Connective tissue I 2024 Connective tissue proper pvanhara@med.muni.cz Petr Vaňhara Epithelial tissue Tissue classification is based on morphology and function: Myofibrils → contraction Mesoderm – skeletal muscle, myocard, mesenchyme – smooth muscles Neurons and neuroglia Reception and transmission of electric signals Ectoderm Dominant extracellular matrix Connective tissue, cartilage, bone… Mesenchyme Continual, avascular layers of cells with different function, oriented to open space, with specific junctions and minimum of ECM and intercellular space. Derivates of all three germ layers CONTEMPORARY TISSUE CLASSIFICATION Connective tissue Nerve tissue Muscle tissue Various functions of connective tissues depend on its mechanical and biological properties • surrounds other tissues and provides structural support • compartmentalization • physical-chemical environment • nutrition • innervation • immunological support • storage of energy • cell signaling and tissue regeneration CONNECTIVE TISSUE ECM Fibrous component • collagen fibers (prototypically col. I, II) • reticular • elastic Amorphous component (ground substance) Complex matrix consisting of • glycosaminoglycans • glycoproteins • proteoglycans All tissues are composed of cells and extracellular matrix In connective tissue, the ECM is dominant GENERAL COMPOSITION OF CONNECTIVE TISSUE Cells Permanent and temporary cell populations • fibroblasts/myofibroblasts • immune cells • phagocytes • adipocytes • adult stem cells • specialized cells of cartilage (chondroblasts/chondrocytes) • specialized cells of bone • (osteoblasts/osteocytes/osteoclasts) Specific composition and properties is dependent on the tissue type (connective  ligament  cartilage  bone) GENERAL CLASSIFICATION OF CONNECTIVE TISSUE Connective tissue (proper) Embryonic c.t. Mesenchyme Mucous Adult c.t. Loose (areolar) Dense Irregular Regular Specialized Reticular Adipose Elastic Permanent • Fibroblasts/fibrocytes/myofibroblasts • Adipocytes • Adult stem cells Transiet (migratory) • Macrophages of c.t. /histiocytes) • Mast cells • Plasma cells • Lymphocytes, granulocytes • … CELLS OF CONNECTIVE TISSUE PROPER Cells of c.t. proper CELLS OF CONNECTIVE TISSUE PROPER • Principal c.t. cells • ECM producers • Originate from mesenchyme and resides in the c.t. permanently • Lack typical epithelial polarity • Migration • Fibrocyte  fibroblast • Myofibroblasts • Different tissues contain fibroblasts with different biological properties Fibroblasts CELLS OF CONNECTIVE TISSUE PROPER Migration of fibroblasts CELLS OF CONNECTIVE TISSUE PROPER https://www.sciencephoto.com/media/1232046/view/fibroblast-tem CELLS OF CONNECTIVE TISSUE PROPER DOI: 10.1038/nrm809 10.1164/ajrccm.161.5.9903102 • Features of fibroblasts and smooth muscle cells • Contractile cellular structures composed of actin microfilaments and myosin • Wound closure and healing Myofibroblasts CELLS OF CONNECTIVE TISSUE PROPER • Histiocytes • Derived from circulating monocytes (monocyte-macrophage mononuclear system) • Phagocytosis • Immunomodulation Macrophages CELLS OF CONNECTIVE TISSUE PROPER • Large, oval, 20-30m • Similar to other leukocytes with granules, but it is tissue resident • Granules – heparin – histamine – serine proteases (inflammation regulators) – eosinophil and neutrophil chemoattractants – leukotriens • Perivascular and mucosal mast cells T. Clark Brelje and Robert L. Sorenson, Minneapolis, Minnesota, USA. • Mediators of immediate hypersensitivity reaction Mast cells CELLS OF CONNECTIVE TISSUE PROPER • Large, ovoid cells • derived from B-lymphocytes • Basophilic