Podocytes

Podocytes

the filtration barrier = an amazing structure filtering something like 200-500 l plasma per day and producing something like 200 l of primary urine

the podocyte which is really standing or sitting on top of the capillaries is one of the key players there in the final regulation of the passage of the proteins or actually preventing the leakage of the proteins

Podocytes

there is a number of molecules located in the slit diaphragm domain

transmembrane or intracellular

these molecules adjust the shape of the podocyte foot processes

Podocytes

Nephrin - neph-1, neph-2, filtrin, hemoglobulin group of molecules, an immunoglobulin family of cell adhesion proteins

They are clustering together with podocin for the functionality of the slit diaphragm

The nephrin molecules extend from neighbouring podocytes and foot processes and induce the interaction between the different podocyte foot processes

Nephrin really forms the framework of the slit diaphragm

Podocytes

The nephrin damage determines lack of normal foot processes and the filtration slit organisation

Specific administration or generation of specific nephrin antibodies lead to proteinuria

In diabetes and diabetic nephropathy there are found circulating anti-nephrin antibodies many months before the actual attack to the kidney

Podocytes

Podocytes

there are quite a number of podocyte diseases = podocytopathies

in the podocytopathies the orderly structure of the podocytes and the foot processes interlinked by the slit diaphragms is lost (effacement of the podocytes

Podocytes

Glomerulopathies - patterns of glomerular injury

the glomerulus interconnected between the efferent and afferent arterioles

the general patterns of glomerular injury reflect the picture that we can see in the biopsy of a patient with either

nephrotic or nephritic syndrome translates to the clinical symptoms with which the patient presents

Glomerulopathies

scanning electron micrograph the arterials and the capillary network

Glomerulopathies

Glomerulopathies

the structure the efferent and afferent arteriole the both lined with continuous endothelium fenestrae in the glomerular capillaries in which the endothelium ends up smooth muscle cells

surround the efferent and afferent arterioles have kind of retracted to the mesangium areano longer covere the capillaries

Glomerulopathies

the basement membrane between the fenestrated endothelium and the epithelium on the outside

the capillary network is interconnected between the efferent and afferent arterioles

the constriction governs the blood flow profusion pessure in the capillary network allows solutes to pass over the

capillary wall under normal conditions - without proteins or cells

Glomerulopathies

a closer look at the scheme the capillary wall functions as a sieve the profusion pressure and flow of the capillaries the passage and filtration

of small molecules over this sieve major determinants of their filtration

the molecular and physical properties of the molecules that are filtered overthe structure of the capillary wall

Glomerulopathies

The capillary wall can be seen as a gel it is also used in the lab in chromotography to separate molecules

based on their size and charge

Glomerulopathies

the sieve can be injured

?the patterns of injury

Glomerulopathies

The capillary wall is a porous network negatively charged due to

the heparin sulphate proteoglycans multiple mucopolysaccharides on the surfaces of cells

The filtration of larger molecules - retarded The filtration of negatively charged molecules - retarded

very important for the filtration of albumin

Glomerulopathies

Glomerulopathies

Filtration is determined not only by the size and charge of the molecules but also by their molecular configuration for example: a globular molecule (the same molecular weight as a dextrin) is retarded because it cannot unfold in contrast to the dextrin molecules

Glomerulopathies

The negative charge it is not only important for the physiology of filtrationit also has a down side

charge of the capillary wall can easily bind, attract, and expose positively charged molecules that bind to the negative charges here; for example, histone DNA-complexes in nucleosomes that are circulating in our circulation all the time can easily bind due to the positive charge of the histone proteins to this negative charged wall and then be exposed to the circulating auto-antibodies directed to DNA

Glomerulopathies

The same is true for positively charged streptococcal and other bacterial cell wallscirculate after an infection bind to the capillary wallexposer to antibodies

form immune complexesbinding to the capillary wall leads to an increased capacity to bind antibodies

Glomerulopathies

Electron micrograph the capillary wall the fenestrated endothelium the basement membrane

made up of the various components produced by the epithelial cells also by the endothelial cells

Glomerulopathies

On the epithelial cells the arborised cell

with its processes interconnected through the slit membranesthe process of 1 cell adheres to the process of its neighbouring cell there

is a constant contact between 2 different cells over this interconnectionimportant for filtration characteritics important for the functioning of the epithelial cell

