Balasubramanyam, M

Mohan, V

Radha, V

Eprints @MDRF

© JAPI • VOL. 53 • JUNE 2005 www.japi.org 507
Editorial
Genomics and Proteomics of Type 2 Diabetes in
Indians
V Mohan, M Balasubramanyam, V Radha
In this context, the two seminal articles that appear
in this issue of JAPI are very relevant to expose further
developments occurring in India in this field.
Gene expression profiling in Type 2 diabetes
Microarray technology is expected to initiate a new
era in genetic linkage analysis that will facilitate the study
of phenotypes of patients and their relatives, providing
new impetus and strategies for mapping disease traits.
Functional genomics is much more powerful than other
techniques in determining mRNA levels—an array can
include tens of thousands of probes and can therefore
measure the expression of an equivalent number of genes
in a single experiment. In this issue of JAPI (page 521-
526), Rao et al4 report rare and/or previously unknown
phenotypes linked to known genes with significant
differential expression in Type 2 diabetes subjects. Such
studies are essential in a population where the
development of disease not only shows exponential
growth but also unprecedented prevalence rates. The
study, although of great interest also has certain
limitations. Minimum biological replicates (n=3) were
used in this study, and much variability can be expected
in microarray measurements  particularly if few samples
are used. The heterogeneity in leukocyte sample
preparation is another problem. However, given these
limitations, it is of great interest that many clinical
disorders (previously not associated with clinical
diabetes) were associated with genes that are
significantly up-regulated in peripheral blood cells
(PBCs) of Type 2 diabetes patients and Rao et al are to be
congratulated for their excellent contribution to the
literature. While our own study5 has shown the
association of polymorphisms of FABP2 (fatty acid
binding protein 2) and Apolipoprotein C-III (APOC III)
genes with metabolic syndrome and dyslipidemia in
Indians, the work by Rao et al4 further substantiate the
differential gene expressions of lipoprotein lipase (LPL)
gene and APOC III in Type 2 diabetes patients with
dyslipidemia. It is expected that further testing of
heterogeneity in diabetes phenotype syndromes may
reveal common pathogenic mechanisms and potential
candidate genes in the development and progression of
Type 2 diabetes.
To some extent, gene expression changes in peripheral
blood cells distinguish variable diabetes states6 and they
Dr. Mohans’ MV Diabetes Specialities Centre and Madras
Diabetes Research Foundation, Gopalapuram,
Chennai – 600 086.
In its search for the causes of Type 2 diabetes, medicinehas now advanced to the molecular level. Genomics
and proteomics are opening the way to a new and deeper
understanding of pathogenesis of diabetes aiming at the
development of precise and targeted interventions. One
of the most useful strategies in the search for genes
underlying complex diseases such as diabetes is to look
at candidate genes. These candidate genes are selected
on the basis of their known or presumed functions and
they are thought to have some plausible role in
pathogenesis of the disease. Some of the candidate genes
reported to be associated with Type 2 diabetes include:
PPARγ (Peroxisome Proliferator Activated Receptorγ),
IRS-1 (insulin receptor substrate 1), KCJN11 (potassium
inward rectifier 6.2), SLC2A1 (glucose transporter 1),
PPARGC-1 (PPARγ -coactivator-1) and CAPN10
(calpain 10).
At the Madras Diabetes Research Foundation, we
have recently studied the plasma cell glycoprotein (PC-
1) gene polymorphism K 121 Q, and showed its potential
role in genetic susceptibility to type 2 diabetes in both
South Asians and Europeans.1 This study was done in
collaboration with Dr. Abate and colleagues at the South
Western University of Texas at Dallas and involved south
Indians living in Chennai, south Asians living in Dallas
(USA) and white Caucasians living in Dallas. The
consistent association of this variant allele with type 2
diabetes in the three different ethnic populations
characterized by different genetic background and
environmental factors suggests that this gene may play
an important role in Type 2 diabetes susceptibility. Yet
another study by our group showed that the A allele of
Thr 394 Thr( G → A) polymorphism of the PGC-1 gene is
associated with type 2 diabetes in Asian Indian subjects
and the XA genotype was shown to confer a higher risk
for type 2 diabetes compared to the GG genotype in our
population.2 The same Thr 394 Thr polymorphism is
also associated with increased visceral fat in our
population.3 All these studies point out to the various
susceptible genes in conferring a greater risk for
developing diabetes in our population which is
considered as the world’s diabetic capital.
508 www.japi.org © JAPI • VOL. 53 • JUNE 2005
could be accessible cell types to study and understand
the biochemical perturbations related to diabetes and
its complications.7 For example, the expression profiling
in leukocytes of diabetic patients may reflect changes in
gene expression related to systemic inflammation and/
or oxidative stress. However, gene expression in most
instances of pathological situations is also tissue-
specific and regulated spatially and temporally.
Alterations in gene expressions may occur as a result of
specific genetic alterations that underlie diabetes, due
to a lack of insulin signaling as a result of insulin
deficiency or insulin resistance, or be secondary to the
hyperglycemia and altered metabolic state that occurs
in diabetes. Therefore, gene expression studies in Indians
should be extended to classical insulin-responsive
tissues (muscle, fat, pancreas and liver). Any global gene
expression changes observed in peripheral blood cells
thus need to be interpreted with caution.
Clinical proteomics
Since the result of gene expression is the production
of proteins that constitute the targets for therapeutic
approaches, the field of proteomics is complementary to
that of genomics. Among various applications, clinical
proteomics is a rapidly developing area of biomedical
research with promise of translation of basic knowledge
into clinical applications. Very recently, urinary
proteomics has received much attention as a means to
better understand renal physiology, to explore the
complexity of glomerular disease mechanisms, and to
identify novel biomarkers and new therapeutic agents.
