ABSTRACT
Objective:To study the in vitro construction of functional and self-renewing cartilage organoids based on cartilage acellular extracellular matrix (ECM) microcarriers.Methods:Fresh porcine articular cartilage was taken. The merely crushed cartilage particles were set as natural cartilage group and ECM microcarriers of appropriate particle size, which were prepared by the acellular method of combining physical centrifugation and chemical extraction, were set as microcarrier group. Cartilage organoids were constructed by loading human umbilical cord mesenchymal stem cells (hUCMSCs) and human chondrocytes (hCho) with a ratio of 3∶1 with microcarriers through a rotating bioreactor. The organoids with different induction times were divided into 0-, 7-, 14-, and 21-day induction groups. The cell residues of the microcarrier group and natural cartilage group were evaluated by 4′, 6-diaminidine 2-phenylindole (DAPI) fluorescence staining and DNA quantitative analysis. The retention of microcarrier components was observed by Safranin O and toluidine blue stainnings, and the collagen and glycosaminoglycan (GAGs) levels in the microcarrier group and the natural cartilage group were determined by colorimetric method and dimethyl-methylene blue (DMMB) method. The microcarriers were further characterized by scanning electron microscopy and energy dispersive spectroscopy. The hUCMSCs cultured with Dulbecco′s Modified Eagle′s Medium (DMEM) supplemented with fetal bovine serum (FBS) in a volume fraction of 10% was used as the control group and the hUCMSCs cultured with the microcarrier extract was used as the experimental group. Subgroups of hUCMSCs cultured at 3 time points: 1, 3 and 5 days were set up in the two groups separately. Cell Counting Kit 8 (CCK-8) was used to detect the biocompatibility of the two groups. The cellular activity of the organoids of the 0-, 7-, 14-, and 21-day induction groups was detected by live/dead staining and the self-renewal ability of the cartilage organoids of the 14-day induced group was identified by Ki67 fluorescence staining. The organoids of the 7-, 14-, and 21-day induction groups were detected by RT-PCR in terms of the expression levels of chondrogenesis-related marker aggrecan (ACAN), type II collagen (COL2A1), SRY-related high mobility group-box gene-9 (SOX9), cartilage hypertrophy-and mineralization-related marker type I collagen (COL1A1), Runt-related transcription factor-2 (RUNX2), and osteocalcin (OCN). Colorimetric and DMMB assays were performed to determine the ability of organoids in the 0-, 7-, 14-, and 21-day induction groups to secrete collagen and GAGs.Results:The results of DAPI fluorescent staining showed that the natural cartilage group had a large number of nuclei while the microcarrier group hardly had any nuclei. The DNA content of the microcarrier group was (7.8±1.8)ng/mg, which was significantly lower than that of the natural cartilage group [(526.7±14.7)ng/mg] ( P<0.01). Saffranin O and toluidine blue staining showed that the microcarrier was dark- and uniform-colored and it kept a lot of cartilage ECM components. The collagen and GAGs contents of the microcarrier group were (252.9±1.4)μg/mg and (173.4±0.8)μg/mg, which were significantly lower than those of the natural cartilage group [(311.9±2.2)μg/mg and (241.3±0.7)μg/mg] ( P<0.01). Scanning electron microscopy showed that the surface of the microcarriers had uneven and interleaved collagen fiber network. The results of energy spectrum analysis showed that elements C, O and N were evenly distributed in the microcarriers, indicating that the composition of the microcarrier was uniform. The microcarrier had good biocompatibility and there was no statistical significance in the results of CCK-8 test between the control group and the experimental group after 1 and 3 days of culture ( P>0.05). After 5 days of culture, the A value of the experimental group was 0.53±0.02, which was better than that of the control group (0.44±0.03) ( P<0.05). In the 0-, 7-, 14-, and 21-day induction groups, hUCMSCs and hCho were attached to the surface of the microcarriers, with good cellular activity, and the live/death rates were (70.6±1.1)%, (80.5±0.6)%, (94.5±0.9)%, and (90.8±0.5)% respectively ( P<0.01). There were a large number of Ki67 positive cells in cartilage organoids. RT-PCR showed that the expression levels of ACAN, COL2A1, SOX9, COL1A1, RUNX2 and OCN were 1.00±0.09, 1.00±0.24, 1.00±0.18, 1.00±0.03, 1.00±0.06 and 1.00±0.13 respectively in the 7-day induction group; 4.16±0.28, 5.09±1.25, 5.65±1.05, 0.47±0.01, 1.68±0.02 and 0.21±0.06 respectively in the 14-day induction group; 13.42±0.92, 3.07±0.21, 1.84±1.08, 2.72±0.17, 2.91±0.18 and 3.32±1.20 respectively in the 21-day induction