La autoedición interesa al rotulista.

Because interesar is commonly used like gustar.

In English, we usually say:

• The signwriter is interested in self-publishing.

But in Spanish, this structure is often:

• Self-publishing interests the signwriter.

So in the sentence:

• La autoedición = the thing causing interest
• al rotulista = the person who feels that interest

Grammatically, la autoedición is the subject, and al rotulista is the indirect object.

A very natural way to think about it is:

• X interests Y → X le interesa a Y

So interesar does not usually mean to be interested; it means to interest.

Because the verb agrees with the subject, which here is la autoedición.

• La autoedición is singular
• so the verb is singular: interesa

It does not agree with al rotulista, because al rotulista is not the subject.

Compare:

• La autoedición interesa al rotulista.
• La autoedición y la impresión casera interesan al rotulista.

In the second sentence, the subject is plural, so the verb becomes interesan.

Al is the contraction of a + el.

So:

• a el rotulista → al rotulista

Here, a marks the person affected by the verb: the person to whom the thing is interesting.

This is not the same as the English preposition to in meaning, but it often helps to think of it as:

• to the signwriter / for the signwriter

Also, since rotulista is masculine singular here, it uses el, which contracts with a to become al.

Good question. Many learners expect:

• La autoedición le interesa al rotulista.

And that is indeed very common, and often more natural in everyday Spanish.

With verbs like gustar, interesar, encantar, etc., Spanish often uses an indirect object pronoun even when the full noun is also present:

• Le interesa al rotulista
• A Marta le gusta
• A los niños les encanta

So your sentence without le is understandable and possible, especially in more formal or compressed style, but many native speakers would more naturally say:

• Al rotulista le interesa la autoedición.

That version sounds especially natural in spoken Spanish.

Spanish uses the definite article more often than English, especially with general or abstract nouns.

So even when English might say simply self-publishing, Spanish often says:

• la autoedición

Here it refers to the concept or field in a general sense, so la is normal.

This is similar to other cases such as:

• La música me gusta.
• La historia le interesa.
• La fotografía es cara.

English often drops the article in these broad, general statements, but Spanish often keeps it.

In Spain, rotulista usually refers to someone who makes or designs rótulos, such as signs, lettering, display text, shop signs, and similar visual text work.

Depending on context, possible English equivalents might include:

• signwriter
• sign maker
• lettering artist
• sign designer

The exact translation depends on the situation. In a design or publishing context, it may suggest someone who works with lettering or visual text professionally.

Also, rotulista is often a common-gender noun, meaning the form can stay the same for a man or a woman, while the article changes:

• el rotulista
• la rotulista

Yes. That is also correct, but it is a different structure.

Compare:

• La autoedición interesa al rotulista.
• El rotulista está interesado en la autoedición.

The first uses interesar = to interest.
The second uses estar interesado en = to be interested in.

Both can express a very similar idea, but the focus is slightly different:

• La autoedición interesa al rotulista focuses more on self-publishing as the thing creating interest
• El rotulista está interesado en la autoedición focuses more on the signwriter’s state or attitude

For English speakers, the second structure often feels more direct because it matches English more closely. But the first is very common and very Spanish.

The sentence is grammatical, but many speakers would more naturally say:

• Al rotulista le interesa la autoedición.

Spanish word order is more flexible than English, and changing the order often changes the emphasis.

Possible versions:

• La autoedición interesa al rotulista.
  Slightly more formal or literary; starts with the thing causing interest.

• Al rotulista le interesa la autoedición.
  Very natural; starts with the person affected.

So the original sentence is fine, but if you want the most everyday-sounding version, the second one is often the safer choice.

No. The ending -ista does not automatically mean masculine or feminine.

Nouns ending in -ista are very often common-gender, which means the noun form stays the same and the article shows the gender:

• el rotulista = a male signwriter
• la rotulista = a female signwriter

So in your sentence, al rotulista tells us the person is masculine because it comes from a + el rotulista.

If the person were female, it would be:

• A la rotulista le interesa la autoedición.

There is no contraction with a la, so it stays a la.