Paracrine and endocrine actions of bone——the functions of secretory proteins from osteoblasts, osteocytes, and osteoclasts

The skeleton is a dynamic organ that is constantly remodeled. Proteins secreted from bone cells, namely osteoblasts, osteocytes,and osteoclasts exert regulation on osteoblastogenesis, osteclastogenesis, and angiogenesis in a paracrine manner. Osteoblasts secrete a range of different molecules including RANKL/OPG, M-CSF, SEMA3A, WNT5A, and WNT16 that regulate osteoclastogenesis. Osteoblasts also produce VEGFA that stimulates osteoblastogenesis and angiogenesis. Osteocytes produce sclerostin（SOST） that inhibits osteoblast differentiation and promotes osteoclast differentiation. Osteoclasts secrete factors including BMP6, CTHRC1, EFNB2, S1P, WNT10B, SEMA4D, and CT-1 that act on osteoblasts and osteocytes, and thereby influencea A osteogenesis. Osteoclast precursors produce the angiogenic factor PDGF-BB to promote the formation of Type H vessels, which then stimulate osteoblastogenesis. Besides, the evidences over the past decades show that at least three hormones or ＂osteokines＂from bone cells have endocrine functions. FGF23 is produced by osteoblasts and osteocytes and can regulate phosphate metabolism. Osteocalcin（OCN） secreted by osteoblasts regulates systemic glucose and energy metabolism, reproduction, and cognition. Lipocalin-2（LCN2） is secreted by osteoblasts and can influence energy metabolism by suppressing appetite in the brain.We review the recent progresses in the paracrine and endocrine functions of the secretory proteins of osteoblasts, osteocytes, and osteoclasts, revealing connections of the skeleton with other tissues and providing added insights into the pathogenesis of degenerative diseases affecting multiple organs and the drug discovery process.

Regulation of spermatogenesis by paracrine/autocrine testicular factors

Spermatogenesis is a complex process regulated by endocrine and testicular paracrine/autocrine factors. Gonadotropins are involved in the regulation of several testicular paracrine factors, mainly of the IL-1 family and testicular hormones. Testicular cytokines and growth factors (such as IL-1, IL-6, TNF, IFN-γ, LIF and SCF) were shown to affect both the germ cell proliferation and the Leydig and Sertoli cells functions and secretion. Cytokines and growth factors are produced by immune cells and in the interstitial and seminiferous tubular compartments by various testicular cells, including Sertoli, Leydig, peritubular cells, spermatogonia, differentiated spermatogonia and even spermatozoa. Corresponding cytokine and growth factor receptors were demonstrated on some of the testicular cells. These cytokines also control the secretion of the gonadotropins and testosterone in the testis. Under pathological conditions the levels of pro-inflammatory cytokines are increased and negatively affected spermatogenesis. Thus, the expression levels and the mechanisms involved in the regulation of testicular paracrine/autocrine factors should be considered in future therapeutic strategies for male infertility.

Adipose-derived stem cells enhance myogenic differentiation in the mdx mouse model of muscular dystrophy via paracrine signaling

Adipose-derived stem cells have been shown to promote peripheral nerve regeneration through the paracrine secretion of neurotrophic factors. However, it is unclear whether these cells can promote myogenic differentiation in muscular dystrophy. Adipose-derived stem cells （6 × 106） were injected into the gastrocnemius muscle of mdx mice at various sites. Dystrophin expression was found in the muscle fibers. Phosphorylation levels of Akt, mammalian target of rapamycin （mTOR）, eIF-4E binding protein 1 and $6 kinase 1 were increased, and the Akt/mTOR pathway was activated. Simultaneously, myogenin levels were increased, whereas cleaved caspase 3 and vimentin levels were decreased. Necrosis and fibrosis were reduced in the muscle fibers. These findings suggest that adipose-derived stem cells promote the re- generation and survival of muscle cells by inhibiting apoptosis and fibrosis, thereby alleviating muscle damage in muscular dystrophy.

