The β2-adrenoceptor agonist formoterol restores mitochondrial
homeostasis in glucose-induced renal proximal tubule injury through
separate integrated pathways
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 2-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 G subunits of the 2-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 G-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 G, 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.