Up- and down-regulation of longissimus tenderness parallels changes in the myofibril-bound calpain 3 protein

Preliminary Results about Lamb Meat Tenderness Based on the Study of Novel Isoforms and Alternative Splicing Regulation Pathways Using Iso-seq, RNA-seq and CTCF ChIP-seq Data

Tenderness is an important indicator of meat quality. Novel isoforms associated with meat tenderness and the role of the CCCTC-binding factor (CTCF) in regulating alternative splicing to produce isoforms in sheep are largely unknown. The current project studied six sheep from two crossbred populations (Dorper × Hu × Hu, DHH and Dorper × Dorper × Hu, DDH) with divergent meat tenderness. Pooled Iso-seq data were used to annotate the sheep genomes. Then, the updated genome annotation and six RNA-seq data were combined to identify differentially expressed isoforms (DEIs) in muscles between DHH and DDH. These data were also combined with peaks detected from CTCF ChIP-seq data to investigate the regulatory role of CTCF for the alternative splicing. As a result, a total of 624 DEIs were identified between DDH and DHH. For example, isoform 7.524.18 transcribed from CAPN3 may be associated with meat tenderness. In addition, a total of 86 genes were overlapped between genes with transcribed DEIs and genes in differential peaks identified by CTCF ChIP-seq. Among these overlapped genes, ANKRD23 produces different isoforms which may be regulated by CTCF via methylation. As preliminary research, our results identified novel isoforms associated with meat tenderness and revealed the possible regulating mechanisms of alternative splicing to produce isoforms.

Ca2+-induced binding of calpain-2 to myofibrils: Preliminary results in pork longissimus thoracis muscle supporting a role on myofibrillar protein degradation

The aim of this study was to investigate the role of Ca²⁺ in the process of calpain-2 becoming associated to myofibrils and the potential of myofibril-bound calpain to degrade myofibrillar proteins. Different Ca²⁺ concentrations were applied to myofibrils mixed with partially purified calpain-2. Ca²⁺ induced binding of calpain to myofibrils in a concentration-dependent manner. The half-maximal Ca²⁺ requirements for binding of calpain-2 to myofibrils and for calpain-2 proteolysis of myofibrils were 0.60 mM and 0.29 mM, respectively. To investigate the proteolytic activity of myofibril-bound calpain, a mixture of myofibrils and calpain-2 was briefly incubated with Ca²⁺. Unbound calpain was removed by washing with a Ca²⁺-free buffer. The myofibril-bound calpain maintained proteolytic activity and degraded desmin when re-activated with Ca²⁺. In conclusion, the results suggest that an increase in Ca²⁺ will activate and induce binding of calpain to myofibrils. Subsequently, calpain is relatively tightly bound and proteolytically active.

Bovine CAPN3 core promoter initiates expression of foreign genes in skeletal muscle cells by MyoD transcriptional regulation

Activating foreign genes in bovine skeletal muscle is necessary in the study of the role of related genes in skeletal muscle development and the effects on skeletal muscle formation, especially in the study of transgenic cattle. At this time, a skeletal muscle-specific promoter should be selected to initiate a functional foreign gene. Here, calpain3 (CAPN3) was found to be highly expressed in skeletal muscle and skeletal muscle cells by real-time PCR. Next, 5' deletion analysis of the bovine CAPN3 promoter was performed and showed that Q5(-495/+40) region was the core promoter of the bovine CAPN3. A key regulatory site (-465/-453) in CAPN3 core promoter was associated with the transcription factor, MyoD, which is a skeletal muscle-specific transcription factor. Furthermore, the mRNA and protein expression levels of MyoD and CAPN3 were positively correlated during skeletal muscle cell differentiation. The overexpression of MyoD enhanced the activity of the bovine CAPN3 core promoter. The core promoter Q5(-495/+40) could drive the exogenous gene EGFP and the fat-specific expression gene PPARγ in skeletal muscle cells. In summary, our study obtained a bovine skeletal muscle-specific promoter and provided a basis for studying the role of functional genes in the growth and development of skeletal muscle. It also provides a basis for studying the transcriptional regulation mechanism of CAPN3.

Effect of the Calpain System on Volatile Flavor Compounds in the Beef Longissimus lumborum Muscle

