammatory conditions that may potentially disturb metabolic homeostasis and thereby negatively impact on COVID-19 progression. To unveil the metabolic abnormalities inherent to hypoxemia caused by COVID-19, we here applied gas chromatography coupled to mass spectrometry to analyze the main metabolic changes exhibited by a population of male patients less than 50 years of age with mild/moderate and severe COVID-19 without pre-existing comorbidities known to predispose to life-threatening complications from this infection. Several differences in serum levels of particular metabolites between normal controls and patients with COVID-19 as well as between mild/moderate and severe COVID-19 were identified. These included increased glutamic acid and reduced glutamine, cystine, threonic acid, and proline levels. In particular, using the entire metabolomic fingerprint obtained, we observed that glutamine/glutamate metabolism was associated with disease severity as patients in the severe COVID-19 group presented the lowest and higher serum levels of these amino acids, respectively. These data highlight the hypoxia-derived metabolic alterations provoked by SARS-CoV-2 infection in the absence of pre-existing co-morbidities as well as the value of amino acid metabolism in determining reactive oxygen species recycling pathways, which when impaired may lead to increased oxidation of proteins and cell damage. They also provide insights on new supportive therapies for COVID-19 and other disorders that involve altered redox homeostasis and lower oxygen levels that may lead to better outcomes of disease severity.

Dual contribution of the mTOR pathway and of the metabolism of amino acids in prostate cancer

BACKGROUND

Prostate cancer is the leading cause of cancer in men, and its incidence increases with age. Among other risk factors, pre-existing metabolic diseases have been recently linked with prostate cancer, and our current knowledge recognizes prostate cancer as a condition with important metabolic anomalies as well. In malignancies, metabolic disorders are commonly associated with aberrations in mTOR, which is the master regulator of protein synthesis and energetic homeostasis. Although there are reports demonstrating the high dependency of prostate cancer cells for lipid derivatives and even for carbohydrates, the understanding regarding amino acids, and the relationship with the mTOR pathway ultimately resulting in metabolic aberrations, is still scarce.

CONCLUSIONS AND PERSPECTIVES

In this review, we briefly provide evidence supporting prostate cancer as a metabolic disease, and discuss what is known about mTOR signaling and prostate cancer. Next, we emphasized on the amino acids glutamine, leucine, serine, glycine, sarcosine, proline and arginine, commonly related to prostate cancer, to explore the alterations in their regulatory pathways and to link them with the associated metabolic reprogramming events seen in prostate cancer. Finally, we display potential therapeutic strategies for targeting mTOR and the referred amino acids, as experimental approaches to selectively attack prostate cancer cells.

GmWRKY21, a Soybean WRKY Transcription Factor Gene, Enhances the Tolerance to Aluminum Stress in Arabidopsis thaliana

The WRKY transcription factors (TFs) are one of the largest families of TFs in plants and play multiple roles in plant growth and development and stress response. In this study, GmWRKY21 encoding a WRKY transcription factor was functionally characterized in Arabidopsis and soybean. The GmWRKY21 protein containing a highly conserved WRKY domain and a C₂H₂ zinc-finger structure is located in the nucleus and has the characteristics of transcriptional activation ability. The GmWRKY21 gene presented a constitutive expression pattern rich in the roots, leaves, and flowers of soybean with over 6-fold of relative expression levels and could be substantially induced by aluminum stress. As compared to the control, overexpression of GmWRKY21 in Arabidopsis increased the root growth of seedlings in transgenic lines under the AlCl₃ concentrations of 25, 50, and 100 μM with higher proline and lower MDA accumulation. The results of quantitative real-time polymerase chain reaction (qRT-PCR) showed that the marker genes relative to aluminum stress including ALMT, ALS3, MATE, and STOP1 were induced in GmWRKY21 transgenic plants under AlCl₃ treatment. The stress-related genes, such as KIN1, COR15A, COR15B, COR47, GLOS3, and RD29A, were also upregulated in GmWRKY21 transgenic Arabidopsis under aluminum stress. Similarly, stress-related genes, such as GmCOR47, GmDREB2A, GmMYB84, GmKIN1, GmGST1, and GmLEA, were upregulated in hair roots of GmWRKY21 transgenic plants. In summary, these results suggested that the GmWRKY21 transcription factor may promote the tolerance to aluminum stress mediated by the pathways regulating the expression of the acidic aluminum stress-responsive genes and abiotic stress-responsive genes.

Extensive exploration of the conformational landscapes of neutral and terminally blocked prolines in the gas phase: A density functional theory study

Proline is an important amino acid that plays unique roles in the structures of peptides and proteins. The conformations of proline are searched by a thorough method, generating 3888 trial structures optimized at the B97D/6-311++G** level. A total of 23 conformations are found and their structural and energetic data are presented. All the proline conformers exhibit a coplanar feature for four of the five pyrrolidine ring atoms. The coplanar rule reduces the cost of the conformational search by a factor of 40. The theoretical composition-weighted infrared spectrum provides a good explanation of the experimental results. A conformational search of capped proline yields seven unique conformers, all with trans C-termini peptide planes. The trans C-termini rule further cuts by half the cost of the conformational search of proline-containing peptides. The theoretical composition of the cis N-termini peptide bonds at room temperature is 5.5%, agreeing with the experimental estimations of 3%–10%.

Beneficial effect of L-Proline supplementation on the quality of human spermatozoa

L-Proline is a natural anti-oxidative and osmoprotectant agent, playing a versatile role in cell metabolism and physiology. The present study aimed to explore the antioxidant effects of L-Proline on human sperm function during incubation. Thirty healthy, normozoospermic men (27-40 years) were enrolled. Sperm samples were incubated in an unsupplemented sperm medium (control group), or supplemented with L-Proline (1, 2 and 4 mmol/L) to evaluate its effect during 0, 1, 4 and 24 h of incubation. Sperm were assessed in terms of motility, viability, morphology, chromatin and DNA integrity. Moreover, the levels of reactive oxygen species (ROS), malondialdehyde (MDA), and total antioxidant capacity (TAC) were determined in the sperm medium. The results indicated that 2 mmol/L of L-Proline significantly improved the maintenance of sperm motility, viability, normal morphology, chromatin and DNA integrity, and TAC levels compared to the control group during 24 h of incubation (p < 0.05). However, 1 and 4 mmol/L of L-Proline could not significantly preserve sperm parameters, chromatin quality, and antioxidant status during different incubation times compared to the control group (p > 0.05). Collectively, the inclusion of L-Proline (2 mmol/L) in the human sperm medium maintains sperm parameters and chromatin quality probably by modulating the oxidative status.

