SMAD2 and obesity due to melanocortin 4 receptor deficiency: Obesity-induced increases in HA deposition and CD44 and RHAMM expression are detrimental to the kidney via activation of the TGF-β1/Smad2/3, P38/JNK MAPK, and ROCK/ERK pathways, leading to glomerulopathy, tubular injury, inflammation, albuminuria, and elevated serum creatinine concentrations.