Michael Samsom

Extraction of basic movement from whole-body movement, based on gait variability.

The aim of this study was to quantify the step‐to‐step variability (SSV) in speed‐variant and speed‐invariant movement components of the whole‐body gait pattern during running. These separate aspects of variability can be used to gain insight into the neuromuscular control strategies that are engaged during running. Ten healthy, physically active, male recreational athletes performed five treadmill running trials at five different speeds (range: 1.3–4.9 m/sec). The whole‐body movement was separated into principal movements (PM) using a principal component analysis. The PMs were split into two groups: a speed‐variant group, where the range of motion (amplitude of PMs) changed with running speed; and a speed‐invariant group, where the range of motion was constant across various speeds. The step‐to‐step variability (SSV) of the two groups was then quantified. The absolute SSV was the summed variability across all gait cycles, whereas the relative SSV was the summed variability divided by the magnitude of the movement. The absolute SSV of the speed‐variant movements increased with running speed. By contrast, the relative SSV of the speed‐variant group (as normalized to the PM amplitude) decreased asymptotically toward a minimal level as running speed increased. Both the absolute and relative SSV of the speed‐invariant movements revealed a minimum at 3.1 m/sec. The whole‐body gait pattern during running can be subdivided into speed‐variant and speed‐invariant movements. An interpretation of the SSV based on minimal intervention theory suggests that speed‐variant movements are more tightly controlled, as evidenced by a lower degree of variability compared to the speed‐invariant movements.

Degradation of proteoglycan 4/lubricin by cathepsin S: Potential mechanism for diminished ocular surface lubrication in Sjögren's syndrome

ABSTRACT Sjögrens syndrome (SS) is an autoimmune disease affecting the lacrimal and salivary glands with hallmark clinical symptoms of dry eye and dry mouth. Recently, markedly increased cathepsin S (CTSS) activity has been observed in the tears of SS patients. Proteoglycan 4 (PRG4), also known as lubricin, is an effective boundary lubricant that is naturally present on the ocular surface. While PRG4 is susceptible to proteolytic digestion, the potential effect of CTSS on PRG4 remains unknown. The objective of this study was to assess the ability of CTSS to enzymatically degrade purified PRG4, and PRG4 naturally present in human tears, and alter ocular surface boundary lubricating properties. To assess the potential time course and dose‐dependency of PRG4 digestion by CTSS, full‐length recombinant human PRG4 (rhPRG4) was incubated at 37 °C with or without CTSS in an enzymatic digestion buffer. Digestion of PRG4 by CTSS was also examined within normal human tear samples, both with and without supplementation by rhPRG4. Finally, digestion of endogenous PRG4 by CTSS, and the effect of a CTSS inhibitor, was examined in SS tears on Schirmer strips. Digestion products were separated on 3–8% SDS‐PAGE and visualized by protein staining and western blotting. The boundary lubricating ability of rhPRG4 samples was assessed using an in vitro human eyelid‐cornea friction test. Finally, SDS‐PAGE protein stain bands resulting from rhPRG4 digestion were submitted for tandem mass spectrometry analysis to confirm their identity as PRG4 and identify non‐tryptic cleavage sites. CTSS digested rhPRG4 in a time and dose dependent manner. CTSS digestion of rhPRG4 at 1% (where % is the mass ratio of CTSS to rhPRG4) resulted in a time dependent decrease in the full‐length, ˜460 kDa, monomeric rhPRG4 band, and an appearance of lower MW fragments. After 20 h, no full‐length rhPRG4 was observed. Furthermore, with an increased relative enzyme concentration of 3%, no protein bands were observed after 2 h, indicating complete digestion of rhPRG4. Western blotting demonstrated PRG4 is present in normal human tears, and that rhPRG4, tears, and tears supplemented with rhPRG4 incubated with 3–9% CTSS demonstrated decreased intensity of high MW PRG4 bands, indicative of partial degradation by CTSS. Similarly, western blotting of PRG4 in SS tears incubated with CTSS demonstrated decreased intensity of high MW PRG4 bands, which was reversed in the presence of the CTSS inhibitor. CTSS treatment of rhPRG4 resulted in an increased friction coefficient, compared to untreated controls. Lastly, the lower MW bands were confirmed to be PRG4 fragments by tandem mass spectrometry, and 6 non‐tryptic cleavage sites were identified. rhPRG4 is susceptible to proteolytic digestion by CTSS, both alone and in human tears, which results in diminished ocular surface boundary lubricating ability. Moreover, endogenous PRG4 is susceptible to proteolytic digestion by CTSS, both in normal and SS tears. Given the elevated activity of CTSS in SS tears, and the role intact PRG4 plays in ocular surface health and lubrication, degradation of PRG4 by CTSS is a potential mechanism for diminished ocular surface lubrication in SS. Collectively these results suggest that tear supplementation of PRG4 may be beneficial for SS patients. HIGHLIGHTSrhPRG4 is susceptible to digestion by cathepsin S (CTSS), both alone and in tears.CTSS digested rhPRG4 has diminished ocular surface boundary lubricating ability.Endogenous PRG4 in normal and Sjogren Syndrome (SS) tears is digested by CTSS.Degradation of PRG4 by CTSS could result in diminished ocular lubrication in SS.Tear supplementation with PRG4 may be beneficial for SS patients.

Hyaluronan incorporation into model contact lens hydrogels as a built-in lubricant: Effect of hydrogel composition and proteoglycan 4 as a lubricant in solution: BIOLOGICAL HYDROGEL LUBRICATION WITH BULK INCORPORATED HYALURONAN

Contact lens friction significantly correlates with subjective comfort. Hyaluronan (HA) and proteoglycan 4 (PRG4) are natural boundary lubricants present in the body. The objective of this study was to assess the effect of crosslinked HA into the bulk of model contact lens materials pHEMA, pHEMA/TRIS, and DMAA/TRIS on surface wettability, protein sorption, and boundary lubricating properties at a material-cornea biointerface, both alone and synergistically with PRG4 in solution. Surface wettability was assessed by water contact angle measurement, protein sorption by lysozyme sorption assay, and boundary lubricating properties using an in vitro friction test method. HA incorporation (HAinc ) increased the surface wettability of all materials, and reduced protein sorption for pHEMA and DMAA/TRIS. HAinc increased friction for pHEMA, and DMAA/TRIS, whereas a decrease was observed for pHEMA/TRIS. A combination of HAinc and PRG4sol had a synergistic effect of reducing friction only for pHEMA/TRIS. This combination had similar friction reduction compared with PRG4sol alone for DMAA/TRIS. These results indicate HA incorporation could be an effective internal wetting agent, antiadhesive, and boundary lubricant for pHEMA/TRIS silicone hydrogels. In conclusion, HA incorporation can reduce friction of hydrogels alone and in combination with PRG4 in solution, though in a hydrogel composition-dependent (e.g., TRIS) manner.