Proline confers acid stress tolerance to Bacillus megaterium G18

Proline plays a multifunctional role in several organisms including bacteria in conferring protection under stress conditions. In this paper we report the role of proline in conferring acid tolerance to Bacillus megaterium G18. An acid susceptible mutant of B. megaterium G18 which required proline for its growth under acid stress condition was generated through Tn5 mutagenesis. Further, targeted inactivation of proC involved in osmo-adaptive proline synthesis in B. megaterium G18 resulted in the loss of ability of the bacterium to grow at low pH (pH 4.5). Exogenous supply of proline (1 mM) to the growth medium restored the ability of the mutant cells to grow at pH 4.5 which was not the same in case of other osmoprotectants tested. Proline was produced and secreted to extracellular medium by B. megaterium G18 when growing in low pH condition as evidenced by the use of Escherichia coli proline auxotrophs and HPLC analysis. Further, pHT01 vector based expression of full length proC gene in the ∆proC mutant cells restored the survival capacity of the mutant cells in acidic pH, suggesting that proline production is an important strategy employed by B. megaterium G18 to survive under acid stress induced osmotic stress.

Stress-induced activation of the proline biosynthetic pathway in Bacillus subtilis: a population-wide and single-cell study of the osmotically controlled proHJ promoter

Bacillus subtilis, in its natural habitat, is regularly exposed to rapid changes in the osmolarity of its surrounding. As its primary survival strategy, it accumulates large amounts of the compatible solute proline by activating the de novo proline biosynthesis pathway and exploiting the glutamate pools. This osmotically‐induced biosynthesis requires activation of a SigA‐type promoter that drives the expression of the proHJ operon. Population‐wide studies have shown that the activity of the proHJ promoter correlates with the increased osmotic pressure of the environment. Therefore, the activation of the proHJ transcription should be an adequate measure of the adaptation to osmotic stress through proline synthesis in the absence of other osmoprotectants. In this study, we investigate the kinetics of the proHJ promoter activation and the early adaptation to mild osmotic upshift at the single‐cell level. Under these conditions, we observed a switching point and heterogeneous proline biosynthesis gene expression, where the subpopulation of cells showing active proHJ transcription is able to continuously divide, and those unresponsive to osmotic stress remain dormant. Additionally, we demonstrate that bactericidal antibiotics significantly upregulate proHJ transcription in the absence of externally imposed osmotic pressure, suggesting that the osmotically‐controlled proline biosynthesis pathway is also involved in the antibiotic‐mediated stress response.

Phytochemical analysis reveals an antioxidant defense response in Lonicera japonica to cadmium-induced oxidative stress

Cadmium (Cd), though potentially beneficial at lower levels to some plant species, at higher levels is a toxic metal that is detrimental to plant growth and development. Cd is also a carcinogen to humans and other contaminated plant consumers, affecting the kidneys and reducing bone strength. In this study we investigated responses of growth, chlorophyll content, reactive oxygen species levels, and antioxidant responses to Cd in honeysuckle leaves (Lonicera japonica Thunb.), a potential Cd hyperaccumulator. Results indicated that plant height, dry weight, leaf area, and chlorophyll content increased when honeysuckle was exposed to 10 mg kg^-1 or 30 mg kg^-1 Cd (low concentration). However, in response to 150 mg kg^-1 or 200 mg kg^-1 Cd (high concentration) these growth parameters and chlorophyll content significantly decreased relative to untreated control plant groups. Higher levels of superoxide radical (O₂^·-) and hydrogen peroxide (H₂O₂) were observed in high concentration Cd groups. The activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase were enhanced with exposure to increasing levels of Cd. Additionally, the Ascorbate-Glutathione (AsA-GSH) cycle was activated for the removal of H₂O₂ in honeysuckle in response to elevated Cd. The Pearson correlation analysis, a redundancy analysis, and a permutation test indicated that proline and APX were dominant antioxidants for removing O₂^·- and H₂O₂. The antioxidants GSH and non-protein thiols (NPTs) also increased as the concentration of Cd increased.

Exploring Thermal Sensitivities and Adaptations of Oxidative Phosphorylation Pathways

Temperature shifts are a major challenge to animals; they drive adaptations in organisms and species, and affect all physiological functions in ectothermic organisms. Understanding the origin and mechanisms of these adaptations is critical for determining whether ectothermic organisms will be able to survive when faced with global climate change. Mitochondrial oxidative phosphorylation is thought to be an important metabolic player in this regard, since the capacity of the mitochondria to produce energy greatly varies according to temperature. However, organism survival and fitness depend not only on how much energy is produced, but, more precisely, on how oxidative phosphorylation is affected and which step of the process dictates thermal sensitivity. These questions need to be addressed from a new perspective involving a complex view of mitochondrial oxidative phosphorylation and its related pathways. In this review, we examine the effect of temperature on the commonly measured pathways, but mainly focus on the potential impact of lesser-studied pathways and related steps, including the electron-transferring flavoprotein pathway, glycerophosphate dehydrogenase, dihydroorotate dehydrogenase, choline dehydrogenase, proline dehydrogenase, and sulfide:quinone oxidoreductase. Our objective is to reveal new avenues of research that can address the impact of temperature on oxidative phosphorylation in all its complexity to better portray the limitations and the potential adaptations of aerobic metabolism.

Proline Dehydrogenase/Proline Oxidase (PRODH/POX) Is Involved in the Mechanism of Metformin-Induced Apoptosis in C32 Melanoma Cell Line

The role of proline dehydrogenase/proline oxidase (PRODH/POX) in the mechanism of antineoplastic activity of metformin (MET) was studied in C32 melanoma cells. PRODH/POX is a mitochondrial enzyme-degrading proline that is implicated in the regulation of cancer cell survival/apoptosis. The enzyme is activated by AMP kinase (AMPK). It has been found that MET induced a significant decrease in cell viability and DNA biosynthesis accompanied by an increase in the expressions of AMPK and PRODH/POX in C32 cells. The mechanism for MET-dependent cytotoxicity on C32 cells was found at the level of PRODH/POX-induced ROS generation and activation of Caspase-3 and Caspase-9 expressions in these cells. The effects were not observed in MET-treated PRODH/POX knock-out C32 cells. Of interest is an MET-dependent increase in the concentration of proline, which is a substrate for PRODH/POX. This phenomenon is due to the MET-dependent inhibition of collagen biosynthesis, which is the main proline-utilizing process. It has been found that the underlying mechanism of anticancer activity of MET involves the activation of AMPK, PRODH/POX, increase in the cytoplasmic concentration of proline, inhibition of collagen biosynthesis, and stimulation of PRODH/POX-dependent ROS generation, which initiate the apoptosis of melanoma cells.

