Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) Pathway Is Induced by Mechanical Load and Reduces the Activity of Hedgehog Signaling in Chondrogenic Micromass Cell Cultures

Abstract

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neurohormone exerting protective function during various stress conditions either in mature or developing tissues. Previously we proved the presence of PACAP signaling elements in chicken limb bud-derived chondrogenic cells in micromass cell cultures. Since no data can be found if PACAP signaling is playing any role during mechanical stress in any tissues, we aimed to investigate its contribution in mechanotransduction during chondrogenesis. Expressions of the mRNAs of PACAP and its major receptor, PAC1 increased, while that of other receptors, VPAC1, VPAC2 decreased upon mechanical stimulus. Mechanical load enhanced the expression of collagen type X, a marker of hypertrophic differentiation of chondrocytes and PACAP addition attenuated this elevation. Moreover, exogenous PACAP also prevented the mechanical load evoked activation of hedgehog signaling: protein levels of Sonic and Indian Hedgehogs and Gli1 transcription factor were lowered while expressions of Gli2 and Gli3 were elevated by PACAP application during mechanical load. Our results suggest that mechanical load activates PACAP signaling and exogenous PACAP acts against the hypertrophy inducing effect of mechanical load.

Passage through the Ocular Barriers and Beneficial Effects in Retinal Ischemia of Topical Application of PACAP1-38 in Rodents

“…PACAP exists in two biologically active forms, PACAP1-27 and PACAP1-38. PACAP has a wide variety of diverse biological effects in different cells and tissues, from thermoregulatory effects [1], actions on cardiac excitability [2], thyroid gland functions [3], chondrogenesis [4] and muscle contraction [5]. Among the well-established and most intensively studied actions are PACAP’s neurotrophic and neuroprotective effects.…”

Role of PACAP and VIP Signalling in Regulation of Chondrogenesis and Osteogenesis

“…Mechanical load of in vitro chondrogenic cell cultures resulted in increased PAC1 receptor and PACAP expression and the activation of IHH (Fig. 20.1 ) inducing the elevated expression of collagen type X which was normalized by PACAP 1-38 addition [ 68 ]. In these experiments, we found that PACAP administration was able to reduce the expression of matrix metalloproteinases (MMP) during oxidative stress in chondrogenic cell cultures (our unpublished data).…”

“…Indeed, the addition of PACAP1-38 during oxidative stress prevented the inhibition of cartilage matrix production by normalizing the phosphorylation of Sox9 and CREB in chicken chondrogenic cells [ 13 ]. Recently, the involvement of PACAP or VIP signalling activation in mechanotransduction of developing articular cartilage has been proved by our group [ 68 ] and the importance of PKA in mechanical cellular response was proposed [ 34 ]. Mechanical load of in vitro chondrogenic cell cultures resulted in an increased PAC1 receptor and PACAP expression, and supported the undifferentiated stage of chondroblasts.…”

Occurrence and Functions of PACAP in the Placenta

“…This does not seem to be specific for this cell line, since agonistic effects were found for example on rat trachea neuropeptide release, retinoblastoma cell survival and cartilage and bone development [55,[62][63][64]. The reason for this might be the expression of a yet unknown splice variant of the receptor or the tumorous nature of the JAR cells.…”