The role of 5′-adenosine monophosphate-activated protein kinase(AMPK)in skeletal muscle atrophy

As a key coordinator of metabolism,AMP-activated protein kinase(AMPK)is vitally involved in skeletal muscle maintenance.AMPK exerts its cellular effects through its function as a serine/threonine protein kinase by regulating many downstream targets and plays important roles in the development and growth of skeletal muscle.AMPK is activated by phosphorylation and exerts its function as a kinase in many processes,including synthesis and degradation of proteins,mitochondrial biogenesis,glucose uptake,and fatty acid and cholesterol metabolism.Skeletal muscle atrophy is a result of various diseases or disorders and is characterized by a decrease in muscle mass.The pathogenesis and therapeutic strategies of skeletal muscle atrophy are still under investigation.In this review,we discuss the role of AMPK in skeletal muscle metabolism and atrophy.We also discuss targeting AMPK for skeletal muscle treatment,including exercise,AMPK activators including 5-amino-4-imidazolecarboxamide ribonucleoside and metformin,and low-level lasers.These studies show the important roles of AMPK in regulating muscle metabolism and function;thus,the treatment of skeletal muscle atrophy needs to take into account the roles of AMPK.

Influences of dietary protein sources and crude protein levels on intracellular free amino acid profile in the longissimus dorsi muscle of finishing gilts

Background： The current study was carried out to determine effects of dietary protein source and crude protein（CP）level on carcass characteristics, meat quality, and muscle amino acid（AA） profile in finishing gilts. The experiment was designed as a 2 × 2 factorial arrangement with two sources of dietary proteins（cottonseed meal, CSM vs. soybean meal, SBM） and two levels of CP（12 % vs. 14 %, as-fed basis）. Seventy-two crossbred gilts（89.5 ± 0.9 kg） were allotted to one of four dietary treatments in a randomized complete block design for a period of 28 d. All diets were formulated to be isoenergetic and similar concentrations of standardized ileal digestible essential AA covering the nutrient requirements of pigs.Results： Growth, carcass characteristics and meat quality were not affected by dietary protein source nor crude protein level（P ＆gt; 0.10） except that average daily feed intake was increased by CSM diets（P = 0.03）. Gilts offered reduced protein diets had lower muscle p H45min（P 〈 0.05）. Neither dietary protein source nor crude protein level influenced N deposition. However, reduced protein diets decreased N intake, N excretion, and serum urea nitrogen content, whilst improved N efficiency（P 〈 0.01）. CSM diets increased N intake（P = 0.04）,but did not depress N efficiency. The concentrations of phenylalanine, tryptophan, cysteine and tyrosine（P 〈 0.05） of the longissimus muscle were decreased when gilts offered CSM diets, while muscle intracellular free valine concentration was increased（P = 0.03）. The gilts offered reduced protein diets had greater intracellular concentrations of free methionine, lysine, and total AA in muscle（P 〈 0.05）.Conclusion： These results suggest that CSM could replace SBM as a primary protein source in finishing pig diets in terms of performance, N efficiency, carcass characteristics, and meat quality, but decrease the concentrations of muscle specific AA. Furthermore, the reduced protein diet played an important role in increasing muscle intracellular concentrations of specific free amino acids（FAA）, and in reducing the relative ratios of specific FAA to lysine in longissimus dorsi muscle of pig, whose biological meaning needs further studies.

Effects of dietary protein restriction on muscle fiber characteristics and m TORC1 pathway in the skeletal muscle of growing-finishing pigs

Background： To investigate the effects of dietary crude protein（CP） restriction on muscle fiber characteristics and key regulators related to protein deposition in skeletal muscle, a total of 18 growing-finishing pigs（62.30 ± 0.88 kg）were allotted to 3 groups and fed with the recommended adequate protein（AP, 16 % CP） diet, moderately restricted protein（MP, 13 % CP） diet and low protein（LP, 10 % CP） diet, respectively. The skeletal muscle of different locations in pigs, including longissimus dorsi muscle（LDM）, psoas major muscle（PMM） and biceps femoris muscle（BFM） were collected and analyzed.Results： Results showed that growing-finishing pigs fed the MP or AP diet improved（P 〈 0.01） the average daily gain and feed： gain ratio compared with those fed the LP diet, and the MP diet tended to increase（P = 0.09） the weight of LDM. Moreover, the ATP content and energy charge value were varied among muscle samples from different locations of pigs fed the reduced protein diets. We also observed that pigs fed the MP diet up-regulated（P 〈 0.05） muscular m RNA expression of all the selected key genes, except that myosin heavy chain（My HC） IIb,My HC IIx, while m RNA expression of ubiquitin ligases genes was not affected by dietary CP level. Additionally, the activation of mammalian target of rapamycin complex 1（m TORC1） pathway was stimulated（P 〈 0.05） in skeletal muscle of the pigs fed the MP or AP diet compared with those fed the LP diet.Conclusion： The results suggest that the pigs fed the MP diet could catch up to the growth performance and the LDM weight of the pigs fed the AP diet, and the underlying mechanism may be partly due to the alteration in energy status, modulation of muscle fiber characteristics and m TORC1 activation as well as its downstream effectors in skeletal muscle of different locations in growing-finishing pigs.