Combined Metabolomics and Network Toxicology to Explore the Molecular Mechanism of Phytolacca acinose Roxb-Induced Hepatotoxicity in Zebrafish Larvae in Vivo

Phytolacca acinosa Roxb (PAR), a traditional Chinese medicine, has been widely used as a diuretic drug for a long period of time for the treatment edema, swelling, and sores. However, it has been reported that PAR might induce hepatotoxicity, while the mechanisms of its toxic effect are still unclear. In this study, network toxicology and metabolomic technique were applied to explore PAR-induced hepatotoxicity on zebrafish larvae. We evaluated the effect of PAR on the ultrastructure and the function of the liver, predictive targets, and pathways in network toxicology, apoptosis of liver cells by PCR and western blot, and metabolic profile by GC-MS. PAR causes liver injury, abnormal liver function, and apoptosis in zebrafish. The level of arachidonic acid in endogenous metabolites treated with PAR was significantly increased, leading to oxidative stress in vivo. Excessive ROS further activated the p53 signal pathway and caspase family, which were obtained from KEGG enrichment analysis of network toxicology. The gene levels of caspase-3, caspase-8, and caspase-9 were significantly increased by RT-PCR, and the level of Caps3 protein was also significantly up-regulated through western blot. PAR exposure results in the liver function abnormal amino acid metabolism disturbance and motivates hepatocyte apoptosis, furthermore leading to liver injury.

Photoinduced Covalent Irreversible Inactivation of Proline Dehydrogenase by S-Heterocycles

Proline dehydrogenase (PRODH) is a flavoenzyme that catalyzes the first step of proline catabolism, the oxidation of l-proline to Δ¹-pyrroline-5-carboxylate. PRODH has emerged as a cancer therapy target because of its involvement in the metabolic reprogramming of cancer cells. Here, we report the discovery of a new class of PRODH inactivator, which covalently and irreversibly modifies the FAD in a light-dependent manner. Two examples, 1,3-dithiolane-2-carboxylate and tetrahydrothiophene-2-carboxylate, have been characterized using X-ray crystallography (1.52-1.85 Å resolution), absorbance spectroscopy, and enzyme kinetics. The structures reveal that in the dark, these compounds function as classical reversible, proline analogue inhibitors. However, exposure of enzyme-inhibitor cocrystals to bright white light induces decarboxylation of the inhibitor and covalent attachment of the residual S-heterocycle to the FAD N5 atom, locking the cofactor into a reduced, inactive state. Spectroscopic measurements of the inactivation process in solution confirm the requirement for light and show that blue light is preferred. Enzyme activity assays show that the rate of inactivation is enhanced by light and that the inactivation is irreversible. We also demonstrate the photosensitivity of cancer cells to one of these compounds. A possible mechanism is proposed involving photoexcitation of the FAD, while the inhibitor is noncovalently bound in the active site, followed by electron transfer, decarboxylation, and radical combination steps. Our results could lead to the development of photopharmacological drugs targeting PRODH.

Redox Regulation and Oxidative Stress in Mammalian Oocytes and Embryos Developed In Vivo and In Vitro

Oocytes and preimplantation embryos require careful regulation of the redox environment for optimal development both in vivo and in vitro. Reactive oxygen species (ROS) are generated throughout development as a result of cellular metabolism and enzyme reactions. ROS production can result in (i) oxidative eustress, where ROS are helpful signalling molecules with beneficial physiological functions and where the redox state of the cell is maintained within homeostatic range by a closely coupled system of antioxidants and antioxidant enzymes, or (ii) oxidative distress, where excess ROS are deleterious and impair normal cellular function. in vitro culture of embryos exacerbates ROS production due to a range of issues including culture-medium composition and laboratory culture conditions. This increase in ROS can be detrimental not only to assisted reproductive success rates but can also result in epigenetic and genetic changes in the embryo, resulting in transgenerational effects. This review examines the effects of oxidative stress in the oocyte and preimplantation embryo in both the in vivo and in vitro environment, identifies mechanisms responsible for oxidative stress in the oocyte/embryo in culture and approaches to reduce these problems, and briefly examines the potential impacts on future generations.

Proline metabolism in cancer

Cancer cells often change their metabolism to support uncontrolled proliferation. Proline is the only proteogenic secondary amino acid that is abundant in the body. Recent studies have shown that proline metabolism plays an important role in metabolic reprogramming and affects the occurrence and development of cancer. Proline metabolism is related to ATP production, protein and nucleotide synthesis, and redox homeostasis in tumor cells. Proline can be synthesized by aldehyde dehydrogenase family 18 member A1 (ALDH18A1) and delta1-pyrroline-5-carboxylate reductase (PYCR), up-regulating ALDH18A1 and PYCR can promote the proliferation and invasion of cancer cells. As the main storage of proline, collagen can influence cancer cells proliferation, invasion, and metastasis. Its synthesis depends on the hydroxylation of proline catalyzed by prolyl 4-hydroxylases (P4Hs), which will affect the plasticity and metastasis of cancer cells. The degradation of proline occurs in the mitochondria and involves an oxidation step catalyzed by proline dehydrogenase/proline oxidase (PRODH/POX). Proline catabolism has a dual role in cancer, linking apoptosis with the survival and metastasis of cancer cells. In addition, it has been demonstrated that the regulation of proline metabolic enzymes at the genetic and post-translational levels is related to cancer. This article reviews the role of proline metabolic enzymes in cancer proliferation, apoptosis, metastasis, and development. Research on proline metabolism may provide a new strategy for cancer treatment.

The Multifaceted Roles of Proline in Cell Behavior

Herein, we review the multifaceted roles of proline in cell biology. This peculiar cyclic imino acid is: (i) A main precursor of extracellular collagens (the most abundant human proteins), antimicrobial peptides (involved in innate immunity), salivary proteins (astringency, teeth health) and cornifins (skin permeability); (ii) an energy source for pathogenic bacteria, protozoan parasites, and metastatic cancer cells, which engage in extracellular-protein degradation to invade their host; (iii) an antistress molecule (an osmolyte and chemical chaperone) helpful against various potential harms (UV radiation, drought/salinity, heavy metals, reactive oxygen species); (iv) a neural metabotoxin associated with schizophrenia; (v) a modulator of cell signaling pathways such as the amino acid stress response and extracellular signal-related kinase pathway; (vi) an epigenetic modifier able to promote DNA and histone hypermethylation; (vii) an inducer of proliferation of stem and tumor cells; and (viii) a modulator of cell morphology and migration/invasiveness. We highlight how proline metabolism impacts beneficial tissue regeneration, but also contributes to the progression of devastating pathologies such as fibrosis and metastatic cancer.

