COL1A1 and diabetes mellitus: The reduction of Col1a1 was larger in the presence of diabetes (diff-in-diff: − 10.61, [− 15.17, − 5.97], PN > 0.999), whereas the reduction of Col3a1 levels (diff-in-diff: − 3.86 [− 10.2, 2.54]) and the accumulation of collagen (diff-in-diff: − 1.76 [− 4.05, 0.51]) did not differ between diabetic and non-diabetic groups.