Effects of estradiol on cell cycle and cyclin proteins of vascular smooth muscle cells in rats

To study the effects of 17β-estradiol(E2) on the growth of cultured rat vascular smooth muscle cells (VSMC).Methods The cell cycle and the expressions of Cyclin D1 and CDK4 proteins were examined by flow cytometry in VSMC cultured in different concentrations (0～100 nmol/L) of 17β-estradiol with or without serum.Results Under serum-stimulating conditions,17β-estradiol(1,10,100 nmol/L) promoted VSMC proliferation by accelerating their cell cycle progression from G1 to S phases,and the cell rates at S were (31.89±9.14)%(35.90±4.59)% and (30.77±1.20)% respectively,significantly higher than the corresponding values of control cells (21.63±1.80)%.This was accompanied by the significantly increased expression of Cyclin D1 and CDK4 proteins.In the cultures without serum,however,high concentrations (10,100 nmol/L) of E2 induced a cell cycle arrest at G1 phase,which was characterizsed by decreased cell rates at S phase [(9.93±1.43)% and (8.76±1.80)% respectively,P<0.05] as compared with the corresponding control values and a down-regulation of expressions of Cyclin D1 and CDK4 proteins.Conclusion E2 can either promote or inhibit VSMC proliferation depending upon the presence or absence of serum mitogens.The underlying mechanism may be associated with the hormone’s action on the expression of Cyclin D1 and CDK4 which act as the G1 phase regulators.4 refs.

Vitamin D receptor (VDR) mediates the quiescence of activated hepatic stellate cells (aHSCs) by regulating M2 macrophage exosomal smooth muscle cell-associated protein 5 (SMAP-5)

An effective therapeutic regimen for hepatic fibrosis requires a deep understanding of the pathogenesis mechanism.Hepatic fibrosis is characterized by activated hepatic stellate cells(aHSCs)with an excessive production of extracellular matrix.Although promoted activation of HSCs by M2 macrophages has been demonstrated,the molecular mechanism involved remains ambiguous.Herein,we propose that the vitamin D receptor(VDR)involved in macrophage polarization may regulate the communication between macrophages and HSCs by changing the functions of exosomes.We confirm that activating the VDR can inhibit the effect of M2 macrophages on HSC activation.The exosomes derived from M2 macrophages can promote HSC activation,while stimulating VDR alters the protein profiles and reverses their roles in M2 macrophage exosomes.Smooth muscle cell-associated protein 5(SMAP-5)was found to be the key effector protein in promoting HSC activation by regulating autophagy flux.Building on these results,we show that a combined treatment of a VDR agonist and a macrophage-targeted exosomal secretion inhibitor achieves an excellent anti-hepatic fibrosis effect.In this study,we aim to elucidate the association between VDR and macrophages in HSC activation.The results contribute to our understanding of the pathogenesis mechanism of hepatic fibrosis,and provide potential therapeutic targets for its treatment.

The skeletal muscle fiber periphery:A nexus of mTOR-related anabolism

Skeletal muscle anabolism is driven by numerous stimuli such as growth factors,nutrients(i.e.,amino acids,glucose),and mechanical stress.These stimuli are integrated by the mechanistic target of rapamycin(mTOR)complex 1(mTORC1)signal transduction cascade.In recent years,work from our laboratory and elsewhere has sought to unravel the molecular mechanisms underpinning the mTOR-related activation of muscle protein synthesis(MPS),as well as the spatial regulation of these mechanisms within the skeletal muscle cell.These studies have suggested that the skeletal muscle fiber periphery is a region of central importance in anabolism(i.e.,growth/MPS).Indeed,the fiber periphery is replete with the substrates,molecular machinery,and translational apparatus necessary to facilitate MPS.This review provides a summary of the mechanisms underpinning the mTOR-associated activation of MPS from cell,rodent,and human studies.It also presents an overview of the spatial regulation of mTORC1 in response to anabolic stimuli and outlines the factors that distinguish the periphery of the cell as a highly notable region of skeletal muscle for the induction of MPS.Future research should seek to further explore the nutrient-induced activation of mTORC1 at the periphery of skeletal muscle fibers.

