Monocytes may promote myofibroblast accumulation and apoptosis in Alport renal fibrosis.
BACKGROUND
In interstitial fibrosis, monocytes and myofibroblasts have been directly implicated in scarring, apoptosis, and tissue necrosis. While much has been done to explore the role of these cell types individually in fibrosis, the interactive dependency of monocytes and myofibroblasts has been only marginally explored.


METHODS
Alport mice were treated or not with a soluble receptor inhibitor for transforming growth factor-beta 1 (TGF-beta 1), which was previously shown to inhibit the accumulation of myofibroblasts, but not monocytes, in the tubulointerstitium. Kidneys were examined for fibrosis using several matrix markers, TGF-beta 1 mRNA expression by in situ hybridization, apoptosis using the terminal deoxynucleotidyl transferase-mediated uridine triphosphate nick end labeling (TUNEL) assay, expression of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPS) by dual immunofluorescence microscopy, MMP activity by gelatin and in situ zymography, MMP mRNA expression by reverse transcription-polymerase chain reaction (RT-PCR), and basement membrane degradation by dual immunofluorescence confocal microscopy and electron microscopy.


RESULTS
Treated mice showed a markedly reduced accumulation of matrix proteins. Tissue monocytes express TGF-beta 1 mRNA, and TGF-beta 1 is required for myofibroblast accumulation. The number of apoptotic cells was not influenced by TGF-beta 1 inhibition. Monocytes express MMP-2, MMP-9, TIMP-2, and TIMP-3. MMP activity and mRNA expression is equally up regulated in treated and untreated Alport mice. Tubular basement membranes (TBM) around clusters of monocytes are notably degraded. TGF-beta 1 inhibition does not extend the life of Alport mice.


CONCLUSIONS
These studies demonstrate that monocytes may influence myofibroblast accumulation via TGF-beta1, and that monocytes, and not myofibroblasts, are associated with tubular atrophy in Alport mice. Elevated MMP expression and activity is associated with TBM destruction near monocytes clusters, suggesting an anoikis mechanism may contribute to apoptosis in this model.
Rodgers
Kathyrn D
KD
Department of Genetics, Boys Town National Research Hospital, Omaha, Nebraska 68131, USA.
Rao
Velidi
V
Meehan
Daniel T
DT
Fager
Nicole
N
Gotwals
Philip
P
Ryan
Sarah T
ST
Koteliansky
Victor
V
Nemori
Ryoichi
R
Cosgrove
Dominic
D
D000818:Animals; D017209:Apoptosis; D001284:Atrophy; D001402:B-Lymphocytes / Q000473:pathology; D005347:Fibroblasts / Q000473:pathology*; D005355:Fibrosis; D007668:Kidney / Q000473:pathology*; D020778:Matrix Metalloproteinase 2 / Q000235:genetics; D020780:Matrix Metalloproteinase 9 / Q000235:genetics; D051379:Mice; D008815:Mice, Inbred Strains; D008817:Mice, Mutant Strains; D009000:Monocytes / Q000473:pathology*; D009394:Nephritis, Hereditary / Q000473:pathology* / Q000503:physiopathology; D012333:RNA, Messenger / Q000032:analysis; D013601:T-Lymphocytes / Q000473:pathology; D019714:Tissue Inhibitor of Metalloproteinases / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000235:genetics; D053773:Transforming Growth Factor beta1
D012333:RNA, Messenger; C508961:Tgfb1 protein, mouse; D019714:Tissue Inhibitor of Metalloproteinases; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9