Biosynthesis & Cholesterol

Cholesterol biosynthesis is a complex, 37-step process that occurs in all animal cells, primarily in the liver. It is an essential structural component of animal cell membranes.

This begins with the mevalonate or HMG-CoA reductase (HMGCR) (pathway) pathway, which encompasses the first 18 steps. HMG-CoA reductase (HMGCR) (pathway) initially biosynthesizes mevalonate from acetyl-CoA.
Geisslinger et al. 2020 Wissenschaftliche Verlagsgesellschaft mbH ISBN 978-3-8047-3663-4

This is followed by 19 additional steps to convert the resulting lanosterol into cholesterol.
Bae et al. 1999 Journal of Biological Chemistry 274(21): 14624-14631

It has been suggested that the 19-step conversion of lanosterol to cholesterol in mammals begins with C14-demethylation and is followed by C14-reduction, C4-demethylation, C8-7 isomerization, C24-reduction, C5-desaturation, and C-7reduction (Gaylor 1981 in Biochemistry of Isoprenoids (Porter, J. W., and Springer, S. L., eds) 1: 482–543, John Wiley & Sons, Inc., New York); this sequence has only recently been established following the determination of the precise location of C24-reduction (Bae & Paik 1997 Biochem. J. 326: 609-616).

abcg2 gene and aqp8 gene are responsible for bile secretion (aqp8 is downregulated), and bile is converted to cholesterol by the gut enzymes
Zhang et al. 2020w BMC Microbiology 20: 308

see also:
Acetyl-CoA
Cholesterol
Colitis / Intestinal Inflammation & Interleukin-10 (IL-10)