The present study was designed to investigate the effects of calpain system on the formation of volatile flavor compounds in Hanwoo beef. In the first experiment (exp.1), Longissimus lumborum (LL) muscle samples were injected with solutions containing 50 mM CaCl2 or 50 mM ZnCl2 and 154 mM NaCl respectively, and aged for 7 d at 4°C. In the second experiment (exp.2), the ground LL muscle was incubated with the aforementioned solutions containing cathepsin inhibitor. The injection with CaCl2 solution greatly elevated the calpain activity and concomitantly, significantly decreased the Warner-Bratzler shear force (p<0.05). The pH, meat color and cooking loss did not differ (p>0.05) between the treatment groups. A total of 51 volatile compounds were identified using the solid phase microextraction with gas chromatography (SPME-GC). Results on volatile analyses from the both experiments showed that the injection with calcium ions led to significant increase (p<0.05) concentrations of pyrazines and sulfuric compounds. These results coincide with a higher rate of protein degradation due to the CaCl2 injection as compared to the control group. Significantly (p<0.05) higher levels of lipid oxidation derived-aldehydes were found in the samples with ZnCl2. The exp.1 showed that cathepsin inhibitors had no effect on the formation of volatile flavor components after 7 d of aging. These results imply that the proteolytic activity of the calpain system is associated with generation of volatile compounds of chiller-aged beef, while the role of cathepsins is likely very limited.

Characterization of the Goose CAPN3 Gene and its Expression Pattern in Muscle Tissues of Sichuan White Geese at Different Growth Stages

Calpain 3 (CAPN3), also known as p94, is associated with multiple production traits in domestic animals. However, the molecular characteristics of the CAPN3 gene and its expression profile in goose tissues have not been reported. In this study, CAPN3 cDNA of the Sichuan white goose was cloned, sequenced, and characterized. The CAPN3 full-length cDNA sequence consists of a 2,316-bp coding sequence (CDS) that encodes 771 amino acids with a molecular mass of 89,019 kDa. The protein was predicted to have no signal peptide, but several N-glycosylation, O-glycosylation, and phosphorylation sites. The secondary structure of CAPN3 was predicted to be 38.65% α-helical. Sequence alignment showed that CAPN3 of Sichuan white goose shared more than 90% amino acid sequence similarity with those of Japanese quail, turkey, helmeted guineafowl, duck, pigeon, and chicken. Phylogenetic tree analysis showed that goose CAPN3 has a close genetic relationship and small evolutionary distance with those of the birds. qRT-PCR analysis showed that in 15-day-old animals, the expression level of CAPN3 was significantly higher in breast muscle than in thigh tissues. These results serve as a foundation for further investigations of the function of the goose CAPN3 gene.

A New Insight into the Role of Calpains in Post-mortem Meat Tenderization in Domestic Animals: A review

Tenderness is the most important meat quality trait, which is determined by intracellular environment and extracellular matrix. Particularly, specific protein degradation and protein modification can disrupt the architecture and integrity of muscle cells so that improves the meat tenderness. Endogenous proteolytic systems are responsible for modifying proteinases as well as the meat tenderization. Abundant evidence has testified that calpains (CAPNs) including calpain I (CAPN1) and calpastatin (CAST) have the closest relationship with tenderness in livestock. They are involved in a wide range of physiological processes including muscle growth and differentiation, pathological conditions and post-mortem meat aging. Whereas, Calpain3 (CAPN3) has been established as an important activating enzyme specifically expressed in livestock's skeletal muscle, but its role in domestic animals meat tenderization remains controversial. In this review, we summarize the role of CAPN1, calpain II (CAPN2) and CAST in post-mortem meat tenderization, and analyse the relationship between CAPN3 and tenderness in domestic animals. Besides, the possible mechanism affecting post-mortem meat aging and improving meat tenderization, and current possible causes responsible for divergence (whether CAPN3 contributes to animal meat tenderization or not) are inferred. Only the possible mechanism of CAPN3 in meat tenderization has been confirmed, while its exact role still needs to be studied further.

Characterization of the expression profile of calpain-3 (CAPN3) gene in chicken

Calpain-3 is a skeletal muscle-specific protease and participates in the regulation of myogenesis. In this study, we quantified the expression of calpain-3 (CAPN3) mRNA in a Chinese local chicken breed (Sichuan Mountainous Black-boned chicken [MB]), to discern the tissue and ontogenic expression pattern. Meanwhile, we compared the CAPN3 mRNA expression pattern in MB chicken at 10 weeks with a commercial meat type chicken line (S01) of the same age to identify the unique expression pattern under different genetic background. A real time quantitative PCR (qRT-PCR) assay was developed for an accurate measurement of its expression in various tissues from chickens at different ages (0, 2, 4, 6, 8, 10, and 12 weeks). Expression of the CAPN3 mRNA was detected in the selected tissues, regardless of age. The breast muscle and leg muscle tissues had a significantly higher expression than the other tissues from the same individual (P < 0.01). Overall, the CAPN3 mRNA level exhibited a "rise-decline" developmental change in detected tissues except for brain. The S01 chicken had a higher expression of the CAPN3 mRNA in detected tissues than the MB chicken at 10 weeks. The present expression data of chicken CAPN3 gene may provide some information to shed light on the tissue and ontogenic expression pattern during chicken development.

