Nephrol Dial Transplant (2007) 22: 1849–1852
doi:10.1093/ndt/gfm098
Advance Access publication 20 April 2007
Translational Nephrology
Familial nephrotic syndrome: PLCE1 enters the fray*
Jonathan Ashley Jefferson and Stuart J. Shankland
Division of Nephrology, University of Washington, Seattle, Washington, USA
Keywords: focal segmental glomerulosclerosis; genetic
disorders; nephrotic syndrome; phospholipase C;
podocyte
Mutations in phospholipase C epsilon 1 gene
cause early onset nephrotic syndrome
Marked advances in molecular biology are constantly
enabling new insights into renal pathophysiology and
the treatment of human disease. In the December 2006
issue of Nature Genetics, Hinkes et al. [1] describe a
novel mechanism for early nephrotic syndrome in
children due to mutations in PLCE1, a gene which
encodes one of a family of phospholipase C enzymes
(PLCe1). Affected children develop proteinuria by four
years of age, with renal pathology demonstrating
diffuse mesangial sclerosis (truncating mutations) or
focal segmental glomerulosclerosis (missense mutations). The majority progress to end-stage renal disease
by 5 years of age; however, of particular interest is that
two children, both with truncating mutations in
PLCE1, responded to treatment with steroids and/or
ciclosporin. This is the first time that an inherited
childhood nephrotic syndrome has responded to
therapy.
Nephrotic syndrome and the glomerular filtration
barrier: is the podocyte slit diaphragm the principal
determinant?
Nephrotic syndrome occurs due to a breakdown in one
or more layers of the glomerular filtration barrier. This
barrier consists of three layers, the fenestrated glomerular endothelium, the glomerular basement membrane
(GBM) and the slit diaphragm of the podocyte,
Correspondence and offprint requests to: Stuart J. Shankland, MD,
Head, Division of Nephrology, University of Washington, 1959 NE
Pacific Street, Box 356521, Seattle, Washington 98195, USA.
Email: [email protected]
*Comment on Hinkes B, Wiggins RC, Gbadegesin R et al.
Positional cloning uncovers mutations in PLCE1 responsible for
a nephrotic syndrome variant that may be reversible. Nat Genet
2006; 38: 1397–1405.
each likely contributing to the charge and size selective
properties. Debate continues over the exact contribution of each layer, but recent evidence has implicated
the previously overlooked podocyte and its slit
diaphragm as major contributing factors. The slit
diaphragm lies between adjacent podocyte foot processes and consists of the structural transmembrane
protein nephrin which forms heterodimers with NEPH1 and NEPH-2 to bridge the slit pore (Figure 1).
Nephrin is anchored to the podocyte membrane by
podocin and CD2AP. Other structural proteins of the
slit diaphragm complex include P-cadherin, FAT and
ZO-1. The slit diaphragm functions to permit a high
hydraulic flux, whilst limiting the passage of macromolecules such as albumin. In addition to this structural
role, the slit diaphragm complex, in association with
TRPC6 (an epithelial calcium channel), signals through
a phosphoinositide 3-OH kinase dependent AKT pathway to modulate cellular processes such as actin
cytoskeletal remodelling and cell survival [2,3]
Mechanisms that disrupt the slit diaphragm complex
result in podocyte dysfunction and/or loss, leading in
massive proteinuria. Mice with target deletions for
nephrin [4], podocin [5], NEPH-1 [6], FAT [7] develop
massive proteinuria, and antibodies to nephrin cause
nephrotic syndrome, notably without foot process
effacement [8]. Moreover, in human glomerulonephritides, such as diabetic nephropathy [9], membranous
nephropathy [10] and minimal change disease [11],
abnormalities in the expression and localization of
certain slit diaphragm proteins have been described,
which may resolve with successful treatment.
Familial FSGS may be caused by inherited
structural abnormalities in podocyte proteins
Families with steroid resistant nephrotic syndrome
(SRNS) secondary to mutations in genes encoding
podocyte structural proteins are now well recognized.
The first to be recognized was NPHS1 (nephrin)
mutations, causing congenital nephrotic syndrome of
the Finnish type [12]. Mutations in the NPHS2 gene
encoding podocin are the commonest cause of SRNS
in children, accounting for some 30–46% of cases of
ß The Author [2007]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.
For Permissions, please email: [email protected]
1850
J. A. Jefferson and S. J. Shankland
F-actin
ligand
G protein
Podocin
CD2AP
P
V
ZO
-1
α-actinin-4
T
PLCε1
Nephrin
NEPH-1,2
P-Cad
DAG
TRPC6
IP3
PKC [Ca2+]
FAT
β−DG
α3
β1
GBM
α−DG
Capillary loop
Fig. 1. Podocyte slit diaphragm: The major molecules comprising the podocyte slit diaphragm are demonstrated. Signalling by PLCe1 is also
illustrated, but note this is limited to podocyte cell body and major processes and not foot processes.
familial SRNS and 11–19% of sporadic SRNS [13–15].