cytoplasm – RER • Clockface nucleus (alternating heterochromatin and euchromatin) • Produce antibodies (immunoglobulins) • Short lifespan (10-20 days) T. Clark Brelje and Robert L. Sorenson, Minneapolis, Minnesota, USA. https://www1.udel.edu/biology/Wags/histopage/histopage.htm Plasma cells • Mesenchymal origin • Adult tissues • Differentiate to many cells of CT CELLS OF CONNECTIVE TISSUE PROPER Mesenchymal stem (stromal) cells DERIVATIVES OF MESENCHYME Mesenchymal stem (stromal) cells • Mesenchymal stem cells are different in different tissues • Mesenchymal stem cells are important tools for tissue engineering and understanding tissue biology CELLS OF CONNECTIVE TISSUE PROPER Mesenchymal stem (stromal) cells MESENCHYMAL STEM CELLS – CLINICAL CONTEXT DOI: 10.3389/fsurg.2015.00001 POTENTIAL APPLICATIONS OF MESENCHYMAL STEM CELLS https://doi.org/10.3389/fbioe.2020.00043 ECM = fibers + ground substance ECM OF CONNECTIVE TISSUE PROPER ECM OF CONNECTIVE TISSUE PROPER Composition of ECM determines biochemical and biophysical properties of c.t. ECM of connective tissue is produced by fibroblasts (or chondrocytes, osteoblasts). However, specific ECM can be produced by virtually any cell of our body (eg. epithelial and muscle cells producing basal lamina). ECM OF CONNECTIVE TISSUE PROPER Extracellular matrix Fibrous component • Collagen fibers (e.g. col. I, II) • Reticular • Elastic Amorphous component (ground substance) Complex matrix consisting of • Glycosaminoglycans • Glycoproteins • Proteoglycans Fibers ECM OF CONNECTIVE TISSUE PROPER Collagen fibers • family of fibrous proteins encoded by >35 genes • polymer – subunit = procollagen and tropocollagen; triple helix • different structural and mechanical properties (strength, elasticity, pliability…) • most abundant protein in human body ( 30% dry weight) EXTRACELLULAR MATRIX – FIBROUS COMPONENT • Polyribosomes bind to RER and synthetize peptide chains 1 a 2 (~250 AA, 28kDa) • In RER peptide chains are modified (hydroxylation of proline and lysine – co-factor vitamin C) Chains assemble into triple helix - procollagen • In GA, procollagen is further modified and secreted from cells EXTRACELLULAR MATRIX – FIBROUS COMPONENT Collagen synthesis EXTRACELLULAR MATRIX – FIBROUS COMPONENT further study: https://www.ncbi.nlm.nih.gov/books/NBK507709/ Procollagen is then modified to tropocollagen (by procollagenpeptidase) Tropocollagen is organized to higher fibrillar structures in ECM (fibrils, fibers) Individual collagen molecules are connected (lysyloxidases) Collagen synthesis EXTRACELLULAR MATRIX – FIBROUS COMPONENT Collagen synthesis CLINICAL CONTEXT Autor: BIOPHOTO ASSOCIATES/SCIENCE PHOTO LIBRARY James Lind 1747 Type Localization Structure Main function I Bone, tendons, meniscus, dentin, dermis, capsules of organs, loose CT 90% of type I Fibrils (75nm) – fibers (1-20m) Resilience in pull II Hyaline and elastic cartilage Fibrils (20nm) Resilience in pressure III Skin, veins, smooth muscles, uterus, liver, spleen, kidney, lung Like I, high content of proteoglycans and glycoprotiens, reticular network Shape formation IV Basal lamina of epithelium and endtohelium, basal membranes No fibrils or fibers Mechanical support V Lamina of muscle cells and adipocytes, fetal membranes Like IV VI Interstitial tissue, chondrocytes – adhesion Connecting dermis and epidermis VII Basal membrane of epithelium VIII Some endothelia (Cornea) IX, X Growth plate, hypertrophic and mineralized cartilage Growth of bones, mineralization COLLAGEN FAMILY AZAN HES HE COLLAGEN IN LIGHT MICROSCOPE Julian Voss-Andreae "Unraveling Collagen" 