Glomerulopathies

Normal glomerulus the capillary tuft fills up the Bowman's space almost adheres to Bowman's capsule, but it is still detached from it Bowman's capsule is thin, it is not thickenedthe tubules are close together the peritubular capillaries - inconspicuous the mesangial and endothelial cells –almost inconspicuous

Glomerulopathies

Severely injured glomeruli -for example a severe post-streptococcal glomerulonephritis

a lot of inflammation in the capillaries that have collapseda lot of extracapillary proliferation infiltration with neutrophils in the Bowman's space and crescent a lot of fibrin

in the extracapillary space in the capillary lumina

Glomerulopathies

This is a bit extraordinary for a post-streptococcal glomerulonephritisusually is not extracapillary but you can get this kind of injury as well (severe form) pathogenic mechanisms

endothelial injury activation of complement and other proteasescoagulation and inflammation

Glomerulopathies

Proteases cascades complement in those 2 glomeruli activation and deposition of complement C3

Glomerulopathies

The different pathways along which complement and other reactants can lead to glomerular injury

(I)The startan antibody complement activation

endothelial injury detachment from the basement membrane denudation and exposure of the extracellular matrix complement activation

endothelial injury due to cytotoxic agents from bacteria thrombotic events complement activation

Glomerulopathies

Considering glomerular antibody deposition as 1 mechanisms by which complement can become bound and activated

(II)

Antibodies by themselves directed to certain surface molecules such as epithelial cells FC-receptor binding injury to glomerular cells (more important than complement binding)

Complement binding direct toxic injury to the glomerular cells

Complement binding binding and splitting off several components lead to chemotactic factors recruit neutrophil,’ platelets and macrophages to the glomerular capillaries cytotoxicity

Glomerulopathies

Glomerular cells react with their own response to injury(III)

glomerular cells, invading macrophages production of chemokines recruition T cells come in and play their role in the inflammatory reaction products of these cells: oxygen radicals and proteases glomerular cells injury proteinuria, hematuria, low of the GFR

Glomerulopathies

Glomerulopathies

There are several plasma serine proteases and cascades involved in inflammatory injury in the glomerulus

Glomerulopathies

The way to understand what happens in the biopsy how to read and translate the biopsy to the clinical expression

Is that the glomerular injury is largely determined by the localisation of injury either

by immune complexes or by other stimuli

Glomerulopathies

For exampleimmune complexes localise under the endothelium or along the basement membrane the binding and activation of complement recruition the leucocytes endothelial pattern of injury

Glomerulopathies

Endothelial pattern of injuryEtiology

post-infectious glomerulonephritis anti-GBM nephritis proliferative forms of lupus

Clinically drop in GFR , hematuria, sometimes with proteinuria

Biopsy inflammation and exodation

Glomerulopathies

Another pattern of injury - epithelial pattern injury at the external of the basement membrane under the epitheliumcomplement activation or a direct effect of substances that are toxic to the epithelial cell epithelial injury

Glomerulopathies

Epithelial pattern in membranous nephropathyin membranoproliferative glomerulonephritis in lupus type V

Clinically associated with heavy proteinuria

Biopsy there is no inflammation

Glomerulopathies

Epithelial pattern - there is no inflammationbecause the injury that happens here complement activation activated complement leaking through the capillary wall complement components cannot go back into the capillary lumen they cannot function as chemotactic agents there will be no recruit of inflammatory cells they will be lost into the urinary space they can be found and measured in the urine

Glomerulopathies

Glomerular injury due to deposition of immunoreactants or other reactants in the mesangial area

IgA nephropathy membranoproliferative glomerulonephritis lupus type II

Glomerulopathies

Examples to illustrate

a patient with post-streptococcal glomerulonephritis infiltrating neutophils intravascular coagulation with fibrin some neutrophils escaping into the extracapillary space

Glomerulopathies

Examples to illustrate

the same patient with post-streptococcal glomerulonephritisthis is associated with massive deposition of C3

Glomerulopathies

Examples to illustrate

the same patient with post-streptococcal glomerulonephritiselectron microscopy

the basement membrane on the outer side the podocyteon the inside very swollen endothelial cells the lost of endothelial fenestraethis is in reaction to an inflammatory reaction to the immune reactants = the dark deposits containing IgG and especially complement at the inner side of the basement membrane

Glomerulopathies

Examples to illustrate

the same patient with post-streptococcal glomerulonephritiselectron microscopy

a neutrophil eating up these deposits on the inside of the capillary wallthere is also epithelial injury