Clinicians would be interested to know how these newer
developments along with the conventional
microalbuminuria (MAU) measurements can aid in
earlier diagnosis and better understanding of the
pathophysiology of diabetic nephropathy,
Microalbuminuria (MAU) is an early sign of incipient
renal disease and a marker of its progression.
Furthermore, it is a key indicator of the need for intensified
treatment in diabetes and hypertension,8 the most
powerful predictor of cardiovascular and atherosclerotic
risk9 and a prognostic marker in the development of end-
stage renal disease (ESRD) and mortality.10 Early
screening for MAU can help identify patients who would
benefit from renoprotective therapy and
antihypertensive treatment. MAU is also indicative of
generalized endothelial dysfunction and some suggest
that it should also be included as part of the metabolic
syndrome.11 Alhough MAU is the best available
noninvasive predictor for risk of diabetic nephropathy,
it occurs after several years of diabetes. Some patients
with MAU have quite advanced renal pathological
changes, for which therapies are less effective than earlier
stages of the disease.12 Additionally, the MAU assay
measures just the immunoreactive fraction of albumin.13
Whereas, ‘immunochemically nonreactive albumin’ has
been claimed to be an earlier predictor of renal damage.14
Moreover, MAU test gives false-positive results in a
number of conditions: uncontrolled hyperglycemia and
hypertension, urinary tract infection, stress, febrile
conditions, heavy exercise, cardiovascular
decompensation, contamination with seminal or
menstrual fluid etc. Therefore, along with MAU, more
sensitive markers and alternative approaches are
essential for diagnosis of early stages of diabetic
nephropathy, for assessing the renal state, for optimizing
the diabetes care and for monitoring the success of
therapy.
Markers other than albumin as predictors of diabetic
kidney disease
In this issue of JAPI (page 513-520), using a combined
proteomic approach of 2-dimensional gel
electrophoresis (2-DGE) and mass spectrometry, Jain et
al15 elegantly demonstrate the presence of 4 additional
urinary markers other than albumin, in diabetic patients
who tested positive for microalbuminuria. These urinary
markers were identified by mass spectrometry as zinc
alpha-2 glycoprotein, alpha-1 acid glycoprotein, alpha-
1 microglobulin and immunoglobulin. Although the
results are preliminary, the appearance of the first three
marker proteins preceding the time-appearance of
albumin in the samples implies that these additional
urinary markers may be early predictors of diabetic
nephropathy. The identification of these additional
urinary markers is a significant advancement in that
they are more specific for tubular and renal abnormalities.
Studies such as these, when performed along with
creatinine clearance and glomeruar filtration rate
measurements may lead not only to better understanding
of the pathophysiology, but also to newer targets of
therapy of diabetic nephropathy.
Peptides present in the glomerular filtrate may
contribute to the progression of renal disease and
dysfunction associated with proteinuria. Mass
spectrometry allows de novo identification of
polypeptides. When combined with separation
techniques, such as liquid chromatography or two-
dimensional gel electrophoresis, mass spectrometry is
well suited to the analytical profiling of complex
biological mixtures. Recently, Thongboonkert and
colleagues16 created a 2-D proteome map for normal
human urinary proteins and using MALDI-TOF mass
spectrometry, they have identified a total of 67 proteins
representing various cellular components. In a rat model,
they have also identified alterations in urinary protein
excretion during acute sodium loading17 and some
proteins identified by them such as diphor-1 growth-
associated protein (which is regulated by transforming
growth factor β) and 1-myc (an oncogene product), had
not previously been identified in the urine by other
techniques. Findings such as these may lead to
identification of new prognostic markers and/or
indicators that can be used to monitor therapeutic
© JAPI • VOL. 53 • JUNE 2005 www.japi.org 509
outcomes for glomerular diseases. Although proteomics
technology may appear expensive and applications to
this field are at an early phase, one cannot underestimate
the possible identification of clinically useful biomarkers
that are more sensitive and specific than MAU for early
diagnosis of diabetic renal disease. This is all the more
important in the Indian context, because India already
has the largest number of diabetic patients in the world
and hence significant morbidity from diabetic renal
disease can be expected.18-20
The allure of the new genomic and proteomic
technologies lies in the vast amounts of information that
these technologies are expected to generate. We believe
that the combination of these approaches will expose
new drug targets in the pathogenesis of Type 2 diabetes
and hence lead to the design of novel therapeutic
treatments. This is perhaps an optimistic vision of what
may be expected in the future. From the skeptic’s point
of view, the cost of applying these technologies and the
need for sophisticated instrumentation could limit their
use to a few advanced centres. Nevertheless, investment
in this type of research will certainly pay dividends in
appropriate health care, longer life expectancy and
improved quality of life of the diabetic patient.
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R, Babu HN, Rao MRS, Mohan V. Peroxisome Proliferator
Activated Receptor Gamma Coactivator –1 alpha (PGC-1α)
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Golden Jubilee Year Celebrations of Diabetic Association of India
The Diabetic Association of India founded in 1955 is celebrating its Golden Jubilee Year and to commemorate
the occasion, an International Congress on Diabetes is being organised in the month of November 2005,
25th – 27th, at Hilton Towers (Oberoi Hotel), Nariman Point, Mumbai – 400 021.
Interested delegates are requested to contact the Organising Secretary for the registration at the following
address : The Organising Secretary, Diabetic Association of India :  Golden Jubilee Year International
Congress on Diabetes S.L.Raheja Hospital Road, Mahim, Mumbai  400 016.
Tel :   91-022-5652 9999; Fax : 91 022 2444 9418; E-mail : dai_golden@yahoo.com


Genomics and Proteomics of Type 2 Diabetes in Indians

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