elastic fibers in dermis

1. Elastic fibres
DR RANJAN JEEVANNAVAR

2. Introduction
• Elastic fibre system is an integral component of
connective tissue and forms a network that is
responsible for resilience and elasticity of various
organs.
• Its required for proper structure and function of
cardiovascular, pulmonary, intestinal system.

3. • In normal individuals, elastic fibres form 3% of
total dry weight of dermis.
• Elastic fibres stores the energy during stretch
and drives the elastic recoil.
• Elastic fibres mainly composed of inner core of
amorphous elastin and outer electron dense
microfibrils .

4. Development
• First elements of elastic fibres that form consists
of bundles of microfibrils seen during the first
trimester .
• The alignment of these microfibrils are parallel so
as to accommodate elastin and grow uniformly.
• During second trimester, fibres remain immature
and branching in the fibres is seen.

5. Development cont.
• Initially elastic fibres show masses of peripheral
microfibrils surrounding a small amorphous
electro lucent core i.e. elastin with only few
internal microfibrils .
• As the fetus matures the amount of elastin and
the number of microfibrils within the core
increases whereas the number of peripheral
microfibrils decreases.

6. • At 32 weeks a well developed network of
elastic fibres is present in both papillary and
reticular dermis .

7. Elastin
• It’s a highly cross-linked amorphous insoluble
protein which forms the core of mature elastic
fibres.
• Its constitutes 85% of mature elastic fibres .
• It is synthesised by smooth muscle cells in
arteries and intestine similarly fibroblasts in the
skin.

8. • Elastin is initially sythesized as a precursor
polypeptide Tropoelastin.
• It consists of 700 amino acids with a molecular
mass of 70kDa.
• It is rich in glycine (33%), proline (10%) and
hydrophobic amino acids , alternating with
lysine and alanine rich sequences.

9. • Characteristic sequence is two lysine residues
separated by three alanine residues.
• The lysine residues in tropoelastin are critical for
the formation of covalent cross links and
desmosines that are unique to elastin.
• First oxidative deamination of three lysine
residues to form its corresponding aldehydes i.e.
allysines and these join with another lysine to
form a stable desmosine compound which
covalently links two tropoelastin polypeptides.

10. • Tropoelastin is secreted by elastin binding
protein and crosslinked on the surface of
fibroblasts by copper dependent enzyme lysyl
oxidase.
• Hence copper deficiency , wilsons syndrome ,
menkes syndrome associated with reduced
elastin.

11. • Additional elastin is added to aggregates
which are then linked to microfibrils that bind
to cell surface via integrins.
• Aggregation of elastin and microfibrils develop
into larger structures to form the functional
elastic fibres.

13. Elastin gene
• Elastin gene is localized to chromosome 7q11
and regulates the synthesis of tropoelastin
molecule.
• The hydrophobic and cross-link domains of
the elastin protein are encoded in separate
exons .
• The mRNA of elastin undergoes extensive
alternate splicing so that the arrangement of
exons coding for cross-linking domains keep
changing with respect to hydrophobic region.

14. • Hence elastin molecules of varying primary
sequence is found.
• Significance of the variation not yet known.
• The defect in this gene leads to autosomal
dominant form of cutis laxa.

15. Microfibrils
• Its electron dense tubular fibrils of insoluble glycoprotein
complexes measuring about 10 to 12 nm in diameter.
• It regulates assembly and organization of elastic fibres.
• It has an outer electron dense shell surrounding an inner
lucid core and appears as a beaded chain.
• It consists of several distinct proteins like fibrillin 1 and 2,
fibulin 1,2,3,4,5 , associated microfibril protein, and elastin
receptor.

16. • Even lysyl oxidase enzyme is found to be a
part of microfibril core.
• The largest and the most important of these is
fibrillin, a 350kDa glycoprotein forming the
integral part of microfibril structure.
• Multiple fibrillin molecules align in parallel
and head to tail fashion to form elongated
tubular structure.

17. • Fibrillin 1 gene on chromosome 15q and mutation of this is
found to cause Marfans syndrome. Fibrillin 2 gene is in
chromosome 5q and its mutation causes contractural
Arachnodactyly.
• Fibulins is essential for elastic fibre formation and assembly and
facilitates cell-matrix interactions. Mutations in its gene is found
in inherited cutis laxa.
• Associated microfibril protein is rich in acidic amino acids like
glutamic and aspartic acid and this helps in assembly of
tropoelastin molecules with its basic amino acid content.

