# Unveiling Functional Roles of Apical Surface Interactions Between Opposing Cell Layers

> **NIH NIH R35** · UNIVERSITY OF WASHINGTON · 2024 · $441,250

## Abstract

PROJECT SUMMARY
 Apical surface interactions (ASIs) arising between cells in opposing three dimensional architectures
are relatively common in tissue structures, including vessels and tubes in a variety of different organs and stages,
but little is known about the function or mechanisms of these interactions. The goal of this proposal is to illuminate
the role of ASIs in tissue architecture and responses as an under-explored dimension of cell-cell interactions.
Based on our data and the literature, we hypothesize that close-range ASIs (< 1 µm) are governed by
electrostatic charge interactions between membrane glycoproteins, while long-range ASIs (1-20 µm) function
through primary cilia which extend up from the cell surface to organize signaling pathways.
 To develop accurate methodologies to measure and characterize the forces arising between whole
sheets of cells with geometrical separation, we have designed a novel method called Bilayer Intermolecular
Force Microscopy (BIFM) to induce and measure ASIs between two opposite surfaces. BIFM will be applied to
measure the force generated between two cell layers as they approach each other from opposite sides.
 For close-range ASIs, we predict that chemicals affecting electrostatic charge interactions will modulate
force-response. Cell sheets with knockout mutations in PODXL, encoding an apical sialomucin (podocalyxin)
with proposed anti-adhesive properties, will exhibit lower resistance force in proportion to reduced electrostatic
charge repulsion. Antibodies targeting podocalyxin, in therapeutic development, will also be assessed.
 For long-range ASIs, we will determine the role of primary cilia, antenna-like organelles with sensory and
signaling functions. Using our BIFM device, we will induce ciliary ASIs and assess their effects on signaling. As
a negative control, we will employ cell lines that we have genetically engineered to ablate primary cilia (KIF3A-/-
or KIF3B-/-). We will furthermore modify our device to enable microfluidic flow to perfuse between two sheets of
cells within the BIFM at adjustable speed, to assess flow start/stop in a physiological context, and monitored for
changes in signaling activity. These studies will reveal how cilia serve as ASI sensors.
 To validate findings in vivo, we will analyze physiological tissue structures exhibiting a range of apical
surface interactions, focusing on arborized networks such as ductal trees and blood vessel plexi. Expression of
podocalyxin or cilia will be correlated with geometric properties and differential gene expression patterns.
 In summary, our project will provide novel conceptual and technical advances for understanding ASIs as
a novel dimension in tissue architecture and physiology. Cross-cutting impact includes (1) revealing functional
roles for both close-range and long-range ASIs; (2) establishing a novel biophysical device to measure
interactions between cell sheets; and (3) testing mechanisms of cell adhesion and signaling...

## Key facts

- **NIH application ID:** 10890595
- **Project number:** 5R35GM149516-02
- **Recipient organization:** UNIVERSITY OF WASHINGTON
- **Principal Investigator:** Hongxia Fu
- **Activity code:** R35 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $441,250
- **Award type:** 5
- **Project period:** 2023-08-01 → 2028-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10890595

## Citation

> US National Institutes of Health, RePORTER application 10890595, Unveiling Functional Roles of Apical Surface Interactions Between Opposing Cell Layers (5R35GM149516-02). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10890595. Licensed CC0.

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