QUANTITATION OF P53 PROTEIN EXPRESSION IN GASTROINTESTINAL SMOOTH MUSCLE TUMORSCLINICOPATHOLOGICAL CORRELATION AND PROGNOSTIC SIGNIFICANCE

Quantitative analysis of P53 protein expression was performed on paraffin-embedded tissues from 55 smooth muscle tumors of the gastrointestinal tract, using immunofluo-rescence and flow cytometry. No positive expression was found in normal smooth muscle tissues of the gastrointestinal tract. Over-expression of P53 gene was found in a significantly higher proportion in leiomyosarcomas (90%) and potentially malignant smooth muscle tumors (75%) as compared to leiomyomas (14%) (P< 0.005). The quantitation of P53 expression was found to be progressively enhanced in the sequence from leiomyoma through potentially malignant smooth muscle tumor to leiomyosarcoma (P< 0.005). It was markedly over-expressed when the mitotic counts ranged from one to more than one per 10 high power fields (P< 0.005) or the mild cytologic atypia was found (P< 0.005). The five-year survival rate was significantly higher in patients with low-expression of P53 than in those with over-expression of P53 (P< 0.005). It was suggested that P53 over-expression might be associated with the transformation of leiomyoma into leiomyosarcoma and could be used as an objective parameter in distinguishing the malignant from the benign and predicting the prognosis of patients with smooth muscle rumors of the gastrointestinal tract.

Contribution of protein kinase C to passively sensitized human airway smooth muscle cells proliferation

Background Airway smooth muscle proliferation plays an important role in airway remodeling in asthma. But little is known about the intracellular signal pathway in the airway smooth muscle cell proliferation in asthma. The objective of this paper is to investigate the contribution of protein kinase C (PKC) and its alpha isoform to passively sensitized human airway smooth muscle cells (HASMCs) proliferation. Methods HASMCs in culture were passively sensitized with 10% serum from asthmatic patients,with non-asthmatic human serum treated HASMCs used as the control. The proliferation of HASMCs was examined by cell cycle analysis,3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazoliumbromide (MTT) colorimetric assay and proliferating cell nuclear antigen (PCNA) immunofluorescence staining. The effect of PKC agonist phorbol 12-myristate 13-acetate (PMA) and PKC inhibitor Ro-31-8220 on the proliferation of HASMCs exposed to human asthmatic serum and non-asthmatic control serum was also examined by the same methods. The protein and mRNA expression of PKC-α in passively sensitized HASMCs were detected by immunofluorescence staining and reverse transcription-polymerase chain reaction. Results The percentage of S phase,absorbance (value A) and the positive percentage of PCNA protein expression in HASMCs passively sensitized with asthmatic serum were (16.30±2.68)%,0.430±0.060 and (63.4±7.4)% respectively,which were significantly increased compared with HASMCs treated with control serum [(10.01±1.38)%,0.328±0.034 and (37.2±4.8)%,respectively] ( P <0.05). After HASMCs were passively sensitized with asthmatic serum,they were treated with PMA,the percentage of S phase,value A and the positive percentage of PCNA protein expression were (20.33±3.39)%,0.542±0.065 and (76.0±8.7)% respectively,which were significantly increased compared with asthmatic serum sensitized HASMCs without PMA( P <0.05). After HASMCs passively sensitized with asthmatic serum were treated with Ro-31-8220,the percentage of S phase,value A and the positive percentage of PCNA protein expression were (11.21±1.56)%,0.331±0.047 and (38.8±6.0)% respectively,which were significantly decreased compared with asthmatic serum sensitized HASMCs without Ro-31-8220 ( P <0.05). The relative ratio of value A of PKC-α mRNA and the positive percentage of PKC-α protein expression in passively sensitized HASMCs were 1.23±0.10 and (61.1±9.4)% respectively, which were significantly increased compared with HASMCs treated with control serum [1.05±0.09 and (34.9±6.7)%,respectively] ( P <0.05). Conclusions The proliferation of HASMCs passively sensitized with human asthmatic serum is increased. PKC and its alpha isoform may contribute to this proliferation.

Effect of high glucose levels on the calcification of vascular smooth muscle cells by inducing osteoblastic differentiation and intracellular calcium deposition via BMP-2/Cbfα-1 pathway

