6.3 Dual blockade of PAR1 and PAR2 in type-1 DKD
The initial studies have addressed the individual roles of PAR1 and PAR2
antagonism in an experimental model of DKD. So far, the beneficial
effects of PAR1 and PAR2 blockade alone have been conclusively known to
abrogate the pathological events associated with experimental diabetic
nephropathy by preventing structural alterations such as
glomerulosclerosis, collagen deposition, mesangial expansion and
attenuating the release of pro-inflammatory and pro-fibrotic mediators
[52-54,59]. Recently, attention has also been focused on inhibiting
both the receptor subtypes concurrently in the development of diabetic
nephropathy (Figure-02). Interestingly, an experimental study conducted
by Mitsui et al [65] investigated the impact of both PAR-1 and PAR-2
inactivation in eNOS deficient type I diabetic Akita mice that is a
well-characterized animal model of renal complication underlying
diabetes [63]. These eNOS depleted diabetic mice present distinct
features of progressive DN, particularly elevated mean blood glucose and
creatinine levels, pronounced albuminuria, mesangial expansion,
CD68+ macrophage infiltration and collagen type IV
deposition in glomeruli leading to deleterious nephropathic changes.
This eventually resulted into critical upregulation of pro-inflammatory
mediators such as TNF-α, MMP-1, EGF-like module-containing mucin-like
hormone receptor-like 1 (Emr1) mainly expressed on murine macrophages
and significantly enhanced the expressions of TGF-β, plasminogen
activator inhibitor-1 ( Pai-1), Collagen type-1 (Col1) which
contributes to the development of tissue fibrosis. In this study,
diabetic mice were administered with PAR1 inhibitor E5555
(60mg/kg/p.o ) and PAR2 antagonist FSLLRY-NH2 (60mg/kg/i.p )
either alone or in combination continually for four weeks. Although, it
was observed that co-administration of E5555 + FSLLRY-NH2 did not
improve creatinine and glucose levels in diabetic rats but appeared to
produce a marked decrease in albuminuria, collagen IV deposition that
halted the fibrotic events as confirmed by downregulation of TGF-β,
Pai-1, Col1 gene expressions. The upregulation of these genes has
pathological implications in glomerulosclerosis and renal interstitial
fibroma [65]. Aside from this, the combination E5555 + FSLLRY-NH2
also diminished pro-fibrotic biomarker Emr1 resulting in reduced
infiltration of CD68 positive macrophage cells, TNF-α, MMP-1. It is
worth highlighting that synergistic effects of dual blockade of PAR
subtypes are more prominent as compared to their individual effects in
DKD. Additionally, in consideration of the wide localization of PAR
subtypes on endothelial cells [2, 28-30] authors examined the
independent and additive effects of PAR1 agonist (TFLLR-NH2) and PAR2
agonist (2f-LIGRLO) in cultured human endothelial cells in vitro. This
treatment resulted in a remarkable rise in mRNA expression of macrophage
chemoattractant protein 1 (MCP-1) or plasminogen activator inhibitor
(PAI-1). The role of MCP-1 and PAI-1 has been well documented in
triggering the migration of leukocytes and acts as a fibrosis-promoting
molecule collectively leading to degrading renal functions [66, 67].
Apparently, PAR1 agonist-mediated increase was found to be completely
subsided when Bay11-708 the inhibitor of NF-kB was pre-added to the
endothelial cells. Whilst PAR2 agonist triggered elevation in MCP-1 and
PAI-1 levels was blocked by MAPK inhibitor U-0126. In summary, it can be
presumed that PAR1 and PAR2 mediated up-regulation in MCP-1 and PAI-1
expressions follow distinct mechanistic pathways in producing injury.
Nevertheless, findings from the present study suggest the synergistic
effects of PAR1 & PAR2 antagonism in type-1 diabetes-induced kidney
disease which is mediated by attenuating fibrosis, inflammatory
cascades, and infiltration of macrophages [65]. However, the
exploration of PAR1 and PAR2 additive renoprotective effects in type2
diabetes are still lacking and needs prompt investigation.