group. Compared with the 7-day induction group, the expression levels of ACAN, COL2A1, SOX9 and RUNX2 in the 14-day group were increased ( P<0.05), but COL1A1 expression level was decreased ( P<0.05), with no significant difference in OCN expression level ( P>0.05). Compared with the 7-day induction group, the expression levels of ACAN, COL1A1 and RUNX2 in the 21-day induction group were significantly increased ( P<0.01), with no significant differences in the expression levels of COL2A1, SOX9 and OCN ( P>0.05). Compared with the 14-day induction group, the expression levels of ACAN, COL1A1, RUNX2 and OCN in the 21-day group were increased ( P<0.05 or 0.01), with no significant difference in the expression level of COL2A1 ( P>0.05), but the expression level of SOX9 was decreased ( P<0.05). The contents of collagen in 0-, 7-, 14-and 21-day induction groups were (219.15±0.48)μg/mg, (264.07±1.58)μg/mg, (270.83±0.84)μg/mg and (280.01±0.48)μg/mg respectively. The GAGs contents were (171.18±1.09)μg/mg, (184.06±1.37)μg/mg, (241.08±0.84)μg/mg and (201.14±0.17)μg/mg respectively. Compared with the 0-day induction group, the contents of collagen and GAGs in 7-, 14-, and 21-day induction groups were significantly increased ( P<0.01), among which the content of collagen was the lowest in 7-day induction group ( P<0.01) but the highest in the 21-day induced group ( P<0.01); the content of GAGs was the lowest in the 7-day induced group ( P<0.01) but the highest in the 14-day induction group ( P<0.01). Conclusions:The microcarriers prepared by combining physical and chemical methods are decellularized successfully, with more matrix retention, uniform composition and on cytotoxicity. By loading microcarriers with hUCMSCs and hCho, cartilage organoids are successfully constructed in vitro, which are characterized by good cell activity, self-renewal ability, strong expression of genes related to chondrogenesis and secretion of collagen and GAGs. The cartilage organoids constructed at 14 days of induction have the best chondrogenic activity.
ABSTRACT
BACKGROUND:Compared with traditional two-dimensional culture,three-dimensional microtissue culture can show greater advantages.However,more favorable cultivation methods in three-dimensional culture still need to be further explored. OBJECTIVE:To evaluate the cell behavior of microtissue and its ability to promote cartilage formation under two three-dimensional culture methods. METHODS:Cartilage-derived microcarriers were prepared by chemical decellularization and tissue crushing.DNA quantification and nuclear staining were used to verify the success of decellularization,and histological staining was used to observe the matrix retention before and after decellularization.The microcarriers were characterized by scanning electron microscopy and CCK-8 assay.Cartilage-derived microtissues were constructed by combining cartilage-derived microcarriers with human adipose mesenchymal stem cells through three-dimensional static culture and three-dimensional dynamic culture methods.The cell viability and chondrogenic ability of the two groups of microtissues were detected by scanning electron microscopy,live and dead staining,and RT-qPCR. RESULTS AND CONCLUSION:(1)Cartilage-derived microcarriers were successfully prepared.Compared with before decellularization,the DNA content significantly decreased after decellularization(P<0.001).Scanning electron microscope observation showed that the surface of the microcarrier was surrounded by collagen,maintaining the characteristics of the natural extracellular matrix of cartilage cells.CCK-8 assay indicated that microcarriers had no cytotoxicity and could promote cell proliferation.(2)Scanning electron microscopy and live and dead staining results showed that compared with the three-dimensional static group,the three-dimensional dynamic group had a more extended morphology of microtissue cells,and extensive connections between cells and cells,between cells and matrix,and between matrix.(3)The results of RT-qPCR showed that the expressions of SOX9,proteoglycan,and type Ⅱ collagen in microtissues of both groups were increased at 7 or 14 days.The relative expression levels of each gene in the three-dimensional dynamic group were significantly higher than those in the three-dimensional static group at 14 days(P<0.05).At 21 days,the three-dimensional static group had significantly higher gene expression compared with the three-diomensional dynamic group(P<0.001).(4)The results showed that compared with three-dimensional static culture microtissue,three-dimensional dynamic culture microtissue could achieve higher expression of chondrogen-related genes in a shorter time,showing better cell viability and chondrogenic ability.