Pre-rigor infusion with kiwifruit juice improves lamb tenderness

The ability of pre-rigor infusion of kiwifruit juice to improve the tenderness of lamb was investigated. Lamb carcasses were infused (10% body weight) with fresh kiwifruit juice (Ac), water (W) and a non-infusion control (C) treatment. Infusion treatment had no effect on lamb hot carcass weight, cold carcass weight and chilling evaporative losses. The infused treatment carcasses of Ac and W had lower (P<0.05) pH values than C carcasses during the initial 12h post-mortem. The LD muscles from Ac carcasses were more tender with significantly lower shear force (P<0.001) compared with C and W carcasses during the six days following infusion with the kiwifruit juice. The enhanced proteolytic activity (P=0.002) resulting from the infused kiwifruit juice in Ac carcasses was associated with significant degradation of the myofibrillar proteins, appearance of new peptides and activation of m-calpain during post-mortem ageing. Thus, kiwifruit juice is powerful and easily prepared meat tenderizer, which could contribute efficiently and effectively to the meat tenderization process.

Effect of calcium chloride, zinc chloride, and water infusion on metmyoglobin reducing activity and fresh lamb color

Calcium chloride (CaCl2), zinc chloride (ZnCl2), or water infusions were used to investigate the biochemical factors that affect fresh lamb color, and to examine the role of metmyoglobin-reducing activity in regulating this important quality attribute. Immediately after exsanguination, lamb carcasses (n = 6 per treatment) were infused (10% of BW) with 0.3 M CaCl2, 0.05 M ZnCl2, or water via a catheter inserted into the left carotid artery. The right LM was excised at 24-h postmortem and divided into two halves. The caudal portion was cut into 2.5-cm-thick chops and displayed for 6 d under 1,076 lx of white fluorescent lighting at 2 degrees C, whereas the cranial half was vacuum-packaged and stored at 2 degrees C for 3 wk before retail display. Objective color measurements and samples for biochemical analysis were taken at 0, 1, 3, and 6 d of display. In infused carcasses, pH decline was more rapid (P < 0.05) than in untreated controls, and it was greatest for CaCl2-infused carcasses. Calcium chloride-infused carcasses had lower (P < 0.01) NAD and higher (P < 0.001) NADPH concentrations than water- and ZnCl2-infused or untreated control carcasses. The negative effects of calcium infusion on fresh lamb color, higher (P < 0.01) metmyoglobin accumulation rate, and lower (P < 0.01) L*, a*, and b* color measurements could be explained by the lower amounts of unbound water (P < 0.01), shorter sarcomere length (P < 0.01), lower NAD concentrations (P < 0.01), and higher lipid peroxidation (P < 0.01). Zinc and water-infusions produced less (P < 0.01) lipid oxidation and improved the color and color stability of fresh lamb (P < 0.001). Rate of lipid oxidation in LM chops was greater (P < 0.01) after 3 wk of vacuum-packaged storage than 24-h postmortem. Metmyoglobin-reducing activities (sarcoplasmic and myofibrillar) were decreased in response to infusion treatments (P < 0.001), and ZnCl2 infusion resulted in the lowest metmyoglobin-reducing activities (P < 0.001). A significant association between the myofibrillar metmyoglobin-reducing activity and lipid peroxidation was observed, but metmyoglobin-reducing activities were not associated with any improvement in lamb color. Strategies to increase the antioxidant levels in lamb are very important to improve lamb quality, especially during vacuum-packaging storage.

Calpain 3/p94 is not involved in postmortem proteolysis1,2

Studies on the correlation between expression and/or autolysis of calpain and postmortem proteolysis in muscle have provided conflicting evidence regarding the possible role of calpain 3 in postmortem tenderization of meat. Thus, the objective of this research was to test the effect of postmortem storage on proteolysis and structural changes in muscle from normal and calpain 3 knockout mice. Knockout mice (n = 6) were sacrificed along with control mice (n = 6). Hind limbs were removed and stored at 4 degrees C; muscles were dissected at 0, 1, and 3 d postmortem and subsequently analyzed individually for degradation of desmin. Pooled samples for each storage time and mouse type were analyzed for degradation of nebulin, dystrophin, vinculin, and troponin-T. In a separate experiment, hind-limb muscles from knockout (n = 4) and control mice (n = 4) were analyzed for structural changes at 0 and 7 d postmortem using light microscopy. As an index of structural changes, fiber detachment, cracked or broken fibers, and the appearance of space between sarcomeres were quantified. Cumulatively, the results of the first experiment indicated that postmortem proteolysis of muscle occurred similarly in control and in calpain 3 knockout mice. Desmin degradation did not differ (P > 0.99), and there were no indications that degradation of nebulin, dystrophin, vinculin, and troponin-T were affected by the absence of calpain 3 in postmortem muscle. Structural changes were affected by time postmortem (P < 0.05), but not by the absence of calpain 3 from the muscles. In conclusion, these results indicate that calpain 3 plays a minor role, if any, in postmortem proteolysis in muscle.