Intravitreal stem cell paracrine properties as a potential neuroprotective therapy for retinal photoreceptor neurodegenerative diseases

Retinal degenerations are the leading causes of irreversible visual loss worldwide. Many pathologies included under this umbrella involve progressive degeneration and ultimate loss of the photoreceptor cells, with age-related macular degeneration and inherited and ischemic retinal diseases the most relevant. These diseases greatly impact patients' daily lives, with accompanying marked social and economic consequences. However, the currently available treatments only delay the onset or slow progression of visual impairment, and there are no cures for these photoreceptor diseases. Therefore, new therapeutic strategies are being investigated, such as gene therapy, optogenetics, cell replacement, or cell-based neuroprotection. Specifically, stem cells can secrete neurotrophic, immunomodulatory, and anti-angiogenic factors that potentially protect and preserve retinal cells from neurodegeneration. Further, neuroprotection can be used in different types of retinal degenerative diseases and at different disease stages, unlike other potential therapies. This review summarizes stem cell-based paracrine neuroprotective strategies for photoreceptor degeneration, which are under study in clinical trials, and the latest preclinical studies. Effective retinal neuroprotection could be the next frontier in photoreceptor diseases, and the development of novel neuroprotective strategies will address the unmet therapeutic needs.

SIMULTANEOUS OVER-EXPRESSION OF INSULIN-LIKE GROWTH FACTOR- Ⅱ (IGF- Ⅱ ) AND IGF- Ⅱ RECEPTOR(IGF- Ⅱ R) GENES IN HUMAN PRIMARY CANCER-IMPLICATION OF AUTOCRINE AND PARACRINE MECHANISM IN AUTONOMOUS GROWTH OF HEPATIC CANCER

This is first report about the simultaneous over-expression of both Insulin-like growth factor (IGF- I ) and its receptor (IGF- I R) at mRNA level in human primary hepatic Cancer (PHC). In 10 PHC samples from China, IGF-I and IGF- I R were both over-expressed, whereas only a background signal was detected in normal liver. In 5 pairs of PHC and its non- tumorous adjacent liver tissues from South Africa, IGF- I and IGF- I R were also over-expressed in PHC. mRNA expression of IGF- I in all 5 cases and IGF- I R in 4 of 5 cases were higher in cancer than non- tumorous adjacent liver tissues. These results strongly implicate that an autocrine and/ or paracrine mechanism might be Involved in formation and progression of PHC.

A paracrine role for white thermogenic adipocytes in innervation: an evidence-based hypothesis

White adipose tissue(WAT) stores energy and also plays an important endocrine role in producing adipokines for communication with the peripheral and central nervous system. WAT consists of the major lipogenic unilocular adipocytes and the minor populations of beige and brite multilocular adipocytes. These multilocular adipocytes express thermogenic genes and have phenotypic similarity with thermogenic brown adipose tissue. According to a current paradigm, multilocular adipocytes have a thermogenic function in WAT. In this mini review, we discuss data revealing heterogeneity among multilocular cell subsets in WAT and their functions beyond thermogenesis. We propose a hypothetical neuroendocrine role for multilocular adipocytes subsets in the formation of adaptive sensory-sympathetic circuits between the central nervous system and adipose tissue, which activate lipolysis and thermogenesis in WAT in high energy demand situations.

Paracrine factors for neurodegenerative disorders:special emphasis on Parkinson's disease

The progressive loss of dopaminergic neurons in the ventral mesencephalon is the main pathological hallmark of Parkinson’s disease（PD）.Drugs currently available only alleviate the principal symptomatic motor-related disturbances and their benefit is counteracted by side effects in the long time.