ABSTRACT
Objective:To investigate the protective effect of hypothermic antegrade machine perfusion against canine ischemic brain injury.Methods:Thirteen beagle dogs were divided into the mild hypothermia with perfusion group ( n=6) and normothermia with perfusion group ( n=7) according to the random number table. The model of ischemic brain injury was established by neck transection. After 1 hour of ischemic circulatory arrest, the perfusion fluid based on autologous blood was continuously perfused through bilateral common carotid artery for 6 hours. The temperature of the perfusion fluid was set at 33 ℃ in the mild hypothermia with perfusion group and 37℃ in the normothermia with perfusion group, respectively. Blood oxygen saturation was recorded at 0, 1, 2, 3, 4, 5 and 6 hours after the beginning of perfusion to evaluate the perfusate oxygen level. The perfusate was collected, and the levels of Na +, K +, Ca 2+ and glucose as well as the pH value of the perfusate were detected in the two groups. At the end of perfusion, the parietal brain tissues of 1 dog from each group were collected to evaluate the water contents of brain tissues. Nissl staining was used to evaluate the morphological integrity of the pyramidal neurons in the frontal cortex and hippocampus. Neuronal nuclei antigen (NeuN) was used to evaluate the structural and morphological integrity of pyramidal neurons. Immunofluorescence glial fibrillary acidic protein (GFAP) and ionic calcium binding adaptor molecule 1 (Iba1) were used to evaluate the integrity and activity of astrocytes and microglia fragments. Results:At 0, 1, 2, 3, 4, 5 and 6 hours of perfusion, there was no significant difference in the blood oxygen saturation or Na + concentrations between the two groups (all P>0.05); the K + concentrations in the mild hypothermia with perfusion group were (4.57±0.12)mmol/L, (4.67±0.14)mmol/L, (4.27±0.12)mmol/L, (4.45±0.10)mmol/L, (6.60±0.15)mmol/L, (7.37±0.18)mmol/L and (9.03±0.16)mmol/L, respectively, which were significantly lower than those in the normothermia with perfusion group [(4.84±0.10)mmol/L, (5.31±0.13)mmol/L, (5.44±0.24)mmol/L, (5.70±0.18)mmol/L, (7.79±0.18)mmol/L, (10.44±0.40)mmol/L, (10.40±0.41)mmol/L] (all P<0.01). At 0, 1, 2 and 3 hours of perfusion, the Ca 2+ concentrations in the mild hypothermia with perfusion group were (0.72±0.15)mmol/L, (1.55±0.16)mmol/L, (1.62±0.15)mmol/L and (1.88±0.15)mmol/L, respectively, being significantly higher than those in the normothermia with perfusion group [(0.41±0.13)mmol/L, (0.99±0.12)mmol/L, (1.29±0.13)mmol/L, (1.57±0.11)mmol/L] (all P<0.01), and no significant differences were found at other time points (all P>0.05). At 0, 1 and 2 hours of perfusion, the glucose concentrations in the mild hypothermia with perfusion group were (5.75±0.19)mmol/L, (5.17±0.15)mmol/L and (4.72±0.15)mmol/L, respectively, being significantly higher than those in the normothermia with perfusion group [(5.30±0.22)mmol/L, (4.89±0.20)mmol/L, (4.30±0.17)mmol/L] (all P<0.01), with no significant differences found at other time points (all P>0.05). At 2, 3, 4, 5 and 6 hours of perfusion, the pH values of the mild hypothermia with perfusion group were 7.32±0.06, 7.25±0.02, 7.23±0.02, 7.24±0.02 and 7.24±0.02, respectively, being significantly higher than those in the normothermia with perfusion group (7.26±0.01, 7.21±0.01, 7.17±0.02, 7.15±0.02, 7.08±0.02) ( P<0.05 or 0.01), with no significant differences at other time points (all P>0.05). The water content of brain tissues in the mild hypothermia with perfusion group was (74.9±0.4)%, which was significantly lower than (79.9±0.9)% in the normothermia with perfusion group ( P<0.01). Nissl staining showed that the pyramidal neurons in prefrontal cortex and dentate gyrus had good integrity in the mild hypothermia with perfusion group. NeuN immunofluorescence staining showed that the morphology and structure of pyramidal neuron cells in the mild hypothermia with perfusion group were better with clearly visible axons than those in the normothermia with perfusion group, whereas the cytosol was full and swollen with scarce axons in the normothermia with perfusion group. GFAP and Iba1 immunofluorescence staining showed that more structurally intact glial cells, more abnormally active cells, thickener axons and better axon integrity in all directions were found in the mild hypothermia with perfusion group than those in the normothermia with perfusion group. Conclusion:Compared with normal temperature antegrade mechanical perfusion, the mild hypothermia antegrade mechanical perfusion can protect canine brain tissue and alleviate ischemic brain injury by maintaining stable energy and oxygen supply, balancing ion homeostasis and perfusion fluid pH value, reducing tissue edema, and maintaining low metabolism of pyramidal neurons, astrocytes and microglia.