Hydroxyproline in animal metabolism, nutrition, and cell signaling

trans-4-Hydroxy-L-proline is highly abundant in collagen (accounting for about one-third of body proteins in humans and other animals). This imino acid (loosely called amino acid) and its minor analogue trans-3-hydroxy-L-proline in their ratio of approximately 100:1 are formed from the post-translational hydroxylation of proteins (primarily collagen and, to a much lesser extent, non-collagen proteins). Besides their structural and physiological significance in the connective tissue, both trans-4-hydroxy-L-proline and trans-3-hydroxy-L-proline can scavenge reactive oxygen species and have both structural and physiological significance in animals. The formation of trans-4-hydroxy-L-proline residues in protein kinases B and DYRK1A, eukaryotic elongation factor 2 activity, and hypoxia-inducible transcription factor plays an important role in regulating their phosphorylation and catalytic activation as well as cell signaling in animal cells. These biochemical events contribute to the modulation of cell metabolism, growth, development, responses to nutritional and physiological changes (e.g., dietary protein intake and hypoxia), and survival. Milk, meat, skin hydrolysates, and blood, as well as whole-body collagen degradation provide a large amount of trans-4-hydroxy-L-proline. In animals, most (nearly 90%) of the collagen-derived trans-4-hydroxy-L-proline is catabolized to glycine via the trans-4-hydroxy-L-proline oxidase pathway, and trans-3-hydroxy-L-proline is degraded via the trans-3-hydroxy-L-proline dehydratase pathway to ornithine and glutamate, thereby conserving dietary and endogenously synthesized proline and arginine. Supplementing trans-4-hydroxy-L-proline or its small peptides to plant-based diets can alleviate oxidative stress, while increasing collagen synthesis and accretion in the body. New knowledge of hydroxyproline biochemistry and nutrition aids in improving the growth, health and well-being of humans and other animals.

How signaling pathways link extracellular mechano-environment to proline biosynthesis: A hypothesis: PINCH-1 and kindlin-2 sense mechanical signals from extracellular matrix and link them to proline biosynthesis

We propose a signaling pathway in which cell-extracellular matrix (ECM) adhesion components PINCH-1 and kindlin-2 sense mechanical signals from ECM and link them to proline biosynthesis, a vital metabolic pathway for macromolecule synthesis, redox balance, and ECM remodeling. ECM stiffening promotes PINCH-1 expression via integrin signaling, which suppresses dynamin-related protein 1 (DRP1) expression and mitochondrial fission, resulting in increased kindlin-2 translocation into mitochondria and interaction with Δ¹ -pyrroline-5-carboxylate (P5C) reductase 1 (PYCR1). Kindlin-2 interaction with PYCR1 protects the latter from proteolytic degradation, leading to elevated PYCR1 level. Additionally, PINCH-1 promotes P5C synthase (P5CS) expression and P5C synthesis, which, together with increased PYCR1 level, support augmented proline biosynthesis. This signaling pathway is frequently activated in fibrosis and cancer, resulting in increased proline biosynthesis and excessive collagen matrix production, which in turn further promotes ECM stiffening. Targeting this signaling pathway, therefore, may provide an effective strategy for alleviating fibrosis and cancer progression.

Comprehensive analysis of diabetic nephropathy expression profile based on weighted gene co-expression network analysis algorithm

Background

Diabetic nephropathy (DN) is the major complication of diabetes mellitus, and leading cause of end-stage renal disease. The underlying molecular mechanism of DN is not yet completely clear. The aim of this study was to analyze a DN microarray dataset using weighted gene co-expression network analysis (WGCNA) algorithm for better understanding of DN pathogenesis and exploring key genes in the disease progression.

Methods

The identified differentially expressed genes (DEGs) in DN dataset GSE47183 were introduced to WGCNA algorithm to construct co-expression modules. STRING database was used for construction of Protein-protein interaction (PPI) networks of the genes in all modules and the hub genes were identified considering both the degree centrality in the PPI networks and the ranked lists of weighted networks. Gene ontology and Reactome pathway enrichment analyses were performed on each module to understand their involvement in the biological processes and pathways. Following validation of the hub genes in another DN dataset (GSE96804), their up-stream regulators, including microRNAs and transcription factors were predicted and a regulatory network comprising of all these molecules was constructed.

Results

After normalization and analysis of the dataset, 2475 significant DEGs were identified and clustered into six different co-expression modules by WGCNA algorithm. Then, DEGs of each module were subjected to functional enrichment analyses and PPI network constructions. Metabolic processes, cell cycle control, and apoptosis were among the top enriched terms. In the next step, 23 hub genes were identified among the modules in genes and five of them, including FN1, SLC2A2, FABP1, EHHADH and PIPOX were validated in another DN dataset. In the regulatory network, FN1 was the most affected hub gene and mir-27a and REAL were recognized as two main upstream-regulators of the hub genes.

Conclusions

The identified hub genes from the hearts of co-expression modules could widen our understanding of the DN development and might be of targets of future investigations, exploring their therapeutic potentials for treatment of this complicated disease.

L-Proline Activates Mammalian Target of Rapamycin Complex 1 and Modulates Redox Environment in Porcine Trophectoderm Cells

L-proline (proline) is a key regulator of embryogenesis, placental development, and fetal growth. However, the underlying mechanisms that support the beneficial effects of proline are largely unknown. This study used porcine trophectoderm cell line 2 (pTr2) to investigate the underlying mechanisms of proline in cell proliferation and redox homeostasis. Cells were cultured in the presence of 0, 0.25, 0.50, or 1.0 mmol/L proline for an indicated time. The results showed that 0.5 and 1.0 mmol/L proline enhanced cell viability. These effects of proline (0.5 mmol/L) were accompanied by the enhanced protein abundance of p-mTORC1, p-p70S6K, p-S6, and p-4E-BP1. Additionally, proline dose-dependently enhanced the mRNA expression of proline transporters [solute carrier family (SLC) 6A20, SLC36A1, SLC36A2, SLC38A1, and SLC38A2], elevated proline concentration, and protein abundance of proline dehydrogenase (PRODH). Furthermore, proline addition (0.25 or 0.5 mmol/L) resulted in lower abundance of p-AMPKα when compared with a control. Of note, proline resulted in lower reactive oxygen species (ROS) level, upregulated mRNA expression of the catalytic subunit of glutamate–cysteine ligase (GCLC) and glutathione synthetase (GSS), as well as enhanced total (T)-GSH and GSH concentration when compared with a control. These data indicated that proline activates themTORC1 signaling and modulates the intracellular redox environment via enhancing proline transport.

