Glycolysis regulates Hedgehog signalling via the plasma membrane potential

Abstract

Changes in cell metabolism and plasma membrane potential have been linked to shifts between tissue growth and differentiation, and to developmental patterning. How such changes mediate these effects is poorly understood. Here, we use the developing wing of Drosophila to investigate the interplay between cell metabolism and a key developmental regulator—the Hedgehog (Hh) signalling pathway. We show that reducing glycolysis both lowers steady‐state levels of ATP and stabilizes Smoothened (Smo), the 7‐pass transmembrane protein that transduces the Hh signal. As a result, the transcription factor Cubitus interruptus accumulates in its full‐length, transcription activating form. We show that glycolysis is required to maintain the plasma membrane potential and that plasma membrane depolarization blocks cellular uptake of N‐acylethanolamides—lipoprotein‐borne Hh pathway inhibitors required for Smo destabilization. Similarly, pharmacological inhibition of glycolysis in mammalian cells induces ciliary translocation of Smo—a key step in pathway activation—in the absence of Hh. Thus, changes in cell metabolism alter Hh signalling through their effects on plasma membrane potential.

Membrane potential regulates Hedgehog signalling in the Drosophila wing imaginal disc

“…Since Rpk and ATP α are expressed at higher levels in the cells that receive Hh, which have been postulated to make synapse‐like projections with cells that produce Hh (González‐Méndez et al, 2017), it is conceivable that these channels could modulate synapse function. Additionally, while our work was under review, it has been reported that reducing glycolysis depletes ATP levels and results in depolarization in the wing imaginal disc, reducing the uptake of Hh pathway inhibitors and stabilizing Smo at the cell membrane (Spannl et al, 2020). Importantly, all these mechanisms are not mutually exclusive and their roles in Hh signalling are avenues for future research.…”

Getting in shape: ATP pumps up the volume in Hh signalling

“…Smo signalling then activates the transcription factor Cubitus interruptus (Ci) and its target genes. The work by Spannl et al (2020) demonstrates that the splicing factor Ecd directly splices several enzymes of the glycolytic pathway, GAPDH , PYK and PDK to drive glycolysis, ATP production and membrane potential via the Na + (blue)/K + (orange)‐ ATP ase pump. The sodium/potassium pump in addition to importing nutrients into the cell is also responsible for transporting a small lipoprotein ( LPP )‐associated inhibitor called N‐acylethanolamides (purple) that destabilises Smo to repress Hh signalling and maintain the correct shape of the developing wing imaginal disc.…”

“…Notably, previous work has hinted at this connection, as inhibition of the pyruvate metabolism pathway has been linked to overgrowth phenotypes reminiscent of Notch signalling activation (Saj et al , 2010). In this issue of The EMBO Journal , Spannl et al (2020) further investigate this association, through elegant genetic studies and the use of bio‐sensors. Together, their data suggest that energy metabolism affects wing patterning, through ATP‐driven membrane import of negative regulators of the Hh signalling pathway.…”

“…In summary, the work by Spannl et al (2020) suggests that energy metabolism drives changes in membrane transport of regulators of developmental signalling pathways and presents a tantalising link in joining metabolic status of a tissue with its ability to form the right shape.…”

Optical Estimation of Absolute Membrane Potential Using One- and Two-Photon Fluorescence Lifetime Imaging Microscopy

“…4 On longer timescales, Vmem displays diverse patterns, including responding to growth factor signals, 5,6 oscillating throughout the cell cycle, 7 and marking developmental boundaries in tissue. 3,8 Further, these voltage signals can be compartmentalized into small areas such as dendritic spines 9 or delocalized over larger tissues. 10 Accurate and non-invasive Vmem recording techniques are required to document and understand the many roles of Vmem.…”