Congenital nephrotic syndrome secondary to diffuse
mesangial sclerosis may also be caused by mutations in
WT1 [16] and LAMB2 [17]. By contrast, in adults,
NPHS2 (podocin) mutations are a rare cause of FSGS
[18,19]. Familial FSGS has been described in adults,
due to mutations in the genes encoding alpha actinin-4
[20] and TRPC6 [2,3].
PLCE1 may play a critical role in glomerular
development
Familial FSGS is typically due to mutations in genes
encoding structural podocyte proteins; however, PLC
is an enzyme. How might PLC mutations result in
glomerular disease? Phospholipase C is a signalling
protein for many G protein-coupled receptors, including angiotensin II, and promotes the downstream
activation of protein kinase C and enhances calciumsignalling events. PLCe1 has a widespread distribution,
but within the kidney the PLCe1 protein is enriched in
glomeruli and localizes to the cytoplasm of the
podocyte cell body and both major and intermediate
processes. Studies in early kidney development demonstrated the appearance of PLCe1 at the S-shaped stage,
with high expression during early capillary loop
stage [1]. It is suggested that the absence of PLCe1
may halt kidney development at the capillary loop
stage leading to the morphological phenotype of
diffuse mesangial sclerosis. Of note, this is associated
with a marked reduction in the expression of nephrin
and podocin.
The role of PLC in renal pathophysiology remains
complex however, as PLCe1 knockout mice do not
appear to exhibit a renal phenotype. In addition,
enhanced (rather than diminished) signalling through a
form of PLC within podocytes (using a mouse
transgenic for Gaq with nephrin promoter giving
targeted podocyte expression of a constitutively
active Gaq) results in podocyte injury, proteinuria
and reduced renal mass [21].
Clinical applications
How can we translate the rapidly emerging data from
molecular studies into clinical practice? At present,
genetic screening in patients with nephrotic syndrome
is mostly limited to mutations in NHPS1 (nephrin) and
NPHS2 (podocin), but this will probably change
dramatically with advances in gene sequencing.
Even today, the detection of NPHS2 (podocin)
mutations in children with nephrotic syndrome greatly
impacts clinical care. Children with homozygous
Familial nephrotic syndrome
1851
Table 1. Clinical disorders of the podocyte
Disease
Pathophysiological mechanisms
Genetic disorders
Congenital nephrotic
syndrome of Finnish type
Familial FSGS
Diffuse mesangial sclerosis Acquired disorders
Minimal change disease
Classic FSGS
Cellular/Collapsing FSGS
Membranous nephropathy
Diabetic nephropathy
Amyloid
Nephrin (NPHS1) mutations
9
Podocin (NPHS2) >
=
TRPC6
a-actinin-4
mutations
>
;
CD2AP
PLCe1
)
WT1
LAMB2
mutations
PLCe1
? T-cell mediated
? permeability factor
glomerular hyperfiltration
reduced nephron mass
viral infection
(HIV, ? parvovirus B19)
toxins (pamidronate,
interferon, heroin, lithium)
Anti-podocyte antibodies
Metabolic derangements
Glomerular hypertension
Amyloid protein deposition
The pathophysiology is unclear for these disorders, the ‘?’ represents
possible explanations.
mutations are known to be steroid- and cyclosporineresistant, and this will allow these therapies, and their
attendant side effects, to be avoided. FSGS commonly
recurs post kidney transplant (30–40%). Fortunately,
the incidence of post-transplant recurrent disease is
much lower in patients with homozygous NPHS2
mutations (8%), although the choice of donor needs
to be carefully considered, as the parents are obligate
heterozygotes [22]. Interestingly, in patients with FSGS
who are heterozygous for NPHS2 mutations, there
seems to be a high incidence of recurrent disease
(60%).
In childhood nephrotic syndrome secondary to
mutations in PLCE1, the majority of children had a
poor prognosis; however, two patients with truncating
mutations are described who responded to therapy [1].
Although there are some reports of inherited glomerulopathies that are responsive to immunosuppression
[23], this contrasts with the majority of inherited
glomerulopathies that are resistant. It remains to be
determined which specific factors are associated with an
improved response and whether there is a time window,
during which intervention may be successful. The
application of this interesting work in decisions regarding renal transplantation will probably also unravel
over time.
In summary, the podocyte is the cellular target in the
majority of nephrotic disorders, whether this is due to
genetic mutations (nephrin, podocin, TRPC6, PLCe1,
a-actinin-4) or acquired disorders (Table 1). These
multiple factors impact the onset and course of disease,
treatment responses and options and the likelihood of
transplant recurrence.
Acknowledgements. This work was supported by National
Institutes of Health grants to S.J.S. (DK60525, DK56799,
DK 51096), and by the American Diabetes Association. S.J.S. is
also an Established Investigator of the American Heart Association.
Conflict of interest statement. None declared.