Proline metabolism and transport in retinal health and disease

The retina is one of the most energy-demanding tissues in the human body. Photoreceptors in the outer retina rely on nutrient support from the neighboring retinal pigment epithelium (RPE), a monolayer of epithelial cells that separate the retina and choroidal blood supply. RPE dysfunction or cell death can result in photoreceptor degeneration, leading to blindness in retinal degenerative diseases including some inherited retinal degenerations and age-related macular degeneration (AMD). In addition to having ready access to rich nutrients from blood, the RPE is also supplied with lactate from adjacent photoreceptors. Moreover, RPE can phagocytose lipid-rich outer segments for degradation and recycling on a daily basis. Recent studies show RPE cells prefer proline as a major metabolic substrate, and they are highly enriched for the proline transporter, SLC6A20. In contrast, dysfunctional or poorly differentiated RPE fails to utilize proline. RPE uses proline to fuel mitochondrial metabolism, synthesize amino acids, build the extracellular matrix, fight against oxidative stress, and sustain differentiation. Remarkably, the neural retina rarely imports proline directly, but it uptakes and utilizes intermediates and amino acids derived from proline catabolism in the RPE. Mutations of genes in proline metabolism are associated with retinal degenerative diseases, and proline supplementation is reported to improve RPE-initiated vision loss. This review will cover proline metabolism in RPE and highlight the importance of proline transport and utilization in maintaining retinal metabolism and health.

Reprogramming of mitochondrial proline metabolism promotes liver tumorigenesis

Dysregulated cellular energetics has recently been recognized as a hallmark of cancer and garnered attention as a potential targeting strategy for cancer therapeutics. Cancer cells reprogram metabolic activities to meet bio-energetic, biosynthetic and redox requirements needed to sustain indefinite proliferation. In many cases, metabolic reprogramming is the result of complex interactions between genetic alterations in well-known oncogenes and tumor suppressors and epigenetic changes. While the metabolism of the two most abundant nutrients, glucose and glutamine, is reprogrammed in a wide range of cancers, accumulating evidence demonstrates that additional metabolic pathways are also critical for cell survival and growth. Proline metabolism is one such metabolic pathway that promotes tumorigenesis in multiple cancer types, including liver cancer, which is the fourth main cause of cancer mortality in the world. Despite the recent spate of approved treatments, including targeted therapy and combined immunotherapies, there has been no significant gain in clinical benefits in the majority of liver cancer patients. Thus, exploring novel therapeutic strategies and identifying new molecular targets remains a top priority for liver cancer. Two of the enzymes in the proline biosynthetic pathway, pyrroline-5-carboxylate reductase (PYCR1) and Aldehyde Dehydrogenase 18 Family Member A1 (ALDH18A1), are upregulated in liver cancer of both human and animal models, while proline catabolic enzymes, such as proline dehydrogenase (PRODH) are downregulated. Here we review the latest evidence linking proline metabolism to liver and other cancers and potential mechanisms of action for the proline pathway in cancer development.

Targeting the Proline-Glutamine-Asparagine-Arginine Metabolic Axis in Amino Acid Starvation Cancer Therapy

Proline, glutamine, asparagine, and arginine are conditionally non-essential amino acids that can be produced in our body. However, they are essential for the growth of highly proliferative cells such as cancers. Many cancers express reduced levels of these amino acids and thus require import from the environment. Meanwhile, the biosynthesis of these amino acids is inter-connected but can be intervened individually through the inhibition of key enzymes of the biosynthesis of these amino acids, resulting in amino acid starvation and cell death. Amino acid starvation strategies have been in various stages of clinical applications. Targeting asparagine using asparaginase has been approved for treating acute lymphoblastic leukemia. Targeting glutamine and arginine starvations are in various stages of clinical trials, and targeting proline starvation is in preclinical development. The most important obstacle of these therapies is drug resistance, which is mostly due to reactivation of the key enzymes involved in biosynthesis of the targeted amino acids and reprogramming of compensatory survival pathways via transcriptional, epigenetic, and post-translational mechanisms. Here, we review the interactive regulatory mechanisms that control cellular levels of these amino acids for amino acid starvation therapy and how drug resistance is evolved underlying treatment failure.

ADP-ribosylation factors improve biomass yield and salinity tolerance in transgenic switchgrass (Panicum virgatum L.)

PvArf regulate proline biosynthesis by physically interacting with PvP5CS1 to improve salt tolerance in switchgrass. The genetic factors that contribute to stress resiliency are yet to be determined. Here, we identified three ADP-ribosylation factors, PvArf1, PvArf-B1C, and PvArf-related, which contribute to salinity tolerance in transgenic switchgrass (Panicum virgatum L.). Switchgrass overexpressing each of these genes produced approximately twofold more biomass than wild type (WT) under normal growth conditions. Transgenic plants accumulated modestly higher levels of proline under normal conditions, but this level was significantly increased under salt stress providing better protection to transgenic plants compared to WT. We found that PvArf genes induce proline biosynthesis genes under salt stress to positively regulate proline accumulation, and further demonstrated that PvArf physically interact with PvP5CS1. Moreover, the transcript levels of two key ROS-scavenging enzyme genes were significantly increased in the transgenic plants compared to WT, leading to reduced H₂O₂ accumulation under salt stress conditions. PvArf genes also protect cells against stress-induced changes in Na⁺ and K⁺ ion concentrations. Our findings uncover that ADP-ribosylation factors are key determinants of biomass yield in switchgrass, and play pivotal roles in salinity tolerance by regulating genes involved in proline biosynthesis.

Expression analysis of immune-associated genes in hemocytes of mud crab Scylla paramamosain under low salinity challenge

To gain knowledge on the immune response in Scylla paramamosain under low salinity challenge, S. paramamosain we investigated digital gene expression (DEG) in S. paramamosain hemocytes using the deep-sequencing platform Illumina Hiseq XTen. A total of 97,257 high quality unigenes with mean length 786.59 bp were found to be regulated by low salinity challenge, among which 93 unigenes were significantly up regulated, and 71 were significantly down regulated. Functional categorization and pathways analysis of differentially expressed genes revealed that immune signaling pathway including cAMP and cGMP signaling pathway were affected in low salinity stress. Cellular immunity-related genes including low-density lipoprotein receptor-related protein 6 (LRP6) and xanthine dehydrogenase (XDH) were down-regulated, indicating phagocytosis and oxygen dependent mechanism of phagocyte were suppressed in low salinity stress; Humoral immunity-related genes serine proteases and serpins 3 were up- and down-regulated, respectively, suggest that the proPO system was influenced by low salinity significantly; Moreover, processes related to immune response including carbohydrate metabolism, protein synthesis and lipid transport were found differentially regulated, implying the integrity of the immune response in low salinity stress. This study gained comprehensive insights on the immune mechanism of S. paramamosain at low salinity stress at the molecular level. The findings provide a theoretical basis for understanding immune mechanisms of S. paramamosain under low salinity stress, and technical reference for evaluating physiological adaptation in fresh water environment.