Activin-Directed Differentiation of Human Embryonic Stem Cells Differentially Modulates Alveolar Epithelial Wound Repair via Paracrine Mechanism

Differentiated embryonic stem cells (ESC) can ameliorate lung inflammation and fibrosis in animal lung injury models;therefore, ESC, or their products, could be candidates for regenerative therapy for incurable lung diseases, such as idiopathic pulmonary fibrosis (IPF). In this study, we have investigated the paracrine effect of differentiated and undifferentiated human ESC on alveolar epithelial cell (AEC) wound repair. hESC line, SHEF-2 cells were differentiated with Activin treatment for 22 days in an embryoid body (EB) suspension culture. Conditioned media (CM) which contain cell secretory factors were collected at different time points of differentiation. CM were then tested onin vitro?wound repair model with human type II AEC line, A549 cells (AEC). Our study demonstrated that CM originated from undifferentiated hESC significantly inhibited AEC wound repair when compared to the control. Whereas, CM originated from Activin-directed hESC differentiated cell population demonstrated a differential reparative effect on AEC wound repair model. CM obtained from Day-11 of differentiation significantly enhanced AEC wound repair in comparison to CM collected from pre- and post-Day-11 of differentiation. Day-11 CM enhanced AEC wound repair through significant stimulation of cell migration and cell proliferation. RT-PCR and immunocytochemistry confirmed that Day-11 CM was originated form a mixed population of endodermal/mesodermal differentiated hESC. This report suggests a putative paracrine-mediated epithelial injury healing mechanism by hESC secreted products, which is valuable in the development of novel stem cell-based therapeutic strategies.

SF/HGF-c-Met autocrine and paracrine promote metastasis of hepatocellular carcinoma

AIM: To explore the role of SF/HGF-Met autocrine and parscrine in metastasis of hepatocellular carcinoma (HCC).METHODS: SF/HGF and c-met transcription and protein expression in HCC were examined by RT-PCR and Western Blot in 4 HCC cell lines, including HepG2, Hep3B,SMMC7721 and MHCC-1, the last cell line had a higher potential of metastasis. Sf/hgf cDNA was transfected by the method of Lipofectin into SMMC7721. SF/HGF and c-met antibody were used to stimulate and block SF/HGF-c-met signal transduction. Cell morphology, mobility, and proliferation were respectively compared by microscopic observation, wound healing assay and cell growth curve.RESULTS: HCC malignancy appeared to be relative to its met-SF/HGF expression. In MHCC-1, c-met expression was much stronger than that in other cell lines with lower potential of metastasis and only SF/HGF autocrine existed in MHCC-1. After sf/hgf cDNA transfection or conditioned medium of MHCC-1 stimulation, SMMC7721 changed into elongated morphology, and the abilities of proliferation ( P < 0.05) and mobility increased. Such bio-activity could he blocked by c-met antibody ( P< 0.05).CONCLUSION: The system of SF/HGF-c-met autocrine and paracrine played an important role in development and metastasis potential of HCC. Inhibition of SF/HGF-c-met signal transduction system may reduce the growth and metastasis of HCC.

Effects of microenvironment and biological behavior on the paracrine function of stem cells

Mesenchymal stem cells(MSCs),the most well-studied cell type in the field of stem cell therapy,have multi-lineage differentiation and self-renewal potential.MsC-based thera-pies have been used to treat diverse diseases because of their ability to potently repair tissue and locally restore function.An increasing body of evidence demonstrates that paracrine func-tion is central to the effects of MsC-based therapy.Growth factors,cytokines,chemokines,extracellular matrix components,and extracellular vehicles all contribute to the beneficial ef-fects of MSCs on tissue regeneration and repair.The paracrine substances secreted by MSCs change depending on the tissue microenvironment and biological behavior.In this review,we discuss the bioactive substances secreted by MsCs depending on the microenvironment and biological behavior and their regulatory mechanisms,which explain their potential to treat human diseases,to provide new ideas for further research and clinical cell-free therapy.