2005 Orange Memorial Park Sculpture Garden, City of South San Francisco, CA COLLAGEN IN ART • less abundant than collagen • polymer – tropoelastin • minimal tensile resistance, loss of elasticity if overstretched • reduction of hysteresis = allow return back to original state after mechanic change • staining – orcein, aldehyde fuchsin EXTRACELLULAR MATRIX – FIBROUS COMPONENT Elastic fibers Elastic fibers Elastin Collagen EXTRACELLULAR MATRIX – FIBROUS COMPONENT Elastic fibers • Similarly to collagen, elastin precursors are secreted and polymerize • Deposition of elastin aggregate along fibers of protein fibrillin • Amount of fibrillin (nonelastic) and elastin (elastic) determines elasticity of CT Fibrillin Elastin Elastin EXTRACELLULAR MATRIX – FIBROUS COMPONENT • collagen 3D meshwork • bone marrow, spleen, lymphatic nodules • microenvironment for e.g. hematopoietic stem cells and progenitors EXTRACELLULAR MATRIX – FIBROUS COMPONENT Reticular fibers RETICULAR CONNECTIVE TISSUE Ground substance ECM OF CONNECTIVE TISSUE PROPER • Amorphous extracellular matrix • Colorless, transparent, homogenous substance consisting of: glycosaminglycans, proteoglycans and structural glycoproteins EXTRACELLULAR MATRIX – GROUND SUBSTANCE Ground substance • linear polysaccharides composed of two disaccharide subunits – uronic acid and hexosamine glucosamin or galactosamin glucuronic or iduronic acid EXTRACELLULAR MATRIX – GROUND SUBSTANCE Glycosaminoglycans (GAGs) • linear polysaccharides composed of two disaccharide subunits – uronic acid and hexosamine EXTRACELLULAR MATRIX – GROUND SUBSTANCE https://doi.org/10.3390/cancers15010266 Glycosaminoglycans (GAGs) Glycosaminoglycan Localization Hyaluronic acid Umbilical cord, synovial fluid, fluid of corpus vitreum, cartilage Chondroitinsulfate Cartilage, bone, cornea, skin, notochord, aorta Dermatansulfate Skin, ligaments, adventitia of aorta Heparansulfate Aorta, lungs, liver, basal membranes Keratansulfate Iris, cartilage, nucleus pulposus, anulus fibrosus bind to proteins (except for hyaluronic acid) EXTRACELLULAR MATRIX – GROUND SUBSTANCE Glycosaminoglycans (GAGs) CLINICAL CONTEXT • glycosaminoglycans = acid mucopolysaccharides (polysaccharides rich in hexosamines) • group of rare genetic diseases – mucopolysaccharidoses – autosomal recessive disease caused by mutation in genes coding for enzymes of GAG metabolism – broad spectrum of problems – typical symptoms – craniofacial dysmorphia, cardiomyopathy, splenomegaly, slow growth and psychomotor development • protein core + dominant linear saccharide component • proteoglycan aggregates • water-binding, volume dependent of hydratation • aggrecan (cartilage) • syndecan • fibroglycan EXTRACELLULAR MATRIX – GROUND SUBSTANCE Proteoglycans • dominant protein + branched saccharide component • interaction between cells and ECM ― fibronectin – connects collagen fibers and glykosaminoglycans, cell adhesion and migration ― laminin – basal lamina – epithelial integrity ― chondronectin – cartilage – adhesion of chondrocytes to collagen EXTRACELLULAR MATRIX – GROUND SUBSTANCE human mesenchymal stem cells (MSC), BD, Alexa Fluor® 488 Mouse Anti-Fibronectin Structural glycoproteins Glycoproteins vs. proteoglycans EXTRACELLULAR MATRIX – GROUND SUBSTANCE COMPOSITION OF ECM COMPOSITION OF ECM Cell – ECM interactions HISTOLOGICAL CLASSIFICATION OF CT PROPER Embryonic mesenchyme Wharton’s jelly Embryonic: • Embryonic mesenchyme and mucous c.t. (Wharton’s jelly) of umbilical cord Postnatal (adult): • Loose collagen c.t. (areolar, interstitial) • Dense collagen regular and irregular