Abstract
Background and Purpose: Mitochondrial dysfunction is a driving factor in
the development and progression of diabetic kidney disease (DKD). Our
laboratory discovered that the β2-adrenoceptor agonist
formoterol regulates mitochondrial dynamics in the hyperglycemic renal
proximal tubule. Here, we identified signaling mechanisms through which
formoterol regulates the mitochondrial fission protein Drp1 and the
mitochondrial fusion protein Mfn1.
Experimental Approach: Using primary cultures of renal proximal tubule
cells (RPTC) exposed to high glucose, we investigated the role of
glucose on RhoA/ROCK1/Drp1 and Raf/MEK1/2/ERK1/2/Mfn1 signaling pathways
using pharmacological inhibitors, and the effect of formoterol on these
pathways.
Key Results: In high glucose, RhoA became hyperactive, leading to
ROCK1-induced activation of Drp1. Using pharmacological inhibitors,
formoterol signals through Gβγ subunits of the
β2-adrenoceptor to decrease RhoA/ROCK1-mediated
activation of Drp1. Formoterol restored this pathway by preventing the
interaction of RhoA with the guanine nucleotide exchange factor
p114RhoGEF. Inhibition of RhoA/ROCK1/Drp1 restored maximal mitochondrial
respiration. Formoterol also restored Mfn1 through a separate
Gβγ-dependent mechanism composed of Raf/MEK1/2/ERK1/2/Mfn1. RPTC exposed
to high glucose exhibited decreased Mfn1 activation, which was restored
with formoterol. Pharmacological inhibition of Gβγ, Raf and MEK1/2 also
restored Mfn1 activity.
Conclusion and Implications: We demonstrate that glucose promotes the
interaction between RhoA and p114RhoGEF, leading to increased
RhoA/ROCK1/Drp1, and glucose decreases Mfn1 activity through activation
of Raf/MEK1/2/ERK1/2. Formoterol restores these pathways and
mitochondrial function in response to elevated glucose. Formoterol
activates three separate integrative pathways that promote mitochondrial
biogenesis, decreased fission and increased fusion in RPTC, supporting
its potential as a therapeutic for DKD.