Question

Some autoimmune diseases show a positive correlation with dramatically decreased expression of histone deacetylase 9 (HDAC9, an enzyme that removes acetyl groups from histones). Why would the decreased expression of HDAC9 cause immune cells to produce inflammatory genes at inappropriate times?

a) Increased acetylation leads to suppressed gene expression.
b) Decreased acetylation triggers repression of immune cell activity.
c) Reduced acetylation prompts a hyperactive immune response.
d) HDAC9 is not involved in immune cell regulation.

Answer 1

The decreased expression of HDAC9, which removes acetyl groups from histones, leads to increased acetylation and a more open chromatin structure, thus potentially causing inappropriate activation of inflammatory genes.

Step-by-step explanation:

The decreased expression of histone deacetylase 9 (HDAC9), which is an enzyme involved in removing acetyl groups from histones, could cause immune cells to produce inflammatory genes at inappropriate times because the acetylation of histones is generally associated with a more relaxed chromatin structure, leading to increased gene expression. When HDAC9 levels are low, there is an increase in histone acetylation that tends to unwind nucleosomes and open the underlying DNA for transcription, including the transcription of genes that regulate inflammation.

Therefore, the correct answer to why the decreased expression of HDAC9 causes inappropriate activation of inflammatory genes is option (a): Increased acetylation leads to suppressed gene expression. However, this statement is inaccurate because it should state that increased acetylation actually leads to enhanced, not suppressed gene expression. The decrease in HDAC9 and therefore a reduction in deacetylation would lead to a more open chromatin structure and potentially inappropriate gene expression.

The correct option is B.