18. Degradation
• The metabolic turn over of elastic fibres is slow.
These are degraded by elastases classically found
in pancreatic sectretions and others are matrix
metalloproteinases , proteinase 3.
• In skin, serine elastases from monocyte –
macrophages involved with elastic fibre turn over.

19. • Elastase inhibitors like α1-antitrypsin , α2-
macroglobulin and lysozyme are found in
body.
• Any alteration in these will lead to increased
elastic fibre degradation as seen in
emphysema.

20. Factors affecting elastic fibre turn over
• Elastin production is increased by
– Insulin like growth factor 1
– Growth hormone
– Epinephrine
• Elastin production reduced by
– Tumour necrosis factor α
– Transforming growth factor β
– Interleukin 1
– Vitamin D3

21. Types
• Elastic fibres are of two types mainly
– Oxytalan fibres
– Elaunin fibres
• Oxytalan fibres contains microfibrillary
component with no elastin, it emerges from
the basement membrane of stratum basale in a
perpendicular orientation and goes deep into
papillary dermis where it merges with elaunin
fibres.

22. • Elaunin fibres : contains microfibrils with
small amount of elastin core forms a plexus
parallel to dermo-epidermal junction in
papillary dermis.
• A dense network of elastic fibres is found in
the matrix of reticular dermis which primarily
consists of elastin and very little microfibrils.

23. Sites
• Walls of arteries, veins , intestine, skin , elastic
cartilage, bronchioles etc.
• The highest concentration of elastic fibres
seen in aorta and to some extent in papillary
and reticular dermis of skin.

24. Elastic property
• Hydrophobic segments of elastin is found in a
loose water containing helicals of β- spirals.
• Multiple random spirals are present in the entire
polypeptide chain of elastin.
• Upon stretching, the spirals distance with each
other and the hydrophobic forces drives the
recoils of the chain.

25. Functions
• Cardiovascular system : During systole the
work of the heart is absorbed by expansion of
the great vessels mainly aorta which is rich in
elastic tissue which then elastically recoil
during diastole maintaining the blood
pressure assuring continuous perfusion of the
tissues .

26. • Respiratory system: inspiration is an active
energy consuming process, and the expiration
occurs passively due to the elastic recoil of the
respiratory tree.
• Intestines : the coils dilates when the food
comes into the segment and with peristalsis
pushing the food forwards, the elastic recoil of
the intestine brings back to original shape.

27. • In skin elastic fibres are responsible for
– Tension : the resistance of the skin to deforming
forces
– Elasticity : ability of skin to resume to its original
shape after deforming forces. This is reduced in
cutis laxa and aged .
– Tensile strength : the degree to which skin can be
elongated before it tears .
• These properties helps the skin to adapt to
local changes in body size and contour, to
allow movements of head and limbs and a
wide range of facial expressions.

28. Histology
• Elastic fibres are not visible in routine stains.
• Special stains required to demonstrate these
fibres are
– Verhoeff-van Gieson Stain : black colour
– Gomori’s aldehyde fuchsin stain : blue-black color
– Orcein stain : red-brown color
– Weigert’s stain: purple-violet color
– Luna stain : briliant purple

29. Elastic fibres
are
interspread
among the
collagen fibres
in dermis

30. Age related changes
• After age of 50 the fibres are loosely arranged.
• Elastic fibres fragments and develop granular,
indistinct borders.
• The microfibrillary component goes on
reducing and increase in elastin portion.
• There is considerable decrease in number of
elastic fibres in papillary dermis and increase
in reticular dermis.

31. Elastic fibre disorders
• Cutis laxa : fragmentation and loss of elastic
fibres
• Pseudoxanthoma elasticum : progressive
calcifictaion and fragmentation of elastic fibres.
• Wrinkly skin syndrome : decreased number and
length of elastic fibres.
• Anetoderma : localized loss of elastic fibres in
dermis
• Mid dermal elastolysis : loss of elastin in mid
dermis

32. • Post-inflammatory elastolysis : localised loss of
elastic tissue secondary to insect bites.
• Marfans syndrome : mutation in fibrillin 1 gene
with abnormal microfibrils.
• Actinic elastosis : accumulation of irregularly
thickened elastic fibres on long term sun
exposure.
• Elastoderma : accumulation of excessive and
deranged elastin

33. References
• Rooks text book of dermatology 8th edition
• Fitzpatricks dermatology 7th edition
• Levers histopathology of skin 10th edition
• Weedons histopathology of skin
• Robins textbook of pathology
• Bolognia 2nd edition
• Moschella 3rd edition
• Rosenbloom J , Abrams WR. Extracellular
matrix 4 : The elastic fibre