In this paper, we investigate the effect and the possible mechanism of high glucose levels on the calcification of human aortic smooth muscle cells （HASMCs）. HASMCs were divided into four groups： normal glucose group （NG）, osmolality control group （OC）, high glucose group （HG, HASMCs culture medium containing 30 mmol/L glucose）, and high glucose plus recombinant human Noggin protein （bone morphogenetic protein-2 （BMP-2） antagonist） group （HN）. The mRNA levels and the protein expressions of BMP-2 and core binding factor alpha-1 （Cbfa-1） were measured by real-time quantitative polymerase chain reaction （PCR） and Western blot. After induced by 10 mmol/L β-glycerol phosphoric acid, cells were had＇vested for assessments of alkaline phosphatase （ALP） activities at Days 1,2, and 3, and intracellular calcium contents at Days 7 and 14, respectively. High glucose levels increased the mRNA levels and the protein expressions of BMP-2 and Cbfa-1 （P〈0.05）. The expression of Cbfa-1 was partially blocked by Noggin protein （P〈0.05）, while BMP-2 was not （P〉0.05）. After being induced by β-glycerol phosphoric acid, high glucose levels increased the ALP activity [（48.63±1.03） vs. （41.42±2.28） U/mg protein, Day 3; P〈0.05] and the intracellular calcium content [（2.76±0.09） vs. （1.75±0.07） μmol/mg protein, Day 14; P〈0.05] in a time-dependent manner when compared with the NG group, while the ALP activity could not be blocked by Noggin protein [（48.63±1.03） vs. （47.37±0.97） U/mg protein, Day 3; P〉0.05]. These results show that high glucose levels can evoke the calcification of HASMCs by inducing osteoblastic trans-differentiation and intracellular calcium deposition via the BMP-2/Cbfa-1 pathway, which can be partially blocked by Noggin protein.

The signal transduction pathway in the proliferation of airway smooth muscle cells induced by urotensin Ⅱ

Background Human urotensin Ⅱ (UⅡ) is the most potent mammalian vasoconstrictor identified so far. Our previous study showed that UⅡ is a potent mitogen of airway smooth muscle cells (ASMC) inducing ASMC proliferation in a dose-dependent manner. The signal transduction pathway of UⅡ mitogenic effect remains to be clarified. This study was conducted to investigate the signal transduction pathway in the proliferation of ASMC induced by UⅡ. Methods In primary cultures of rat ASMCs,activities of protein kinase C (PKC),mitogen-activated protein kinase (MAPK) and calcineurin (CaN) induced by UⅡ were measured. The effect of CaN on PKC and MAPK was studied by adding cyclosporin A (CsA),a specific inhibitor of CaN. Using H_7 and PD_ 98059 , inhibitors of PKC and MAPK,respectively,to study the effect of PKC and MAPK on CaN. The cytosolic free calcium concentration induced by UⅡ was measured using Fura-2/AM. Results UⅡ 10 -7 mol/L stimulated ASMC PKC and MAPK activities by 44% and 24% ( P <0.01), respectively,after incubating for 20 minutes. It increased CaN activity in a time-dependent manner,being 1.68 times as that of control for 24 hours ( P <0.01). It promoted the cytosolic free calcium concentration increase of 18% ( P <0.01). CsA 10 -6 mol/L and H_7 50 μmol/L inhibited UⅡ-stimulated CaN activity by 45% ( P <0.01) and 21% ( P <0.05),respectively,while PD_ 98059 50 μmol/L had no effect on CaN activity ( P >0.05). CsA 10 -6 mol/L inhibited UⅡ-stimulated PKC activity by 14% ( P <0.05),while having no effect on MAPK activity ( P >0.05). Conclusions UⅡ increases cytosolic free calcium concentration and activates PKC,MAPK and CaN. The signal transduction pathway between PKC and CaN has cross-talk.

Bone microenvironment regulative hydrogels with ROS scavenging and prolonged oxygen-generating for enhancing bone repair

Large bone defects resulting from fractures and disease are a major clinical challenge,being often unable to heal spontaneously by the body’s repair mechanisms.Lines of evidence have shown that hypoxia-induced overproduction of ROS in bone defect region has a major impact on delaying bone regeneration.However,replenishing excess oxygen in a short time cause high oxygen tension that affect the activity of osteoblast precursor cells.Therefore,reasonably restoring the hypoxic condition of bone microenvironment is essential for facilitating bone repair.Herein,we designed ROS scavenging and responsive prolonged oxygen-generating hydrogels(CPP-L/GelMA)as a“bone microenvironment regulative hydrogel”to reverse the hypoxic microenvironment in bone defects region.CPP-L/GelMA hydrogels comprises an antioxidant enzyme catalase(CAT)and ROS-responsive oxygen-releasing nanoparticles(PFC@PLGA/PPS)co-loaded liposome(CCP-L)and GelMA hydrogels.Under hypoxic condition,CPP-L/GelMA can release CAT for degrading hydrogen peroxide to generate oxygen and be triggered by superfluous ROS to continuously release the oxygen for more than 2 weeks.The prolonged oxygen enriched microenvironment generated by CPP-L/GelMA hydrogel significantly enhanced angiogenesis and osteogenesis while inhibited osteoclastogenesis.Finally,CPP-L/GelMA showed excellent bone regeneration effect in a mice skull defect model through the Nrf2-BMAL1-autophagy pathway.Hence,CPP-L/GelMA,as a bone microenvironment regulative hydrogel for bone tissue respiration,can effectively scavenge ROS and provide prolonged oxygen supply according to the demand in bone defect region,possessing of great clinical therapeutic potential.