c.t. • Elastic c.t. • Reticular c.t. • Adipose c.t. HISTOLOGICAL CLASSIFICATION OF CT PROPER • Permanent fibroblasts, macrophages (histiocytes), occasionally adipocytes • Other transient cell types (leukocytes) • Collagen and elastic fibers • Amorphous ground substance is dominant • Most abundant type of CT • Rich vascularization and innervation • Walls of hollow organs, interstitium, mucosal and submucosal CT http://medsci.indiana.edu/a215/virtualscope/docs/chap2_1.htm Loose collagen c.t. HISTOLOGICAL CLASSIFICATION OF CT PROPER Dense collagen c.t. HISTOLOGICAL CLASSIFICATION OF CT PROPER Elastic membranes of aorta Lig. flava HE 50X Weigert, 50X Elastic c.t. HISTOLOGICAL CLASSIFICATION OF CT PROPER Niche for immune cells Reticular c.t. • Adipocytes, fibroblasts, reticular, collagen and elastic fibers, capillaries • White and brown adipose tissue HISTOLOGICAL CLASSIFICATION OF CT PROPER Adipose c.t. • rich vascularization • unilocular adipocytes with only one lipid droplet • endocrine activity - leptins (adipokinins) HISTOLOGICAL CLASSIFICATION OF CT PROPER 10.1038/s42255-019-0095-y White adipose c.t. • small cells with numerous fat droplets • typical localization – between shoulder blades, axilla, mediastinum, around kidneys, pancreas, small intestine • fetus and children up to 1st year of life • fast source of energy HISTOLOGICAL CLASSIFICATION OF CT PROPER Brown adipose c.t. • Mesenchyme = loose tissue between germ layers • Complex network of small, undifferentiated star- or spindle-shaped cells • Jelly-like amorphous ground substance rich in hyaluronic acid • Origin in mesoderm (=germ layer) or neural crest http://www.mun.ca/biology/desmid/brian/BIOL3530/DB_Ch02/DBNModel.html Trilaminar germ disc EMBRYONIC ORIGIN OF CONNECTIVE TISSUE Mesenchyme Connective BoneCartilage Mesenchyme EMBRYONIC ORIGIN OF CONNECTIVE TISSUE C.t. derivatives of mesenchyme MESENCHYME Mesenchyme as embryonic c.t. and a cellular phenotype • Embryonic mesenchyme – undifferentiated embryonic cell population Term from embryology • Mesenchymal phenotype – set of cell properties: ECM production and remodeling, migration, absence of epithelial polarity and intercellular junctions Term from cell biology https://doi.org/10.1172/JCI39104. SUMMARY OF CONNECTIVE TISSUE Collagen Structure Function and distribution Loose collagen CT Abundant ground substance, collagen fibers with random arrangement Microvascularisation Innervation Irregular dense collagen CT Few ground substance, few cells, many collagen fibers, random arrangement Mechanically resistant organ capsules Regular dense collagen CT Tightly arranged collagen fibers with fibroblasts intercalated between them Part of musculoskeletal system. Tendons, ligaments Embryonic Mesenchyme Undifferentiated cells uniformly dispersed in ground substance, few collagen fibers Undifferentiated progenitors Wharton’s jelly Viscous amorphous matrix with collagen fibers. ECM-producing stromal cells with MSC properties. Matrix of umbilical cord Special Reticular CT Network of collagen III fibers and reticular cells Support of hematopoietic and lymphatic cells Elastic Rich in elastic fibers Lig. flava, lig. vocale. Lung interstitium, flexible support to elastic arteries and aorta Adipose Adipocytes Energy storage (white fat), heat production (brown fat) Cartilage Chondroblasts, chondrocytes Mechanical support Bone Osteoblasts, ostecoytes, osteoclasts Mechanical support, calcium and phospate metabolism Blood See lecture on blood & hematopoiesis this semester FURTHER STUDY http://www.histology.med.muni.cz Thank you for attention pvanhara@med.muni.cz