Nephrol Dial Transplant (2009) 24: Editorial Comments
(See related article by A. Haase-Fielitz et al. The predictive performance
of plasma neutrophil gelatinase-associated lipocalin (NGAL) increases
with grade of acute kidney injury. Nephrol Dial Transplant 2009; 24:
3349–3354.)
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Received for publication: 28.7.09; Accepted in revised form: 30.7.09
Nephrol Dial Transplant (2009) 24: 3265–3268
doi: 10.1093/ndt/gfp010
Advance Access publication 23 March 2009
Kidney injury molecule-1 (KIM-1): a urinary biomarker
and much more
Joseph V. Bonventre
Renal Division, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
Correspondence and offprint requests to: Joseph V. Bonventre; E-mail: [email protected]
Keywords: acute kidney injury; TIM-1; acute renal failure;
phagocytosis; apoptosis
KIM-1 kidney expression and function
The kidney injury molecule-1 (designated as Kim-1 in rodents, KIM-1 in humans) mRNA was identified using techniques of representational difference analysis, a PCR-based
technique [1], which we carried out to find genes whose expression was markedly upregulated 24–48 h after ischaemia
in the rat [2]. Kim-1 was the gene found to be most highly
upregulated in this screen. A large pharmaceutical company consortium, using an unbiased genomic approach to
evaluate genes upregulated with the nephrotoxin cisplatin,
determined that Kim-1 was upregulated more than any other
of the 30 000 genes tested [3]. There are a large number
of studies in animals showing robust Kim-1 protein production in the affected segments of the proximal tubule
whenever a toxin or pathophysiological state results in ded-
ifferentiation of the epithelium (e.g. [4–6]). Dedifferentiation is a very early manifestation of the epithelial cell
response to injury [7]. KIM-1 is also expressed, at much
lower levels, in lymphocytes and has also been referred to
as T-cell immunoglobulin mucin (TIM)-1 and HAVCR-1,
hepatitis A virus cellular receptor-1. The protein has also
been reported to be expressed in the cochlea in response to
cisplatin-induced injury [8]. The KIM/TIM family consists
of eight members in mice, six in rats and three in humans
[9,10].
Using standard northern or western blot analyses and
immunocytochemistry, KIM-1 gene or protein expression
is undetectable in the normal kidney. With injury KIM-1
mRNA is rapidly made and protein is generated and localized at very high levels on the apical membrane of proximal
tubule in that region where the tubule is most affected. In
the case of experimental ischaemia in rodents, Kim-1 expression is predominantly in the S3 segment of the proximal
tubule. In human ischaemic and toxic acute kidney injury
(AKI) it is found in the three segments of the proximal
tubule.
C The Author 2009. Published by Oxford University Press [on behalf of ERA-EDTA]. All rights reserved.
For Permissions, please e-mail: [email protected]
3266
Nephrol Dial Transplant (2009) 24: Editorial Comments
juxtamembrane protein secondary structure affects susceptibility to the metalloproteinase-mediated KIM-1 cleavage
[18]. The role of shed KIM-1 within the tubule remains
unknown and the implications of the long-term expression
of KIM-1 in patients with chronic kidney disease, albeit, at
levels lower than that found in AKI, remain to be defined.
KIM-1 as a biomarker
Fig. 1. Structure of KIM-1. KIM-1 is a type 1 membrane glycoprotein that
contains, in its extracellular portion, a novel six-cysteine immunoglobulinlike domain, two N-glycosylation sites and a T/SP rich domain characteristic of mucin-like O-glycosylated proteins. There is one transmembrane
domain and a short intracellular domain with a tyrosine phosphorylation
signalling motif present in the renal form (KIM-1b).
KIM-1 is a type I cell membrane glycoprotein which
contains, in its extracellular portion, a novel six-cysteine
immunoglobulin-like domain, two N-glycosylation sites
and a T/SP rich domain characteristic of mucin-like
O-glycosylated proteins. The structure of the protein led
us to initially believe it had adhesion molecule properties
[11] (Figure 1). KIM-1 is also expressed at high levels in patients with clear cell-type renal cell carcinoma (RCC) [12].
RCC, like renal tubular injury, is associated with proximal
tubule cell dedifferentiation.
We are beginning to appreciate the functional role of
KIM-1 in the kidney. KIM-1 confers on epithelial cells the
ability to recognize and phagocytose dead cells that are
present in the post-ischaemic kidney and contribute to the
obstruction of the tubule lumen that characterizes AKI.
KIM-1 is a phosphatidylserine receptor that recognizes
apoptotic cells directing them to lysosomes. It also serves
as a receptor for oxidized lipoproteins and hence is adept
at recognizing apoptotic cell ‘eat me’ signals. Given these
properties KIM-1 is unique in being the first non-myeloid
phosphatidylserine receptor that transforms epithelial cells
into semi-professional phagocytes [13,14]. In addition to
the facilitation of clearance of the apoptotic debris from the
tubular lumen, KIM-1 may play an important role in limiting the autoimmune response to injury since it is known
in many systems that phagocytosis of apoptotic bodies is
one mechanism for limiting the proinflammatory response.