Heparinized PGA host-guest hydrogel loaded with paracrine products from electrically stimulated adipose-derived mesenchymal stem cells for enhanced wound repair

The microenvironment of the wound bed is essential in the regulation of wound repair.In this regard,strategies that provide a repairing favorable microenvironment may effectively improve healing outcomes.Herein,we attempted to use electrical stimulation(ES)to boost the paracrine function of adipose-derived stem cells from rats(rASCs).By examining the concentrations of two important growth factors,VEGF and PDGF-AA,in the cell culture supernatant,we found that ES,especially 5𝜇A ES,stimulated rASCs to produce more paracrine factors(5𝜇A-PFs).Further studies showed that ES may modulate the paracrine properties of rASCs by upregulating the levels of TRPV2 and TRPV3,thereby inducing intracellular Ca^(2+) influx.To deliver the PFs to the wound to effectively improve the wound microenvironment,we prepared a heparinized PGA host-guest hydrogel(PGA-Hp hydrogel).Moreover,PGA-Hp hydrogel loaded with 5𝜇A-PFs effectively accelerated the repair process of the full-thickness wound model in rats.Our findings revealed the effects of ES on the paracrine properties of rASCs and highlighted the potential application of heparinized PGA host-guest hydrogels loaded with PFs derived from electrically stimulated rASCs in wound repair.

Use of priming strategies to advance the clinical application of mesenchymal stromal/stem cell-based therapy

Mesenchymal stromal/stem cells(MSCs)have garnered significant attention in the field of regenerative medicine due to their remarkable therapeutic potential.MSCs play a pivotal role in maintaining tissue homeostasis and possess diverse functions in tissue repair and recovery in various organs.These cells are charac-terized by easy accessibility,few ethical concerns,and adaptability to in vitro cultures,making them a valuable resource for cell therapy in several clinical conditions.Over the years,it has been shown that the true therapeutic power of MSCs lies not in cell engraftment and replacement but in their ability to produce critical paracrine factors,including cytokines,growth factors,and exosomes(EXOs),which modulate the tissue microenvironment and facilitate repair and regeneration processes.Consequently,MSC-derived products,such as condi-tioned media and EXOs,are now being extensively evaluated for their potential medical applications,offering advantages over the long-term use of whole MSCs.However,the efficacy of MSC-based treatments varies in clinical trials due to both intrinsic differences resulting from the choice of diverse cell sources and non-standardized production methods.To address these concerns and to enhance MSC therapeutic potential,researchers have explored many priming strategies,including exposure to inflammatory molecules,hypoxic conditions,and three-dimensional culture techniques.These approaches have optimized MSC secretion of functional factors,empowering them with enhanced immunomodulatory,angiogenic,and regenerative properties tailored to specific medical conditions.In fact,various priming strategies show promise in the treatment of numerous diseases,from immune-related disorders to acute injuries and cancer.Currently,in order to exploit the full therapeutic potential of MSC therapy,the most important challenge is to optimize the modulation of MSCs to obtain adapted cell therapy for specific clinical disorders.In other words,to unlock the complete potential of MSCs in regenerative medicine,it is crucial to identify the most suitable tissue source and develop in vitro manipulation protocols specific to the type of disease being treated.

间充质干细胞促进肌肉组织修复的应用前景

背景:间充质干细胞是从骨髓、脂肪、脐带等多种组织中分离出来的多能基质细胞,可分化成不同的细胞类型,并分泌多种具有治疗潜能的蛋白,在肌肉组织修复中有良好的应用前景。目的:综述间充质干细胞促进肌肉组织修复的研究进展,为进一步临床应用提供理论依据。方法:检索中国知网、维普、万方、PubMed、Embase及Web of Science数据库从建库至2022年相关文献,检索词为“间充质干细胞,肌肉组织,肌肉损伤,肌肉萎缩,外泌体,支架”和“mesenchymal stem cells,muscle tissue,muscle injury,muscle atrophy,exosomes,scaffolds”。筛选间充质干细胞促进肌纤维增殖修复的文献,共纳入98篇文献进行综述分析。结果与结论:①间充质干细胞促进肌纤维增殖修复的相关机制复杂,多以抗炎、抑制间质纤维化、抑制脂肪形成等方式促进肌纤维增殖修复;②基于间充质干细胞的相关生物支架、细胞共培养等可明显弥补间充质干细胞定植后存活率低的缺点;③当前间充质干细胞疗法仍有明显的局限性,未来间充质干细胞联合其他治疗方式应当成为主要的发展趋势。

