This is how I would put it

I think cerniera here means a bridge, in the sense of "to be a bridge between two countries".

È un'espressione idiomatica che è anche molto vicina alla traduzione letterale

Piemonte led all neighbouring regions by serving as the primary interface between the national electrical power network and those beyond the Alps.

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Note added at 1 hr (2009-08-02 16:06:50 GMT)
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dictionary.com
in⋅ter⋅face  /n. ˈɪntərˌfeɪs; v. ˈɪntərˌfeɪs, ˌɪntərˈfeɪs/ Show Spelled Pronunciation [n. in-ter-feys; v. in-ter-feys, in-ter-feys] Show IPA noun, verb, -faced, -fac⋅ing.
Use interface in a Sentence
–noun 1. a surface regarded as the common boundary of two bodies, spaces, or phases.
2. the facts, problems, considerations, theories, practices, etc., shared by two or more disciplines, procedures, or fields of study: the interface between chemistry and physics.
3. a common boundary or interconnection between systems, equipment, concepts, or human beings.
4. communication or interaction: Interface between the parent company and its subsidiaries has never been better.
5. a thing or circumstance that enables separate and sometimes incompatible elements to coordinate effectively: The organization serves as an interface between the state government and the public.
6. Computers. a. equipment or programs designed to communicate information from one system of computing devices or programs to another.
b. any arrangement for such communication.