Acute protective responses, however, may not necessarily
translate to chronic effects of KIM-1 expression, a clinically relevant issue, since we [15] and others [16] have
found that many individuals with chronic renal failure express the KIM-1 protein in their proximal tubules.
The ectodomain of KIM-1 is shed from cells in vitro
[11] and in vivo into the urine in rodents [4,5] and humans
[17] after proximal tubular kidney injury or in patients with
RCC [12]. This shedding is regulated, at least in part, by
MAP kinase signalling pathways that are activated with
stress [18]. Metalloproteinase activity results in the release
of soluble KIM-1. Mutagenesis studies demonstrate that the
There were a number of characteristics of KIM-1 that led us
to believe that the protein might make it an ideal biomarker
of kidney injury: the absence of KIM-1 expression in the
normal kidney; its marked upregulation and insertion into
the apical membrane of the proximal tubule; its persistence
in the epithelial cell until the cell has completely recovered;
the rapid and robust cleavage of the ectodomain and the
ex vivo room temperature stability of the ectodomain. There
is an urgent need for better biomarkers for acute kidney injury (AKI) for its timely diagnosis, for the prediction of
severity and outcome and for the monitoring of proximal
tubule injury in AKI as well as chronic kidney disease. The
classical methods of assessing renal function involve the
measurement of serum blood urea nitrogen and creatinine,
biomarkers that are insensitive and nonspecific, especially
in the setting of AKI. It is also important to recognize that
changes in serum creatinine and blood urea nitrogen concentrations primarily reflect functional changes in filtration
capacity and are not true ‘injury markers’. We have recently
reviewed KIM-1, and other biomarkers of kidney injury
that are currently being evaluated, in the context of the definitions and diagnosis of AKI [19,20]. The restrictions of
length in this commentary dictate only a brief discussion
of animal data and the increasing volume of clinical data
on this marker. There are a growing number of studies in
animals that demonstrate the utility of Kim-1 in the urine
as a noninvasive marker for kidney injury. A partial list of
the settings in which the utility of Kim-1 has been demonstrated includes: ischaemia and angiotensin-mediated injury in the Ren rat, various toxins including cisplatin,
S-(1,1,2,2-tetrafluoroethyl)-l-cysteine (TFEC), folic acid
[4], gentamicin, mercury, chromium [6], cadmium [21],
iodinated contrast agents [22], vancomycin, ochratoxin A,
cyclosporine [23], d-serine, protein overload nephropathy
[24] and ageing-induced nephropathy. Kim-1 othologues are
present in many species besides rodents and man, including
zebrafish, monkeys and dogs.
The first human subjects studies with KIM-1 were published in 2002 [17] where we demonstrated that there was a
markedly increased expression of KIM-1 in kidney biopsy
specimens from patients with a pathology diagnosis of acute
tubular necrosis, and there were very high levels of KIM-1
ectodomain in the urine of patients with clinically significant AKI. Urinary levels of KIM-1 increased prior to the
appearance of casts in the urine. There was less KIM-1 in
the urine in less severe cases of AKI related to contrast
exposure, but even in a limited number of these cases it was
apparent that the level of urinary KIM-1 tracked the severity
of disease as estimated by peak serum creatinine (analysis
not included in paper). We subsequently showed that KIM1 is also a sensitive marker for kidney injury in children
Nephrol Dial Transplant (2009) 24: Editorial Comments
undergoing cardiac surgery [25]. Liangos et al. evaluated urinary KIM-1 and another biomarker, Nacetylglucosaminidase (NAG) in 201 patients with clinically established AKI and reported that elevated levels
of urinary KIM-1 and NAG were significantly associated
with the clinical composite endpoint of death or dialysis
requirement, even after adjustment for disease severity or
comorbidity [26]. We evaluated the diagnostic performance
of nine urinary biomarkers of AKI—KIM-1, neutrophil
gelatinase-associated lipocalin (NGAL), interleukin-18
(IL-18), hepatocyte growth factor (HGF), cystatin C (Cys),
N-acetyl-β-D-glucosaminidase (NAG), vascular endothelial growth factor (VEGF), chemokine interferon-inducible
protein 10 (IP-10; CXCL10) and total protein—in a crosssectional comparison of 204 patients with or without clinically documented AKI. In the case of each biomarker, the
median urinary concentrations were significantly higher in
patients with AKI than in those without AKI. The area under
the receiver operating characteristics curve (AUC-ROC) for
KIM-1 was 0.95 when the AKI patients were compared to
healthy control patients. A combination of biomarkers using a logic regression model [risk score of 2.93 × (NGAL >
5.72 and HGF > 0.17) + 2.93 × (PROTEIN > 0.22) −2 ×
(KIM < 0.58)] was significantly greater (0.94) than individual biomarker AUC-ROCs when a number of hospitalized
control groups were included (some of which likely had
clinically silent AKI). Age-adjusted levels of urinary KIM1, NAG, HGF, VEGF and total protein were significantly
higher in patients who died or required renal replacement
therapy (RRT) when compared to those who survived and
did not require RRT [15].
