Cyclin D3 mediates synthesis of a hyaluronan matrix that is adhesive for monocytes in mesangial cells stimulated to divide in hyperglycemic medium.

Serum-starved, growth-arrested, near confluent rat mesangial cell cultures were stimulated to divide in medium with low (5.6 mM) or high (25.6 mM) glucose. In high glucose cultures Western blots showed large increases in cyclin D3 and CCAAT/enhancer-binding protein alpha (C/EBPalpha) at 48-72 h, concurrent with the production of a monocyte-adhesive hyaluronan matrix, whereas low glucose and mannitol osmotic control cultures did not. Cyclin D3 small interfering RNA inhibited both the synthesis of this matrix and the up-regulation of C/EBPalpha in cultures exposed to high glucose, indicating that cyclin D3 is a key mediator in regulating responses of dividing mesangial cells to hyperglycemia. A complex with cyclin D3, cyclin-dependent kinase 4, and C/EBPalpha was observed at 48-72 h in the hyperglycemic cultures, and cyclin D3 and C/EBPalpha were spatially co-localized in coalesced perinuclear honeycomb-like structures with embedded hyaluronan. Furthermore, microtubule-associated protein 1 light chain 3, a marker for autophagy, colocalizes with these structures. These results suggest that cyclin D3 is a central coordinator that controls the organization of a complex set of proteins that regulate autophagy, formation of the monocyte-adhesive hyaluronan matrix, and C/EBPalpha-mediated lipogenesis. Abnormal deposits of hyaluronan, cyclin D3, and C/EBPalpha were present in glomeruli of kidney sections from hyperglycemic rats 4 weeks after streptozotocin treatment, indicating that similar processes likely occur in vivo. Mesangial cell cultures treated with poly(I:C) or tunicamycin in normal glucose media synthesized monocyte-adhesive hyaluronan matrices but with concurrent down-regulation of cyclin D3. This indicates that the cyclin D3 mechanism is induced by hyperglycemia and is distinct from those involved in these cell stress responses.