低氧和氧化应激对不同来源间充质干细胞旁分泌的差异性影响

背景:间充质干细胞的生物学行为受所处生存微环境的影响,微环境条件预处理是调控间充质干细胞功能的重要手段。目的:对比氧化应激和低氧条件下脐带间充质干细胞、脂肪间充质干细胞旁分泌功能的差异,为治疗不同疾病选择适当的间充质干细胞预处理方式提供理论依据。方法:培养脐带间充质干细胞和脂肪间充质干细胞,分别加入不同浓度的H_(2)O_(2)或不同体积分数的O_(2)干预,检测细胞形态、增殖、活力和旁分泌因子表达。结果与结论:①普通培养环境下,脐带间充质干细胞中脑源性神经营养因子和转化生长因子β的表达水平显著高于脂肪间充质干细胞,而脂肪间充质干细胞中基质细胞衍生因子1α和肿瘤坏死因子刺激因子6的表达水平显著高于脐带间充质干细胞;②中低浓度水平(≤100μmol/L)H_(2)O_(2)对2种间充质干细胞活力的影响无显著差异,但H_(2)O_(2)浓度从50μmol/L增至100μmol/L使脐带间充质干细胞中血管内皮生长因子表达水平显著增高,脂肪间充质干细胞中碱性成纤维细胞生长因子、血管内皮生长因子、基质细胞衍生因子1α和白细胞介素10表达水平均显著升高;③体积分数1%O_(2)促进2种间充质干细胞增殖;体积分数1%O_(2)干预24 h后,2种间充质干细胞中基因表达水平均有升高,但脂肪间充质干细胞中血管内皮生长因子、白细胞介素10和肿瘤坏死因子刺激因子6的表达水平显著高于脐带间充质干细胞;④结果提示:低氧和氧化应激预处理可提高间充质干细胞旁分泌功能,但2种间充质干细胞对低氧和氧化应激的响应不同,治疗疾病可选择适合的间充质干细胞预处理方式进一步提升其治疗潜力。

γ-氨基丁酸在肿瘤微环境中的研究进展

氨基丁酸是神经系统中经典的抑制性神经递质,由γ-氨基丁酸能神经元合成并释放至突触间隙,作用于突触后膜,引起抑制性突触后电位。近年来研究发现,肿瘤微环境中γ-氨基丁酸代谢通路的相关代谢酶存在异常表达,γ-氨基丁酸得以过度累积,相关受体也存在异常亚基组成或表达。γ-氨基丁酸一方面可作为额外的碳源回补进入TCA循环,另一方面可分泌至胞外,与各细胞成分的膜受体结合,启动下游信号转导。γ-氨基丁酸通过代谢燃料补给、自分泌及旁分泌作用,影响肿瘤细胞增殖、侵袭和转移,并存在着调节肿瘤免疫微环境的潜力。

Both Juxtacrine and Paracrine Signaling Indispensable in Spermatogonial Stem Cell Cultures

Objective To prove that juxtacrine and paracrine signaling are essential in the culture of spermatogonial stem cells （SSCs） with Sertoli cell feeder layer in vitro. Methods Mice aged 7 d were chosen to harvest testes. A two-step enzyme digestion method was applied in testis suspension. The SSCs and Sertoli cells were separated by adherence distinguishing methods and biologically identified by immunofluorescence and Oil Red 0 staining methods. Flow cytometry was used to analyze purity of SSCs. Three groups were constructed according to different culture conditions. SSC and Sertoli cell co-culture group, SSC conditional culture group and SSC routine culture group. The conditional medium was collected from supernate of culture Sertoli cell in vitro and double-concentrated with DMEM/F12 and fetal bovine serum in a proportion of 4.5 ： 4.5 ： 1. The routine medium was DMEM/F12 containing 10% fetal bovine serum. Adherence rates were measured by Trypan blue staining. Absorbance of SSCs of each group was measured by MTT assay and proliferation curves shown to demonstrate proliferative features of SSCs. Proliferative features and colony formation were observed by inverted microscope. With 24 h difference in adherence rates, proliferations were compared and analyzed.Results The adherence rate of co-culture group was greater than that in the others（P〈0.05）, with insignificant difference in conditional culture group and routine group （P〉0. 05）. SSCs of co-culture group showed stable proliferation immediately following inoculation..4 stable colony formed within 7-10 d and maintained for 30 d. SSCs in conditional culture group and routine group decreased rapidly following transient proliferation. Conclusion The actions of SSCs in Sertoli cell cultures in vitro depended on both juxtacrine and paracrine signaling, Sertoli cell paraerine signaling was unable to promote SSC adherence and proliferation alone.