Van Timmeren et al. stained for the presence of KIM1 protein in tissue specimens from 102 patients who underwent a kidney biopsy for a variety of kidney diseases
and showed that positive KIM-1 staining in dedifferentiated
proximal tubular cells correlated with tubulo-interstitial fibrosis and inflammation. In a subset of patients who underwent urine collection near the time of biopsy, urinary KIM-1
levels correlated with the tissue expression of KIM-1 [16].
In an analysis of a small number of patients with nondiabetic renal disease, urinary KIM-1 levels were increased
in proteinuric patients and were reduced if the proteinuric
patients were treated with renin–angiotensin–aldosterone
inhibition, sodium restriction and or diuretic therapies that
reduced the proteinuria, thus linking the degree of proteinuria to proximal tubule injury as quantitated by KIM-1 in
the urine [27].
In studies of transplantation we quantified human KIM-1
protein expression in renal transplant biopsies by immunohistochemistry and correlated these findings with renal
functional indices [28]. Although protocol biopsies showed
no detectable tubular injury on histological examination,
we found focal positive KIM-1 expression in 28% of the
cases. This does not reflect a false positive test but rather the
result of superior sensitivity of KIM-1 expression in detecting proximal tubule injury when compared to morphology
alone. In this study of renal allografts KIM-1 expression
was detected in 100% of biopsies from patients with deterioration in kidney function and histological changes indicative of tubular damage. KIM-1 expression was significantly
correlated with levels of serum creatinine and BUN concen-
3267
trations and inversely correlated with estimated glomerular
filtration rate on the biopsy day. KIM-1 was expressed focally in affected tubules in 92% of kidney biopsies from
patients with acute cellular rejection reflecting the epithelial cell injury that results from a severe cellular rejection.
Van Timmeren et al. also evaluated the utility of urinary KIM-1 in renal transplant recipients. They looked at
a cohort with a median of 6 years post-transplant, and we
measured baseline KIM-1 excretion in stored urine samples. Graft loss was monitored over time [29]. The occurrence of graft loss increased with increasing tertiles of
KIM-1 excretion. High KIM-1 levels were associated with
low creatinine clearance, proteinuria and high donor age.
KIM-1 levels predicted graft loss independent of creatinine
clearance, proteinuria and donor age.
In summary, urinary KIM-1 is a scavenger receptor on
renal epithelial cells which converts the normal proximal
tubule cell into a phagocyte. KIM-1 expression is not measurable in normal proximal tubule cells and is markedly
upregulated with injury/dedifferentiation. It is highly expressed on the apical domain of the cell and its large
ectodomain is cleaved and is stable as it is excreted in
the urine. Its presence in the urine is highly specific for
kidney injury. No other organs have been shown to express
KIM-1 to a degree that would influence kidney excretion.
It has been shown to be much more sensitive than BUN
and creatinine as a marker for injury in a large number of
preclinical studies with a large number of kidney insults,
including various toxins. It is a true translational biomarker
in that its behaviour in man mirrors its behaviour in animals
and hence is likely to be very useful in drug development
and kidney safety monitoring. In fact the FDA and EMEA
have included KIM-1 in the small list of kidney injury
biomarkers that they will now consider in the evaluation
of kidney damage as part of their respective drug review
processes of new drugs [30]. More prospective studies are
in progress in humans to delineate the many kidney disease
processes that will be better detected and followed by using
a simple urinary test that may serve as a surrogate for the
kidney biopsy. While the role of KIM-1 as a biomarker has
a robust future, it will be particularly interesting to explore
further its role in acute and chronic kidney disease as this
knowledge may lead to a role not only as a biomarker but
also as a therapeutic target.
Acknowledgements. The author thanks Drs Takaharu Ichimura, Vishal
Vaidya and Suskrat Waikar as well as many collaborators in my laboratory
and around the world who have contributed to the work presented. Work
described that has been performed in Dr Bonventre’s laboratory has been
supported by US National Institutes of Health grants DK39773, DK72831
and DK74099.
Conflict of interest statements. Dr Bonventre is a coinventor on KIM-1
patents that have been licensed by Partners Health Care to Johnson and
Johnson Inc. and Biogen Idec. He serves as a consultant to Johnson and
Johnson, Inc.
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Received for publication: 30.12.08; Accepted in revised form: 5.1.09