References
1. Hinkes B, Wiggins RC, Gbadegesin R et al. Positional cloning
uncovers mutations in PLCE1 responsible for a nephrotic
syndrome variant that may be reversible. Nat Genet 2006; 38:
1397–1405
2. Reiser J, Polu KR, Moller CC et al. TRPC6 is a glomerular
slit diaphragm-associated channel required for normal renal
function. Nat Genet 2005; 37: 739–744
3. Winn MP, Conlon PJ, Lynn KL et al. A mutation in the TRPC6
cation channel causes familial focal segmental glomerulosclerosis. Science 2005; 308: 1801–1804
4. Putaala H, Soininen R, Kilpelainen P, Wartiovaara J,
Tryggvason K. The murine nephrin gene is specifically expressed
in kidney, brain and pancreas: inactivation of the gene leads to
massive proteinuria and neonatal death. Hum Mol Genet 2001;
10: 1–8
5. Roselli S, Heidet L, Sich M et al. Early glomerular filtration
defect and severe renal disease in podocin-deficient mice. Mol
Cell Biol 2004; 24: 550–560
6. Donoviel DB, Freed DD, Vogel H et al. Proteinuria and
perinatal lethality in mice lacking NEPH1, a novel protein with
homology to NEPHRIN. Mol Cell Biol 2001; 21: 4829–4836
7. Ciani L, Patel A, Allen ND, ffrench-Constant C. Mice lacking
the giant protocadherin mFAT1 exhibit renal slit junction
abnormalities and a partially penetrant cyclopia and anophthalmia phenotype. Mol Cell Biol 2003; 23: 3575–3582
8. Topham PS, Kawachi H, Haydar SA et al. Nephritogenic mAb
5-1-6 is directed at the extracellular domain of rat nephrin. J Clin
Invest 1999; 104: 1559–1566
9. Langham RG, Kelly DJ, Cox AJ et al. Proteinuria and the
expression of the podocyte slit diaphragm protein, nephrin, in
diabetic nephropathy: effects of angiotensin converting enzyme
inhibition. Diabetologia 2002; 45: 1572–1576
10. Koop K, Eikmans M, Baelde HJ et al. Expression of podocyteassociated molecules in acquired human kidney diseases. J Am
Soc Nephrol 2003; 14: 2063–2071
11. Wernerson A, Duner F, Pettersson E et al. Altered ultrastructural distribution of nephrin in minimal change nephrotic
syndrome. Nephrol Dial Transplant 2003; 18: 70–76
12. Kestila M, Lenkkeri U, Mannikko M et al. Positionally cloned
gene for a novel glomerular protein–nephrin–is mutated in
congenital nephrotic syndrome. Mol Cell 1998; 1: 575–582
13. Weber S, Gribouval O, Esquivel EL et al. NPHS2 mutation
analysis shows genetic heterogeneity of steroid-resistant nephrotic syndrome and low post-transplant recurrence. Kidney Int
2004; 66: 571–579
14. Ruf RG, Lichtenberger A, Karle SM et al. Patients with
mutations in NPHS2 (podocin) do not respond to standard
steroid treatment of nephrotic syndrome. J Am Soc Nephrol
2004; 15: 722–732
15. Caridi G, Bertelli R, Di Duca M et al. Broadening the spectrum
of diseases related to podocin mutations. J Am Soc Nephrol
2003; 14: 1278–1286
16. Jeanpierre C, Denamur E, Henry I et al. Identification of
constitutional WT1 mutations, in patients with isolated diffuse
mesangial sclerosis, and analysis of genotype/phenotype correlations by use of a computerized mutation database. Am J Hum
Genet 1998; 62: 824–833
17. Hasselbacher K, Wiggins RC, Matejas V et al. Recessive
missense mutations in LAMB2 expand the clinical
1852
spectrum of LAMB2-associated disorders. Kidney Int 2006; 70:
1008–1012
18. Caridi G, Bertelli R, Scolari F, Sanna-Cherchi S, Di Duca M,
Ghiggeri GM. Podocin mutations in sporadic focal-segmental
glomerulosclerosis occurring in adulthood. Kidney Int 2003; 64: 365
19. He N. Recessive NPHS2 (Podocin) mutations are rare in
adult-onset focal segmental glomerulosclerosis. CJASN 2007;
2: 31–37
20. Kaplan JM, Kim SH, North KN et al. Mutations in ACTN4,
encoding alpha-actinin-4, cause familial focal segmental glomerulosclerosis. Nat Genet 2000; 24: 251–256
J. A. Jefferson and S. J. Shankland
21. Wang L, Fields TA, Pazmino K et al. Activation of
Galpha q-coupled signaling pathways in glomerular
podocytes promotes renal injury. J Am Soc Nephrol 2005; 16:
3611–3622
22. Caridi G, Perfumo F, Ghiggeri GM. NPHS2 (Podocin)
mutations in nephrotic syndrome. Clinical spectrum and fine
mechanisms. Pediatr Res 2005; 57: 54R–61R
23. Ruf RG, Fuchshuber A, Karle SM et al. Identification of
the first gene locus (SSNS1) for steroid-sensitive nephrotic
syndrome on chromosome 2p. J Am Soc Nephrol 2003; 14:
1897–1900
Received for publication: 1.2.07
Accepted in revised form: 5.2.07