间充质干细胞及其旁分泌途径在软骨退行性疾病治疗中的研究进展

间充质干细胞(MSC)是一类多功能干细胞,具备自我更新、多向分化、旁分泌和外泌体(Exos)分泌等特性。它们在椎间盘退变和骨关节炎(OA)治疗中备受关注。MSC通过释放生长因子和Exos促进细胞代谢和软骨细胞增殖,改善基质合成。此外,MSC还能抑制炎症反应、促进软骨修复和抑制骨质破坏,为改善OA病情提供新思路。但MSC治疗仍面临诸多挑战,包括来源不清、治疗剂量和长期效果不明确等。未来应深入研究MSC的分子机制、开发更有效的治疗策略以及进行大规模临床试验,以验证其疗效和安全性。

Paracrine Fibroblast Growth Factor-Based Therapy:An Unexpected Panacea for Metabolic-DysfunctionAssociated Fatty Liver Disease(MAFLD)

Metabolic-dysfunction-associated fatty liver disease(MAFLD)is a group of highly heterogeneous multi-system diseases,which is closely related to metabolic dysfunction and is one of the most important public health problems in the world.Studies have shown that paracrine fibroblast growth factors(FGFs)play an important role in the occurrence and development of MAFLD by regulating glucose and lipid metabolism,inflammation,and fibrosis.This article reviews the latest progress in understanding of the distribution,function,and metabolic regulation of paracrine FGFs,which paves the way for future FGF-based therapies targeting MAFLD.

Paracrine signaling in stem cell renewal and in neoplastic tumor growth

Paracrine pathway activities are being increasingly recognized as instrumental regulatory mechanisms of epithelial-stromal interactions that play important roles in physiological and pathological self-renewal of stem cells and in the initiation and maintenance of neoplastic tumor development.Stromal-specific Hedgehog(Hh)responses and epithelial-associated Wnt pathway activities have been recently appreciated as important factors in stem cell self-renewal and carcinogenesis.Furthermore,Hh and Wnt pathways frequently crosstalk with each other to regulate the growth of epithelial cells in a context-dependent manner.Because small molecule modulators of Hh and Wnt pathway activities are readily available,emerging roles of Hh-Wnt pathway crosstalk in epithelial-stromal interactions will shed light on the development of regenerative and anti-cancer medicines.

Different priming strategies improve distinct therapeutic capabilities of mesenchymal stromal/stem cells:Potential implications for their clinical use

Mesenchymal stromal/stem cells(MSCs)have shown significant therapeutic potential,and have therefore been extensively investigated in preclinical studies of regenerative medicine.However,while MSCs have been shown to be safe as a cellular treatment,they have usually been therapeutically ineffective in human diseases.In fact,in many clinical trials it has been shown that MSCs have moderate or poor efficacy.This inefficacy appears to be ascribable primarily to the heterogeneity of MSCs.Recently,specific priming strategies have been used to improve the therapeutic properties of MSCs.In this review,we explore the literature on the principal priming approaches used to enhance the preclinical inefficacy of MSCs.We found that different priming strategies have been used to direct the therapeutic effects of MSCs toward specific pathological processes.Particularly,while hypoxic priming can be used primarily for the treatment of acute diseases,inflammatory cytokines can be used mainly to prime MSCs in order to treat chronic immune-related disorders.The shift in approach from regeneration to inflammation implies,in MSCs,a shift in the production of functional factors that stimulate regenerative or anti-inflammatory pathways.The opportunity to fine-tune the therapeutic properties of MSCs through different priming strategies could conceivably pave the way for optimizing their therapeutic potential.