NBCe1-mediated Regulation of HCO3- is a Novel Mechanism Underlying Metabolic Reprogramming and Cystogenesis

PROJECT SUMMARY/ABSTRACT
The loss of glucose-stimulated insulin secretion (GSIS) is a critical pathophysiological event precipitating
development of hyperglycemia in Type 2 diabetes mellitus (T2DM). Recent evidence suggests that loss of
GSIS in diabetes is associated with metabolic reprogramming toward reduced mitochondrial function; however
mechanisms underlying these observations remain largely unknown. Recent single cell transcriptomics studies
of human β-cells identified SLC4A4 as one of few unique genes highly expressed in T2DM β-cells and
repressed in non-diabetic β-cells. Slc4a4 encodes for Na+-nHCO3- cotransporter, NBCe1B in the pancreas and
plays a key role in regulating intracellular pH (pHi). Importantly, increased activation of NBCe1 has been
associated with enhanced intracellular glycolysis and impaired mitochondrial function suggesting it may
contribute to loss of GSIS and consequent development of T2DM. Preliminary dissertation studies support this
hypothesis and demonstrate that inhibition of NBCe1B activity in β-cells improves GSIS in vitro and enhances
glucose tolerance in vivo. These cumulative observations led us to develop a doctoral dissertation direction
with an overall objective to characterize the role of NBCe1B as a novel regulator of β-cell metabolism and
dysfunction in T2DM. Accordingly, Specific Aim 1 (F99) will test the hypothesis that β-cell dysfunction in T2DM
is driven by metabolic reprogramming mediated by cellular alkalization through activation of NBCe1B. Given
the critical role of NBCe1 in maintaining systemic pH homeostasis, the F99 uniquely positions me to elucidate
novel mechanisms associated with dysregulation of acid-base balance in the kidney during the K00 phase.
Specifically, the A-isoform of NBCe1 (NBCe1A) functions as the key mechanism of HCO3- reabsorption in the
kidney. Deletion of NBCe1A is associated with metabolic acidosis and cortical cysts within the collecting duct
(CD). Soluble adenylyl cyclase (sAC) has been identified as a HCO3- sensor within the CD. Previous work
demonstrated that impaired NBCe1A-mediated HCO3- reabsorption activates sAC-cAMP/PKA mediated
signaling. Interestingly, persistent cAMP/PKA activation within the CD has also been demonstrated to be a key
mediator of cyst development and proliferation in polycystic kidney disease (PKD). Therefore, the main
objective of my proposed postdoctoral research direction is to characterize the role of NBCe1A as a novel
regulator of cystogenesis through activation of sAC-cAMP/PKA signaling pathway. Accordingly, Specific Aim 2
(K00) will test the hypothesis that impaired NBCe1A-mediated HCO3- reabsorption activates a soluble adenylyl
cyclase-cAMP/PKA signaling cascade in the collecting duct promoting proliferation and cystogenesis in models
of PKD. Together, the F99 and K00 will propel me to achieve my long-term goal to lead an independent
research program in nephrology.

Grant Number: 5K00DK123834-06
NIH Institute/Center: NIH
Principal Investigator: Matthew Brown