Glucocorticoids protect and enhance recovery of cultured murine podocytes via actin filament stabilization.
BACKGROUND
Nephrotic syndrome is a common kidney disease in both children and adults that is characterized by dramatic structural changes in the actin-rich foot processes of glomerular podocytes. Although glucocorticoids are the primary treatment for nephrotic syndrome, neither the target cell nor mechanism of action of glucocorticoids in nephrotic syndrome is known. For the last 30 years glucocorticoids have been presumed to act by reducing the release of soluble mediators of disease by circulating lymphocytes. In contrast, we hypothesized that glucocorticoids exert their beneficial effects in nephrotic syndrome by direct action on podocytes.


METHODS
Cultured murine podocytes were treated with glucocorticoids in the presence and absence of mifepristone (to inhibit glucocorticoid-induced transcriptional activation) and challenged using our previously reported in vitro model of puromycin aminonucleoside (PAN)-induced podocyte injury, as well as by direct disruption of actin filaments with latrunculin and cytochalasin. Cell viability, actin filament distribution, total polymerized actin content, and actin-regulating guanine triphosphatase (GTPase) activities were measured.


RESULTS
We demonstrated that treatment of cultured murine podocytes with the glucocorticoid dexamethasone both protected and enhanced recovery from PAN-induced injury. Dexamethasone also increased total cellular polymerized actin, stabilized actin filaments against disruption by PAN, latrunculin, or cytochalasin, and induced a significant increase in the activity of the actin-regulating GTPase RhoA.


CONCLUSIONS
These data suggest that, contrary to the current therapeutic paradigm, the beneficial effects of glucocorticoids in nephrotic syndrome may result, at least in part, from direct effects on podocytes leading to enhanced actin filament stability.
Ransom
Richard F
RF
Pediatric Nephrology Division, University of Michigan, Ann Arbor, MI 48109, USA. rransom@umich.edu
Lam
Nancy G
NG
Hallett
Mark A
MA
Atkinson
Simon J
SJ
Smoyer
William E
WE
D008841:Actin Cytoskeleton / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002461:Cell Line, Transformed; D002470:Cell Survival / Q000187:drug effects; D015638:Cytochalasin D / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D004347:Drug Interactions; D006727:Hormone Antagonists / Q000494:pharmacology; D050527:Mesangial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D015735:Mifepristone / Q000494:pharmacology; D041681:NIH 3T3 Cells; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D050199:Podocytes / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D011108:Polymers / Q000378:metabolism; D011692:Puromycin Aminonucleoside / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines; D020741:rho GTP-Binding Proteins / Q000378:metabolism
D000893:Anti-Inflammatory Agents; D000903:Antibiotics, Antineoplastic; D019086:Bridged Bicyclo Compounds, Heterocyclic; D006727:Hormone Antagonists; D019384:Nucleic Acid Synthesis Inhibitors; D011108:Polymers; D013844:Thiazoles; D053778:Thiazolidines; D015638:Cytochalasin D; D015735:Mifepristone; D011692:Puromycin Aminonucleoside; D003907:Dexamethasone; D020741:rho GTP-Binding Proteins; C037067:latrunculin A