Metabolomic Analysis of the Ameliorative Effect of Enhanced Proline Metabolism on Hypoxia-Induced Injury in Cardiomyocytes

Background

Coronary heart disease is currently the leading cause of death in humans. Its poor prognosis and high mortality are associated with myocardial ischemia, which leads to metabolic disorder-related cardiomyocyte apoptosis and reactive oxygen species (ROS) production. Previous cardiovascular metabolomics studies in humans and mice have shown that proline metabolism is severely altered after cardiomyocyte hypoxia. Proline dehydrogenase (PRODH) is located on the inner mitochondrial membrane and is an enzyme that catalyzes the first step of proline catabolism, which plays an important role in improving the cellular redox state. In vitro oxygen-glucose deprivation can mimic in vivo myocardial ischemic injury. This study is aimed at investigating whether enhancing proline metabolism by overexpressing PRODH can ameliorate hypoxia-induced injury in cardiomyocytes and to reveal the related altered metabolites and mechanistic pathway via untargeted metabolomics analysis.

Methods and Results

First, through public database analysis and RT-qPCR and western blot analyses in a cardiomyocyte hypoxia model, we found that the expression of the proline-degrading enzyme PRODH was downregulated after myocardial infarction and hypoxia exposure. Second, LDH assays, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), DHE staining, flow cytometric apoptosis analysis with DCFH and Annexin V-FITC/PI, and western blot analysis were used to assess the injury level in cardiomyocytes. Enhanced proline metabolism induced by PRODH overexpression reduced the levels of reactive oxidative stress and apoptosis, whereas PRODH knockdown had the opposite effects. Third, untargeted metabolomics analysis revealed that the protective effect was associated with significant changes in metabolism linked to sphingolipid signaling pathways, unsaturated fatty acid biosynthesis, phosphocreatine, glutathione disulfide, aminoacyl-tRNA biosynthesis, and ABC transporters.

Conclusions

Our study demonstrated a protective effect of enhanced proline metabolism in cardiomyocytes under hypoxia, providing a novel strategy for exploring new treatments for coronary heart disease.

Inhibition of Distinct Proline- or N-Acetylglucosamine-Induced Hyphal Formation Pathways by Proline Analogs in Candida albicans

Candida albicans undergoes a yeast-to-hyphal transition that has been recognized as a virulence property as well as a turning point leading to biofilm formation associated with candidiasis. It is known that yeast-to-hyphal transition is induced under complex environmental conditions including temperature (above 35°C), pH (greater than 6.5), CO₂, N-acetylglucosamine (GlcNAc), amino acids, RPMI-1640 synthetic culture medium, and blood serum. To identify the hyphal induction factor in the RPMI-1640 medium, we examined each component of RPMI-1640 and established a simple hyphal induction condition, that is, incubation in L-proline solution at 37°C. Incubation in GlcNAc solution alone, which is not contained in RPMI-1640, without any other materials was also identified as another simple hyphal induction condition. To inhibit hyphal formation, proline and GlcNAc analogs were examined. Among the proline analogs used, L-azetidine-2-carboxylic acid (AZC) inhibited hyphal induction under both induction conditions, but L-4-thiazolidinecarboxylic acid (T4C) specifically inhibited proline-induced hyphal formation only, while α-N-methyl-L-proline (mPro) selectively inhibited GlcNAc-induced hyphal formation. Hyphal formation in fetal bovine serum was also inhibited by AZC or T4C together with mPro without affecting the proliferation of yeast form. These results indicate that these proline analogs are ideal inhibitors of yeast-to-hyphal transition in C. albicans.

Effect of Proline on Cell Death, Cell Cycle, and Oxidative Stress in C6 Glioma Cell Line

Since proline metabolism has been implicated to play an underlying role in apoptotic signaling and cancer, and hyperprolinemic patients present susceptibility to tumors development, this study investigated the effect of proline on cell death, cell cycle, antioxidant enzymes activities, and immunocontent/activity of proteins involved in cell death/survival signaling pathways in C6 glioma cells. C6 cells were incubated with proline (0-5 mM) for 1 h, 24 h, 48 h, 72 h, or 7 days. Proline in high concentrations slightly decreased LDH release, and no cytotoxic effect was seen by Annexin-PI staining. Superoxide dismutase and catalase activities were increased by proline (1 mM) after 72 h, suggesting an increase in reactive species levels. Acetylcholinesterase activity was inhibited by proline at 1, 3, and 5 mM. The cell cycle progression was not altered. Results from Western blot analyses showed that proline at 1 mM after 72 h increased p-NF-ĸB and decreased acetylcholinesterase immunocontent but did not altered AKT, p-AKT, GSK3β, and p-GSK3β. Taken together, the data suggest that high proline levels seems to favor the signaling pathways towards cell proliferation, since acetylcholinesterase, which may act as tumor suppressor, is inhibited by proline. Also, p-NF-κB is increased by proline treatment and its activation is related to tumor cell proliferation and cellular response to oxidants. Proline also induced oxidative stress, but it appears to be insufficient to induce a significant change in cell cycle progression. These data may be related, at least in part, to the increased susceptibility to tumor development in hyperprolinemic individuals.

PINCH-1 regulates mitochondrial dynamics to promote proline synthesis and tumor growth

Reprograming of proline metabolism is critical for tumor growth. Here we show that PINCH-1 is highly expressed in lung adenocarcinoma and promotes proline synthesis through regulation of mitochondrial dynamics. Knockout (KO) of PINCH-1 increases dynamin-related protein 1 (DRP1) expression and mitochondrial fragmentation, which suppresses kindlin-2 mitochondrial translocation and interaction with pyrroline-5-carboxylate reductase 1 (PYCR1), resulting in inhibition of proline synthesis and cell proliferation. Depletion of DRP1 reverses PINCH-1 deficiency-induced defects on mitochondrial dynamics, proline synthesis and cell proliferation. Furthermore, overexpression of PYCR1 in PINCH-1 KO cells restores proline synthesis and cell proliferation, and suppresses DRP1 expression and mitochondrial fragmentation. Finally, ablation of PINCH-1 from lung adenocarcinoma in mouse increases DRP1 expression and inhibits PYCR1 expression, proline synthesis, fibrosis and tumor growth. Our results identify a signaling axis consisting of PINCH-1, DRP1 and PYCR1 that regulates mitochondrial dynamics and proline synthesis, and suggest an attractive strategy for alleviation of tumor growth.

