Collagen Unfolding Determines Fluid Transfer in the Interstitial Matrix

Abstract

Local unfolding of collagen at physiologic temperatures is thought to facilitate interactions with enzymes and scaffold molecules during inflammation, tissue remodeling, and wound healing. Previous data showing high interstitial hydration potential (HP) in human and porcine dermis after collagen thermal unfolding and fibroblast death suggest that it also plays a role in local modulation of interstitial flows. To test this hypothesis, collagen was progressively unfolded in situ, and changes in HP and water influx-rate within the matrix were measured as a function of the extent of unfolding, which was quantified by differential scanning calorimetry in full-thickness dermal samples after timed heat-treatment at 60°C and equilibration at 4°C. HP was determined by osmotic stress techniques, and influx-rates from time-dependent gravimetric changes under 35mmHg osmotic counterpressure. Both increased linearly with the proportion of unfolded collagen: the HP by 1.08 ± 0.16 mmHg, and the influx-rate by 3.19 ± 0.39 μl/min /100g per each 1% of collagen unfolded (R2= 0.93 and 0. 95, respectively). The relative humidity and intensity of T2-weighed magnetic resonance images of the dermis also increased with the extent of collagen unfolding, confirming interfacial energy contributions to the HP - as predicted by the Kelvin relationship - and the expected hydrophobic nature of the newly formed protein/water interfaces, respectively. These results are fully consistent with the hypothesis and point to yet another potentially important function of local collagen unfolding in tissue homeostasis. As a plausible mechanism for HP and influx-rate increases with collagen unfolding, we propose that the surface tension of vapor/water interfaces under exposed hydrophobic clusters is higher than at hydrophilic interfaces; at nanometer scales, these differences generate local surface-tension gradients in the matrix that accelerate water influx and shift the HP.