Glomerulopathies

Endothelial pattern of injury - rapid decline of GFR

endothelial injury due to antibodiesanti-GBN nephritis

Good Pasture's syndromesystemic vasculitis

idiopathic cresentic GN(probably a limited form of ANCA-associated vasculitis)

endothelial injury not due to antibodies but due to endothelial injury because of other causes

bacterial cytotoxinsmalignant hypertensionimmune complex deposition in lupus nephritis and membranoproliferative

Glomerulopathies

Glomerulopathies

Examples to illustrate

a patient with anti-GBN disease - an endothelial pattern of injury extracapillary proliferationBroken Bowman's capsule infiltration into the periglomerular area

Glomerulopathies

Examples to illustrate

a patient with anti-GBN disease - an endothelial pattern of injuryelectron microscopy

typical wrinkling of the injured basement membranedo not see real immune deposits because they are located all along the

basement membrane

Glomerulopathies

Examples to illustrate

another patient - an endothelial pattern of injury a systemic vasculitis - Wegener's granulomatosis

segmental spared part of the glomerulus a segmentally involved part of it with fibrin exodation, inflammation, and

extracapillary proliferation

Glomerulopathies

Examples to illustrate

another patient - an endothelial pattern of injuryan acute phase malignant hypertension

arterial injury and thrombosis in the same pattern in the glomerulus leading to acute renal failure

Glomerulopathies

Endothelial pattern of injury - rapid decline of GFR

•Some of these diseases - quickly heal•Sometimes - find some sequele •A lot of these diseases - will continue to go on

Glomerulopathies

Examples to illustrate

a patient with typical patterns of prolonged endothelial injury because of prolonged accumulation of immune deposits

membranoproliferative GN a continuous but also possibly interrupted deposition of immune

reactants or other causes for endothelial injury will lead to doubling of capillary walls and inflammatory reactions

Glomerulopathies

Glomerulopathies

Examples to illustrate

the epithelial pattern of injurya typical example of membranous nephropathy

the interrupted immune complexes along the capillary wall

Glomerulopathies

Examples to illustrate

a typical example of membranous nephropathyelectron microscopy

immune deposits under the epithelium spikes of newly formed basement membrane material between themthe endothelial cells have fenestrae and are completely normal non-inflamed with no

adhesion of influx of neutrophils, even though there is a lot of complement activated at the outer side of the capillary wall

Glomerulopathies

Examples to illustrate

the same typical example of membranous nephropathyat light microscopy

the capillaries completely open and normal with no inflammatory cellsbut a basement membrane with spikes and complement deposition injury to the epithelial cell but no injury to the inner part of the capillaries

Glomerulopathies

Examples to illustrate

the same typical example of membranous nephropathyin a PAS stain

the membranous nephropathy with its thickened walls

Glomerulopathies

There are many other diseases which can lead to epithelial cell injury auto-antibodies directed to epithelial cell antigens

becouse of circulating antigens that end up in this space for example, in young patients with hepatitis

Glomerulopathies

There are many other diseases which can lead to epithelial cell injury toxinsvirusescongenital abnormalities of the key proteins

that are important in making up the epithelial cells structure and functionmolecules involved in the cell matrix interaction

injury to the epithelial or a congenital abnormality in any of these molecules epithelial cell loss of integrity loss of integrity of the capillary wall proteinuria

Glomerulopathies

Glomerulopathies

Examples to illustrate

the mesangial pattern of injurythe IgA nephropathy

typical deposits of IgA and complement in the mesangial area

Glomerulopathies

Examples to illustrate

the mesangial pattern of injury electron microscopy

the depositsin mesangium

Glomerulopathies

Examples to illustrate

the mesangial pattern of injurylight microscopy

a varying pattern of injury depending probably on the affinity and amount of antibodies and response of the patient

Glomerulopathies

Examples to illustrate

the mesangial pattern of injurylight microscopy

the association of some sclerosis of the mesangial area

Glomerulopathies

Glomerulopathies

The mesangial pattern of disease can be caused byIgA

the typical form of the disease affecting the mesangium

IgM nephropathy often associated with nephrotic syndrome

hypertension

diabetescombination with capillary wall abnormalities thickening deposition of material

amyloidosis associated with capillary wall injury and with nephrotic syndrome

light chain nephropathyassociated with capillary wall injury and with nephrotic syndrome