Proline Protects Boar Sperm against Oxidative Stress through Proline Dehydrogenase-Mediated Metabolism and the Amine Structure of Pyrrolidine

Simple Summary

Reactive oxygen species that accumulate during liquid storage of boar semen lead to oxidative stress to sperm. In this study, we found that proline significantly improved boar sperm quality and protected sperm against oxidative damages during liquid storage at 17 °C. Using the model of artificially induced oxidative stress, we found that proline exerted an antioxidative role by modulating redox homeostasis in boar sperm. The secondary amine structure of proline and proline dehydrogenase-mediated metabolism are involved in the antioxidative role. We suggest that addition of proline to the extender would be beneficial to improve boar sperm quality.

Abstract

Proline was reported to improve sperm quality in rams, stallions, cynomolgus monkeys, donkeys, and canines during cryopreservation. However, the underlying mechanism remains unclear. The aim of this study was to investigate the effect of proline on boar semen during liquid storage at 17 °C and explore the underlying mechanism. Freshly ejaculated boar semen was supplemented with different concentrations of proline (0, 25, 50, 75, 100, 125 mM) and stored at 17 °C for nine days. Sperm motility patterns, membrane integrity, ATP (adenosine triphosphate), reactive oxygen species (ROS), and GSH (glutathione) levels, and the activities of catalase (CAT) and superoxide dismutase (SOD) were evaluated after storage for up to five days. It was observed that boar sperm quality gradually decreased with the extension of storage time, while the ROS levels increased. Addition of 75 mM proline not only significantly improved sperm membrane integrity, motility, and ATP levels but also maintained the redox homeostasis via increasing the GSH levels and activities of CAT and SOD. When hydrogen peroxide (H₂O₂) was used to induce oxidative stress, addition of proline significantly improved sperm quality and reduced ROS levels. Moreover, addition of proline also improved sperm quality during the rapid cooling process. Notably, addition of DL-PCA (DL-pipecolinic acid) rescued the reduction of progressive motility and total motility caused by H₂O₂, and THFA (tetrahydro-2-furoic acid) failed to provide protection. Furthermore, addition of proline at 75 mM increased the activity of proline dehydrogenase (PRODH) and attenuated the H₂O₂-induced reduction in progressive motility. These data demonstrate that proline protects sperm against oxidative stress through the secondary amine structure and proline dehydrogenase-mediated metabolism.

Proline-dependent regulation of collagen metabolism

This review is focused on recent data on the role of proline (Pro) in collagen biosynthesis and cellular metabolism. It seems obvious that one of the main substrates for collagen biosynthesis Pro is required to form collagen molecule. The question raised in this review is whether the Pro for collagen biosynthesis is synthesized "de novo", comes directly from degraded proteins or it is converted from other amino acids. Recent data provided evidence that extracellular Pro (added to culture medium) had significant, but relatively little impact on collagen biosynthesis in fibroblasts (the main collagen synthesized cells) cultured in the presence of glutamine (Gln). However, extracellular Pro drastically increased collagen biosynthesis in the cells cultured in Gln-free medium. It suggests that Pro availability determines the rate of collagen biosynthesis and demand for Pro in fibroblasts is predominantly met by conversion from Gln. The potential mechanism of this process as well as possible implication of this knowledge in pharmacotherapy of connective tissue diseases is discussed in this review.

Heterologous Expression of a Glycine soja C2H2 Zinc Finger Gene Improves Aluminum Tolerance in Arabidopsis

Aluminum (Al) toxicity limits plant growth and has a major impact on the agricultural productivity in acidic soils. The zinc-finger protein (ZFP) family plays multiple roles in plant development and abiotic stresses. Although previous reports have confirmed the function of these genes, their transcriptional mechanisms in wild soybean (Glycine soja) are unclear. In this study, GsGIS3 was isolated from Al-tolerant wild soybean gene expression profiles to be functionally characterized in Arabidopsis. Laser confocal microscopic observations demonstrated that GsGIS3 is a nuclear protein, containing one C2H2 zinc-finger structure. Our results show that the expression of GsGIS3 was of a much higher level in the stem than in the leaf and root and was upregulated under AlCl3, NaCl or GA3 treatment. Compared to the control, overexpression of GsGIS3 in Arabidopsis improved Al tolerance in transgenic lines with more root growth, higher proline and lower Malondialdehyde (MDA) accumulation under concentrations of AlCl3. Analysis of hematoxylin staining indicated that GsGIS3 enhanced the resistance of transgenic plants to Al toxicity by reducing Al accumulation in Arabidopsis roots. Moreover, GsGIS3 expression in Arabidopsis enhanced the expression of Al-tolerance-related genes. Taken together, our findings indicate that GsGIS3, as a C2H2 ZFP, may enhance tolerance to Al toxicity through positive regulation of Al-tolerance-related genes.

Metabolic pathway analyses identify proline biosynthesis pathway as a promoter of liver tumorigenesis

BACKGROUND & AIM

Under the regulation of various oncogenic pathways, cancer cells undergo adaptive metabolic programming to maintain specific metabolic states that support their uncontrolled proliferation. As it has been difficult to directly and effectively inhibit oncogenic signaling cascades with pharmaceutical compounds, focusing on the downstream metabolic pathways that enable indefinite growth may provide therapeutic opportunities. Thus, we sought to characterize metabolic changes in hepatocellular carcinoma (HCC) development and identify metabolic targets required for tumorigenesis.

METHODS

We compared gene expression profiles of Morris Hepatoma (MH3924a) and DEN (diethylnitrosamine)-induced HCC models to those of liver tissues from normal and rapidly regenerating liver models, and performed gain- and loss-of-function studies of the identified gene targets for their roles in cancer cell proliferation in vitro and in vivo.

RESULTS

The proline biosynthetic enzyme PYCR1 (pyrroline-5-carboxylate reductase 1) was identified as one of the most upregulated genes in the HCC models. Knockdown of PYCR1 potently reduced cell proliferation of multiple HCC cell lines in vitro and tumor growth in vivo. Conversely, overexpression of PYCR1 enhanced the proliferation of the HCC cell lines. Importantly, PYCR1 expression was not elevated in the regenerating liver, and KD or overexpression of PYCR1 had no effect on proliferation of non-cancerous cells. Besides PYCR1, we found that additional proline biosynthetic enzymes, such as ALDH18A1, were upregulated in HCC models and also regulated HCC cell proliferation. Clinical data demonstrated that PYCR1 expression was increased in HCC, correlated with tumor grade, and was an independent predictor of clinical outcome.

CONCLUSION

Enhanced expression of proline biosynthetic enzymes promotes HCC cell proliferation. Inhibition of PYCR1 or ALDH18A1 may be a novel therapeutic strategy to target HCC.

