Enhanced gap junction intercellular communication inhibits catabolic and pro-inflammatory responses in tenocytes against heat stress

Abstract

Elevation of tendon core temperature during severe activity is well known. However, its effects on tenocyte function have not been studied in detail. The present study tested a hypothesis that heat stimulation upregulates tenocyte catabolism, which can be modulated by the inhibition or the enhancement of gap junction intercellular communication (GJIC). Tenocytes isolated from rabbit Achilles tendons were subjected to heat stimulation at 37 °C, 41 °C or 43 °C for 30 min, and changes in cell viability, gene expressions and GJIC were examined. It was found that GJIC exhibited no changes by the stimulation even at 43 °C, but cell viability was decreased and catabolic and proinflammatory gene expressions were upregulated. Inhibition of GJIC demonstrated further upregulated catabolic and proinflammatory gene expressions. In contrast, enhanced GJIC, resulting from forced upregulation of connexin 43 gene, counteracted the heat-induced upregulation of catabolic and proinflammatory genes. These findings suggest that the temperature rise in tendon core could upregulate catabolic and proinflammatory activities, potentially leading to the onset of tendinopathy, and such upregulations could be suppressed by the enhancement of GJIC. Therefore, to prevent tendon injury at an early stage from becoming chronic injury, tendon core temperature and GJIC could be targets for post-activity treatments.

Different Frequency of Cyclic Tensile Strain Relates to Anabolic/Catabolic Conditions Consistent with Immunohistochemical Staining Intensity in Tenocytes

“…There have been several previous reports investigating the effects of mechanical strain on the gene expression of tenogenic markers. Some studies have shown that cyclic mechanical loading within a physiological range can be beneficial for the tenogenic differentiation and proliferation during the in vitro cultivation of tenocytes [10][11][12][13][14], while others reported that excessive stimulation induced an up-regulation of tenocyte catabolism or apoptosis [15][16][17]. The selection of bioreactor type, amplitude, stimulation time profile, and frequency can affect the extent of stimulation to cells [9,18].…”

Cell-cell junctions in developing and adult tendons

“…85 Interestingly, when connexin-43 was overexpressed, expression of Col I and IL-1β was significantly lower, and MMP-1 and IL-6 expression trended lower in the heated tendon cells, compared to cells heated without overexpression of connexin-43. 85 Taken together, these findings show that connexins may influence inflammatory markers in tendon cells following intense exercise that results in heat.…”

“…Adult rabbit Achilles tendon cells subjected to 30 min of heat (37°C, 41°C or 43°C, to simulate the heating of tendon that can occur following intense exercise) had decreased cell viability and increased expression of the proinflammatory markers matrix metalloproteinase (MMP)-1, interleukin (IL)-1β and IL-6, and decreased expression of Col I, 24 h after heat stimulation. 85 Connexin-43 expression was not affected by heat treatment, but inhibiting gap junctions using 18 β-glycyrrhetinic acid resulted in further increases in expression of MMP-1, IL-1β, and IL-6, compared to cells subjected to heat but with functional gap junctions. 85 Interestingly, when connexin-43 was overexpressed, expression of Col I and IL-1β was significantly lower, and MMP-1 and IL-6 expression trended lower in the heated tendon cells, compared to cells heated without overexpression of connexin-43.…”

“…85 Connexin-43 expression was not affected by heat treatment, but inhibiting gap junctions using 18 β-glycyrrhetinic acid resulted in further increases in expression of MMP-1, IL-1β, and IL-6, compared to cells subjected to heat but with functional gap junctions. 85 Interestingly, when connexin-43 was overexpressed, expression of Col I and IL-1β was significantly lower, and MMP-1 and IL-6 expression trended lower in the heated tendon cells, compared to cells heated without overexpression of connexin-43. 85 Taken together, these findings show that connexins may influence inflammatory markers in tendon cells following intense exercise that results in heat.…”

“…92 Higher strain magnitudes may mechanically disrupt the cell-cell junctions and lead to the increased inflammation that follows gap junction inhibition. 85 Strain magnitudes were further assessed in a follow-up study. Cells from adult rabbit Achilles tendons were left unstrained, or subjected to 4% or 8% strain for 24 h, and an intercellular diffusion coefficient was used to quantify gap junction communication.…”