Biomedical subjects

Janeta Nikolovski

Publications and source records attributed to Janeta Nikolovski.

4 recordsLinked to original sources

PubMed2004

Mechanical stimulation and mitogen-activated protein kinase signaling independently regulate osteogenic differentiation and mineralization by calcifying vascular cells.

Ectopic calcification of vascular tissue is associated with several cardiovascular pathologies and likely involves active regulation by vascular smooth muscle cells and osteoblast-like vascular cells. This process often occurs in sites with altered mechanical environments, suggesting a role for mechanical stimuli in calcification. In this study, we investigated the effect of mechanical stimulation on the proliferation, osteogenic differentiation, calcification, and mitogen-activated protein kinase (MAPK) signaling in calcifying vascular cells (CVCs), a subpopulation of aortic smooth muscle cells putatively involved in vascular calcification. Application of equibiaxial cyclic strain (7%, 0.25 Hz) to CVCs had no effect on cell proliferation, but accelerated alkaline phosphatase expression and significantly increased mineralization by 3.1-fold over unstrained cells. Fluid motion in the absence of strain also enhanced mineralization, but to a lesser degree. Because MAPK pathways mediate mechanically regulated osteoblast differentiation, we tested whether similar signaling was involved in mineralization by CVCs. In static cultures, pharmacological inhibition of the extracellular signal-regulated kinase (ERK1/2), p38 MAPK, and c-Jun N-terminal kinase pathways significantly attenuated mineral production by as much as -94%, compared with uninhibited CVCs. Strikingly, although mechanical stimulation activated each of the MAPK pathways, inhibition of these pathways had no effect on the mechanically induced enhancement of alkaline phosphatase activity or mineralization. These novel data indicate that mechanical signals regulate calcification by CVCs, and although MAPK signaling is critical to CVC osteogenic differentiation and mineralization, it is not involved directly in transduction of mechanical signals to regulate these processes under the conditions utilized in this study.

Alkaline Phosphatase↗

PubMed2003

Elastic biodegradable poly(glycolide-co-caprolactone) scaffold for tissue engineering.

Cyclic mechanical strain has been demonstrated to enhance the development and function of engineered smooth muscle (SM) tissues, and it would be necessary for the development of the elastic scaffolds if one wishes to engineer SM tissues under cyclic mechanical loading. This study reports on the development of an elastic scaffold fabricated from a biodegradable polymer. Biodegradable poly(glycolide-co-caprolactone) (PGCL) copolymer was synthesized from glycolide and epsilon-caprolactone in the presence of stannous octoate as catalyst. The copolymer was characterized by (1)H-NMR, gel permeation chromatography and differential scanning calorimetry. Scaffolds for tissue engineering applications were fabricated from PGCL copolymer using the solvent-casting and particle-leaching technique. The PGCL scaffolds produced in this fashion had open pore structures (average pore size = 250 microm) without the usual nonporous skin layer on external surfaces. Mechanical testing revealed that PGCL scaffolds were far more elastic than poly(lactic-co-glycolic acid) (PLGA) scaffolds fabricated using the same method. Tensile mechanical tests indicated that PGCL scaffolds could withstand an extension of 250% without cracking, which was much higher than withstood by PLGA scaffolds (10-15%). In addition, PGCL scaffolds achieved recoveries exceeding 96% at applied extensions of up to 230%, whereas PLGA scaffolds failed (cracked) at an applied strain of 20%. Dynamic mechanical tests showed that the permanent deformation of the PGCL scaffolds in a dry condition produced was less than 4% of the applied strain, when an elongation of 20% at a frequency of 1 Hz (1 cycle per second) was applied for 6 days. Moreover, PGCL scaffolds in a buffer solution also had permanent deformations less than 5% of the applied strain when an elongation of 10% at a frequency of 1 Hz was applied for 2 days. The usefulness of the PGCL scaffolds was demonstrated by engineering SM tissues in vivo. This study shows that the elastic PGCL scaffolds produced in this study could be used to engineer SM-containing tissues (e.g. blood vessels and bladders) in mechanically dynamic environments.

Absorbable Implants↗

PubMed2003

Cyclic strain inhibits switching of smooth muscle cells to an osteoblast-like phenotype.

Ectopic calcification is commonly associated with cardiovascular disease, injury, aging, and biomaterial implantation. We hypothesized that the normal mechanical environment of smooth muscle cells (SMCs) inhibits a phenotypic switch to a pattern of gene expression more typical for bone and inducive for calcification. This hypothesis was tested using a 3-D engineered smooth muscle tissue model subjected to cyclic mechanical strain. This simplified model maintained a 3-D tissue architecture while eliminating systemic effects as can be seen with in vivo models. All engineered tissues were found to express bone-associated genes (osteopontin, matrix gla protein, alkaline phosphatase, and the transcription factor CBFA-1). Strikingly, however, expression of these genes was down-regulated in tissues exposed to cyclic strain at all time points ranging from 5 to 150 days. Furthermore, long-term strain played a protective role in regard to calcification, as unstrained tissues exhibited increased calcium deposition with respect to strained tissues. The results of this study suggest that without an appropriate mechanical environment, SMCs in 3-D culture undergo a phenotypic conversion to an osteoblast-like pattern of gene expression. This finding has significant implications for the mechanisms underlying a variety of cardiovascular diseases and indicates the broad utility of engineered tissue models in basic biology studies.

Animals↗

PubMed2002

Quantification of fibronectin adsorption to silicone-rubber cell culture substrates.

As the role of mechanical force in cellular signaling gained recognition, investigators designed a number of devices to deliver controlled regimens of mechanical force to cultured cells. One type of device uses thin silicone-rubber membranes to support monolayer cell adhesion and to transmit mechanical force in the form of biaxial strain. We have observed that cell attachment and spreading are impaired on these membranes compared to polystyrene, even when both are passively coated with identical amounts of extracellular matrix. The purpose of these studies was to quantify the efficiency and stability of passive matrix adsorption onto commercially available elastic culture substrates. A theoretically saturating density (1 microg/cm2) of fibronectin was added to each well, and the initial efficiency of adsorption to the walls and elastic membranes was found to be 31 +/- 2% of the protein added. Strikingly, when the protein adsorbed specifically to the membranes was quantified after seven days, only 10-26 ng/cm2 fibronectin were present, revealing that most of the adsorption is to the sides of the wells. These results indicate that the adsorption of matrix proteins to silicone-rubber substrates is relatively inefficient and that investigators who use these systems must be aware of this fact and design their experiments accordingly.

Adsorption↗