LAY SUMMARY

Even with the recently approved immunotherapies against liver cancer, currently available medications show limited clinical benefits or efficacy in the majority of patients. As such, it remains a top priority to discover new targets for effective liver cancer treatment. Here, we identify a critical role for the proline biosynthetic pathway in liver cancer development, and demonstrate that targeting key proteins in the pathway, namely PYCR1 and ALDH18A1, may be a novel therapeutic strategy for liver cancer.

Design and Development of Spray-Dried Microsystems to Improve Technological and Functional Properties of Bioactive Compounds from Hazelnut Shells

An extract obtained from hazelnut shells by-products (HSE) has antioxidant and chemopreventive effects on human melanoma and cervical cancer cell lines, inducing apoptosis by caspase-3 activation. A clinical translation is limited by poor water solubility and low bioavailability. Dried plant extracts often show critical characteristics such as sticky/gummy appearance, unpleasant smell, and instability involving practical difficulties in processing for industrial use. A spray drying method has been applied to transform raw HSE in a microparticulate powder. The biopolymeric matrix was based on l-proline as loading carrier, hydroxyethylcellulose in combination with pectin as coating polymers; lecithin and ethanol were used as solubility enhancers. A Hot-Cold-Hot method was selected to prepare the liquid feed. The thus prepared powder showed good technological properties (solid-state, particle dimensions, morphology, and water dissolution rate), stability, and unchanged chemopreventive effects with respect to the unprocessed HSE.

Proline biosynthesis is a vent for TGFβ-induced mitochondrial redox stress

The production and secretion of matrix proteins upon stimulation of fibroblasts by transforming growth factor-beta (TGFβ) play a critical role in wound healing. How TGFβ supports the bioenergetic cost of matrix protein synthesis is not fully understood. Here, we show that TGFβ promotes protein translation at least in part by increasing the mitochondrial oxidation of glucose and glutamine carbons to support the bioenergetic demand of translation. Surprisingly, we found that in addition to stimulating the entry of glucose and glutamine carbon into the TCA cycle, TGFβ induced the biosynthesis of proline from glutamine in a Smad4-dependent fashion. Metabolic manipulations that increased mitochondrial redox generation promoted proline biosynthesis, while reducing mitochondrial redox potential and/or ATP synthesis impaired proline biosynthesis. Thus, proline biosynthesis acts as a redox vent, preventing the TGFβ-induced increase in mitochondrial glucose and glutamine catabolism from generating damaging reactive oxygen species (ROS) when TCA cycle activity exceeds the ability of oxidative phosphorylation to convert mitochondrial redox potential into ATP. In turn, the enhanced synthesis of proline supports TGFβ-induced production of matrix proteins.

Proline-Dependent Induction of Apoptosis in Oral Squamous Cell Carcinoma (OSCC)-The Effect of Celecoxib

Background: Oral squamous cell carcinoma remains a significant worldwide public health challenge, associated with high morbidity and mortality. Treatment of this type of cancer lacks effective medication. Moreover, there are very few specific biomarkers that are useful in early diagnosis or treatment optimisation. Proline metabolism may prove to be of importance in the search for new treatment modalities. Methods: To evaluate the significance of proline metabolism in the development of oral cancer, proline concentration was assessed in oral cancer tissue and normal oral mucosa. The results were compared to the clinical stage and histological grade of the tumours. Moreover, the expression of proteins involved in proline metabolism via proline dehydrogenase/oxidase (PRODH/POX, PPARγ, HIF1-α) was determined. In the next stage of the study, conducted on cell lines of tongue cancer treated with celecoxib, the aforementioned factors involved in proline metabolism were evaluated. Cellular viability and cell proliferation, as well as apoptosis, were also assessed. Results: Our research results indicate that a high intracellular proline concentration and expression of factors involved in its metabolism correlate with the clinical stage and histological grade of oral cancer. Moreover, we are the first researchers to demonstrate that celecoxib can affect proline metabolism, causing an increase in pro-apoptotic factors (PRODH/POX, PPARγ), reducing the expression of HIF-1α and activating apoptosis. Conclusions: Proline metabolism, due to its involvement in the process of apoptosis, can be of great importance in anticancer therapy. It appears that celecoxib, which influences the PRODH/POX pathway, may be a promising therapeutic compound in oral cancer treatment.

Characterization of the Poplar R2R3-MYB Gene Family and Over-Expression of PsnMYB108 Confers Salt Tolerance in Transgenic Tobacco

The MYB, one of the largest transcription factor families in plants, is related to various biological processes. For an example, the R2R3-MYB family plays an important role in regulation of primary and secondary metabolism, plant growth and development, and responses to hormones and stresses. However, functional studies on the poplar R2R3-MYB genes are limited. In this study, we identified 207 poplar R2R3-MYB genes that are unevenly distributed on the 19 chromosomes of poplar, followed by characterization of their conserved domains. On the basis of phylogenetic analysis, these genes can be divided into 23 groups. Evidence from synteny analyses indicated that the poplar R2R3-MYB gene family is featured by tandem and segmental duplication events. On the basis of RNA-Seq data, we investigated salt responsive genes and explored their expression patterns. Furthermore, we cloned the PsnMYB108 gene from poplar, which is significantly up-regulated in roots and leaves in response to salt stress. To validate its function, we developed transgenic tobacco plants that over-express the PsnMYB108 gene. It appears that the transgenic lines are more tolerant to salt stress than the wild type does. Evidence from physiological analyses demonstrated that over-expression of PsnMYB108 may improve tobacco salt stress tolerance by increasing the reactive oxygen species scavenging ability and the accumulation of proline. These results laid the foundation for future analysis and functional studies of poplar R2R3-MYB family members, and revealed that PsnMYB108 plays an important role in improving plant salt stress tolerance.

Functional characterization of poplar WRKY75 in salt and osmotic tolerance

The WRKY transcription factor family is one of the most important families in plants, playing a significant role in plant growth and development, as well as in stress responses. However, functional studies on the family in response to abiotic stresses are limited in poplar. In the present study, we cloned a WRKY transcription factor gene PagWRKY75, which was down-regulated during early stages of salt and osmotic stresses. The PagWRKY75 protein belongs to the WRKY IIc subfamily. It is located in the nucleus and can bind to the W box. We obtained transgenic poplar lines with PagWRKY75 overexpression or inhibited expression by RNA interference. Stress treatment experiments indicated that the transgenic poplar lines overexpressing PagWRKY75 were more sensitive to salt and osmotic stresses, compared to wild type. The transgenic lines with PagWRKY75 inhibition displayed opposite effects. Furthermore, our results showed that PagWRKY75 can reduce the ability of reactive oxygen species scavenging and the accumulation of proline under stresses, and positively regulate the water loss rate of leaves. These results indicate that the transcription factor PagWRKY75 can negatively regulate salt and osmotic tolerance by modulating various physiological processes.